-EBLBX 100 eOOIlATOI DB SAIITIS - McGill...
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, . o " .. HYDROGBH OP LRAD PROM -EBLBX 100 by eOOIlATOI DB SAIITIS A thesis submitted to the Facu1ty of Graduaie Studies and Research in partial fu+ fi 11ment of for l, the degree of Masters of Engineering'. 1 . o • Department of Mining Meta1lurgieal Engineering McGill University' , March, 1987 Montreal, Quebee qanada " 1 - .. - --- <)
Transcript of -EBLBX 100 eOOIlATOI DB SAIITIS - McGill...
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HYDROGBH RBbo~IOH OP LRAD PROM
-EBLBX 100
by
eOOIlATOI DB SAIITIS
A thesis submitted to the Facu1ty of Graduaie Studies and
Research in partial fu+ fi 11ment of t~e req~irements for ~/ l,
the degree of Masters of Engineering'. 1
. o •
Department of Mining
Meta1lurgieal Engineering
McGill University'
, ~
March, 1987
Montreal, Quebee
qanada
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Permission has been granted to the" National Library of Canada to microfilm this thesis and to lend or sell copies of the film.
The author (c·opyright CNné'r) has reserved" other public!tion rights, and neither the thesis nor extensive ex tracts from it may -be printed or otherwise reproduced without his/her written permission.
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LI auteur (titulaire du droit d'auteur) se réserve les autres droits de publication7 ni_ la thèse ni de longs extraits de celle-ci ne doivent être imprimés ou autrement reproduits sans son autorisation écrite. ~
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ABS'fACT
In this study the possibility of producing lead metal by
loading lead into KELEX 100 (an alkylated 8-hydroxyq\.li'no1ine
'commercial extractant produced by Sherex Chemical Company) from
an aqueous acetate solution and then reacting the loaded
organic with.hydrogen was investigated.
Pri~r to hydrogen reduction, the extraction of lead by
KELEX 100 was studied, a10ng with the stripping abilities of
bGth nitric and acetic acid for re~oving lead from loaded KELEX
100. Lead was ~ound,\ by the method of slop~ analysis, to be
extracted as a 2 to 1 organi~ ligand to meta1 species (i.e. as
PbR2) , and cou1d easi1y be stripped from, KELEX 100-by either
~itric or acetiè acid to produce supersaturated lead aqueous (
solutions.
The thermal ~nd chemical stabi1ity of the extractant .
was
Oinvestigated using, gas-liquid chromatography ,and infrared .
spectroscopy and found to exhibit excellent .stability· within 1
the temperature and pressure range used to study the kinetics
of reductton (493-533 K and 1.38-,4.14 D MPa H2). However,
pressure hydrogen stripping above the me1ting point of lead 0-
resu1ted in decomposition o~ the organic molecule. \ .
The kinetics of l~ad reduction was studied wtth respect to , "
the effects of temperature, hydrogen partial p~e~ure, 'seed
addition, agitation, an4 chelate age on the reaction rate. On1y
temperature~ pressure, and seed addition- influenced -the
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- r~ac~ion rate, and the effects of<seeding suggest a heterogeneous ~...A.
nucleation mechanism. ., .
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The cqaracte-ristias of the lead metal produced., by hydrogen
reduction were also invesfigated. 'r
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Cette &tude . &value\ possibilit' ae produire du plomb . 1
m~allique par r'duction d recte d'un agent d'extraction charg&
dans une autoclave sous atmosphere d'hydrogène. J:,' agent
d'extraction' est le KEL
d'extraction commercial
"èhemical Co., il est cha
d'ac&tate dé plomb.
100. C~ produit est un agent
fabriqu~ . par la compagnie Sherex
à. partir- d ',une SOluti?'~ - aqueuse
En pr~alable à la red tion .par l'hydrogène, l'extraction'
du plomb par KELEX 100 es &tudi~ ainsi que les capacit&s dès ~ / "
- acides nitrique et ac&tiq es de re-extraire le plomb à partir
des solutions de KELEX 100 Nous avons mis en &vidence par ~a
mètl10de d'analyse de pent que ,le plomb est extrait" ~ous forme
. de ch~late avec un rappo t l~gand/plomb de 2 à 1 (comme par
exemple PbR ). Le plomb 2 ut être facilement extrait du KELEX
. ~OO par l'acide nitrique 0 ac~tique, produisant des solutions
• \ 1
aqueuses supersa~ur&es. i 1
La stabilit& thermiqu~ et chimique de l'agent d'extraction , :
est ~tudie~ par chromatog~aphie en phase liquide et gazeuse et
'par spectroscopie infra-xoùge. L'agent, possède une stabilit'
chimique et physique exc~llente )pour des temp~ratures compri,ses
entre 493 a 533 K et des pression d'hydrogène allant de 1.38 et·
4.14 MJ»a. Par contre, on a
temp'rature plùs &le~&e' que
montr' que l'utilisation de ~
le point de, fusIon du plomb
provoque la d'composition de la phase organ,iq~e.
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..... . .. Oe travai~ presénte des dônn'es d'crivant les.effets de la
.~ (\
~~mp'rature, dé la pression d'b~drogène, de l'introduction du 4 ,
plomb m'ta1li~ue ed poudre comme ~~ermes, du degr~ d' ag i tati.on
et du vieil1issemetrt du èb'late de plomb sur 1a,cin~tique de ,
Ces r'su1tats ,d~montrent que la vitesse
r~actione11e ne>~~pend que de la temp'rature, de la pression et , de la pr'sence de germes. Ce dernier
m'canism~ de nuc1~ation h~tèro~ene. J4 Il'
facteur
Les' car~ct~rist~ques- du plomb m~talliques
reduction SUOS hydrogène fuen~ aussi &tudi~es.
D
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suggère un
prodlli t par J
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ABS'l'RAC'l' '. •
RESUME •
TABLB OP CONTBNTS
LIS'!' or r~ORBS
LIST OP TABLES •
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• • ,. •
~BR 1 IRTRODOÇTION .. CHAPTBR 2 LI'l'BRATORB SOQVBY
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TABLB or COI'!'O'!'S
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• • • •
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• • .~ •
• • •
• · , • •
2.1 SOLVBH'l' UIfRAC'fION IN B'fDROME'l'ALLORG'f • • 0
2.1.1 Conventiona1 Solvent Extraction, •
•
•
•
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•
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2.1.2 Components 'in the Organic fhase • • 2.1.3 Ektractants Invo1vinq Solvation • • 2.1.4 Extraceants Involvinq Ion'Association • 2 .'1 .5~ Extracta~ts .Involvinq • Compound Formation
2 .2 HYDROMftALLORGICAL PROCBSSING OP LOD • • . . .
2.2.1 Hydrometal,turq ical Processes for prod uc i nq Lead •• ••
2:2.2 Removal of tead from Co,per Anode Slimes 1, \
2 .3 HYDROGBN RBDUCTION OP MBTALS • • 0 • • •
• f{ydrogen Reduct i.o.n' of Meta1s' from Aqueous
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•
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Solutions •• • · . . .. 2.3.2 Hydrogen Reduction of Metais fram orqani'c'
Solutions • • • "'-.",
.. CHAP'l'ER 3 BXPERIMEftAL' • • r •
3.1 SOMMARY or IŒPIRIMEII'l'AL ' .-~3.2 CHBMICAL REAGBH'!'S • • •
3.2.1 Orqanic Phase Composition 3.2.2 Aqueous Phase Composition 3.2.3 Reduction Gases • •
• •
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• · ' • ..
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3 6 7 8 9
• 13
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• 23
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.. 3.3 AO~AVI~A8SBMBLY • .' •
3.3.1 Reaction Nesse1 ' ••• 3.3.2 -Heating a~d Temperature Control
3.4 IXPBRIMBH~AL'PROCBDURB • • • , .s
• •
• • • •
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3.4.1 Shake-out Tests • • • • • a.4.2 Loading the Organic Phase for RedQction 3 .4 .3 Hydrog en Reooct ion. • ., •
3.5 CHBMlCAL ANALYSIS • • • · . 3.5.1 Determination of Lead Concentration 3.5.2 Organic Structure Analysis • •
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~dAPTBR 4 RESULTS AND DISCUSSlOH: 'PRBLI~IHARY BVALUA~IOH
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., 35 :' 37, • 37
• 3'9
• 39 • 41
01' 'l'HB LBAD-ltELEX 100 SYSTBM. • • • fi 4~ -' p
4.1 EXTRAC'I'IOH AND ~S~RIPpn1G OP LEAD • •
fr' ~
4.1.1 ~ct of pH on Extraction • 4,.1..-1'/ tripping,of 1ead from KEL.EX 100
• •
4.2 CBBMlCAL AND THBRMAL S'l'ABILI'l'Y •
• .". • •
4.2.1 Gas-liquid Chromatography 4.2~2 Infrared Spectroscopy • 4.2~3 Ultraviolet Spectroscopy 4.2.4 Thermal Dissociation under
• • Nitrogen
• •
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•
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CHUTBR 5 RBSUL~S AND DISCUSSIOH: PRESSURE HYDROGBH ., S'fRI PP'I HG • • • • •
5.1 ltIlftICS • • • •
5.1.1 Sëeding and Platfng • 5.1.2 5.1.3 5.1.4 5.1.5 5.1.6
Effect o~ Agita~ion • Lead Chela te Age • • Temperature Effect. • Hydrogen Partial Pressure Reproducibility and Organic
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• • Recyeling
5.2 MftAL- PRODDC'f ~C!'DIS'r~CS " .: •
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CBAPHR 6 COYCLOSIOHS • J • 95 • • "1 l • • •
6.1 PIIIl )lIIGS ,- • • • • • • • '. • • 95
6.2 J?OR'l'BBR IIIVBS'fIGÀ.,IOHS • • • • • • • 96
6.3 CLAIM TG ORIGIRALrr~ , • • • • • • 97
.'"' ACDONLBDGBMBR'fS •
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APPBHDIX • • • • • • · . • .100
RBPBRBNCBS • • • ,') • · -- • • .106
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LIS'!' OP PIGURBS
PlGURB .. 2.1 'Flow ~iagrams of (a) c~~entiona1 solvent extractip~
and (b) solvent extraction wi th hydrogen str ipping. •
2.2
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2.4
3.1
3.2
4.1
4.2
4.4
4.5
4.6 •
4.7
4.8 -
Removal of lead fram copper anode slimes by leaching wi th ammonium acetate. '.' •• ••
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Lead removal in the INER process. •
Var ratio~ of reduct~on potential, E, for metals at different metal ion activities, different hydrogen pressures and pH. •
• •
Sectioned ves!'!l __
view- of 0. •
the autoclave assembly •
, various
and for " .
reac~or
Components of' the apparatus for reduction: autoclave (2) temperature controlleJ( (3) power (4) stirrer controller (5) reduction gas ••
( 1) pack
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Effect of equilibrium pH on the extraction of lead by KELEX 100.. • • ~ '.. •
Variation of the'logarithm of the distribution ceof-ficient, log D , with equi1ibrium pH. • • •
Str ipping of lead from KELEX 100 wi th 20 and 50 nitric acip.. • • • ., ;.~::_-. •
gpl •
"'Stripping of 1ead from KELEX 100 wi th 20 and 5Q gpl acetic acid. • • • • • • •
Kinet~cs- of stripp' gpl nitric acid.
Gas-liquid'chro 100. • • •
oetailed gas~liquid unreduced KELEX 100 components.. •
•
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léad from KELEX /00 wi th 50 •
of unloaded, • •
chromatogram showing peaks ..
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unreduc~d KELEX •
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oof unloaded, of 'the major
• • •
Gas-liquid chromatogram of unloaded KELEX 100 ,after reduction at 475 K and 2. 7-6 M~ "2 fC?r six hours. 1 60
PAGB
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17 C
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4.9 Infrared spectra .of unreduced, unloaded KELEX 100~ '. 62
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Infrared spectra of (a) un»educed, un10 "and (b) 10aded, unred/"ed 'KELEX, 100 •• •
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100 • •
4.11 Infrared specera of (a) unreduced, un10 ded KELEX 100
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., and (b) unloaded KELEX 100 recyéled th ee times. • 66
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4.12 Ultraviolet spectra of the lead-KELE 100 chelate (.j versus (a) L90 v/o kerosene-lO v/o deca 01 bl~nk, and
(b) KELelLl00 blank.. • • • • • • 70 \
4.13 Comparison between the thermal pree:ipi. ation, of lead and .,popper under ni trogen. • • 72
'" 4.14 Proposed mechanism for thermal disso iation of the
copper-KELEX 100. comp 1 ex. • • • '3
4.15 Infrared spectra of (a) unreduced, unlo ded KELEX 100 and (h) decomposed KELEX 100 after redu tion at above _the mel ting point of lead t611 K). .. • • ,,76
5.2
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5.4
5.5
5.6
Effect of seed ing on react ion rate. • • •
Effect of agi tation .on reaction rate. , + • • •
Effe,ct of chel ate age on re~ction rate. r ~
Effelt of temperature on reaction rate
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Effect of hydrogen pàrtia1 p~ssure on reaction rate. ... Reproducibility and r~(:ys:1e of the for reduction. • • l . .
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or arïic solution •
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5.7 Reduction product produced at 518 K a d 2.76 MPa H2 (a) without seed aÇldi"'tion, and (b) wit seeding. 92·
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5.8 Cross section of the massive ag'glomet ated particle pro~uced by hydrogen r.educt.ion a.t "518. IK an.d 2.7.6 MPa. H2'" • • • 92
5.9 Micrograph of the original fine lea1 powder see~. (x125). •• ••• 1 --' • •• 93
5.10 Microg~aph of powdered portion of th lead product produced at 518 K and 2.76 MPa H2' wi thout seed. ' (x125). • • .• • • • • • • 94
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5.11 Micrograph of powdered portion of the lead product produced at 518 K and 2.76 MPa H2' wi th seed. (x 125) 94
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LIST OP TAB~ES
Some solvent extraction reagents for hydrometal-1 urgy.. • •• ••
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Relevant informa tion on the hydrometall urgical production of Pb from PbS by the MINIMET RECHERCHE and U.S.B.M. processes.
Availablé stabil ity data for extractants. tested for pressure hydrogen stripping. [2] .' •
Sunnnary of metal organic reduction systems. [2]
Physical properties of-components in the organic phase. •
Quality of hydrogen and nitrogen gases used in the reduction experiments ••
Components of KELEX 100 determined by gas-liquid chromatography and mass spectrometry. [66].
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CHAPTER 1
INTRODUCTION
Sol vent ex tract ion is pr.esently bei n9, ·used commerc i aIIy in
the hydrometallurgical industry as a unit process to purify and
concentrate metal values from very pilute leach liquors.[l.] ,
This is accomplished by transferring the metal~into and out of
immiscible aqueous and organic solvents. The organic phase in
this process is used sOle,ly. as a transfer -medium for the metal ..
But, investigations haVIe been performed whéreby • • chemlcal
reactions are conducted di.t:..ectly in the (\ - -----
organic phase, to
prodUce metal.[2]
Burkin [3] was the first to suggest that metais couid be
reduced 6in organfc solutions with the use of hydrogen 'gas to
produce high purity metal powders ~nd regenerate the organic r
extractant. Recent attention on the study of such a process
has 'focused on the -KELEX IOO/decanol/ke~,?sene system. [2] This
--.system has been shown to have good chemical (resistant to
hydrogenation) and thermal (resistant to pyrolysis) '~tability
'[4], and was therefore chosen as the organic phase for, this
ihvestigat ion. "-
Since the ex tractant used was designed for the extraction
of cop~er 'fran sulphate solutions [5] , its extraction
char acter i st ies for -1ead were not known. Therefçre, it was
necessary to determine under what conditions it was possible to . ,
extract lead, .and what species is extracted.
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Research in the hydrometallurgical processing of lead and , ,
base metai sulphides has cQncentrated on chloride media
as the lixiviant.[6,7,8,9] But none of these processes has yet
to see commercial applic::.,a.tion. On the other hand, the use of
acetate media. nas been applied for the lea~hing of lead fram
copper refinery anode slimes with two processes in commercial ~ .
operatlon.[IO,ll] Extraction of~~ead with KELEX 100 fram an
acetate sol~tion followed by hydrogen reduction may pr~vide a
suitable means for pro~ucing lead m~tal.
Successful application of pressure hydrogen stripping
requires that the ex tractant moiecule exhibit good chemical and
the~mal stability under the experimental~~onditions required to .
produce acceptab,le kinetics and sood metal product , J
cha~acteristics. Therefore, the chemical and thermal stability
of lead loaded KELEX 100 during the reduction of lead with
hydrogen~ at 'high temperature'and pressures was investi9a~ed. ... -
. The effects of temperature, pressure, agitation, seeding,
" and ~ead-KELEX 100 chelate age on the kinetics of reduction,
a-long with the lead metai product èharacteristics, J
were
examined.
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CllAPfBR 2
LI,.ZRA1'OU SORVBY
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2.1 SOLvn'r IX'rRAC'l'IOIi lB BYDROMBTALLURGY
- In this chapter the generalized . hydro~etallurgical
flowsheet will be briefly reviewed with emphasis on solvent
extraction. R~cent ,advances in the hydrometallurgical
processing of lead materials will also be presented with
emphasis on the extraction of lead from galenà (PbS). A
'~det~iled description of t~ use of ammonium acetate leaching . ...
" processes for the removal of lead from copper anode slimes will
then be given • The final section of the chapter deals with .
previous work on the reduction of metals from aqueous and'
,organic solutions with hydrogen. t·
2.1.1 CONVBN'rIOHAL SOLVBHT.BXTRACTIOH .
S~lvent extraction is now~ weIl established process in , ,
hydrometallurgy. Its first applicatiQn was to ~he recovery of "
f ,
nuc~sar materials.[121- Sut, solvent extraction sees its
greatest application in the extraction of copper. It has been
by ~ome, as the Most importaftt development in o
; separations since the ihtroduction of" selective flotation "
~agents in the early 1920's.[13]
A gene~alized flowsheet using sofvent extraction to purify
" and co~.è,entrate metal values prior to metal recovery is shown , . in Figure 2~1 (a), and compare~ to a novel fl~wshe~t proposed
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• STRIPPED ORGANIC
"LEACH
IOlUTIO N
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AQUEOUS <
IAFFINATE
a) CONVEllllOIAl IOlVENl EITRAcnON . .
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lOADED , .. .
ORGANIC .
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STRIP ITRIPP'NG
, SOLUTION j
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STRIPPED ORGANIC "2 lEACH
IOLUTION ~
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LOADlla
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AQUEOUS RAFFINATE
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LOAOED
ORGAIIC .
" IOL'EIT EXTRACTIOI .IlH HYDROaEN STRIPPINa
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...... HYDROaEI ITRIPPlla
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Filin. 2.1 Flow ..... of a) c ........ lOIvIII ,*adoIlid b) .olvelt .m.caol ... .,. ....... u ....
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RECOVEilv ~ Il ETAL !J
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'IIETAL
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for t'he recovery of metals from loaded organic extractants
using hydroge,n.
There a~e two main stages in conventional solvent "
êxtraction, namely' l oad ing and s tr ippi ng. In the loading stage , . e
( -the leach solution is brought into ~ontact with an immiscible
organic phase into which the metal value is transferred. The
aqueous raffinate from loading is then recycled to leaching. «\
The loaded organic moves on to stripping where the metal is
transferred to an aqueous str ip sol ution. The str ipped organic
is recycled to'th~ loading stage and the me~al is re~overed
fr-om the strip' solution, regenerating i.t to be reus~d for
stripping.
The best example .of this type of operation in commercial , ,'b
use is the sulphuric acid dump or heap ~eaching of low grade (2
to 3 percent) copper oxide ores f'ollowed by solvent extraction o. . ~ ()
and S ~bsequen tel ec trow i nn i ng (of copper. [14,15];> Leach
SOlutions contain between 1 and 2"'grams per liter (gpl) copper 1 •
and a/greater concèn.~ration of H::on at a' pH lying between land
2. The copper is, sel~ctively extracted into the organiç phase •
and then stripped by spent electrolyte '(100-120 gpl H2S04)' - \ uP9radln~ it from about 2S to 30 gpl coppe~.
~
A novel process for pr"Oducing copper directly from
chelati~g type extractants by hydrogen reducti~n has been
proposed.[l~] In this process the organic phase ls stripped of , . "
the cOpper to produee fine copper powder and regenerate ,he
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. ex tractant by ~reaction wi th hydrogen gas at high temperatures
'a~d pressures (known as pr~ss~re hydrogen stripping). This
combines the stripping and metal recovery step in conventional
solvent extraction into one stage. A more detailed description
of the chemistr'y of hydrogen reduction of metals fram brganic
solvents will be given later in'the chapter.(Section 2,3.2)
2.1.2 COMPOHENTS IH THE ORGAHIC PHASE
The successful application of sol-vent extraction to
hydrometallurgy has been due to thé production a~d use of -
extractan,ts highly selective for the required metai. It is ,
usual to put the ex tractant in a diluent to enhance ~arious
aspects of the e~tractio~and stripping process. ~ dilUel1t' is
used to decrease the viscosity of the extractant, since MOst
extractants used in commercial solvent extraction are viscous
4
b
a~d cannot be used in the 'as-received form. Other reasons for / "' /
using a diluent are to provide a suitable conce~tration of th1 ex trac tant às requ i red ~or a part icu 1 ar purpose, 'to decrease
.-----/
emulsion-forming tendencies of the extractant~ and to improve -
dispersion and coalesence properties of the ~cilvent. Both .. aromattc and aliphatic materials are available for use as .
. d1l uents in' sol vent extraction processes and arfi fractions of 1 •
crude oil~ which makes them available in bulk and relatively
cheap •.
Modifiers are commonly used to overcome third phase and . ... emulsion tendencies in a solvent' system. The four Most used
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rea9,eqts aré isodecanol, 2-ethylhexanol., ,p-nonylphenol and~ tril .
but:y 1 phospha te • Researchers have found tha t di 1 uents and 1
modifie~s play' il sûbstantial \ role in)de\:ermining , \
charactèristics of an extraction system [17~~8,19].
the
Ther~ are several w~ys of c'lassifyi.ng extfactants. In a
rec~ntly published authoritative,book on solvent extraction in
hy~rometall urgy the authors classi fy t~e ~ var iO\HI-,kxtractants '"
accordin~ to the followtng classes:[20] . ' ..
( l) those which involv$ solvation .l-
of the metal v . ion'
(2) those whic;:h involve ion. associatiorl l'
(3) those which involve compound ~~rmation' 0
'2.1.3 'O'l'RAC'l'AH'l'S INVOLVING SOLVA'l'IOH
, '~xtractants in thls' group have an oxygen atan with a lone\' h
pair of electrons which extract 'electr~cally neutral 'inorganic . .
species. by ·solvat,ion • Solvation of the inorganic metai . containing species'm~y odeur either by coordination of the
oxygen bearing e~tracta~t moiecules tO,the central metai ion or
by hydrogen bond'ing between the. proton in t,he extracted species /
an'd the oxygen in the sol vent molecul·es [21]. " \
Ritcey and Ashbrook [20] ~Iace this type of extractant ~
lnto two.main groups. Those organic reagents containing oxygen J
, . t4 '
bonded to carbon, such as ethers, esters, alcohois and ketones,.
and those containing oxygen or suI,phur bonded to phosphorus, as
in alkylphospnates o~ alkythiophosphates. .. .
J
-JExamples of f 1
1 1
1
o
o
o
8
commercial ~,y aval lable' extractants of this type are tri-n-butyl -
phosphate (TBP), tri-n-pctylphosphine ,oxide (TOPO), methyl
isobutyl ketone (MIBK), and dibutyl carbitol (BUTEX).
Examples of metal extract~on by sol~ating reagents are
shown below:
2 J. , .
(org)
TBP -Ir
Solv~tion due to coordination to the central metal Jon (2.1)
. [(C4H90CH2CH2) 20'] + [HAUCI 4 ] ~ L(C4H90CH2CH2) 20--- [HAuCI4]
"
(brg) (aq) (org) \
Solvation due ,to hydrog~n bonding-BUTEX (2.2)
2.1.4 EXTRACTANTS INVOLVING ION ASSOCIATION [20,22]
This type of extractant comprises amines and quarternary
amm 0 ni um F\ ha 1 ide s • ~i9h molecular weight primary (RNH 2)
secondary (R2NH) and tertiary (R3N) amines that are
organophilic weak basee are used ~or solvent extraction of v
anionic species fran acid/ie solution. While the s~mple amtnes rv
are ineffectiv~ at high pH, quarte'r·,\'lary ammonium hal ides (R4N) - - '
- • '''4 extract metal-anionie species fram strong a1ka1i solutions.
Ih order for primary, seeondary, and tertiary- amines t.o
form ion-pairs with an~onic metal speeies in s~lutio~ ~hey must
.0
i •
o
. -.
.. .,'', ~. ~ ... ,',
.', . 1 t
9
, first be converted to the appro~riate amine salts t~ provide an
". anion to exchange with the metal' specte.$. The general c
reactions for the extraction of an anionic species with 'an , ,.
amine ls shown below: ., 1. Formation of ammonium ~alt
[R3N]org + [HX]aq --2. Anion-exchange process
[R3 NH+x-]org
ion-fair
[R3NH+x-]org + [MY-]aq ;: [R3NH+MY-]org + [X-]aq
(2.3)
(2.4)
Basic extractants have been-us~ widely for a variety of
applications. in the extraction of U,V,W, and Co [231'. For the
case of uranium extraction' from sulphate media with a tertiar~
ammine, the following extraction mechanism has bee'n shown to
operate: '
First! the amine forms its corresponding ammonium salt,
2 [RaN]org + [H2S04]aq •• [(~3NH+)2S04-2]org
~ and then the anion exchange reaction take~.place
(2.5)
~
. 4 ' 2[(R3 NH ) 28°4] : [U92(S04)3]- ~ [(R3 NH)4 U02(S04)3] + 2 [804 -2]
(org); (aq) (or~)
"
2_1.5 .UlfRACI'UlfS INVOLVIIiG COMPOUND PORMAIfIOR
(aq). (2.6)
Extraction involving compound formation occurs when using
aci~ic and chelating extractants~ Acidic extractant~ are
cationic 1 i,quip ion excha'ngars and extract: metal s by' a cation
~ , .
,
..
o
--
o
o ~
(
.. - - -. -.---.--~ -~-----"'II!"!#.
-.. 10
exchange m~chanism.[24] In its simple form i t ls expr(ssed by \&.." 1
the following eCJ,uation:. .
< Mn+(aq) + nHR(org) -- ~ . MRn(org) + nH+(aq) (2.7)
,. ,
One organic reagent of this type used extenslvely in the
metallurgical industry ls ......----
di-(2-ethyhexyl) phosphorie acid
(D2EHPA). D2EHPA sees applications in- uranium recovery,nickel-
cobalt ''separation, and europium extraction.[25,26] T~ virtues , .
of this extractant in solvent extraction processing are its
chemical stability, general1y good kinetics of extraotion, good
loading and stripping characteristics, low solubility in the
aqueous phase, versatility in extraction, and availability.
Al soi n cl u d ed in th i s cl as s 0 f ex· t r a c tan t s are the . -synthetically prodû'ced 'versatia'. ~arboxylic acids (Shell.
Chemica 1 Co.). 'f
• •• In terms of tonnages o~ ..metai p~oduced and reagent u·se,
chelating type extractants a're the Most intensively used. It
ls thè development of copper-specific reagents which has made .
copper '~olvent extraction ~ commercial reality, and many plants
hav~ ~een b~ilt.[27] To date, Most of these plants trea~
dilute leaci1-l-iquors from the sulphuric abid leachi·ng of low
grade oxide ores. Copper production in this manner accounts
for about 15 p~rcent of the wor ld's primary copper metal
production. [1] -
Chelating type reag~~ts for use in copper solvent
extraction were .first developed in the sixties and their , .
•
o
•
o
, .
. '
•
. . .,.. ... '1 .. .~ ... " - ~ " .
Il
deYelopment has continued r such that today there exists a wide
var1ety for use in copper extraction as weIl as for the ~
e~traction of other metals. A summary of the Most widely.
available chelating type extractants is give-n in Table 2.1 [23]. >
KELEX 100.was developed in 1968 as an extractan~
for -copper [ 5] • The application . of this reagent to
Table 2.1 Some solvent extraction reagents for hydrometallurgy. ~}
Type Trade Name Manufacturers
Hydroxyoximes LIX6~,LIX64N, Henkel Corp.
oxine deriva~ives
Oil$etones
(LIX6SN,LIX70, ~ LIX7l,LIX73
" y ,
1SME 529 Shell Chemical Co.
P5000 S'er ies
KELEX 100 & KELEX 120
LIX54
Acorga Lt~
Sherex Chemical Co.
Henkel Corp.
Commercial Uses
Cu extraction & Ni extraction {LIX65N) • Pd extraction.
Cu extraction
Cu elètraction
Proposed for Cu elÇtraction
Proposed for Cu extraction
1
coml1l,ercial operation has not been as silccessful as the LIX or \
ACORGA reagents, but i t has recei ved extensi ve investigat ions .. ~
Up'to the pilot p~ant stage [28,29,30J. A combinatio~ of 20 ~ ,
v/o KELEX 100 in p-no.nyl phenol 1s a1so avai1ab1e by.the b-rand
name o·f KELEX 120. This mixture w8s formulated to' imp-r-ove the . .
o •
. ' . . ' .
,~ , .
o
o
o
o ...
",_R __ _
12 0
physica1 characteristics of extraction, compared to
K EL EX 10 0 • [31 ]
t Ini tJial investigations of KELEX Ida for copper extract ion
from both dilute and concentrated solutions were encouraging, "-
with KELEX 100 r.eported a~ having superior extra:tion ~inetics
and a greater extraction power when compared to extractants
available at the timè.[31,32] Discrimination of KELEX 100 for
copper over iron, attrJ.buted to kinetic factors, was also
reported as very good. [33]
KELEX. 100 is an alkyl derivative of a very commonly used
analytlcal reagent 8-~xdroxyqinoline (aiso known as oxine or 8-.. quinolinol). 'The main acti;;-component ~~ KELEX 100 used to be
7- (l-v inyl-3,3 ,5,5 ,-tetramethyl h,:x y 1) - 8-).Yd~OX~U ino 1 i ne. [34,
35] In "1976, the manufacturing process was'changed such that
the active component is now 7-(4-ethyl-:l-methyloctyl)-8-1
hydroxyq~inolin~ and its struct~e Is shown be1ow.
. ~ , R - -CH-(CH )~H-(CH ) -CH 1 2 233
CH 3 C Hs 1
. OH ~
1
..
1
The problem with KELEX 100, which hasjprevented it from 1
being applied commercially for the recover of copper, Is its ,_ J,""1.
ability to form salts with acids. -This is d e to the fact that o .
the tsrtiary nitrogen on the molecule behav s as a base and can ., t
o
.0
"
13
pic~ up acid during stripping, whieh must be-removed before , "
recycling to the extraction stage. Protonation of the KELEX
100 molecu le is shown below •
. Wo (org) R N ..
OH JaSie nitrogen
(org) (2.8)
OH
\
This problem 1s eliminateq if hydrogen stripping,. is used.
b . 2.2 HYDROMBTALLORGlCAL PROCESSING OP LEAD
. The past twenty-five years has seen a boom in the
development of- hydrometallurgical techniques tôr, the winning of )
lead and ot~er ba,se metals ('Cu and Zn) from both primary and .' - 1 .<
• secondary sources [36]. The impetus bas come from the need to
~"find à more environmentally acceptable alternative to smelting, .
and the desire to exploit eomplex materials for which \
hydrqmetallurgical techniques are particularly suited.
2.2.1 HYDRO"ETALLURGICAL PROCESSES .. l'OR PRODOCING J:,BAD,
Foeus on the extraction of lead from primary sources~has (
been centered on the processing of PbS concentrates, bu,lk
complex sulphide concentrates, and the so-called- 'd1rty' PbS ) concelltrates obtained from the differential flotation .of
complex sulphides. Bulk concentrates are produced from tl'le
f lot a t ion- 0 f fin e - 9 rai ne d , .y intimate associations of
chalcopyrite {CuFeS2)', sph~lerite (ZnS) and galena (PbS) fr~ely
disseminated i~ a pyrite (FeS2) or pyrrhotite (Fel_xS) Itlatrix ..
'. , p
o
o
o
14
which sometimes cont.alns valuable amounts of pr~'Cious ;? , metals [37]. Many processes have been deve,lopf?d, and
exploitation strategies proposed, for the treatment of complex ,
sulphides [8,9] •. Of the leaching media investigated cilloride
based systems are the MOst extensively studied [6,7].
-{t' The MINIMET RECHERCHE [38] and U.S.S.M. {39] processes
have been developed dedicated solely to the hydrometallurgical
treatment of PbS' concentrates capable of directly producing
commercial lead. Both processes have similar flowsheets and use "
a chlo~ide leach followed by a purification step and th~n.
electrowinning. Table 2.2 shows relevant information for the
d'ifferent unit processes.
Problems encountered with th~ operation of the'molten salt il
electrolytic cell used in _the U.S.B.M. ~rocess, and the desire
to produce a 1 ead d epos i tin ·a compac t f 0 rrn f r om a-queo us \
chloride media has spur red on in v est i 9 a ~i 0 n sin t 0 the
electrowinning of,lead from various aqueous solutions. 1
Investigators have reported that peposits obtained from "
the ~lectrowinnCing of 'lead from aquèous chloride media are)
ch.aracteristically dendritic and n0':l-comp~ct [40]. The -
el ectrodeposi tion of lead from buffered el ectro lytes con ta in i'ng
ammoni um aceta te and acet ie ac id has been stud i ed wi. th the
reseaùrchers reporting that lead had' 'been deposi t,ed, in, a smoot;h , , '
and compact form, on 1ead and, coppér e1ectro~es [41]. Tlle high • . ,
solubility of PbC12 crystals in aceta te med ia makes this
"
, . , #
o
o
• " ,
15
\ -~
process attractive as an alternative to molten s'alt
electrolysis.
Table 2.2 Relevant information on the hygrometal1urgica1 ',' p.;.oduction of lead from PbS by the MINIMET RECHERCHE and U.S.B.M. Proce~ses.
PROCESS, LEACHING PURIFICATION EL ECT ROWI NN 1 NG
. ,-----------------------------------------------------------------MINIMET RECHERCHEa
\ b"' U.S.B.M.
FeC1 3 (+NaCI) br i ne leacl1 of PbS concentra te
FeC1 3 (+NaC1) brine leach . of PhS concentrate
2 sta~e solution puriflcation: 1. Coarse
"Purification: Cu,Ag,Si cementation _
2. Fine , Purification: Ion ex.change of Cu+ and Ag+
Crysta11ization Qf PbC12 from leach 1 iquor by cooling .
.
, Pb electrowon from c1ear . ch10ride ' sQlution' in a special cell (Ti cathode and C anode) produci ng fine Pb powder
E1ectr01ys1.s of PbCl2 in LiC1~KC1-PbCl'2 fused saI t electrolyte
,a--deve10ped to treat PbS concentrates 'from.mixed su1phide ores
b- developed to treat PbS concentrate$
"
The use of 'acetate media has a1so been i·nv·estigated t6 .. process PbS concentrates. A study o~ ttte kinetics of oxidation
1
of PbS in ammonium acetate solution and oxygen cnder pressure
has shown' tllat the reaction products are 1eaa ace,tatè in
'solution and elemen.tal sulphur, the latter farming a'
nonpermeab1e fi lm on th~ Pb~ cryostal making. this process
~
.0
o
"
o
i~
16
unsuc,cess'ful [42]. But a successfûl attempt to use acetate •
electrolyte for direct electrowinning of lead from PbS
concentra te compact anodes has recently béen reported [43] • . ~.2.2 REMOVAL OF LBAD FROM COPPER ANODE SLIKES
Use of acetate media has been applied successfully to
the treatment of copper anode slimes p'reviously unsuitable for 4
treatment l;>y conventional means becau'se of high lead content
[5].. This patent describes a process for the removal q
of lead . content in anode sI im,es by primary and secondary leaches in
ammonium acetate solution at a temperature not exceeding 353 K.
Lead dissolution'is maximized, with minimal coextraction of
other metals. The I~ach solution is then separated from the
undissolved slime resid'ue, whJle lead is crystalliz,ed 'and . recovered from the separated
acetate.(See Figure 2.2)
leaçp' solution as ,1
le~d
A similar process has been developed by Kidd Creek Mines
Ltd" of Timmins, Ontario, Canada, in which an acetic acid .
pre~sure le~ch is used to remove the lead from their anode
~limEts. The lead is recovered as lead aceta~e cr'ystals and
sold as a marketable product. Detai 1 s oÊ the prpcess are not 1
weIl known sînce a patent searc"h is ongoing [11]. '"
Whereas the above patents C'aii for the residue from
leaching t~be treated for recovery of preci~us metais and ~
'" . other me~al values by co~ventional me~ns, the INER Proeess
(10) is a totally hydrometaïlurgical process 'which recovers
• ';<'.
,:w-. , .
l'
Ci • .' N.'
.
Ammonllln
SO''''
o AmmonIUm
L
SollIIoII .
.
..
< ~ ...
• .,
AgIn 2.2
.. t \ ~
. , ,
RllwSllc-. ~ ".
, ~ ,
lo -'f
Prllllàly Laach Stage , ~
A .
, -
,
,
, .
,
• -
--.
.
-.. r
,
, --
• ..... ' -'
SIL~ j,
-. .
~ .. . , AnI'no .... AcatItI -.-
( Sacondaly LIacII stage . \ . .
. . --
. ,. .. ,-. • " . , ~ . ... , .'
S"'.aIIoq p Cry-' 'DMIIon SaJaaIIofI. \ - .. --..
~ . - , . < , . -. . ..
Resldues CeadAœtÈlte
. .-
17~
, .
.1 '.
o \
o
o
) '.
.'
.'
18
aIl Metal values (inclu~ing Au,Ag,Te,Se and Sn) fram copp~r .
anode slimes. This process has, been tested successfully in a . )
p~lot plant, and based on those résults a production plant
with a capacity of 3~0 tonnes of anode slime per year has been
constructed. Figure 2.3 shows ~ha~ part of thi ~rocess which
involves removal 'of lead. Five to seven normal ace'tate so~ution
is used as the leaching reaqent. The parfially decopperized ....~"
t, \ slimes are leached at a temperature ranging from 273 K to 343K. ,
After 2 to 3 hours, 95\ of the lead content is dissolved along
with a small amount of copper. The lead and copper are co-• extracted artd seiectively stripped usinq LIX 34 [44] or LIX
64N [45].
. As ev idenced from above, future hyd rometa 11 uIg ica 1 1
techniqùes 'developed to treat anode slimes containing
appreciable amoun/ts of lead will focus sorne attention on ... the , !
processing of lead from acetate solutions.
2.3 HYDROGEN REDUCTION OP METALS
2.3.1 HYDROGBN RBDUCTION OP METALS PRO" AQUBOUS SOLUTIONS
Many l abora tory stud ies ha ve been cpnduc'ted on the
reduction of metals in aqueous solutions by hYdrogin,
[46,47,48,4~] and ~ommercial application of ihis process ~s been realized [50,51]. ,Ptessure hydrometallurgy,is used by
J
companies, such as Sherritt Gordon Mines Ltd., for both
leach/ng and hydrogen reduction to produce nickel and cobalt t
powders as well as small amounts of copper powder f?r ~pecial o
• ,~~ \
.'
'.
o 1
...
"
...
7
o ,
'.
,
.....
......... rrom deo",
, ,
Aœf&IB Leach ,
Le.Ch tOIutIon . (Pb a CU)
SaIMd EJdJidIon, pH -8.5
" Pb. cu lMded orpnIo
,
l,aadSb .... G
,
Pb·Act .... 'olUion
1 ReducIIDn
~
, .
,
--. RelldUl
.
.. ,
-' ... .
,
Cu 10 ... r
0I'gIIII0
..
.
• figura 2.3 Lead removaIln'tha INER process.
19
. • "
c
. ,
. ;--
,
.'
" . . SII~ 0fPIII0
0
~
H280 .. . -
0 . ~ . -
CoppIwSb~ ... -
- ~
eopper ...... , -- -
. r.
•
o
o
·0
:
1
'\
20
purposea. ,. The overaii reactio,n for the reQu-Ct~'0n of metàls in ..
aqueous so~ution by hydrogen gas ia shown beiow.
;::e M (a) + nH+ (aq) (2.9)
The thermodynamics 'of this reactlon ·can be explained using
the electrode potentials, E , of the fO.I10wing opposing ha1f-
reactibna
Il
Mn+ + ne---.. M (2.11)")
--... H2 (2.11)
The Nernst poxéntia1s for the above reacti~ns at.29B K are
given by
• . . EM ~ EMO + d~0592 ln [aMn+]
n
for re~ction 2.10, and
EH = -0.0592 pH - 0.0296 log PH 2 . \( Q 2
for reaction 2.11, where ,
,
EMO' = standard Nernst reduction·~potentia1
n • number of electrons per ion
aMn+ ~ metal ion activity
PH = hydrogen pressure 2 .'
(2.12 )
(2.13)
. -
- ; , "
o
1 ~
. ,
o
i i'!, (}
• r
21
, . The total'potential,ET' for reaction 2.9 is given by the
s,um of potentiàls-'of the opposing ha~ f-~e-;ctions {E'r =- EM +
('EH) }. For reduction to occur ,the f,ree energy chang~,ilG , of 2
the ~vera1~ .re~ction ~ust be negatjve. The free'energy~chànge ~
of r~\action 2.9 i s gi ven by
\ \ ~ 2.14)
where ,F • Faraday. \
In Figur'e .2.4 the potentia1, EM, of equation 2.12 is
, 'plotted as a function of metal 'ion acti vi ty for various metal.s • .. \
Superimposed on this is. a plot of the potential, EH t given by , 2
aguation 2.13 ~s a ~unction of pH at various constant PH 2
values. In Figure 2.4 the requirement for metal reductio,n lS
satisfied when the ,line representing the potent~al of the 1
Metal is above that rep~esentin9 th~ potential of hydrogen.
,For an uncomplexed metal ion in sol ution the thermodynami'c' .. dri\v in9~ force for reduction ia increased by increasing pH. [47]
The increase in pH ls limited by hydrolysis and precipitation
of the metal saI t. In' commercial operations, the operafing pH
is maximiz,ed by the use of cpmplexing agents SUeCh as ammonik.
Complex formation of the metal prevents hydrolysis. In turn, . , .complex fo~ation makes hydrogeh red~ction more difficult since
~ , iii
,hyqrogen m,ust overcoine the affinity of the ,metal for the ,J 1
com'plexing ligand instead ?f just displaçjng the water of
hyd rolysis • In dete~ining the t~ermody*amics of hydrogen
reduction whan the metal 15 complexed, the electrode potential
. ' ,
!
0
.,
0
o
, .
<'1;,
r
Met~1 10n activlty
o.sl.O - 10" -- 10-2
- , Cu
eu+! .
00 -~
...... Pb ., .. - NI ~ Co -w F t2
• •
Zn+2 .
-~OL.----~2----~4~_----~8----~'~--~IO~--~1~2~--~14
pH
Figure 2.4 Variation of reduction potential, E , fdr various . rnetals at ~ifferent metal. ion activities, and for different hydroqen pressures and pH.
.,;
."'".-'
22
",0
o
.' -.
ct
.. '
23
of the compl,~ed metal ca,tion must be used [52].
Both ho~ogeneous and heterogeneous catalysi~ have beenl
,observee in l the kinetics of hydrogen reductio.n of metal s from " ~aqueous solutions. For systems where heterogeneou~ catalysi's
-la in operation, a seed such as nickel, cobalt, or pallad.ium is .p •
added to avoid plating of the pressure vessel's internal parts,
which may act as a catalysing surface in the absence of s.e.ed
ma~eriai. Metal ions in solution such as Cu+ 2 , Cu+, and Ag+
act as homogeneous catalysts. Autocatalytic kinetics have also ,
been observed, whereby no external sol,id catalyse is required . for the r~action to start, but freshly deposited metal
accelerates the process [53]. J
.pa.rtiGfe growth during metal reduction by hydrogen occurs
not only by precipitation at metal surfaces, but also by
~gglomeration. Agglomeration Fesults jll- Ilpnuniform particles
which tend to become plastered on the walls of the reduction
vessel. Plastering is defined as the bonding of discrete
finite particles~to the walls, whereas plating is the catalytic
precipitation of metal to form a continuous phase. Organic
additives such as ammonium polyacrylate'ahd lignid are added in t , ,
ord,r to prevent plas'tering [54]. In order to obtain more
uniform deposits organie addit.i-ves such as anthraquinone may -
also be added [541. '
2.3.2' HYDROGBN RBDU~IOH OP ~ALS ~RQM ORGANIC SOLO~IONS 1
Hydrogen stripping of base metals from 60mmercial
"
o
o 1
o
!. ~ a
24
1 ex tractants was fi rst app1 ied successf..u.l-1y· to 'Versa tic'
(carboxy1ic) acid and organophosphoric acid ex'tractants (3,S5].
This concept was extended to the more wide1y used c~elating " \ ....
extractants, especia11y KELEX 100- [16]. . '
Research in the hydrogen stripping of metals.from organic
solutions involves three types of expetiments. 'Experiments are
conducted to examine the stability of the organic structure,. to
study the kinetic-s of redw=tion, and to determine the
characteristics of the sol id proJucts ~f reduction (e.g. metal
powders, meta1 salts). --
For hydrogen stripping to he successful, the Metal must he
recovered in a manner that regenerates ynloaded organic without
attacking the ex tractant mol~~l!le either by hydrogenation or -
tpermal decomposition. The stability behavior of extractants ''''~
, tes,ted for -hydrogen stripping are shown in Table 2.3 [2]:
'AS might be deduced from Table 2.3, successful pressure
hydrogen stripping, which yields Metal and regene~ated , -
extractant, fo Ilows ·one of two reaction paths. Fe>!: cl'lelati ng
and acidic extractants the reduction reaction may he
represented, for example, as follows.
- Cu (s) + 2 HR (org) (2.15)
For the solvating ex tractan~ex:. the 'teduction .
reaction may be represented as follows (56).
•
•
~."o
, '
~
.... -~\. .... 1,'" p :Xli~" ...... '- ':" -( -,,- .. ~ .
• 'C "' ( .0
o
Yabl. 2.3 ~vallable atability data for e.tractant. tested for pre •• ure bydrogen .tripping. (2)
\
"
.!U! CbelaUng Un tero .. ne + decanol,
. /
(
,1CIDIC Un ehelhol ,. or kero.ene,
SOLVA'I'UIG
(ln SheUaol If)
MSIC (lp SheUsol T)
"
a-KIloSX 100 b-LIX re.gents
Satraètant
Yrade ~a-e
ItSlou 100
LIX34
LIU."
LIX63
LIX6S*
SMI S29
Acorga P-5100
Veraatic 911
Bute'
Al_ine 336
Aliquat 336
Alaalne 336, Aliqu.t 336 C-SME-529, Versatic 911
Shenaol T d-Acorga P-5100 e-Bute. l-the only coditions reported.
~
Conditlona ,.èated
Ch_Ical ~
7-alkylated 8-hydroaiqulnolln~
8-alkarylsulphonaaldO quinoUne
L1I603 in LIU511 (a.e below)
8liphatic G-bydrolyod~e
2-hydroxy-S-nonyl benzophenon~ o.i.e
2-hydroay-5-nonyl acetophenone o.i.e
5-nonyl aalicylaldo.j~e ln 4-nonylphenol"
,..rtiary carboJyllc acid
DI-2-ethylhe.yl. phosphoric acid (D2EHPA)
Ma. '1' .!!.L.
598
453
4n f
473 f
.73
473
373
573
453
Dlethyl.ne glycol dibutyl 403 ether (D'but yi carbitol)
'l'ributyl phoaphate ('fBP)
'l'eJ:tiary allline
Quarternary amine
~ "1
Sherex Chelllicai Co. Henkel Corp.
Shell Chemlcal Co. Ltd.
Acorge lotd. Ansul Co. Ltd.
t73 f
4n f
t73 f
Max Pa ~2
4.14
:l.76
2.U f
:l.il f
:l.76
2.76
2.41
6.90
2.76
2.76
2.n f
2.41 f
2.41 f
..
'. a_ark.
No degrAdation after 40 recyclea et valioua '1' and PH2
,Sub.tantial degradatlon abov. 453 It-H2S for ••
Very unatable
Very unatable
Ho 6bgradatlon after 9 recycle. at 473 K
Graduai degradetion durtn9 recycling at 473 K
Subatantial degra4ation at 373 K-HH3
Very atable J Stabl:-below 45 K 6ubatantail degradation at 373 K-greeniah aolid for..
No degradatlon after 10 recycle.
verf un. table
Non-Illetalilc prodUct forlll~ '"
Non-Illetaille produet for.ed
...,
N VI
G
, .
"
. '
o
\, ,
...
o ,
o
1 --7
1 26
1
20BC HAuÇ14(org)+ 1H2(g) - 2A\l(S) + 2DBC(Org) + 8HCl (aq)
(2.16)
In' t-his system, a small amount of di lute hydrochloric ,
acid solution is added to the organic phase to dissolve the
hydrogen chloride ~as generated.
Pressure hydrogen str~pping kinetics have been
demonstrated to follow one of the two paths,homogeneous or • 1
,hetergeneous metal nucleation. In homogeneous nucleation ~he
-meta'l is easily reduced requiring no catalyst. , M inor amounts
or no metai plàting is observed on wetted autoclave surfaces. , ~
Heterogeneous nucleation prevails when base metals are
hydrogen reduced. In gener'a l, heterogeneous 1.' nucleation
requires higher reduct.ion temperatures than homogeneous
nuclea~ion, and seed addition is necessary to prevent."
deposition on reaçtor surfaces. Seed addition is aiso seen to
increase~reduction rates. Table 2.4 shows a summary of the .. ,~
kinetics of the metal organic reductian systems already
studied. [2]
Most of the hydrogen reduct ion stud ies invo 1 v ing organic
solvents have been conducted on organic phases loaded fram pure
~queous solutions as opposed ta real leach solutions.
T~erefore, the main impurities in the very fine metal powder
prqduct, have been carb~n" .hydrogen, and oxygene Carbon and
hydrogen contamination is thought to be a result of organic
entrainment during filt~ation. Oxy~en contamination i8
•
,i
'l~ " .' • y.t_
··tractant ~
p _a.a 100 ,",U Pd
LIX 65. "
Veu.tic 911
D21D1PA
/8ute.
, ,
Cu
Pb
au Co
re
Cu • CU
NI
CO
( re
NI
Co
Fe
Au
o o '\
7able 2.4 Sa.aary of .. tal organlc raduction .y.t .... 121
Ca.E!Ioe.
AUC1.- 'H2&'t
PdL2 chehte
CuL2 .chelate
PbL2 chelate
MIL2 chlate
COL3 chelate
reL] chelate
CuL2 chelate
CuA2 .a1t
NU2 .alt
CoA2 s.lt
reA] .alt
... 2··,t COA2 .alt
FeAl .a1
QBC'HAuC14
Reduction COndition •
1 2'IIt! PI"Pa H2)
298-373- 0.35-0.69
373-423 0.69-2.78
U3-488 0.52-4.14 c
473-518 2.76
523-598 1.01-3.79
523-598 1. 38-3.45
473-598 2.76
433-473 0.69-2.76
393-473 0.10-6.90
433-473 0.1O~6.90
431-473 0.10-6.90
573 6.90
411 2.07
413 2.07
398 2.76
353-403 0.34-2.76
~
Mueleatlon
Ha.ogeneou.
HOiaogeneoua
Heterogeneoua
Chanet.rlat1es
Kinetle.
Under .tudy
Under atudy
Autoeatalytic
R .. ark.
Minor platine) occu[red
l Ho platine)
_ Seed needed to aviod plating
------------------------------Under study----------------------------------",
Heterogeneous
Heterog eneoua
No .etal foi.ed
Heteroge~ou.
HOIIIogeneous
Heterogeneous
Weakly Autocatalytlc
Weakly Autocatalytlc
Very slow
Weakly Autocatalytic
Autocatalytic
Faat
Heterogeneous Fast
Heter09 eneOUS
Heterageneoua
Heterogeneou.
No metai for.ed
HOIIIageneoua
,.. "
Very alow
Very fast
Very slow
Faat
FIrat arder in Au
..
Seed needed to avoid plating
Aa above
re(II) for.ad. Catalyat needed.
Seed needed ta aviod p~tin9
NH) addition facilitate. reductlon and prevents colloid formation
-,
Reduction to re(II). Metal for.ad only when NH3 added • Co/lU aeparation po.~ib1e
re{ll) foxmed. Catalyat1needed
No platlnq (, :
CI
t\) .......
,
o
o
o
o
, '.
28
eonsideted to be probably causéd by surface oxidation of the
highly 'acti ve metai powder9.
1 n general, wh,en precipi tation occurs throélgh homogeneous
nucleation, the partieles are fine, and no coarsening i9
observed if seed is added. If heterogeneous nucleation oceurs,
seed' is added to prevent ~lating and a coarseniI'ig effect of the
seed, onto which fresh metal deposits, is 'oHserved. \
...
o ,
o
••
29
CBAPTER 3 =
EXPERIMBNTAL
3.1 SOMMARY OF EXPERIMENTAL'
Mix ing. of the two phases dur ing thg s_hak'e-out tests was
performed in separatory funnels by mechanical shaking. Loading .
~f the organic for reduction was achieved by mixing in a
separatory funnel with the adœition of concentrated ammonium
hydroxide for pH control. Hydroge'n reduct ion at high
temperatures and pressures was carried out in an autoclave.
·Measurement of lead concentration was accomplished by Atomic _ ft1
Absorption Spectroscopy (AAS). Organic structure analysis was
performed using Infrared Spectroscopy (IRS) , Ultra-Violet {
Spectroscopy (UVS) and Gas Liquid Chromatography (GLC). ,
,3.2 ""' CHBMICAL RBAGENTS
,3.2.1 ORGAHIC PHASB COMPOSITION
The organic phase used in this work conslsted 'of KELEX 10-0 . . .
dissolved in a low aromatic. « 1%) kerosene diluent and a \ .
decanol modifier. The mixture contained. ,15 volume percent
(v/o) KELEX 100 (Sherex Chemical Company), 10 volume peréent
decan~l. (Eastman Kodak Chemicals), and 75 volume petcent . ..
kerosene (Fisher'Scientific). The physical properties of the
three components of the organic phase are present~d in Table
3.1. ~Decanol was added ~s a modifier because it has been shown
to enhance the ch~mical stability of the extractants'in simila~
'a
•
o
o
o· )1
...
30
1-systems using copp~ niC~:l [561, copper [57J, and èobalt [58l.
Table 3.1 PhYS~l properties of componenta in the organic phase.
Component
KELEX 100
Decanol
"
Physica1 Property
Spe<H'f'ic Gravit y
.976
.714
• 83
Boi1in9 Point (K)
533 at 760 mm Hg
D~stillation Range 10% 475 50% '487
,\ 90% 513 \
502 at 760 mm Hg
Prior to use the organic liquid was "purified" by acld {'
washing (29]. Any water soluble impurities in the as-received
_organic were' removed by washing, at an organic to aqueous,> ratio
of 2 ·t 0 1 , w i th a 10 v/o H2S0 4 solution. The co l ored
raffinate was discarded, and the organic scrubbed with
distilled water to remove any extracted acid.
\ 3.2.2 AQOBOOS PHASB COMPOSITIO~
r ,
The aqueous phase used in this work consisted of, a leao ~
acetate solution prepared by the dissolution of reagent -grade
leaà acetate trihydrate (Anachemia Ltd.) in distilled water
with glacial acetic acid (Fisher Scientific Ltd.) added as '
", r, ...
o
0
..
" -
31
'backing electrolyte. Ammonium hydroxide (Fisher scién~i~ic \
Ltd.) was added as base to increase the pH.
3.2.3 RBDUC'f,IOH GUBS
Gases were supplied' to the rea~tion vessel via high lo.
pressure cyl inders. Prepurified grade hydrogen and nitrogen
gas, pro~uced by'un!on carbide.Ltd. and distributed b~ Welding .
P~oducts Ltd., were used. The purity, moisture content, and ,
oxygen content are listed in Table 3.2.
Table 3.2 Ouality of hydrogen and nitrogen gases used in the reduction experiments.
Hydrogen Nitrogen
r
Minimum Purity 99.99% 99.998% \ 1
Maximum Moisture 5 ppm 5' ppm
.. Maximum O~gen 3 ppm /'
" 3 ppm \
\:,; <>
3.3 AO~OCLAVB ASSBMBLY .~ !,
.The reduction experiments'we~e conducted in a two litre
autoclave manufactured by Parr Instrument Company. Two m?in ,
components comprise the ,autoclave assembly~ a reaction vessel
• and a heating circui t •
3.3.1 RBA~IOH VBSSBL ( Figure 3.1 shows the main features of the stirrer asse~b1y'.
"\
....
0,
'. -
o
\.
0
. ...
32
and bomb .whieh were eonstructed of titanium. The .glass liner
used to hold the otganic liquid was made of Pyrex~
Agitation of the organie liquid and lead °powder seed was '\
'provided by a belt-driven stirring shaft ·fitted with two, 6 " pit~hed-blade, turbine impellers. The impellers were adjusted ~
" verticaily on the shaft resultinq in ~ positioning of • the
impellers 3 cm f~om the .bottom of the reactor and 3 cm below
the llquid level. Stirring speed could b~ adjusted from 0 to
1000 rpm by means o~ a vari~ble speed motor. 'il>
Liquid could be wlthdrawn from th~ autoclave for sampling
through the dip tube by opening of a sampling valve attached to
the head of the autoclave while the 9utoclave was pressurized.
Gas was introduced through this same dip tube under the liquid . . . l ' level via the gas fnlet valve, also attached to the head of the
" . 1
autoclave., Care was taken to close the gas inlet valve during
sample withdraw'al to ensure that the gas lines. from the -
press,ure cylinders were not contaminated with organic liquid.
Removal of gases from the reaction vessel was achieved by . . ~
means of a needle valve in the autoclave head, .JI'
which released , .
gas into a kerosene trap via a Tygon tube. Gas pres~~re was
measur,d by a bourbon-tubé pressure gauge having a pressure ... .' range Ifrom 0 ta 6.9 Mpa. Safety from overpressure was provided
by a 6.9 MPa golq-plated rupture dise instaIled in the head of
the react,or.
"'.
\ .-
~
""-"",;
" - fi - ••
",
33 .. , , o , .
' .
•
.....--- StirtlSJtg .... ft •
Thennowell------'""'i ~-_- Gas i"i ••• ftd liquiâ
wmplin9 tube
1 , . .
•
Figure 3.1 Sectioned view of the autoclave assembly reactor ). vessel.
o
o
34
3.3.2. BBA!IHG ABD TEMPBRATURB CONTROL '. . ',. r ,-The autoclave was heated by a sealed 1500 watt element
'. built into an insulat;.e§ stai~less steel shei.l s"iro~ndin9 the
bomb cylinder. bur'ing initial stages of the work , '[16], the . . standard Pro.portional Contro 1 Type automatic temperature
• l, control 1er supplied with the autoclave by the manufacturec
proved to bé inadequate for achieving and maintaining the
requiréd set point temperature for the process. A large
overshoot was observed during the initial heating period,
,'. followed by an unacceptably large deviation. It was surmised
that although this temperature control system was cons.idered . . adequate for aqueous solutions it was unsatisfactory for J:he
present ~ork due to the low specific heat·of the kerosene
sol vent used (-0.5 ca l/gm/oC). ?
Temperature control was achieved with the use of a
Proportional Integral Derivative action control 1er. , , The new
system, manufactu.éed by Leeds. and Northrop Limit:ed; was a
Current Adjusting Type (Soft) 'Electromax 3' controller wh1ch l "
provides a 0-5 mA OC .output, and \tfhose magnitude varies with
the deviation of input fram the set point • Power was supplied ..
to the beating element via a Zero-Vo1tage-Firing sol id-state
power .package. The accuracy obtained from 'this' temperature
control system was wi thin + 1 K of the set point temperatb-re.
Accurate reading of the temperature was obtained by the use of
a digita~ thermometer,
. . ~ .. '
h a vin 9 0 n e d e9 r e e 0 f r es 0 lut i O"n , ,
..
o
• o
"
e
. ,
3S
measuril}g the output of an iron-constantan • (J-type)
. thermocouple ins.erl!~ int~ the bomb thermowell.(see Figure 3.~)
. , '3.4 EXPBRIMENTAL PROCEDURE
.3.4.1 SUAIB OUT TBSTS
The shake-out tests were conducted using a 'Wrist. Action' -
MOdel 75 (Burrell Corporation) mechanical shaker. The aqweous ,
and organic phases were placed into 12S-ml Nalgene brand
polyproopylene separator~ funnels and shaken at room
temperature~ Ta determine the extraction of lead by KELEX 100
as a function of pH, lO.ml aliquo~s of an'aqueous'so1ution,
with 3 9pi initial lead concentration and pH:sS.OS, and an p
organic phase were shaken mechanically for,5 minutes and the \
phases allowed to separate. The pH of the aqueous phase was (
measured and adjusted, ,'I ïf necessary, by the addition of NH4oH. Q ,
Then, the p~ases weré re-equilibrated. The above procedure was
r"epeated unti 1 the d.esired pH -val ues were obtained. After ~
, shàking, the aqueous phase was filtered through WHATMAN l type
filter 'paper and analyzed for lead. The app~opriate mass
balance calcûlation was then performed t~ determine the amount
of lead in the organic phase. The slight volume change caused
~ the additioO'n of NH40H was cons,idered"\~9l igible and an
.' • i' / J , aqueous to organlc phase rat 0 (A 0) of one was used in the
extraction calculations.
"
,
•
o
Figure 3.2
'.
o
,. ,,~ - • it , 1 l ,1 ~
t
36
\
)--
- ,ô
Components of the apparatus for reduction: (1)
,
autoclave (2) tempe~~ture contr~ller (3) pow~r pack (4) stirrer control 1er (5) reduction g88. . , '
.-s' -
~.
. . '0
o
• (
' ..
pj .
37
3.4.2 LOADIMG ~B ORGAMIC PRASE rOR REDUCTION . .
Lead was loaded into the organic phase prior to reduction
by contact with an aqueous phase ana1yzed to contain 20.18 !
f .64 9pl lead and initial pH ,of 4.t5.
The aqueous and organic phases were mixed at an-initial
A/O of ,1 in a 'pyrex' gla·ss separatory funne1 into which a
"- té 'f 1 0 n s tir rë?: h f)'d . b e e n i n s e rte d • A t 0 t a lof 1 5 m 1 '0 f ,
concentrated NH40H was added to the aqueous phase in increments
of 5 ml by periodica11y stopping t'he stirring and ~eparating
the phases at 15 minute irttervals. After the final addition of
NH40H, the pha.ses 'were stirred for one hour to ensure
equi1ibrium. This res,u1ted in a raffinate having an
equilibrium pH of 5,.90 arid an organic phase of 19.54 + .86 gp1
l'sad'.
After phas~ v di sengagement and separation, the loaded
Qrganic phase was.filtered t?rough WHATMAN, IPS filter pa~er to
ensure tha t no -wate'r was brans ferred into the. au toc 1 a v e. l t
was necessary to ensure that no water was transferred into the "
autoclave in order to avoid the possi<bility of hydro1ytic
~tripping and for reasons of safety. The vapor pressure of p
~ter is much higher than that of kerosene, at the operating ..
temperatures used.
"-3.4.3 BYDROGBH RBDUC~IOH
One litre of the loaded organic w'as poure.d into,a 91a-"ss .. , liner .hich was placed ,into the autoclave bomb ànd the,stirrer
'/
...
.~.~~~,""~ç~,~-----------------~----"~,~.~,----------"~"~",,,,,,,,,,~J
o~
o
o
38
assembly fastened. Twenty grams of fine lead powder (-200 ..
mesh, Fisher C~talog 'L-29) was also added with the lo~ded
organic as a seed material "'hen experiment~l conditions ,
warranted. The bomb assembly was then inserted into the
~eating jacket and the cooling wate~, thermocouple, and stirrer
pulley attached. -
Entrapped air was removed from the autoclave by purging
for '15 minutes at a pressure of 1.04 MPa with N2 gas while -r'
-stirring at 800 rpm. After purging, the loaded organic was
. heated to the set ctemperature under an inert nitrogen"O. ~ ..
at~o~phere while stir~ing continued.
Once the temperature had stabilized a sample was withdrawn
to be anaIyzed and' taken as the initial Iead concentration. AlI
samples were taken by stopping the stirrer tor sixt Y ~econds,
in order to ailow set~ling of Most of the lead powder suspended
in the organic, flushing out of the sampling tube with 5 ml of 1
solution, and collecting 10 mIs for metal analysis •. p.' • .
After the first sample was taken, hydrogen was introduced
into the autoclave and the pressure adjusted. Uppn initial
-introduction of the· hydrogen gas into the· a.lltoclave a sl ight , ,
drop in temp~rature was observed, attributed to the cool
hydrogen masse 'Thermal equilibrium wa~ estabrished quick1y, ..
however. After final sample withdrawal, heating was turned off· 1
and the hydragen pressure reduced by open~ng the gas outlet .
valve. The autoclave was thèn purged. with nitrogen for 15
,-,
l ' :
( "
, o
o
\
•
---;;'" .. -~ -,", -r i
39
>!
minutes at 1.40 HPa ~nd allowed to cool- overnight while being
stirred. ,
The autoclave was dismantled the following morning and its
contents fi ltered through a 350 ml Buchner funnel hav Ing a
fritted dise of fine porosity. Filtration was aided by the use t
of vacuum •. The orga~ic was acid stripped using 50 gpl HN03 of "
any remanining lead and recycled~ the organic loss due tQ ~
sampling and handling was replaced by fresh organic. The '
residue of filtration was washed thoroughly w~th acetone,
allowed to dry at room temperature, collected, and stored.
After reduction, the i~p~ller assembly had a very thin
lead coatrng and small amounts of agglomerated lead chunks ,
adhered'to its surfaces. The surfaces were cleaned by scraping
them with a small brush', ao'd washing with acetone. Any lead
metal retnaining adhered to ~the s,tirrer assembly was rem~_ed by
soaking ~n a '50 v/a HN03 solution for one hour. ~fter rinsing
with,distilled water and drying, thè autoclave was .ready for
the nèxt expe'r iment.
3.5 CHlMlCAL ABALYSIS ~
3~5.1 DEfBRMIHATIOH OP LBAD CORC~RA~ION ~ Q
Dire~t determination of l,~ad concentration in 1;,he ~rgan.ic
phase was not pefo~ed. Lea~ concentration in the organic phase
for the extraction tests was determined by analysis of the , - - (
aqueous phase and calculation of t,he mass bëllance.
Lead concen~ratioq of the organie samples ~aken during the
..
o
..
o
"
,
tt
40
reduction experimel1ts was determined by ac.'id stripping of the
leaâ. ~ ,
an app-ropriate strlpping medium, .stripping To find e .
isotherms were determined for various concentrations of acetic .. and nitric acid -solutions. ,
J ~
The stripping ~iSO~he.rms "o.~ere cons;.ructed by shaking
varying amounts of aqu ous and organic phSses and determining
the lead distribution etween the two phases. The organic
phases used in these experiments had been loaded prior to
stripping from a lead acetate solution. Samples were
equi l ibrated for 30 minutes in separa tory funnel s after which
the strip solution, was ana1yzed for lead, and a mass balance
performed. The aqueous to organic phase ratio was varied from
. an A/O of 1/5 to 5/1. 1
In order to ensure that 30 minutes of shaking was
sufficiènt to strip aIl ~he 1ead fram the organic, the .kinetics
of lead stripping by 50 gpl HN0 3 was studied. Separatory
funnels containing 10 ml of acid and 5 ml of loaded organic
were shaken for time intervals·of 30 seconds, 1, 5,15 and 30
minutf!s, the phases separated and the strip solution analysed
for lead. CI
Lead concentration of the organic sampI-es t~ken &uring the
reduction experiments was determibed by stripping 5 ml of "
s~mple with 10 ml of 50 gpl HN0 3 • prior to stripping, the 1
~ o~ganic samples were centrifuged for 15 minutes at 1500 rpm in . -
order to settle out the lead powder product that was taken when
(J
- .~
flf-t
•
o
"
o
•
, \
41
. s~mpl il'1g. These samples were then fi 1 tered thr"ough WHATMAN lPS
filter paper. The organic and aqueous phases were mechanically
shaken for 30'minut&5 and the pnases separated. The strip
solution was then diluted and ana1ysed for 1ead using atomic
absorption spectroscopy on an Instrumental Laboratory 357
.Spectrophotometer.
3.5.2 ORGAHIC STRUCTURE AHALYSIS
The infrared spectra of KELEX 100 were recorded in the
wavenumber ra nge of 400 to 4000. cm- l using a Perk i n- Elmer 467
Grating Infrared Spectrophotometer. The KELEX 100 solution was .
injected into a liquid sample cell made up of two NaCl crystals
w i th a spa c e r 0 f .12 5 mm. T he r e fer e n ces 0 1 li t ion use d wa s 10
v/o decanol, 90 v/o kerosene.
1 uv' wave1ength sc~n from 201 to 900 nm was pel:'fOr-~ed with
an LKB-BIOCHROM Ultraspec 4050 Spectrophotometer. The samples
and' reference sol ution were he Id in l '~cm 'Spectrosi l' ce11 s.
Pretreatment of the KELEX 100- samples was necessary pri·or r-
to ana11ysis by gas-liquid chromatography. The KEL EX li) 0
mixture is insufficiently volatile to pass throQgfi the
chroma,tographic column. 'Si1y1ation is a common derivation.
method used in carrying out gas chromatography on organic .
compounds of low volatility. 1 n th i s pro ces 5 " the '.
trimethysi1y1 group (-Si (CH3) 3) ls su15stituted f-or active
hydrogen in a compound •. Sma11 al iquots of KELEX 10p. ~amples ,
were converted to the trimethysilyl de~ivatives with bis~
o
I~ "
..
,0 , .
, l'.
..
42
si1yltrif1uoroaceta~ide (BSrOFA - Pier~e Chemical Company) and
heated at" ~33 K for 20 minutes. A sma 11 al iguo t 0 f the
react ion mixture was i nj ected into a GC- MS chromatogràph,
having a 183 cm column coated with 6% OV-I01, and temperature
programmed from 423 K at 16 K per minute. Mass spectrometer . ~
sc ans were made f;rom 40 to 600 atomic mass units every 3
seconds.
"
"
..
\ , -
-
..
o
1
o
, 1
•
•
1
43
CHAP'1'BR 4
RBSUL!S AIID DISCUSSION: , .
PRBLIMIRARY BVALUA'l'IOH OP 'l'HB LBAD-KBLEX 100 SYSTEM ?
,4.1 BX!RAC'l'IOH ABD STRIPPIHG 01' LEAD ,
4.1.1 BPPBC'I' OP pH OH EXTRACTION
"1 The effect of pH -on the extract ion of lead by ltEL'EX 100 is • 1
shown in Figure 4.1. As the equilibrium pH of the aqueous
acetate solution was increased the amount of lead extracted
also increased. This can be exp1ained by examining the
equilibrium of the reaction whiéh describes the extraction of a ~ ~
metal cation by a chelating extractant. ~
.. Mn+ (aq) + nRH (org) ~ MRn (org) + nH+ (aq) (2.7)
As can be seen from the above, the equi1ibrium position of'
this reaction favors the formation of the products (extraction
of lead) wfth an inc'rease ~n equilibrium pH. o ~
T.he effect of pH on the Îogarithm of the distribution \.. .
coeff~c ient., log ~' for the data in Figure 4.1 is- shown lin
Figure 4'.2. The data in Figure 4.2 can be seen to comp,.rise two
distinct regions; a non-linear portion at pH's be10w 4.5 and a 1
1 inear port ion above pH 4.5. The 1inear pc;>rtion of Figure 4.2 1
can be used' to provide useful information on the stoichiom~try
of the extracted species. by the method of slope ana1ysis. The .
conditions required for the use of slope analysis have been
met" in that the extraction was conducted in large excess èif ...
"
-
/
o
o·
, 1
r
o
IOOr---~~--~----~~"~----~~--P---~ ... '
90
, \
80
• 70
80 " (
40.
. l
30
20 \ 10
...
J 4
0 fJ 4 8 7 8 9
'\
EQUILIBRIUM pH .' .
Figure ~.l Effect o~ equilibrium pH on the e~traction of lead by KELEX 100.
44
, /
-'
o
o
\
"
, l
• t
slope.2.04
ï c
c g- • -
,1
•
~1~----~4~----~a~-----e~----~7------·8------· EQUILIBRIUM pH
·~iqure 4.2 Variation of the coefficient, . log
- -~-~ --:: ____ ......;:-:::_ .-.;-1
• ., ?'~~~~,
loqarithm' of th~ distr~butiQn;:;k~~;::~-=-~ ~-1 D , wit!l equilibrium pH. ,-~~-,-/ /
/ -___ /~ _ r : . -
•
..
o
\ 46
KELEX 100 campared to lead concentration, al10wing us ta assume .
constant extractant concentration. Also, the use of a large \ ,
ex cess of acetic acid 'as a backi..1lg electrèqyt,e a"nd low me~al ~ 1 - ~' .,
" 11 f h \ ," . concentratIon a ows or t e use o~ co~centratlons to ''\ \,
approximate aétivities. The app1i<=-ab·ility df ,s)ope analysis to
th i s s ys t ~ mis bas e don t,he fol 1 0 w i .ri,g sim pli f yin 9
" assumptions [59]. \ \
1.
2.
3.
4.
5.
No polymeric spec,ies are formed id el ther phase.
Only uncharged species are extracted.a
T'h e f 0 rm a t ion 0 fin te rm ed i â te non - ex t r a c ta b 1 e
complexes' can be n,eglected •
No adduct formation between complexes and
undissociated extractant molecules or the "
organic diluent or modifier takes place.' .
All hydrolysis reactions are insignificant.
For the range corresponding to .90< logo <30" in Figu~e 4.2
linear regression yields a slope of 2.04 + ,.28 with a
regress,ion coefficient, r, of 0.97 and a pH. 5 of 4.79. The
re1ativ.ely large deviation in slope (!:14%) may be due to the
non-water soluble i~purities present in KELEX 100 which cannot
be'removed by acid washing. Present in minor amounts, =ûme
posses. chelating abilities of their own.
Thus, the extractio~ reaction for iead by KELEX 100 for
the system under investigation at pH values above 4.5 can be
. ' wr i tten as the followlng.
"
o
o
. ,
'.
~ .
'.
47
. P,e+2(aqr\+ 2[KELEX 100] (o~g):= Pb[KELEX lOO]2(org) + 2H+(aq)
(4.1)
In 1 ta structural ,fotm, i t May be represented as the following. )
--(org)
(org)
6
~he determination of a stoi.chiometry of~2 to l for KEt.EX •
100 and"lead Is consistent with the sp'ecies reported by other
researchers who have studied the extraction of lead with KELEX 4
100 and other chelating type extractants. Hoh and co-workers o
[44,45] have assumed the structure ~f the extracted speçies \
from aceta te so 1 ut ion. wi th LIX 34 and LIX 64N as being the same
as determined in this work. In addi~iqa" organic liga~nd to
, lead stoichJometry of 2 has been reported for the extraction of •
1 ead from chI or ide med ia [60] .by LIX 34, LIX 54, LIX 70 and
KELEX 100, and fram highly alka1ine media by KELEX 100 [61,62]. , , .
At pH values be10w 4.5 a different extraction mechani"sm than ~
.that described b~ equation ~.1 se~ms to be in operation.
Grad ien ts for ,~<?g 0 versus pH i.n thi s reg io.n a're ~ 1 ess than " '.
2,which ls' probably due ta mixèd species being extracted into ,
the organic phase. 'Lead forms .several stable acetate .species
.,.
o
~
o
o
48
1
in aqueous solution [63], and it is possi~le that aceto-lead-
KELEX 100 specles~may be extracted in this reglon. This is
only speculation ,Y and more detailed study of the extracted .. -
species formed ~n ,th"is region is required. For the purposes of
this investigation it is sufficient to determine the ~tructure )
of the extracted species under the conditions of loading ~sed ,
(pH> 4.5) prior ta- pressure hydrog~n stripping.
4.1.2 STRIPPING.oF r;SAD FROM KELEX 100 •
A study of the stripping characteristics of lead 10aded
KELEX 100 was undertaken to determine the suitab~lity of using'
solutions of HN03 or HOAc for lead concentration determination •
of the organic samples from pressure hydrogen strippin.g.
Results obtained for the stripping of lead from KELEX 100,by . . ,. HN0 3 and HOAC under the experimental conditions described in
the previous chapte~ (Section 3.5.1) are shown in Figure 4.3
.and 4.4.
The shape of these curves ls not indi'cative of stripping ,
isotherms under equi librium conditions.: The aqueous samples
from these' tests were analyzed d~rectly after stripping and
none of the samples contained v i:sib1e precipi tates. But, 'ove): ..a
a period of time precipitates were formed in most of the
solutions. ~trippirtg of lead f~om LIX 34 with 1 v/~ HO Ac was
not reported to' have had the same prob"lem with
precipi tation. (~4 ,45] However, Kordosky et al [64] d id report
that Pb{N03)2 was precipitated after stripping 14 v/o LIX 34 in
...
.., .
'.
-
0
'"
••
•
, , . ,
• 70
6C ~
-- • 200Pl HN03 Cl. • eOOpl HN03 ~. 50
~. Ot ') I.&J !
::::) 40 ........,
~ Z -.0 Q.. , '.
'"
<!> .,
.1 -.... .;.
~
"- ...
"
O~---------------------------------------o 5 10 15 20 25
Pb LN ORGANIC COPi)
\
Figure 4.3 Stripping of lead from KELEX 100 with 20 and 50 gpl nitric acid.
l '
'49
.'
'. '" .. '. ,1,1%1
50 .-'
80 ',,;,\ ,
• 70
60
""" • 20gpl HOÀc
-Q. • 50gpl HOAc 0 50 ......
Cf) ...
;:). 0 LtJ
· ·0 ;:) 40_ 0 <l: ,~\~fJ' (', ( \
~ '.ff
Z \
..a 30 • a.. "
\ ...
...
)
0 0 5 10 15 20 25 30 " 35
Pb IN ORGANIC (gpl)
0 F~gure 4.4 Stripping of 1ead from KELEX 100 with 20 and 50 gpl
acetic acid.
r
o
-0
•
51
Napoleum 470B, 'loaded to 9.56 gp~ lead, at- a' st):ipping O/A of
6/1 with 150 9Pl HN0 3• e
a •
The delayed precipitation observed in this investigation
is thoug'ht to be due to supèrsaturation of the aqueous phase
under the stripping conditions used. The stripping lines reach
a constant maximum lead concentration in the aqueous phase.
This is thought to represent the supersaturation 'point of the
strip sOr}-uti.on. This is more clearly seen when HN03 is used as
the stripping -medium. From" Figure 4.3, we see that the. maximum
,lead concentration for 20 gpl HN03 is about 30 gpl lead, and
fOl: 50, gpl )HN03 it is about 72 gpl lead.
A comparison of the stripping curves in Figu~es 4.3 and
4.4 sh~ws that at an A/O of 2 aIl of the lead has been s'tripped
from the organic ihase contain~ng 20 gpl 1 ead _in one stage wi th
either 20 gpl HN03 or 50 gpl HN03. In contrast 2 stages o~ . . .
strip.ping ar-e required to strtp 20 gpl lead wlth either 20 or'
50 gpl HOAc' at A/a of 2. Therefore.the use of nitric acid
medi~ would facilitate chemicàl analysis. ..
It ls important to note that·since the analysis of
. supersaturated solutions of lead were used ta c'onstruct Figures
4.3 and 4.4, they do not represent equilibrium stripping
isotherms. Nevertheleas, ·the information obtained frem these,
tests can still b~ qsed to produce an effective analyticai 1
method for determining the lead concentration in the organic ",
phase. This Is ~ccomplished by exploiting the kinetic
..
o
o
, ....
o
52 or
requirements of lead precipitation from solution. Oefinea,-,
supersaturation is an~effect resulting from the,appreciab~e .
time 1ag required for the condensation of ions upon invisible
nuc1ei to form partié1es large enough to precipitate, even .<
though the' ~olubi1ity prodùct (Ksp) has been exceeded..(651 By
ana1ysing the aqueous samples quick1y enough ~fter stripping to \
ensure that precipi tation has not begun, accurate me~surement can be achieved.
Apart from the kinetics of precipitation in the strip
solution, the kirl\etics of stripping are a1so important in
~ssuring that,the lead concentration measured in the strip
solution can be used to measure accurate1y the 1ead 4-
concentration in the organic phase. Figure 4.5 shows the
kinetics of stripping ~n organic phase with 5Q gp1 HN03 at an " 4
A/O of 2/1. As can be seen, the stripiing kinetics are very . @>o
fast with a1most a1l the lead being stripped after 30 seconds. ~ 0
the above information, it can be said that stripping , ~
From o •
with 50 gp1 HN03 at an A/O of 2 for 30 minutes fo11owed by "
. immediate ana1ysis of the aqueous 'phase for lead gives an
. accurate measurement of the 1ead concentration' in the o·rganic
samp1es f;om pr'essure hydfogen stripp-ing. It shou1d a1so be
noted that, in addition to application as an ana1ytica1
technique, nitric and, acetic acid' stripping could be considered ,-.
as suitable stripping media in a' praetical process involvi~9 ,
lead solvent extraction.
, r ..
•
....
fi i,
o
o
o
-~ /IJt!!k,i! , .
S4 ...
4.2 CHBMlCAL AND THBRMAL STABILITY • •
Reaction of KEt.EX 100 witli hydiogen at elevated \
temperatures and pressures could lead either to hydrogenation.
of the aroma~ic rings or, under more drastie conditions, to , )
decomposition due to breakage of the rings (hydrogenolysis).
Tne effect of high temperatures could in itsel f lead to -ring
breakage (pyrolysis). Any'of these conditions would make KELEX
100 unsuitable for pressure hydrogen stripping since organic
1 regeneration and recycling is essential for the process.
Evaluation of an extractant for conventional
hydromoetallurgical solvent extrac.tion involves consideration of
thermal stability up to 323-333 K. However, for the hydrogen
stripping of lead fran loaded KELEX 100, thermal stabil ity at l
much higher ternperatures is required. It should be noted that
during manufacturing KELEX 100 is s~bjected to temperatures up
to 533 K in a reducing atmosphere (O.l~ MPa H2) with no signs
of organic decomposition [16]. However, heating in the presence
o,~ air gr e a t 1 Y a cc e 1 e rat e s d ec om po s i t ion 0 f the e'X t ra ct a nt.
This suggests that reactions with KELEX 100 at high i ..
temperatures cannot be conducted in the presence of air.
In ôrder to determine the chemica~ and thermal stability of . .
the lead-loaded organic phase, the structure of KELEX 100 was
compared, "uJJing gas 1 iquid chJlomatography and infrared
spectroscopy, before and after reaction with hydrogen. \
o
• .. .
. . lOj' ,. , .
. .
55
4.2.1 GAS-LIOOID CHROMATOGRAPHY
The gas-1iquid chromatogram of the unreduced, acid
'purified', KELEX 100 used in this investigation is shown in
Figure 4.6. The sample displayed a prominent peak .at slightly .
over 1rminutes retention time. The molecu1ar weight bf the ,
compound represe,n ted by th i s peak was found, us i ng mass
spectroscopy, to be 299.
Detailed analysis of' the different components in the
organic phase is not possible using thJJ chromatogram, but muc~ ,
information has been published on the composition and structure
of the various components of KEIEX 100.[4,66]
A typical gas-liquid chromatogram of the same batch of , ~
KELEX 100 (Lot No. 83l3R) that was used in this investigation
with major peaks numbered is shown in Figure 4.7.[58] In
addition to the main active c9mponent the commercial ex tractant
also contains severaJ. by products 'of the manufacturing prpcess. , ~
The attenuator setting for, aIl peaks, with, the e'xception of
.#
peak 4; was X500. The setting for peak 4 was XIOOO, ind icating 1 ~.
that thil\J peak should be twice as big as it appears.' Moleéular 1
weights 'of th,e components, as identified by mass spectrometry,
• along with their assigned structures are shown in Table
. . 4-.1.[66] Also shown in this table is the weight percent of
each component present which~was estimated by measuring the -\
areas enclo'sed by the re'specti ve pe~ks _in the chromatogr~m of ) )
KELEX' 100. t
)
, .
o
\
\ "
\
o ~
..
."," ..
;)
J
,-~
1 1 --.,
Q
-, ----.- 1 -r ... ---~ t ) ~ 1 A-i
0 1 2 3 4 e 8 7- 8\ 9' -
4 RETENTIQN TIME (mlnj
)
1 10
1 1 1
\ ,
1
~
l) • I~ 13
Figure 4.6 Gas-liquid chromatogram of unloaded, unreduced KELEX 100.
...
r
1
' . '14 15
'0
/
..
<
U1
'"
~
- \
. . , \
. -
, '.1
~
iii-
CI o - ~ 0" ,
- - - . Kelex100
.. ,. -
Before Loading 4 ' ,
--
. ' -. .
0 . , -- . • . ~
k 2 \. ,
- /f " - , -
,
l \. -
~
.-
-- .
, .' . . r - .
.. , 7 '" " - .
~ -: . .
-,
. - - 8 -. - 8 9
.... 3 1
~ 1- '
1 '6 10 - "-A l ILJ llL L l , 1 1 • ~ • • • 1 • • • • • 190 210 230 260 270 290 .
TEMPERATURE ('0)
Figure 4.7 Detailed gas-1iquid chromato9ram of un1oaded, unreduced KELEX 100 showing peaks of the maJor components. ,_
Ul .....
~
58 . 1""- ~ Table 4.1 Componenta of l!L!X 100 determ1ned by q •• -l1qu1d 'it<, .. \ ' , chrolUtography and ma .. lpectrolcopy. (661 JIll
0 '1
Peale Mol.culer "t.' MOl.cular Itructure we19ht
l 145 0.5 A, R - "
1
2 197 8.0 b, Rl - ft -..
-~ - C2HS
\ /C2HS \ , 3 257 1.0 A, R • -CU2CH"
C.H9 '
4 299 82. a li, /C2"5
R -tHICH2)2CU""
CH) C4"9
5 297 0.5 /C2HS
A, R • taCHCH2CH ~ CH3 C4"g
0 - /C2HS
6 297 0.5 c, Rl • -cH2CH""
C.H9
R2 • CH 3
7 295 4.5 b, /C2HS
Rl • -CH2ca"" ' C.H9
,R2 • CB3
8 453 3.0 ?
~ ~ ~. , " . Itructure a iltructure b Itructure è:
0
, $
.' .. '-.. ~ ...
o
o
-8
F .
,
59
Two types of organic structures were reported to be
present, those based on 8-hydroxyquinoline (structure a) and
furoquinoline derivatives (structures band cl. Those -
components based on 8-hydroxyquino 1 ine contain 'the exchangeable
hydrogen that takes part in the loading reaction but the
fu~oquino1ines do °not have complexing properties.
,The main active component (peak 4) was reported to
comprise 92 weight percent with a mo1ecular weight of 299. , cCl
Therefore the peak found by gas-1 iquid chromatography in this
investigation is that of the main domponent in' KELEX 100, and
comparison of this peak befo~e and after hydrogen reduction of
1ead loaded KELEX 100 will determine the chemical and thermal
stabi1ity of the organic phase. The lack of de~ailed
information displayed in the gas-1 iquid chromatogram of Figure
4.6, compared to previous work[16,58], is thought t-o be due to
" the different procedures and equipment used to generate the
gas-liquid chromatograms. Differences in start~ng temperature,
adsorption co 1 Ul!'ns', heating rates, attenuator settings, and gas
flow rate, aIl affect the gas-liquid chromatogram.generated
[67] •
The'gas-liquid cbromatogram of a sample of lead-loaded
KELlX 100 which had been reacted with hydrogen is shown' in
Figure 4.8. An organic phase, analysed to contain 26.90 gp1
---lead, was reacted at 2.76 MPa H2 and 47.5 K for six hours. Any
rféma'ining l,ead was stripped, and the sample analysed. A
,.:"'f'""i."~
•
'" . ~ .;.-
/
o
\
,
01· r' lJl,A i i ~
-. • • 1 , • .~ , 9 II~ 0 1 2 3 4 6 10 Il
RETE-NTION TIME (min)
Figure 4.8 Gas-1iquid chroma~gram of un10aded KELEX 100 after reduction at 475 K and 2.76 MPa H2 for s~x hours.
.-' ,
'.
1 1 13 .• 4
o
•
15
c:7\ o
.'
o
o
.' ",
, '.
o
•
, .... ,- ';.... ~
...
61
dominent peak is again e1uted at just over 8 minutes ~etention • tima and was found to have a molecu1ar weight of 299, the sarne.
as was found for tl1e organic prior to hydrogén 'stripping.
Nonidentica1 retention times are the resul t of the d ifficu1 ty
of rnatching starting temperatures in the program mode.
Reappearance of the peak for the)major component of KELEX
100 (peak 4) after pressure hydrogen stripping suggests good
chernical 'stability of lead 10aded KE~EX 100.\ Furthet evidence \
will be presented in a study of the infrared spectra. , l
4.2.2 IRPRARED SPECTROSCOPY
The structural changes which KELEX 100 undergoes,during
the 10ading of lead, and hydrogen stripping, are better shown
using infrared spectroscopy. Figure 4.9 shows the spectra of
·unreduced, unloaded KELEX 100 in the wavenumber range between
4000 and 400 cm-l. Harrison et al [68] have reported <;ople
cha~acteristic frequencies of the infrared spectrum of KELEX
100. For instance, the OH-ppenolic stretching frequency was" .. ~ ...
measured ~~ 3400 cm-l, the C-N stretching frequency at ~280
cm-l, the C-N bend1.ng frequency at 720 cm-l, and the C-O
stretching frequency at 1090 cm-l. "
Ashbrook [,69] maintained that the phenol ic hydroxyl group
in KELEX 100 is involved in intramo.~ecular hydrogen bonding.
This was deduced from the presence of -,an absorption peak around
3400 cm-l, which was in evidence down to a concentration of .. O.002SH in carbon tetrachloride. This i5 similar to a peak
-, .r
---------------------------------------000
~ ~.o
! ... 2 40
! .... 0
4000
2
l '
lIIqO 1I()CJ(J,
9
8
2000 1800 .800 1400 .aoo
WAVENUM8ER (CM"')
Figure 4.9 Infrared spectra of ~nreduced, unloaded KELEX 100.
.. . 1000
12
11 800
13 1
14 . 15
eoo
~ '" " N
o
'0
, ' 1 1
.. li ('..:
·8
j (. \~" -'" ".
63
present in the spectr~m df 8-hydroxyquinoline àt 3410 cm-l,
which has also been associated with hydrogen bonding. . (
The infrared spectra' of the parent compound of KELEX 100, "-
, 8-hydroyquinoline and its met~l chelates, have been studied in
much greatel: detai1 than the ,ïnfrared spectra of KELEX 100.[70,
71] In Most studies thus far, sol id samples of 8-'
hydroxyquino1in,e and its chelates were used. In the present
investigation, only liqui.d samples of KELEX 100 were analysed.
Structural changes undergone by the Molecule of the active
componen t of KELEX 100 when loaded wi th l,ead can be shown by
examining the spectra of the 'loaded ex tractant shown in Figure ,
4.10 •• Changes in both transmittance and frequencies of the
peaks is expected when comparing loaded and unloaded, KELEX' H}O
, du, to the effects of the lead on both bend ing and stretc~ing
vibrational modes of the va~ious functional groups of the
Molecules. Darkened arrows in Figure 4~lO indicate those peaks
for which changes are considerable. (shi ft' > .:!:. 5 cm- l ). ï
The peaks at 3400 cm- l ' (peak 1) and 1330 cm- l (peak 7)
h~ve been attr ibut~ to repr"'esent the stretc,hing and bend i ng, 1
respectively, of the phenolic-hydroxyl) group on the KELEX 100 ---0.../-
Molecule. [35,68] ~beir d~stic reduction in the spectra of
10aded KELEX ~O~ signifies the replacement of hydrogen by lead. , \.
Shifting of peak 4 fr-om 1572 cm- 1 to 1550 cm-l,and peak 6 from 1
1405 cm-1 to l~~à-cm-l is attr'ibuted to th~ effects of ~ad on
hetero-ring stretching and atomatic : ring stretching " .
ai -
•
2
• Ch)
- 4000 !BOO 3000 2100 2000 1800 .800
• WAVENUMBER (CM"')
17
10
1400 1200 1000
12 f 14' , 13
11 t 800 800
Figure 4.10 Infrared spectra of (a) un~educed, un10aded KELEX 100 and (h) loaded, unreduced KELEX 100. -
~
20
- . '-
'" ~
-..1 ....
o
o
•
65
respective1y [66]; Simi farly,: -C-N stretching is thought to be
represented by the shift of péak 8 from 1272 cmJI to 1250 cm-l;.
(68], while c-o stretching< has been assigned to the shift of \
peak 10 from 1090 cm-l to 1100· cm-l. [721 The shift in peak 1-3 c _
from 7,20 cm-l to 735 cm- l is attributed to C-N bending.[68]
Figure 4.11 compares the infrared spectra of KELEX 100
before,~nd after hydrogen reduction~ The spectra in Figure
4.11 (b) 'fs of KELEX 100 wh ich has been subj ected to three
recycles of loading and hydrogen stripping under. various
cond i tions of temperature and pressure used in the study of the'
kinetics of reduetions (493K to 533K and 1.38 to 4.14 MPa H2)·
The 1ead which had not been removed by hydrogen reduction was
stripped from the organic with nitric acïd pric;>r to infrared
analysis.
A comparison of FJgure 4.ll{a) and Cb) reveals that the
major .peaks have returned to their original heights and
positions. The on1y exception is with peak 3 <i 7'20 cm- l ), •
discussion of which will be taken up in the section dealing
with thermal dissociation under nitrogen (Section 4.2.4).
Peaks 1 and 7, corresponding to OH-phenolic stretçhirig and
bending respectively, have returned to their original heights. , From the changes of the se peaks, i t is apparent tha t hydrogen
exchange took place between the 1ead loaded extractant and
hydrogen •
1 1 1
'" o o o .. 1001 "V\. K ____ -= , _ _ ;:::oz;: ilOO
...... } .
o
~.
67
'-KELEX 100 "istucture 1)" being a Cll a-l kylate of 8-l"
hydroxyqu4noline, has structural similarities to quinoline
(structure II) and 8-hydroxyquinol ine (structure III). Because
of this, an insight into the possible hydrogenation and/or
pyrolysis 'of KELEX 100 can be obtain~d from infotmation about
hydrogenation and pyrolysis of these compounds.
OH \ OH 1 II III
In the literafure, a number of references desctibe the
catalytic hydrogenation of quinol ine unde~ a variety of .
temperatures, hydrogen pressures, and catalyst environments.
[73,74,75,761. Quinolines are usually reduced preferentially
in the het~ro-r ing, regard less of ca talyst, producing 1,2,3,4 •
tetrahydroquino~ine ("structure IV). [74] Under stronger ~ .
hydrogenation conditions (>10 MPa H2), decahydroquinoline 1s o
produced,(structure V), while under extreme conditions (>15 MPa
H2), the ring system'breaks down yielding ammonia, amines, and
hydrocarbons. [77] ,
8-Hydroxyquino~ine exhibits the same behaviora1 pattern as
quinoline when catalytic hydrogenation is carried out. The
1,2,3,4-tetrahydroquinolinol compound (struct4re VI) was the
,reporteà hydrogenation product. [74]
,
.1
·0
o
o .. , .,
..
. ..,
~~ 'j' ll~"'·-t-"'If ... l,fi" ...
..
IV
1 H
Q
V
1 H
, , ~---y-~-------.....,)~. ""'~4I11!!!tS"!ffi§Ej_" '
68
. OH
VI
Catalytic hydrogenation of the KELEX 100 molecule has .
reported for the pressure, hydrogen stripping of copper when
decanol was not present, and was attributed to hydrogenation of
the hetero-r·ing of the active component of KEt.EX 100 [16]. In " 4k/,
addition to the actlve compc;>nent of the extractant, sorne
impurities in the as-received reagent were also found to be .
unstable in the absence of decanol. These impurit~es were
identified as dihydrofuroquinoline (peak 6, Table 4.1) and r
duroquinoline (peak 7, Table 4.1).
Resistance to hydrogenation for the lead-KELEX 100 system
under the pre'"ssure condi tions employed in the
pre'sent work may be exp! by taking into account\.."tlYe "
inactivity of lead mètal as an hydrogenation catalyst becàuse
of its inability to chemisorb hydrogen gas (78).
Further experimental evidence of the resistance to
hydrogenation of KELEX 100 ia that in parallel systems of .. nickel [56], coppet (57] and cobalt [58] precipitation, no
~ problems of degradation due to extractant hydrogenation were
" encountered at" higher temperatures and pressures than used in
this investigation in the p~esence of these wèll-kQown
hydrogenation catal ysts [79,80].
1
. ().
.1/
• o.,
, . •
69
Reappearance of the major peaks for both the gas-Li.quid
chromatogram and infrared spectra, in conjunction with the fact
.} that no detectable 10ss in loading effic iency was observed when
the organic 14;{uid was recycled, indi.cates that hydrogenatio'n
did not occur and that KELEX 100 is a suitable extractant for
. '
. press~re hydrogen stripping of lead •
•• 2.3 ULTRAVIOLET SPEC'l'ROSCOPY 1
A wavelength scan was performed from 201 nm to 900 nm of
lead loaded KELEX 100 versus both a lOv/o decanol; 90v/o
'kerosene blank, anLl a 15v/o KELEX 100,10 vlo decanol, 75v/o
kerosene b1ank. Both the sample a'nd the reference solutions , ~
()
were diluted the same amount wi th kerosene. The peaks ~
observed for a sa.mple containing 38.4 ppm 1ead are shown in
Figure 4.12. On1y the wavelength region from 325 nm to 500 nm "
erov ided useful information and is shown in Figure 4.12. ~ fil
In the absence 'of KELEX ~100 from the, referen'ce solution,
two peaks are observed, at 337 nm and 425 nm. When KELEX 100 . ls 'included in the reference solution only the peak at. 425 nm
appears. Therefore, i t fs surmi zed tha t the' peak - a t 337 nm i s •
due to KELEX> 100 and the .lead-KELEX 100 chel a te absorbs at 425
nm •
The absorpt i on of KELEX IpO a t 337 nm i\S s imi 1 arc, to one 0 f ~ .
the peàks r~ported by,Cote and Bauer [811 at 330 nm of pre-1976 1 1 1 \
manufacture KELEX 100 in pure hexane. Attempts ~o use
ultraviolet spectroscopy " . c 1
for quantitative. analysis were , . •
"
\ .
..
o
o
o
/
O~~~ __ ~~ __ ~~~ __ ~~ ____ ~~ __ ~. 328 360 a95 4ao 465 " eoo
WAVELENGTH (nm) tti ~ 4
( a)
-"-- .
~'~~~~~----~!95~~~43~o~--~~~e~--~500 WAV~TH (nm) .
le b) .
'\ 'i
Figure 4.12 Ultraviolet spectra of the lead-KELEX 100 , · ver~us (a) 90 v/c kerosene-lO v/o decanol
and Cb), KELEX 100 blank.
. ,
.0
chelate blank,
70
r
o
e
71
/ ~ (
unsuccessful because Beer' s law was not sati sfied, even at very
di 1 ute concentrations of the metal che1àte.
4.2.4 'l'HBRMAL DISSOCIATION UNDER NITROG,R ..
As mentioned in the experimental section of the thesis,
the initial, heat-up period to the experirnental temperature was
conducted under a chemically inert atmosphere of nitrogen gas
/
. '\ . unti1 the reaction temperature was establisned (standardized té
1
2 hrs).
Dut;ing the initial hydrogen reductio'n experiment it was
noticed, after chemical analysis, 'that t~e lead concentration
of the sample at time equals zero was different from the lead
concentratiof) of the organic phase"before heat up. Also, lead .
powder was observed to be par~ of the .initial sample. It was
therefore speculated tbat lead was precipitating during the l'
initial heating periode The 'extent of this phenomenon can be
seen from Figure 4.13 where at 518 K, under a nitrogen -<
at~osphere, about 5 percent of the lead had --precipitated after
6 hours. . ,
This ph~nomenon, of metal precipitation under an inert
atmosphere, was a1so reported by Demopoulos [16] in bis q,
invest igation of a !\paraI 1 el sys tem wi th copp.er. A compar i son
,of reaction curves for the two systems under sim'ilar conditions
.. of temperature (as shown in Figure 4.13) indicates that the
aoppe~. chelate is more suscept ible to thermal precipi tation
than is lead.
72
o
\ V--:-J (.)
60 -Z '\ ct
(!)
0 0: 0
.l Z - 40 .ca
.Pb .Cu Il.
~ Temperature (K) 518 517
~ Pressure (MPa N2 ) .35 .35
20 Stirring (rpm) 800 5q9 Chelate age (hrs) , 24 "24 , 'Initial cenc. (M) .10 .16 Seed no no
0 0 2 3 ·4 5 e
;.- •
'p-IME ( hrs) /_ .. ~ ... l~ .. ,." . 1 \, , )
Figure 4.13 com~arison between the thermal precipitation of . 1ea and copper under nitrogen.
""
0
o
;
o
•
, ,
73
Simi larly as observed in this investigation, Demopoulos
[4] reported regeneration of the organic solvent a~ter pressure
hydrogen stripping of copper. However, infra-red spectroscopy
revealed sorne changes due to thermal precipitation of copper
du~ing heating under a nitrogen atmosphere. Notabl~ the peak at
3400 cm-l was slightly reduced while a relatively strong peak
at 1720 cm -1 was observed.
Sorne speculation concerning ~ plausible pyrolysis
mechanism prevai1ing during thEYthermal dissociation of the
copper,chelate when heated under nitrogen ~as put forward and ":\1 1
is shown in Figure 4.14 •.
J, , . a'" - • Cu J
_. -Figure 4.14 proposed mechanism for the thermal dissociation of
the copper-KELEX 100 chelate. [4]
" Adoption of this mechanism explains the differences in the
infrared spectra of KELEX 100 before and after pressure
hydrogen stripping of lead. ,Heat-up a~d cool-down periods •
under ni trogen resul ted in production of polymerie speeies çf
o
o
74
the KELEX 100 molecule. The decreased peak at 3400 cm -1 ,
associ'at~d w{th KELEX 100 after" reduction (representing the -";.~ ~
stretchiog frequency of OH) and the strong peak at 1720 cm -1
(representing the keto group "t=O) are indicative of the /
assumed tautomerism.
Bui~d-up of these polymerie species would affect loading
and stripping pe~formance in a practical operation involv ing
ex tractant recycling, but èould be avoided if the encire
process (including heat-up and cool-down) were conducted under
hydrogen. Because the reproducibili~y of loading upo~ recycle
o f the 0 r 9 an i c ph a se wa shi 9 h '( 2 0 .18 .:!:. .6 4' g P Ile ad)
polymerization is not èonsidered to be a significant problem in
the study of the kinetics of hydr~gen stripping of lead. 1
The pyrolytic behavior~ in an inert atmosphere (argon), of
a se rie s .' 0 f diva 1 en t met ale h el a tes der i v ed 'f r om 8-
hydroxyquinoline has been studied by'Charles et al. [821 The t
order of decreasing heat stability of the solid chelates was
reported as' being Ca>Mg>SrAMn>Ba>Co>Ni>zn>Pb>Cu., principal
products of decomposition include hydrogen, 8-hydroxyquinoline,
the free metal or metal oxide, and carbçnaceous materials in
which a portion of the metal chelate ring systems is retained.'
The order of thermal stability found by these researchers
correlates weIl with observations of thermal precipitation
reported in the various ~tudies with different metals and KELEX
100. Thermal precipitation was reported not to occur in the
, , r
,0
o
. , .
75
nickel [56] or cobalt [58] -KELEX 100 systems at temperatures
below 573 K (the maximum temperature studied). Whi1e, as shown 1
in Figure 4.13, copper is more .. susceptible to thermal \
precipi tation than 1ead.
Charles [82] also reported the decomposition of the 1ead
chelate o~ 8-hydroxyquinol ine to occur at tempyatures above
583 K. Assuming similar thermal characterisitcs for KELEX 100,
decornposition of the 'lead-KELEX 100 chelate mi~ht be expected
to oeeur near, at or above 583 K •
A reduction test run at above the me1ting point of 1ead
(600.5 K) was eonducted to see if r~duction was possible df a
metal in molten forme The experimenta1 conditions were 611 K ,
2.76 MPa H2', 20.0 grâms of 1ead seed, 800 rpm ag i tation and 24-
hour chelate age • upon o.pening of the autoclave after
. reduçtion it was apparent from the foul smell of the organlc
phase that decomposition had occurred. Infrared speeroseopy
eonfirmed this observation and a comparison o~ the infrared
~ spectra befo~e and after redue~~on'is shown in Figure 4.15. A
drastic red~etion in transmittanee is observed for peak l, \ .
suggest i ng destruct ion 0 f the OH-pheno 1 ie group on the KELEX
100 molecu1e •
-~-
o o o 100ft 'V\.. K .:::: 5 'A..-. ;:::::tZ _ "1100
li -1
2
r Jo - (a)
5 6 1 IIg
8
0' , , , , , , , ft
~ 1-4000 3500 moo 2IlOO 2000 l8QO ,.00 ._-- ._--
WAVENUMBER (C .... )
13 1 ~ -Lo Il 14
15 12
1 -Iao
11 1 1
NOO 800 800
1001 :::;::o:z::::;; 1 ,...! .... ~ _ ~ ,:==x:; r-....' "'1
li 1 1 2
~.o t
~ V ~
, , ... !::40 6 ",.J :lE " 3 5
1 (b) V 9
10 Y 8 11 o. 1 1 1 1 1 1 1 1 1 1
4000 3500 moo 2IlOO 2000 IlOO 1100 1400 1100 1000 8OQ, 800
WAVENUMBER (CU")
Figure 4.15 Infrared spectra of (a) unreduced, un10aded KELEX 100 and (b) decomposed , KELEX 100 after reduction above the me1ting point of 1ead (611 K). ....
0\
·0
o
'.~. '$>.
, , ,
77
• CHUTER 5
RBSULTS AND DISCUSSION:
PRBSSURE HYDROGEN STRIPPING
5.1 KIHB'l'ICS
The effects on the rate of lead precipitation from loaded
KELEX 100 using hydrogen was investigated with respect to
several process parameters. The parameters studied were seed , '
addition, and its effect ,on pla,ting, agitation, lead chelate
age, temperature, and hydrogen, partial pressure.
5.1.1 SEEDING AND PLATING , \
In a chemical precipitation system where a solid phase is
produced fram a solution, it is important to clarify if the
nucleation taking place is homogeneous, heterogeneous or if
both mechanisms are occurring. The effects of the presence of 1
external seed and immersed metallic surfaces on . the reaction
rates of lead precipitation will give an indication of the
nucleation mechanism.
Reaction rates are presented as percent lead in the
organic phase versus time. Time 'zero cor,r'esponds to the time 1
at which the operating tempera ture was reached and the' hydrogen
gas was introduced into the autoclave. One hundred percent
lead in the organic represents the initial lead concentration
a t time zero\
The eff~t of adding 20 grams of fine lead powder as seed
on lead precipitation rates is shown in Figure 5.1. Although
,.
o
0
'.
0 -Z CI: (!) 0: 0 Z -.a Q.
~-
~
80
·60
40
20
..... _ .. --.--------:-~----~---~---•• , ... , .!II!!$ ...... : .. .-l-p ... ,(,
\
Temperâture: 518 K 2.76 MPa H2
: 800 rpm
helate age: 24 hrs
.. ~~
78
• no seed • 20.0 g seed
po'
o~----------~------______________ --____ ~ 00 '2 4
TIME (hrs) - .)
FigUre 5.1 Effect of seeding on reaction rate.
r
',;
o
. ,
o
o
)
79
external seed addition is not necessary to precipitate lead,
the rate is increased if fine lead powder is added. The effect
of seed addition is not very greèt, yet obs~rvable. At six ) .. -
hours reaction time the amount of lead in the organic phase has ,
been reduced to 21 percent of the initial concentration when
seed is present compared to about 36 percent when seed is not
present. This enhanced reaction rate when seed is added
indicates that the nucleation kinetics are hetergeneous. It is
unlikely that 'homogeneous nucleation is important in the . present system because of the requirements for homogeneous
nucleation. From nucleation t~eory, it is known that there are
two requirements in order for homogeneous nucleation to occur
·[83]:.
1) A h i 9 h c o.n ce nt rat ion 0 fit h e r e a ct in 9 s pee i es
(preferably uncomplexed) to the point of supersaturation.
2) A &ufficiently high temperature to provide~the high " ..-
activation energy of nucleation.
,The submerged titanium surfaces of the impeller assembly,
thermowe11, and s~~pling tube may also act as nucleation sites,
and it was observed that a fine coating of lead always adhered ,
to the surface of the submerged surfaces.
When hydrogen cornes in contact with titanium, molecular
hydrogeh dissociates and ionizes to sorne extent due to the
the pot e n ,,~, f ,i e 1 ~~ ~ f the met a 1 [ 84 J. l n th i seo nd i t ion,
titanium surface would be expecte,d. to be cata1ytically very
, , L
,
o
o
o )
< • 't" - . . ; j, _,' 1 _ 21"
'"
80
active.
It is also believed that during cl~aning of the stirrer
assembly, titanium adsorbs hydrogen which ls produced during
dissolution of platedllead with nitric aéid as shown below:
;s ~b+2 + 2N03- + H2
t Pb + 2HN03 (5.1)
In 'addition to the 1above mechanism, it ia presumed .that
nydrogen is also adsoqbed during the reduction experiment, thus
enhancing is the cat~~Y~iC activity of the.metallic surfaces.
Massive plating of the stirrer assembly was not observed
in this sytem as was reported for copper [16] and cobalt [85]
in the absence of catalytic seed. This is bel ieved tè'--be due
to the much greater c::atalytic activities of cobalt and copper
for the chemi:sorption of hydrogen on their sur faces than
lead [78]. Once the submerged surfac~s have been coated with
lead, the catalytic activity of these surfaces becomes greatly
reduced and further plating occurs very slowly.
-The 'effect of adding seed may have been better studied if .
", nickel or copper powder had been added. However, the l~ad
product would have been impure. It is probable that an
increased reaction rate would be observed in the initial stages
of reduction if nickel or copper seed were added. Up to that
point where the seed particles become covered with lead and
effectively begin to behavè chemically similar to lead seed.
Although plating of the stirrer assembly was not severe,
\J.
-
, -)i
o
o
e
\
, .
• < • 11
81
agglomeration of seed and newly precipitated lead powder was
severe. This is thought to be enhanced by the high
temperatures (very clo~e to the melting point of lead of 600 K)
and pressures required for the hydrogen stripping of lead.
Because the evidence suggests that pt;ecipitation i5
heterogeneous in nature a quantitative study of the kinetics is
not possible ~ue to the varying surface area caused by
agglomeration. Thus, only a qualitative study is presented in
this report.
As was observed in the rest of the reduction tests and as
is shown in Figure 5.1, the reaction curves aré generally s-I
shaped with an initially slow rate followed by fairly constant
reduction, ending in à slowing down of the rate of reduction • . It ls proposed that in the initial stages the temperature
decrease observed (of about 5 K for the first 5 minutes) when
the hydrogen gas is first introduced into the autoclave lowers
the reaction rate. Once temper"à'ture equi'l ibrium has been
established the reaction assumes a fairly constant r-ate', as is o •
observed •. Depression of the reaction rate as the reactiQn ,
progresses is thought to be due to the d~creas~ in specific .
surface area resuiting from increased ~gglomeration of the seed
material and fres'hly de'posited lead. That is to say, it is
expected that agglomeration increases with time, at constant "
o
témperature and pressure, resuiting,in less exposed surface
avai I a.bIe for reaction.
o
o
o
(
82
The rate of hydrogen dissolution ~into the organic phase is )
not considered to have any effect on th~ reaction rate o~lead~ reduction because ~f experimental ev idence showing that
h Y d r 0 go e n 9 a s dis S 0.1 v es , rapidly the KELEX
lOO/decanol/kerosene- sys tem. Tpe appar,ent so 1 ub il i ty 0 f
hydrogen in ~ the unloaded organic ~ol vent haS' been 'prev iousl y
detennined [41. Under similar conditlpns of temperature and
pr.essure, as were used in this investigation, the pressure was
found to stabllize within 1 to 2 minutes resulting in a
hydrogen saturated solution very early. Thus initial hydrogen
starvation is co~sidere~ to have only an insignificant
influence on the' slow reacti9n rate' observed at the begillning ,
of reduction. The reaction ls considered to proceed under lj
conditions of apparent hydrogen saturation becauQse copper and s •
nickel are prec ipi ta ted much more r api91 y than 1 eâd, and , l
~ca~culations sh9w that they react under'c6nditions of apparent
hydrogen saturation. Thus, lead is cons1dered to be reducied .
under conditions of hydrogen saturation. \ ~
/'
5.1.2 BPPBCT OP AGITATION ,
The"reduction of lead from loaded KELEX 100 involveS' gas,
liquid, and solid phases ... Agitation of the loaded organic
sol vent 15 requi.red for two reasons: good las disp~rsion, and -
suspension of precipitated sol ids to' allow for complete 1
expo,sure of meta Il ic surfaces to the sol ution. Figure 5.2 eh.ows
the reaction curves obtained for stirring rates 'o'f 600 and 800
1:'
'-'
o
o
<..> -Z ~ (!) a::: o Z
.ca 0.. LL. o ~
Temperature: 518 K
Pressure
Seed
2.76 MPa H2 20.0 g Pb
Chelate age: 24 hrs
• 600 rpm
• 800 rpm
O~----~----~------~----~----~~--------o 2 3 4 6
TIME (hrs)
Figure 5.2 Effect of agitation on reaction rate.
1
o
o
o
, . .---- - 84
rpm a t a temperature of 518 K and 2.76 MPa H2.
1 t appea r s tha t the r e a ct ion rat e i s no t ~ f f e e t ed b y l ,
increasing the stirring rat e f r om 600 t 0 800 1 r pm. The 1
~ independence of reaction rate onlstirring suggests that the
overall precipitation process is not diffusion dontr01led. 1
j
Burkin [86], in his report on the physical cbemistry of
meta 1 pree ip-lta t ion from loaded carboxy1 ic ac ids wi tth hyd rogen,
reported that in his system the' rate controfï ing step was the
transfer of hydrogeh from the gas phase into sol ut i on. But in
Burkin's work hydr"Ogen was introduced above the liquid phase,
whi1e in the present investigation hydrogen gas was drawn down
and dispersed as sma11 bubb1es below the liquid surface by. the
action of the impeller. Therefore, under the present
experimenta-l conditions, a chernica1 reaction appea9 to be the
rate contro1ling step for the overa11 reduction process.
5.1.3' ,LBAD CHELATB AGB J
prev i ous exper i ence wi th the copper-KE,LEX 100 [16] and - ~ 1
e 0 bal t - K E LEX 1 0 0 [ 8 5 ] s Y stem.$ S u 9 9 est s th a t p r El c i pit a t i ô n .
kineties in the present:ease may be affeeted by chelate age •. f,
Strong ,aging effeets in these former-systems Ihave been
attributed to the metal-bearing KELEX 100 molecu~es forming
polymerie associ''ations, whicn h~ve a suppressing efifeet on the j •
hydrogen stripping" kinetic-s. oifficulty in reductiojn increases ~
wi th age.
The effeet of lead-KELEX 100 chelate age on the kineties
..- ~ - --
o
, .
O·
'--
o
'85 ,
of reduction at 518 K and 2.76 MPa H2'·following storage for 24,,
and 72 hours is shown in Figure 5.3. The reaction curve for'
both the 24-hour old chelate and 72-hour chelate is similar,
and there seems to be no change in reaction rate due to aging
-within this time periode
5.1.4 TEMPERATURE EPPECT
It is expected that as the temperature is incr'eased, lead
precipitation rates will also increase. The reaction curves ,. obtained hy varying ttf'e temperature between 493 K and 533 K are
showrnElin Figure 5.4. At 493 K the reaction rate is very slow
-and about 85 p.8*cent of the initial lead remains in the organ-ic , 0 •
phase after 6 hours. Ho we ver,' r e a c t ion rat e s fi e em t 0 b e
enhanced greatly by an increase in temperature beyond 493 K.
An increase of 25 degrees, to 518 K, results in only about 20
'<- percent of the i,nitial lead remaining dissolved after 6 hours, 1
while a further increase of 15 degrees, to 533 K, reduces the
6-hour dissolved lead level to about 10 percent of the initial
concentr a t ion.
5.1.5 HYDROGEH PARTIAL PRESSURB
C!langes in hydrogen partial pressure are al~o expected to
affect lead reduction rates. Figure 5.5 shows the effeces on
the reaction rate of increasing the hydrogen partiai pressure
from 1.38 MPa to 4.14 MPa H2. As the hydrogen partial p~essu~
incr'eases so does the- ,rate of reduption. After 6 hours
\,
J
.. ,l?-
I 0 · • 86
0 ,
Temperature: 518 K
" Pressure 2.76 MPa Ii2 • 24 hours St1rr1ng 800 rpm • 72 hours Seed 20.0 g pb
U 60 -Z
C
" 0 a: 0 z - 40 ..Q D.
~ ~
"t 0 0 2 3 4 5 6
.r
TIME ( hrs) .
" "-
F1qur~ 5.3 Effect of chelate .
age on reaction rate.
• \;>
•
; p '.'. i . r ,II i
,"1 :-
~~ -87
r
'. f>
Pressure 2.16 MPa H2 • 493 K . Stirring 800 rpm • 518 K Seeod . 20.0 g Pb .. 533 K Chelate age: 24,hrs
0 -Z ct
0 C) 0: 0 Z
~
- 40 .a Q.
lLo 0 ~
20
o .. ----~~----~------~---------------~------~~ o 2 3 4 6' , )
Ir TIME lhrs) '\ .. ' .
Figure 5.4 Effect of temperature on reaction rate.
·0 /
~ 1
L __
--~--~-------------~;!IIII!,.!IlII,_!!II, ......... ~ ___ ... __ •
88
Temperature: 518 K _c'
• 1.38 MPa H2 . Stirr1ng 800 rpm
• 2,.76 MPa H2 'Seed : 20.2 g Pb • 4.14 MPa H2 Chelate age: 24 hrs
; 80
( c-
U 60 -Z é( 0
C)
,0 a: 0 z' -.Q
"40
D. . . ~~
- -.... , ~ t"j 20
O~--------.-~----~----~ ______ ~ __ ~ __ ~ o , 1 2 4 6 ,
TIME (hrs)
• 6 -Figure 5.5 Effect of hydrogen partial pressure on reaçt~on
rate.:- p /
e--\
, '
- , ..
Od
.;~ - ,
o /
o
-89
reac.tion, about 40 perceI?t of the lead remains in sol ution at.
,1.38 MPa H2 , about 21 percent t 2.76 MPa H2 and about 1
percent at 4.14 ~Pa H2. Again the S-shaped -nature of the curve
is observed.
Ac cor d i n 9 toM a c k i w et a 1 [8 7], a me as ure 0 f t'h e : t te a t
which a reaction ,takes place can 'e given by (100/t50)' ~1!~e
t so is th& time required for reduction of 50 percent of the
. met a 1 i n sol ut ion. -I t wa s em p i r i cal 1 Y 0 b s e r v ed t li a t a 1 i ne a l;
;,eiationshiJ;; exists between ~ln(10 /t50 ) and ln (PaaL. usincf' the
results in Figure 5.5, at 1.38 HP , 2.7~ MPa, and 4.14 MPa H2 Î'i 1
t 50 equa1s 5.3g, 3.45, and,1.75 hours r~spectiyely. Using
lineàr-~regression the slope of l' (100/t 50 ) versu~ .ln(PH2 ) is
0.98 with a eorrel'ation coefficient of 0.96 •. The rate 6f l
" reduction is almost d.ir,ectly p opoi:tiona1 to the partial
pressure of hydrogen in the pressu e range investigated.
Similar dependency of the reduction rate on hydrogen . . 'partial pressu're was observed in thè hetereg-eneous system~ of
n i c k el' pre c i pit a t ion 0 f rom a que 0 u s am mon i a cal sul ph a t e
solutions, [87] the reduction of cobalt from aqueous ammine \) . -. -
sulphate solutions [88], and- the reduction of copper [16J and l '
cobalt [85] from loaded'KELEX 100.
5.1.6 RBPRODOCIBILITY AND ORGANI RBCYCLIMG
Replic~te expe~iments were o nd u ct ed a t 518 K, 2. 7 6 M P a
H2' 800 rpm agitation, 24 hour late 'age, and 20.0 grams of
$eed 'in" order to dectermine the -reproducibi1 ity of the
..
o . .
..
,
, --"
0 '"
r
•
,1"
~, -80 CI C!). a:: 0 z~ - 40 .a Q.
~ a'b
20
Q 0
Temperature: Sa18 K ~~f Pressure'. :,2.76 MPa :2 Stirring . ':, aOO:'rpm Chelate age: 24'hrs Seed 20. Q 9 Pb
.' - -
~
2 3
.. ,.' ~:
r 4
TIME (hrs) " , - ~',
90 -,
• run 1
• run 2
• !5 6'
Figure" 5.6. Reproducibili ty and recycle of the organic solution for redtzct.ion.
, , \ ~
.. ' Il
- , \
, "
o '.
o
o
" " ... <,
Il
1 •
-experi~e~ta1 procedure. 'As can be seerr from Figure 5.6
excellent exper}mental reprod.ucibility was obtained. ,. ,
The effects of organic recy"t1 ing are also shô~m in Figùre ,
5.6, sinc.t the second ,experimel'ltal rurt was conducted with .
r~cycled organic, as weremost of the reduction experiments.
It is apparent that, recycl{ng does not adversely affect the
organic phase. Good recyclability of the extrac~ant is also
evidenced in the reproducibility of loading after reduction
which resulted, after 10ading, of solutions of 20.18 .f& .64 gpl , lead (a deviation" of only 3.2 percent) •
. 5.2 METAL PRODUC'l' CUARAC'l'BRIS1'ICS
The 1ead produced by pressure hydrogen stripping,
regardless of whether sèed was add.~ or not, consistéd of large
and pmall agglomerated chunks o~ metal mi~e~ with fine 1ead - ..
powCier. A photograph of the' le?d produèt recovered' after
filtration is ~ho~n in Fi~ùre 5.7. The largest portion of the
a~glomerated'chunks of lead metal was characterized by a rough ..
porous'upper face and a smooth po~ous opposite side·with an . )
imprint of the bottom of the glass liner. It is believed that ,
this large chunk of metal forms'at the vortex which occurs
direct1y un"der the bottom impellor due to rotation. A cross-
. section of this chunk of metal, shown in Figure 5.8, revea1s
that the porof?itr is found throughout the par_ticle. T,his
, massi ve ag9 lomera tion of meta 1 is thought to be due t~ ~he dua 1
at~ions.of sinter~ng and intergrowth'of partidl~s cause~by
•
• ( 1 t'
1
0,
..
92 ,
. Figure 5.7 \letion 'produet produeed at ,518 K and 2.76 MPa H2
(a) without seed addition, and (b) with seeding •
Figure
.'
5.8 Cross section of the massive ag91o~erated particle produced by-hydrogen reduction at 518 K and 2.76
,,' MPa K2. t '
, "
. ,
..
o
, .
o·
q
, J
j
i 1 , ,
1
93
metaI1 ie deposi tion al1d growth. The large chunks qf meta1 are - ù
very. fr iab 1 e and can eas il Y be'.broken by l'land.
Figures 5.9, 5.10, and 5.11 ~re micrographs of tihe or ig ina 1
se~d material and the powdered portions of the lead pr~du~t
produeed with and without seed addition- at 5ïsK wlth 2.76'MPa . . .. . ,
H2 • The original s.eed materiàl (Figure - 5.9)- consists of
unifoJ]O siz~ distinct .partic1es. The morpho1ogYtof the fine 1
1ea'd powder produced when no seed 19 added consists of porous
spongy particies. _ The powder~ pr'odu'ct produced when seed is ,
added ,is observed to be a com~ination of the product .produced ",
without seeJ as wèl1 as agglomerated particles of seed
material.
, ~,
- ,
Figure 5.9 Micrograph. of the or iog ina1 fine Iead powder seed. (x125)
" ,-'
, ,
•
--.
.1
94
\
Figure 5'.10 Micrograph of the powdered portion of ,the lea-d product produced at 5·18 K and 2.76 MPa H2,
- without seed.{x1.2s)
.. .
•
Figure 5.11 Micro9Iaph of the powdered portion of th~ead product produced at 518 K and 2.76 MPa H2' wi th seed. (x125)
(
If
o
r 6.1 PINDINGS
.' / CHAP'rBR 6
CONCLUSIONS
0&
95
\
The experiments conducted in this in~estJgation permit the
fOl1owing conc1usionsj .,-r-,
1) The method of slope analysis revealed that lead is
extracted from acetate solutions as a 2 to 1 organic
molecule to lead chelate speci~s. . .... .. 2) Lead can be efficient1y and rapid1y str ipped from
(
3)
KELEX 100 with both 20 and 50 gp1 solutions 'of either
acetic or nitric acid to produce supersaturated lead
aqueous strip solutions. Rapid ana1ysis of these
strip SOlutions_ÎProvides~ good method to determine
the lead concentra~i~n in the organic Ph~se.
(Lead loaded KELEX 100, which has been
:"
pressure
i1.&
hydrogen stripped' at temperatures between 493 K and .
"
4)
. 533 K with hydrogen partial pre~sure petween 1.38 MPa
and 4.14 MPa H2 , shows excellent chemical and .. thermal stabi1ity resu1ting in regeneration of the -organic molecu1e for recycle. However, pressur~
hydroge~ stripping at above the melting point of lead
resulted in decomposition of the organic Molecule.
Fine
trom
lead .powder has been obsetved to
loaded KELEX 100 when heated
.. ,
preci~itate
to high
"
,
o
)
•
96
tempe~atures in an inert atmosphere of nitrogen gas.
It is proposed that this May be du~ to the formation
of polymerie speeies of KELEX 100.
5) A wavelength scan in the ultra violet region of the
spectrum between 201 nm a~d 900 nm revealed an ,
ab sor b'~ n cep e a k for K EL EX 10 a a t 33 1, nm and 42 5 nm
for the lead chelate. ~
1
J
6) A study of the effeets of various parameters on the "- <
rate of l~ad reduetion Jreveat"ed that the add H:ion of
fine lead powder as seed ine~eases the rate of lead
precipitation slightly. An increase in operating
temperature and/or hydrogen pressure aceelerates the
reaction rate in the temperature and pressure range
investigated: There was no observable effect on the
rate by varying -the cHelate age between 24 and 72 . " hours,' or the agitation speed _from 600 rpm to 800
rpm.
7) TQe lead metal product produeed in both the presence
and absence of seed eon..stisted of large and smail
agglomerated ehunks of metai mixed with fine powder.
6.2 r~RTHER INVESTIGATIONS
..:: A 1. th 0 u 9 h mu c h k n a w l e dg e ha s b e e n gai ne dl i n the
inv1!stigatJon of pressure hydrogeh stripping of lead from ,
,1oaded KELEX 100, the f0110wing poi~ts are suggestions as to
, '
,b •
o
\
o
\
0-
97
where more knowledge could be gained in further study of this
system:
6.3
1) Owing ta the low ca~alytic activity of lead and the
agglomerating properties of the reduction product, a J.:
nucleation model or reaction mechanism was not
determ ined in- this i nvest iga t ion. Further work shou Id
be conducted to clarify the react~on chemistry.
2) Heat up and cool down cycles of the loaded organic
solution should be- conducted under a hydrogen instead
3)
of a nitrogen armosphere in ord~r to determine if the j .~
changes ,revealed by infrared spectroscopy are inde~d
due to the as.sumed tautomerism.
The addition of various organic reagents known to .
affect the physical properties of metals produced by
hydrogen reduction in aqueous so~utions should be .
in v est i 9 a t ed i n a n a t t em ptt 0 i m pro v eth e ph Y sic a 1
cha,~acteristi-c-s' of the reduced lead product. A high
purity, unifdrm sized, non-porous metal product is
the most desLrable, especially for powder metallurgy
applications.
CLAIM '.PO ORIGINALI'.PY
Original aspects of this work are thought ta be, in
autnor' s opinion, the following.
1. ). It is the first time that the st 0 chi om e t r y of the ,
-
j
'"
·2)
8 ..
98 wo ..
lead-KELEX 100 chelate has been determined when lead
is extracted from an ao.etate sol ution.
It is the first time that lead has been successfully
r~duced fram loaded KELEX 100' with hydrogen under
. pressure.
.. .... 1
,
..
'Î
=
.1
o
o
o
,
99
ACKHOWLBDGEMBHTS
The author gratefully acknowledges the helpful comments 0 -and assistance received from his thesis supervisor Qr. P. A.
Distin. Also, -the author wishes to thank Dr. G. P.
Demopoulos, and fellow graduate students, P. Kondos and V.
Papangelakis for the discussions held during the course of this ~
work. .
Thanks are also due to teQhnic~ans M. Riendeau'and M.
Leroux for their techni.cal assistan~e during the experimental
portion of this investigation.
"
•
) ,.
"
100
0 APPBNDIX
,II> EXPBRIMENl"AL DAl"A '-'L ....... , ,
I. BX'fRACl'IOM HO S'fRIPPING
1. Effect of pH on extraction: Figures 4.1 and 4.2
pH lPb10 [Pb1 r 0 log O' % .... Pb '" (gp1) (gp1 EXTRACTED
3.95 .63 2.26 .28 -.553 21.8
4.18 .74 2.15 .34 -.469 25.6
4.26 .75 2.14 .35 -.456 26.0
;..,.. 4.42 .99 1~.91 .52 -.284 34.1
4.81 1.39 1.51 .92 -.036 47.9
4.95 2.22 .72 3.08 .489 75.5
0 5.09 2.19 .70 3.18 .502 75.8
5.12 2.46 .4fr 5.13 .710 83.7 "-
5.40 2.68 .22 12.18 1.09 . 92.4 'f
5.43 2.84 .10 28.40 1.45 96.6
6.80 2.92 .02 146.0 2.16 99.3 IJ
2. Stripping with 20 and 50 gpl nitric acid: Figure 4.3 ", "
20 SI~l HN03 50 SlÈ1 HN03 " -
[Pb]r [Pb)o [Pb]r [Pb].o "- (SlPl ) (Slpl) (Slpl (Slpl
" " 6.36 N.D. 6.36 N.D •
15.40 N.D. 15.30 .,
N.D.
30.10 .46 29.81 0.74
0 30.0 15.56 60.41 0.35 "'
29.61 '" 19.00 72.33 12.47
73.52 1.14
'"
1,
" ...
..
0
~
.. r
o
•
102
2. Loaded, unreduced KELEX 100: Figure 4.10 1
Peak number ... J 1 2 3 4 5 6" . Wavenumber Ccmr1 ) : 3400 3050 1715 1550 1500 '1420
0
7 8 9 '19 Il 12 14 15
N.D. 1300 1250 1100 815 797 685 589
. 3. Un1oaded, KELEX 100 recy1ced 3 times: Figure 4.11
• ,
Peak number : 1 2 3 4 5 6
Wavenumber (cm-1) : 3395 3050 1740 1572 1500 1405 ...
7 .-8- 9 10 Il 12 13 14 15
1328 1272 1245 1090 820 800 720 685 590
III. BYDROGBH REDUCTION
EXPERIMENT CONDITIONS 518 K, 2.76 MPa H2, 0.0 9 s~ed, 800 rpm, 24 hr che1alte age ~
1 COMMENTS Effect of seeding
TItiE (hrs) o .5 1 '2 3 4 5 6
[Pb]o (gp1): 20.6 20.2 19.3 17.4 13.5 10.3 8.6 7.5
, Pb IN THE: 100 98.2 93.4 84.2 65.5 49.8 41.9 6.2 ORGANIC
EXPERIMENT CONDITIONS: 518 K, 2.76 MPa H2' 20.0 9 seed, 800 rpm, 24 hr chelate age
2 COMMENTS Effect of seeding, temperature, ana pressure
TIME (hrs) p .5 1 2 3 4 5 6
[Pb]o ,(gp1): 2L.2 20.8 20.4 15.3 Il.6 9.1 6.7 4.5 .. " Pb IN THE: 100 98.3 96.2 75.2 54.6 42.9 31.9 21.2 ORGANIC ~
•
. -
o .r,
o ..
o
•
"
-..
EX·PERIMENT CONDITIONS: 518 K, '2. 6 'MPa H2' 0.0 9 sead, 800 ·rpm, 4 hr chelate age .'
3 COMMENTS • Thermal d ssociation under nitrogen . TIME (hrs) : 0 .5 1 2 3 4 5
[Pb]o (gp1): 19.1 19.51 19.5 -19.1 19.1 18.9 18.7
98~~ % Pb IN THE: 100 96.2 75.2 54.6 42.9 31.9 ORGANIC
EXPERIMENT CONDITIONS: 518 K, 2.16 MPa H2' 20.0 9 s~ed, 800 rpm, 72 hr chelate age
4 " COMMENTS : Chelate age effect
TIME (hrs) o .5 1 2 3 4 5
103
6
18.7
21.2
6
[Pb]Q (gp1): .18.3 17.9 16.9 14.6 Il.5 7.0 5.0 3.5
% Pb IN THE: 100 98.0 92.4 79.9 62.7 38.~ 27.3 19.3 ORGANIC
EXPERIMENT CONDITIONS: 518 K, 2.76 MPa H2' '20.0 9 seed, '600 rpm, 24 hr chelate age
5 ÇOMMENTS · Effect of ag i,tation · TIME (hrs) · 0 .5 1 2 3 4 .5 6 · [Pb]o (gpl) : 18.8 18.5,17.1 14.5
~ 11.1 7.6 5.2 le?
% Pb IN THE: 10-0-- 98.5; 90.7 71 .. 3 59.2 40.4 27.6 19.7 ORGANIC -
1 •
(Ô
EXPERIMEN~, CONDITIONS : 518 K, 1.38 MP~ H2,' ~ 20.0 9 seed, 800 rpm, 24 hr chelate age
6 COMMENTS : Pressure Effect
TIME (hrs) : 0 .5" 1 2 3 4 ..... 5 6 \
[ Pb 1 0 ( 9 pl): 2 2 .4 2 1.3 21.0 19 .1 16 • 1 15 .4' 1 2 .1 9 .4
, Pb IN THE: 100 95.2 94.1 85.6 74.6 65.7 51.7 40.0 ORGANIC Î
..
-
,- " - '
104 } -
G EXPERIMENT CONDITIONS • 518 K, 4.14 MPa H2' 20.,0 9 seed, • 800 rpm, 24 hr/Chelate .age
7 COMMENTS .. Pressure Effeo. .. 1
1 TIMf: (hrs) : 0 .5 1 2 3 4 5 6
[Pb]o (gp1) : 18.8 17.0 12.3 8.6 5.0 3.'1 1.4 0.3 ..
, % Pb IN' THE: 100 90.3 64".9 f45.1 25.9 15.8 6.8 1.4 ~' ORGANIC "
.. EXPERIMENT CONDITIONS :' 493 K, 2.76 M'Pa H2' 20.0 9 seed,
800 rpm, 24 hr chelate age \
" 8 COMMENTS : Temperature Effect
TIME (hrs) · 0 .5 1 2 3 4 5 . 6 • . , ,
(gp1) : '18.3 [-Pb] 0 18.1 17.5 17.7 17.1 16.8 16.3 1·5.4
'% Pb IN THE: 100 98.9 95.9·96.7 93.7 91.8 89.2 83.9
0 '" .. ~ ORGANIC \
. EXPERI'MENT ·CONDITIONS · 533 K, 2.76 MPa -H2' 20.0 9 seed, · 800 rpm, 24 h; chelate age
9 COfiMENTS · ~emperature Effect · TIME (hrsJ • 0 .5 1 2 3 4 -- S, 6 •
'! 19p1) : [Pb)o 16.6 16.6 15.4 11.3 8.3 5.3 ~ •. 2 . 1.8
% Pb IN THE:' 100 99.6 92.5 68.2 49.9 31.9 19.3 10.8 , bRGANIC \.
.. \ (
EXPERIM~NT CONDITIONS • 518 'K, 2.76 MPa H2' 20.0 9 seed, · 800 rpm, ~4 hr chefate\age "
10 COMMENTS • Organie recyc1ing • ~
TIME (hrs) .: 0 .5 1 2 . 3 4 5 6 ... ,
• [Pb]o (gpl): 20.8 20.1 19.2 16.4 11.4 8.7 -6.5 4.3 --- , Pb IN THE: 100 96.5 92.3 78.8 54.7 42.1 31.4 20.6
ORGANIC
, '\
o
o
"
o
EXPERIMENT CONDITIONS: '517 K, 0.0 MPa H2' 0.0 9 seed, 5QO rpm, 24 hr chelate age
105
Thermal COMMENTS dissociation
Comparison with thermal dissociation of Pb
of Cu '
"
TIME (hrs) :
[ Cu] 0 ( gp 1) :,
-% Cu IN THE.: ORGANIC
o
-'9.55
100
Source: Reference No;16
..
1.25
9.05
95.0
3.25
7.00
73.0
p. 222
\
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.. (
5
4.025
48.5
"
1.
, 106
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110
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V---
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