Presented at the conference on Desalination and the Environment. Sponsored by the European Desalination Society

containing different carriers: compared kinetic study

Gerardo Leóna*, María Amelia Guzmánb aDepartamento de Ingeniería Química y Ambiental, Universidad Politécnica de Cartagena,

Paseo Alfonso XIII, no. 44, 30203 Cartagena, Spain Tel. +34-968-32 5669; Fax +34-968-32 5555; email: gerardo.leon@upct.es

bS.O.I.V.R.E. Murcia, Spain

Received 3 January 2007; accepted 7 January 2007

Abstract

The discharge of heavy metals into the environment is a serious problem facing numerous industries. Heavymetals tend to accumulate in living organisms causing various diseases and disorders. So the search for extractiontechniques to remove those heavy metals are of increasing interest. Liquid membranes have shown great potentialin this way, especially in cases where metal concentrations are relatively low and other techniques cannot beapplied efficiently. A comparative kinetic study of the facilitated counter transport of copper ion through bulk liquidmembranes containing D2EHPA, CYANEX 272 and LIX 984N as carriers and protons as counter ions is carriedout is this paper. The transport kinetic was analysed by means of a kinetic model involving two consecutive irre-versible first-order reactions. The rate constants of the extraction and stripping reactions and the maximum transportfluxes of copper(II) through the bulk liquid membrane were determined for the three carriers.

Keywords: Bulk liquid membranes; Copper; CYANEX 272; D2EHPA; LIX 984N

1. Introduction

The discharge of organic and metal pollutantsinto the environment is a serious problem facingnumerous industries. Because heavy metals arenot biodegradable in natural conditions, theytend to accumulate in living organisms causingvarious diseases and disorders [1]. Furthermore,

the presence of heavy metal ions in wastewaterinhibits biodegradation of organic pollutants,which might be present in the wastewater [2].Therefore their concentrations must be reducedto acceptable levels before discharging them intoenvironment.

A variety of industries are responsible for therelease of heavy metals into the environmentthrough their waste waters, among them mining,hydrometallurgy, pulp and paper, petrochemical,*Corresponding author.

Facilitated transport of copper through bulk liquid membranes

Desalination 223 (2008) 330–336

0011-9164/06/$– See front matter © 2008 Published by Elsevier B.V.

and Center for Research and Technology Hellas (CERTH), Sani Resort, Halkidiki, Greece, April 22–25, 2007.

doi:10.1016/j.desal.2007.01.216

G. León, M.A. Guzmán / Desalination 223 (2008) 330–336 331

refinery, fertilizer, electroplating, etc. [3]. Accord-ing to World Health Organization (WHO) themetals of most immediate concern are chromium,copper, zinc, iron, mercury and lead [4].

Different disorders have been described asa consequence of copper accumulation in ani-mals and humans [5–7]. Acute copper poisoningcauses severe gastroenteritis characterized byabdominal pain, diarrhoea, anorexia, dehydration,and shock. Chronic copper poisoning resultsin Wilson’s disease, characterized by a hepaticcirrhosis, brain damage, demyelination, renaldisease, and copper deposition in the cornea.

Several methods have been described for cop-per removal from wastewater during last years,including chemical precipitation [8], adsorption[9–11], biosorption [12–14], ion exchange [15],complexation [16,17], pressure-driven membraneprocesses [18,19], electrochemical processes[20,21] and combined methods (sorption orcomplexation plus pressure-driven membranesprocesses) [22,23].

Liquid membranes have also been used forthe removal of copper from aqueous solution[24–27]. Liquid membranes have shown greatpotential, especially in cases where solute concen-trations are relatively low and other techniquescannot be applied efficiently, since they combinethe processes of extraction and stripping in a singleunit operation [28]. The extraction chemistry isbasically the same as that found in liquid–liquidextraction, but the transport is governed by kineticrather than equilibrium parameters, that is, it isgoverned by a non-equilibrium mass transfer.

Metal ion extraction in the liquid membranesystem, can be facilitated by carrier mediatedtransport. In such transport, an ion exchangereagent is incorporated in the membrane phaseto carry the diffusing specie across the membraneto the product phase, a process that is usuallyaccompanied by the transport of other chemicalspecie from the product to the feed phase (facili-tated counter transport). This coupled transportmechanism is interesting because it offers the

possibility of transporting a component againstits own concentration gradient [29].

A comparative kinetic study of the facilitatedcounter transport of copper through bulk liquidmembranes containing D2EHPA (di-2-ethylhexylphosphoric acid), CYANEX 272 (bis-2,2,4-trimethyl pentyl phosphinic acid) and LIX 984N(mixture of 5-nonylsalicylaldoxime and 2-hydroxy-5-nonylacetophenoneoxime) as carriers and pro-tons as counter ions is described in this paper.

2. Experimental equipment and procedure

The experimental studies were carried outapplying the bulk liquid membrane technique,using a stirred transfer Lewis type cell with bulkliquid membrane layered over the feed and prod-uct phases (Fig. 1). 0.025 M cuprous sulphatesolution was used as feed phase. The membranephase was constituted by 10% solutions of carrierin kerosene. 1 M sulphuric acid solution was usedas product phase. The volumes of feed, mem-brane and product phases were 25 mL. The areasof both feed membrane and membrane productinterfaces were 3.2 cm2. The stirring speed was200 rpm and all the experiments were carriedout at 25°C.

Copper(II) ion concentrations in both feedand product phases were determined by atomic

f p

m

Fig. 1. Schematic representation of the experimentalsystem (f, feed phase; m, membrane phase; p, productphase).

332 G. León, M.A. Guzmán / Desalination 223 (2008) 330–336

absorption spectrometry, using a ShimadzuAA-6200 instrument at a wavelength of 324.8 nm.Copper(II) ion concentration in the membranephase was established from the material balance.For practical reasons, dimensionless reducedconcentrations of copper(II) in the feed (Rf),membrane (Rm,) and product phases (Rp) wereused (Rf = Cft/C0, Rm = Cmt/C0 and Rp = Cpt/C0,the sum of Rf + Rm + Rp obviously being unity).

3. Results and discussion

The facilitated transport of Cu(II) ions throughliquid membranes containing CYANEX 272,D2EHPA, or LIX 984N as carrier and H+ ascounter ions is illustrated in Fig. 2. The carrierdiffuses from the bulk membrane phase to thefeed membrane interface, where copper(II) ionsare exchanged for protons. The copper(II) carriercomplex formed diffuses through the membraneto the membrane product interface, where protonsare exchanged for copper(II) ions, which arereleased into the product phase. The carrier isregenerated, thus beginning a new separationcycle. The copper(II) transport mechanism istherefore a coupled counter ion transport mecha-nism, with Cu(II) and H+ travelling in the oppo-site direction.

Variation with time of the reduced concen-trations of copper(II) ion in the feed, membraneand product phases for the three carriers areshown in Fig. 3. Best recovery of Cu(II) ion isobtained using LIX 984N as a carrier (higherof 80%), whereas CYANEX 272 (75%) and

Feed phase

HR

CuR2

Membrane phase Product phase

2H+

2H+

H+

Cu+2

Cu+2

Cu+2

Fig. 2. Diagram of the facilitated counter transport ofCu(II) ions using D2EHPA, CYANEX 272 or LIX984N as carriers (HR) and H+ as counter ions.

00.2

0.40.6

0.81.0

R

Rf Rm Rp

00.20.40.60.81.0

R

Rf Rm Rp

00.20.40.60.81.0

0 5 10 15 20 25Time (h)

0 5 10 15 20 25Time (h)

0(a) (b)

(c)

5 10 15 20 25Time (h)

R

Rf Rm Rp

Fig. 3. Time dependence of Rf in feed phase, Rm in membrane phase and Rp in product phase in the facilitated countertransport of Cu(II) using as carriers CYANEX 272 (a), D2EHPA (b) and LIX 984N (c). (points, experimental values;line, model values) (feed phase: Cu(II) 0.025 M; membrane phase: 10% carrier in kerosene; product phase: H2SO4 1 M).

G. León, M.A. Guzmán / Desalination 223 (2008) 330–336 333

D2EHPA (lower that 70%) do not reach sucha high value.

It can be appreciated that in all cases Rf

decreases monoexponentially with time, whileRp follows an increasing sigmoided type curveand Rm presents a maximum. These results sug-gest that copper(II) transport obeys the kineticlaws of two consecutive irreversible first-orderreactions, the extraction (rate constant, k1) andthe stripping (rate constant, k2) reactions. Thismechanism has been used to describe the trans-port of some divalent ions through bulk liquidmembranes [30–33]. The irreversibility is to beexpected because Rd and Rm tend to zero, while Rp

tends to one, that is, the transport from the feedphase to the product phase seems to be virtuallycomplete. The kinetic irreversibility of the wholetransport process is expected to derive from thehigh proton gradient across the membrane.

This kinetic behaviour can be describedaccording to the following equations [30]:

(1)

(2)

(3)

Integration of those differential equationsgives [30]

(4)

(5)

(6)

These equations show that the time depen-dence of Rf is monoexponential and the timedependence of both Rm and Rp is biexponential.

Rm has a maximum, the time at which itoccurs being obtained from dRm/dt = 0.

(7)

the value of Rm at that time being [30]

(8)

Combining Eqs. (7) and (8) the followingrelationship can be obtained:

(9)

First-order time differentiation of Eqs. (4–6)leads to the final form of the flux equations [32].

(10)

(11)

(12)

By substituting the expression of tmax givenfor Eq. (7) in Eqs. (10–12), maximum fluxes canbe obtained [32].

(13)

(14)

(15)

d

df

f f/m

R

tk R J= − ≡1

d

dm

f m

R

tk R k R= −1 2

d

dp

m m/p

R

tk R J= ≡2

R k tf = −exp ( )1

Rk

k kk t k tm =

−− − −[ ]1

2 11 2exp( ) exp( )

Rk k

k k t k k tp = −−

− − −[ ]11

2 12 1 1 2exp( ) exp( )

t

k

k

k kmax

ln

=

⎛⎝⎜

⎞⎠⎟

−

1

2

1 2

Rk

k

k

k k

mmax =

⎛⎝⎜

⎞⎠⎟

−−

1

2

2

1 2

kR

t2

1

=

⎛⎝⎜

⎞⎠⎟

ln

max

mmax

d

dfR

tk k t= − −( )1 1exp

d

dmR

t

k

k kk t k t=

−−( ) − −( )⎡⎣ ⎤⎦

1

2 11 2exp exp

d

dpR

t

k k

k kk t k t=

−−( ) − −( )⎡⎣ ⎤⎦

1 2

2 11 2exp exp

d

df

f

R

tk

k

kJ

k

k k⎡⎣⎢

⎤⎦⎥

= −⎛⎝⎜

⎞⎠⎟

=−

−

max

max1

1

2

1

1 2

d

dmR

t⎡⎣⎢

⎤⎦⎥

=max

0

d

dp

p

R

tk

k

kJ

k

k k⎡

⎣⎢

⎤

⎦⎥ =

⎛⎝⎜

⎞⎠⎟

=−

−

max

max2

1

2

2

1 2

334 G. León, M.A. Guzmán / Desalination 223 (2008) 330–336

(16)

Numerical analysis of experimental resultsby nonlinear curve fitting permits the rate con-stants of the kinetic process to be determined(Table 1). The values of k1 are directly obtainedby iteration from Eq. (4). This value is intro-duced as a constant value in Eqs. (5) and (6). Aninitial value of k2 is obtained in each case fromEq. (9), then introduced in Eqs. (5) and (6) anditerated. Two values of the rate constant k2 areobtained in each case, one derived from Eq. (5),k2m, and the other derived from Eq. (6), k2p. Goodagreement between k2m and k2p constants wasobserved in all experimental conditions.

Model curves of time dependence of Rf, Rm

and Rp, calculated from Eqs. (4) to (6) are alsoshown in Fig. 3. Good agreement between exper-imental and model data can be observed.

The results show that LIX 984N is the bestcarrier for the transport of Cu(II) ions. Althoughits stripping constant is a bit lower than that ofCYANEX 272, the high value of its extractionconstant leads to the highest recovery of Cu(II)in the product phase and to the highest maximumflux of the three carriers studied. On the contrary,D2EHPA is the worst carrier. The low values ofits extraction and stripping constants lead to thelowest Cu(II) recovery in the product phase andto the lowest maximum flux.

4. Conclusions

A comparative kinetic study of the facilitatedcounter transport of copper through bulk liquidmembranes containing D2EHPA, CYANEX 272or LIX 984N as carriers and protons as counterions is described in this paper. The transportkinetics were analysed by means of a kineticmodel involving two consecutive irreversiblefirst order reactions. The rate constants of theextraction and stripping reactions were deter-mined for the three carriers by numerical analysisof experimental results. Good agreement betweenmodel and experimental data is observed. Maxi-mum transport fluxes of copper(II) through thebulk liquid membrane were also determined forthe three carriers. Values of kinetic constantsexplain that the highest maximum flux and thebest Cu(II) ion transport is obtained using LIX984N as a carrier (higher than 80%), whereasthe lowest maximum flux and the worst coppertransport is obtained using D2EHPA (lowerthan 70%).

Acknowledgements

We would like to thank Mr. A. Guzmán andMr. J.A. López for the manufacture of the experi-mental cell and to CYTEC (Phosphine andPhosphorus Specialties Europe) and to COGNIS(Europe) for the kindly supplied of CYANEX 272and Lix 984N respectively.

− ⎡⎣⎢

⎤⎦⎥

= +⎡

⎣⎢

⎤

⎦⎥ ⇒ − = +

d

d

d

df p

f pR

t

R

tJ J

max max

max max

Table 1Rate constants for extraction (k1) and stripping (k2) processes and maximum flux (Jmax) for the counter transport ofCu(II) using different carriers

Carrier k1 (h−1) k2m (h−1) k2p (h

−1) k2 (h−1) (average value) Jmax (h

−1)

CYANEX 272 0.0996 0.1743 0.1706 0.1725 0.0470 D2EHPA 0.0826 0.1466 0.1395 0.1430 0.0399 LIX 984N 0.1343 0.1644 0.1600 0.1622 0.0540

G. León, M.A. Guzmán / Desalination 223 (2008) 330–336 335

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