, i, .6I

Brookhaven National Laboratory Report

BNL-NUREG-35597 (1984)

submitted to CORROSION

Potential--pH Diagrams and Solubility Limits of Ti, Cu and Pb for

Simulated Rock Salt Brines at 250C and 1000C

T. M. Ahn and S. Aronson*Department of Nuclear EnergyBrookhaven National Laboratory

Upton, Few York 11973

KEY WORDS: Potential--pH Diagrams, Solubility Limit, Ti, Cu, Pb

*Address: Brooklyn College, Brooklyn, New York 11210

1

-a,./ ~? Cx * .-

ABSTRACT

Titanium, lead and copper have been considered as candidate materials for

high level nuclear waste containers in rock salt repositories. The thermo-

dynamic properties are characterized for the systems of Ti, Cu and Pb in simu-

lated rock salt brines at 250C and 1000C. The potential--pH diagram of Ti

in the brines is close to that for pure water, and, in neutral solutions,

stable oxides are present and Ti dissolution is not significant. In acidic

environments at low potential, however, titanium dissolves in ionic forms.

Such cases include crevice or pitting corrosion. For copper, new domains of

copper chloride or copper sulfate compounds are introduced into the potential

--pH diagram for pure water. The dissolution of copper chlorocomplexes re-

sults in a significant metal loss by uniform corrosion. Lead chloride domains

are also introduced and this compound is considered to affect the uniform cor-

rosion of lead. However, metal loss by chlorocomplexes is not observed for

lead. The implications of the calculated results are discussed for both

uniform and local corrosion processes.

2

T L

FIGURES

1. Potential-pH equilibrium diagram for the titanium-brine system

at 25 0C . . . . . a * * * * * * * * * * * * * * * * a * * * * * * * * * 14

2. Potential-pH equilibrium diagram for the titanium-brine system

at 1000C.. . . . . . . . . . .

3. Log [ratio of titanium compound activity a~z to titai

for brine A at 25C . . . . . ..........

4. Log [ratio of titanium compound activity a~y to titam

for brine A at 100C . . . . . . .........

5. Log [ratio of titanium compound activity aXy to titai

for brine B at 25C .. .............

6. Log [ratio of titanium compound activity a y to titai

for brine B at 100C ................

7. Potential-pH equilibrium diagram for the copper-brine

at 25°C .......................0 * & 0

...i .. activity a 15

nium activity aTil

** 0 0 0 * * .. * 17

Aium activity aTi]

..... .............. 17

anium activity aTi]

18* *C C C * * C C

Aium activity aTi]

C & C C * C C

sys ten

* * . . . . C

. 19

. . 20

8. Potential-pH equilibrium diagram for the copper-brine system

at 1000C .............................. * & 0 a 0

9. Log [ratio of copper compound activity aXY to copper activity aCu]

for brine A at 25C . . . . . . . . . . . . . . . . . . . . . .

10. Log ratio of copper compound activity a/,y to copper activity aCul

for brine B at 25 0C . . . . . . . . . . . . . . . . . . . . . . .

11. Log [ratio of copper compound activity aXy to copper activity aCul

for brine A at 100'C .. . .. ... . . * C C C C . .*

. 21

. . 22

. . 23

. . 24

3

t

I I I ;

12. Log [ratio of copper compound activity a y to copper activity aCu]

for brine B at 1000C . . . . . . . . . . . . . . . . . . . . ...

13. Potential-pH equilibrium diagram for the lead-brine system

at 25°C . . . . . . . . . . . . . . .

14. Potential-pH equilibrium diagram for the lead-brine system

at 1000C .. .. . . . . . . .................. * . * * * * *

15. Log [ratio of lead compound activity a Y to lead activity apb]

for brine A at 25°C . . . . . .............

16. Log [ratio of lead compound activity ap4,Xy to lead activity apb]

for brine B at 25*C . . . . . . . . . . . . . . . . . . . . . .

17. Log [ratio of lead compound activity apx to lead activity aI

* a 25

, . 26

, a 27

. 28

. 29

for brine A at 100C . a. ........... * * . .... * . *. .

I8. Log [ratio of lead compound activity ak- y to lead activity ab]

for brine B at 100%C . .. . . *. . . . . . * . . * *.

* . 30

. . . 31

4

I

TABLES

1. Representative composition of simulated rock salt brines . . . . . . . . . 32

2. Activites (moles/liter) used in the calculations . . . . . . . . . . . . . 33

3. Reactions used in the calculations for the titanium-brine system . . . . . 34

4. Reactions used in the calculations for the copper-brine system . . . . . . 35

5. Reactions used in the calculations for the lead-brine system . . . . . . . 36

5

-

I b I I

ACKNOWLEDGMENTS

This work was supported by the Nuclear Regulatory Commission (RC) andthe program was coordinated by Dr. M. MeNeil of the NRC. The authorsacknowledge Dr. E. D. Verink, Jr. of University of Florida for his helpfulsuggestions in the beginning of this work.

6

t

1. INTRODUCTION

One of the major criteria for high level nuclear waste storage is the

containment of radioactive ions 300 to 1000 years.(l) Metal containers are

expected to be the waste package components that will be used to meet this

criterion. Rock salt is a potential repository host rock and titanium and

titanium base alloys(2) are candidates for the container material because of

their corrosion resistance in high chloride environments formed in rock salt

brine pockets. Copper(3) is also considered because of its noble character-

istics and simple microstructure. Lead is used to shield radiation fields

from the waste.(4) Thermodynamic characterization of these systems is

essential to understand the corrosion properties of these materials in

hig-chloride waters.

The usefulness of potential--pH diagram is widely recognized for the

study of corrosion, along with solubility limit diagrams. Although pure

metal-water systems have been well studied and tabulated(5) at room tempera-

ture, high temperature data for the present systems are not available. This

paper presents potential--pH diagrams and solubility limit diagrams for

titanium, copper and lead in simulated rock salt brines at room temperature

and 1000C.

2. CALCULATION PROCEDURES

Table 1 shows the compositions of simulated rock salt brines.(6) In

the calculations, C, S04-2, I-1, HC03 - and H1I are considered

to be the most detrimental ions with respect to corrosion. The compounds

formed from these ions are potentially stable. However, HCO3- and I-

7

are not considered in certain cases because of the instabilities of their

compounds. Table 2 lists the ionic activities for these ions and these acti-

vities are assumed to be equivalent to concentrations. The differences be-

tween activities and consentrations do not significantly affect the calcul-

ations. If there are differences, the calculations are conservative since

activity is generally lower than concentration. Tables 3, 4, 5 are lists of

reactions used in the calculations and values for the equilibrium constant (K)

of the reactions for titanium, copper and lead. The values for copper were

obtained primarily from Swedish work(3> while those for lead and titanium

were calculated from free energy data.(7) The anhydrous state of the com-

pound was considered for all the calculations. Values of log K for titanium

and lead at 250C were calculated from free energy data AGO using the

equa tion

log K - -AGO/(2.303 RT)

Values of log K for lead and titanium at 1000C were calculated from enthropy

data (ASO) using the relation

d(AGo) , _ ASo

dT

assuming that AS0 and the enthalphy value (AHO) are constant from 250C

to 1000C.

8

In the potential--pH diagrams, lines a and b are drawn representing the

equilibrium potentials for the hydrogen and oxygen reduction reactions in the

aqueous solutions, respectively. Besides the potential--pH diagram, figures

are made for the log of the ratio of activity of products to activity of re-

actants versus ESHF (potential versus standard hydrogen electrode) using the

relation

AG0 RT aProductsEm + - innF nF aReactants

where F is Faraday's constant, n is the valence number for each reaction.

aproducts and areactants are activities for products and reactants respec-

tively. The calculations were performed for the activities and pH values

listed in Table 2. Positive values for the log ratio of activities refer to

stable solids while negative values indicate that the products are dissolved

species.

3. RESULTS AND DISCUSSIONS

Titanium

The compounds formed from I and HCO3- are very unstable and,

therefore, were not considered for the calculations. TiO was not considered

because it is not stable in the present potential range. Figures 1 and 2 show

the potential--pH diagrams at 250C and 1000C respectively for the two

solutions, and Figures 3-6 are diagrams showing solubility for each compound

with respect to pure substance. The standard reduction potential of titanium

is -1.63 V and its corrosion potential in 0.5 M aerated sodium chloride solu-

tion is 181 mV(3) which is much more positive than the standard reduction

potential. The anodic oxide film is stable for this reason. Depending on the

9

V T

degree of aeration, the corrosion potential is probably in the range of 0 to

200 mV. Therefore, the present potential--pH diagrams indicate that a stable

passivating film should be present in all cases. In the range of our pH

values, the concentration of dissolved titanium species will be negligible and

there are no stable chlorocomplexes of titanium. However, when the environ-

ments are occluded, crevice or pit solutions will be formed. The crevice and

pit solutions are typically acidic and deaerated.(8) Figures 3-6 show the

possibilities of high dissolution of Ti+2, Ti+3 ad TiO+2 for such

cases. It is observed in the above mentioned figures that solid titanium

chlorides are much less stable than the titanium oxides. Therefore, the

chloride compounds should not be present as stable compounds and high chloride

content should not affect the uniform corrosion behavior of titanium.

Copper

The compounds formed from I- are not very stable and, therefore, were

not be considered. Figures 7-8 show the potential--pH diagrams at 250C and

1000C, respectively, for the brines and Figures 9-12 are diagrams showing

solubility for each compound with respect to pure substance. The standard

reduction potential of copper is +337 mV and its corrosion potential in 0.5 M

aerated sodium chloride solution is reportd to be +58 mV.(9) Depending on

the degree of aeration of the solutions, the corrosion potential of copper

should range between -200 mV and +50 mV. If the potential is positive, the

solid phases Cu20, CuO, Cu(OH)3 /2Cll/2 or Cu(OH)1 /2(SO4)1/4 or

Cu(OH)4 /3 (S04)1/3] and or CuCl will form depending on the temperature

and the composition of the solution. Other stable phases are those observed

in the system Cu-water.(5) Another effect of the high chloride content is

the high solubility of copper in the form of chlorocomplexes (Figures 9-12).

10

If the potential is between 0 and -200 m, dissolution of copper to form

aqueous copper chlorocompelxes is very high based on a simple mass balance

calculation of the dissolved ions using a diffusivity 10-5 cm2/sec(l0)

for the copper complexes in water.

The concentrations of S04-2 and HC03- are significant in the pre-

sent solutions. The compounds Cu(OH)3/2 (S04)1 /4 and

Cu(OH)4 /3(S04)1 /3 are only slightly less stable than Cu(OH)3/2 C 11/2.

These phases as well as Cu(OH)(C03)1/2 may, therefore, play a role in

corrosion and appear as corrosion products.

The line referring to the formation of metal sulfide is the only cathodic

corrosion reaction shown in Figures 9-12 where a negative slope is shown for

metal sulfide. In the cathodic corrosion, sulfate ions are reduced to sulfide

ions in reacting with the metal. These reaction may be kinetically slow and,

hence, do not seem to significantly affect the corrosion.(3) It is also

noted that the interaction of ions other than those in Table 2 has not been

considered in producing the Potential--pH diagrams. In particular, the pro-

posed g+2 content in brines is 1.5M. At high pH values (above 8.5), solid

Mg(OH)2 and possibly gCO3 should form. Their presence could also have

some indirect effects on the corrosion.

Lead

The stability of PbSO4 (or PbC12, or PbCO3) are highlighted in the

potential--pH diagram as shown in Figures 13-14 compared to its absence in the

lead-water system.(5) Figures 15-18 are diagrams showing solubility for

each compound with respect to pure substance. The standard reduction poten-

tial of lead is -126 mV and its corrosion potential in 0.5M aerated sodium

11

chloride solution is -312 mV.(9) Depending on the degree of aeration of the

solutions, the corrosion potential may range from -500 mV to -300 mV. Dis-

solution of lead into soluble species may not be a major problem at these

potentials and temperatures of 250C and 1000C as shown in Figures 15-18.

At temperatures above 1000C and at pH above 8, the concentration of aqueous

HPbO2- could become sufficiently large to cause a possibly significant

dissolution of lead. No solid compounds of lead are formed at potentials more

negative than -300 mV. Data in these figures show that lead might be stable

if the oxygen content of the aqueous environment is low, resulting in a more

negative ESHE value and if the pH remains between 6.5 and 8.1. The primary

effects of high chloride content are the formation of solid PbC12 since

stable aqueous hlorocomplexes of lead do not occur. The formation of this

compound may affect the passivity of any solid film formed on the metal.

4. CONCLUSIONS

The thermodynamic properties have been characterized for the systems of

Ti, Cu and Pb in simulated rock salt brines at 250C and 1000C. For

titanium, no new domain has been introduced in the potential -pH diagram and

metal dissolution is not significant. For copper, new domains of copper

chloride or copper sulfate compounds have been introduced. The dissolution of

copper chlorocomplexes are the source of significant metal loss. Lead sulfate

domains are introduced in the lead potential -pH diagrams. Metal loss by

chlorocomplex formation of lead has not been found. Effects of other minor

ions are discussed.

12

5. REFERENCES

1. Code of Federal Regulations, 10CFR60, "Disposal of High-Level Radioactive

Wastes in Geologic Repositories, Technical Criteria," U. S. Nuclear

Regulatory Commission, Washington, DC.

2. T. M. Ahn and others, "Nuclear Wastes Management Technical Support in the

Development of Nuclear Waste Form Criteria for the NRC, Task 4, Test

Development Review," NUREG/CR-2333, BNL-NUREG-51458, Vol. 4, 1982.

3. Copper as Canister Material for Unreprocessed Nuclear Waste - Evaluation

with Respesct to Corrosion, KBS Teknisk Rapport 90, 1978.

4. AESD-TME-3142, "Waste Package Conceptual Designs for a Nuclear Repository

in Basalt," Westinghouse Electric Corporation, 1982.

5. M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions,

NACE, 1974.

6. R. Dayal and others, "Nuclear Waste Management Technical Support in the

Development of Nuclear Waste Form Criteria for the NRC, Task 1, Waste

Package Overview," NREG/CR-2333, BNL-NUREG-51458, Vol. 1, 1982.

7. Handbook of Chemistry and Physics, 56th Edition, CRC Press, 1976.

8. T. M. Ahn, B. S. Lee and P. Soo, "Identification of Crevice Corrosion in

Grade-12 Titanium in Rock Salt Brine at 1500C," to appear in ASTM STP

Titanium and Zirconium in Industrial Applications, 1982.

9. N. D. Tomashov, The Science of Corrosion, p. 468, McMillan 1966.

10. A. Lerman, Geochemical Processes of Water and Sediment Environments,

John Wiley and Sons, Inc., p. 103, 1979.

13

1.0

wMI-co 0.5

5,J0 0.0

w-j -0.5I-

zL.&'- -I O0C-

-1.5 2-2

pH

Figure 1. Potential--pH equilibrium diagram for the titanium-brine system at

250C.

14

*

1.01

wU,40

'I

4I-zw0C-

0.51

0.0

-0.5

-1.0

-1.5

'I I I I I I I

TiO+2 e -

-s .~ - - HTiO3

-Ti+3 z()Ti ~~~~~i

"v~~~~~ -

Ti+2 As vi2~~~~~~

-2 0 2 4 6 8 10 12 14 16pH

Figure 2. Potential--pH equilibrium diagram for the titanium-brine system at

100lC.

15

46 e

'Cxaxl

0

-50

-a0 -1.0 0POTENTIAL E (VOLT vs SHE)

1.0

Figure 3.1/x

Log [ratio of titanium compound activity aTixY to titanium

activity aTi] for brine A at 250C 7 I? 6A

16

* 9

x XI-

0

- 0 -1.0 0POTENTIAL E (VOLT vs SHE)

1.0

Figure 4.

1 /x

Log [ratio of titanium compound activity aTixy to titanium

activity aTi] for brine A at 1000 C.

17

a 0

100

50

x !x:

0o0

-50

-2.0 -l.0 0POTENTIAL E (VOLT vs SHE)

I.0

Figure 5.1/x

Log [ratio of titanium compound activity aTixy to titanium

activity aTi] for brine B at 250 C.

18

*

IC

x axl ~50a

0

0

-50

-1.0 0POTENTIAL E (VOLT vs SHE)

Figure 6.1 /x

Log [ratio of titanium compound activity aTijy to titanium

activity aTi] for brine at 1000C.

19

* Tl I .

0.8

0.6

0.4Mx-J, 0.2

0> 0

w

-j -0.2

o -0.4

-0.6

- .\_Iss _\

-0.8

pH

Figure 7. Potential--pH equilibrium diagram for the Copper-Brine system at

250C.

20

a

0.8

0.6

0.4wz(n

co 0.2

-J0> 0.0

w

-J

zw

0 0.

-0.6

-0.8

0 2 4 6 8 10 12 14pH

Figure 8. Potential--pH equilibrium diagram for the Copper-Brine systeT -

100lc.

21

x X~tQ-CCG2C4~//

-5 ui

-10 C~(q

CuC0 3 (q)

CuS0 4 (oq)

-ISI I I s I l l~~~~~~~~~~~I I

-0.5 -O4 -0.3 -0.2 -t 0 0.1 0.2 0.3 0.4POTENTIAL E (VOLT vs SHE)

l/xFigure 9. Log [ratio of copper compound activity aCuxy to copper

activity aCu] for brine A at 250C.

22

a

I . I

C _

-0.5 -Q4 -0.3 -0.2 -I 0 0.1 0.2POTENTIAL E (VOLT vs SHE)

0.3 0.4

1/xFigure 10. Log [ratio of copper compound activity aCuxy to copper

activity aCul for brine B at 250 C.

23

* I

a'0

-5

-10

-I5

POTENTIAL E (VOLT vs SHE)

1/xFigure 11. Log [ratio of copper compound activity aCuxy to copper

activity aCul for brine A at 1001C.

24

* &

i e

x

C7- -5

-I0~

- 15t / I -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1

POTENTIAL E (VOLT vs SHE)

1/xFigure 12. Log [ratio of copper compound activity aCuxy to copper

activity aCu] for brine B at 1000C.

25

a *

. . *

0.8 - %PO

2~~b.

0.6

0.4 26 80 1

PbSO4 1

~ 0.2 {PbCI2 PbCO3 }

pH~~1

0-0.0

w ~~~~~~~~~PbO

N~~~~~~~~~-

-0.4 NNN

0 Pb 8 1 2 1

Figure 13. Potential--pH equilibrium diagram for the Lead-Brine system.

at 20C.

26

C C

.

0.8 _ "PbO 2

0.6

w x~~~~~~~~

0.4

PbSO4

Z 0.2 _ b

o {PbC_2 PbO3J

L& 0.0 i~

-0.6 Pb :PbO

0

-0.4 _IN

-0.6~~-0.6 ~Pb

-0.8 N

0 2 4 6 8 10 12 14pH

Figure 14. Potential--pH equilibrium diagram for the lead-prine s

1000C.

27

t

'x. I .0

00o b i

.2

-5 1 1 I I If z I

-Q8 -0.6 -4 -2 0 0.2 0.'POTENTIAL E (VOLT vs SHE)

0.8

l/xFigure 15. Log [ratio of lead compound activity apbxy to lead

activity abi for brine A at 25 0C.

28

I . -1

-5 0 10-l / /

0

-20-

-40

-1.0 -0.8 -0.6 -0.4 -0.2 0 Q2 0.4 0.6 0.8POTENTIAL E (OLT vs SHE)

1/xFigure 16. Log [ratio of lead compound activity abxy to lead

activity apb] for brine B at 250 C.

29

7

aA01

0

70

60

50

40

30

20

10

0

-0

-20

-30

-40

-1.0 -0.8 -0.6 -0.4 -Q2 0 0.2 0.4 0.6 0.8POTENTIAL E (VOLT vs SHE)

l/xFigure 17. Log [ratio of lead compound activity abxy to lead

activity apb] for brine A at 1000C.

30

r - I

. K

-0 P Pb0_02

0

-20 Hbi

-30

-40

-50 I l l l -1.0 -0.8 -Q6 -0.4 -2 0 0.2 Q4 Q6 0.8

POTENTIAL E (VOLT vs SHE)

l/x

Figure 18. Log [ratio of lead compound activity apbXy to lead

activity aPb] for brine B at 1000 C.

31

4 - 1 i

Table 1. Representative compositionof simulated rock saltbrines

Ion Brine A Brine B(ppm) (ppm)

Na+ 42,000 115,000K1 30,000 15Mg+ 2 35,000 10Cat 600 900Sr+2 5 15C1- 190,000 175,000SO- 2 3,500 3,500I- 10 10HC03- 700 10Br- 400 400B03- 1,200 10pH 6.5 6.5

32

A a

Table 2. Activities (moles/liter)used in the calculations.

Ion Brine A Brine A

C1- 5.4 4.9S04-2 3.6x10-2 3.6x10-2I- 7.9xlO-5 7.9xlO-5HCO3- 1.1x10-2 1.6x1O-4H+ 3.2x10-7 3.2x1O-7

33

I I , * I

Table 3. Reactions used in the calculations for the titanium-brinesystem.

Log KReaction

Number Equations of the Reactions 25°C 100°C

1. TiO + 2H+ + 2e - Ti + 20 -44.89 -36.50

2. Ti203 + 2+ + 2e - 2TiO + 20 -36.07 -29.523. Ti+2 + 2e - Ti -54.99 -42.97

4. TiO + 2H+ Ti+2 + 20 +9.83 +7.63

5. Ti203 + 6+ + 6e - 2Ti+2 +3H20 -128.80 -100.83

6. 2TiO2 + 2+ + 2e - Ti203 + 20 -18.73 -15.797. TiO2 + 4+ + 2e - Ti+2 + 220 -17.58 -15.02

8. TiO2 + 4H+ + e - Ti+3 + 220 -22.77 -22.63

9. Ti+3 + 3e - Ti -61.21 -46.02

10. TiO2 + 4+ + 4e - Ti + 220 -66.19 -51.5911. TiO+2 + 2+ + 4e - Ti + 20 -59.53 -45.86

12. Ti305 + IOH+ + lOe - 3Ti + 520 -195.13 -152.5413. TiC13 + 3e - Ti + 3C1- -45.68 -35.83

14. TiC12 + 2e - Ti + 2C1- -24.38 -19.09

15. TiCl4 + 4e - Ti + 4C1- -26.21 -21.93

16. Ti + S04-2 + 8H+ + 6e - TiS + 4H20 80.40 67.08

34

I . .0. -, t' . . -,O

Table 4. Reactions used in the calculations for the copper-brinesystem.

Log KReaction

Number Equations of the Reactions 25°C 1000C

1. Cu+ + e - Cu 8.79 7.662. Cu+2 + 2e - Cu 11.61 10.723. 1/2Cu20 + H+ + e - Cu + 1/2H20 8.54 8.234. CuO + 2+ + 2e - Cu + 20 19.25 16.00

5. CuCO3(aq)* + H+ + 2e - Cu + C03- 14.88 11.426. CuCO3 + + + 2e - Cu + HC03- 12.04 9.437. CuCl(aq)* + e - Cu + C1- 6.06 4.938. CuC12 2 + e - Cu + 2C1- 3.26 1.989. CuC1 + e - Cu + 3C1- 3.06 3.42

10. 1/2Cu2 Cl14- 2 + 3 - Cu + 2C1- 2.21 3.5711. CuCl+ + 2e - Cu + C1- 11.04 -

12. CuSO4(aq)* + 2e - Cu + S04-2 9.08 -

13. CuCl + e - Cu + C1- 2.03 1.4914. Cu + 1/2SO472 + 4+ + 3e

- 1/2Cu2S + 220 25.00 14.0015. Cu2(OH)2CO3 + 3H+ + 4e

- 2Cu + HC03 + 2H20 29.36 24.6316. Cu(OH)3 /2 Cll/2 + 3/2 H+ + 2e

- Cu + 1/2C1- + 3/2H20 15.14 13.0617. Cu(OH)3/2(S0 4)1/4 + 3/2H+ + 2e

- Cu1/4 SO42 + 3/2H20 15.69 -

18. 1/2Cu2 + + + C1-- CuCl + 1/2H2O 6.51 6.74

19. CuO + H+ - 1/2Cu2O + 1/2H2O 10.71 7.7720. CuCl + 3/2H20 - Cu(OH)3/2Cll/2

+ 3/2H+ + e -13.11 -11.5721. CuC + 1/4S042 + 3/2H20

- C1- + Cu(OH)3/2(SO4)1/4

+ 3/2 H+ + e -13.66 -22. CuO + 1/2H+ + 1/2 C1- + 1/2H20

- COH)3/2 Cll/2 4.11 2.94

23. CuO + 1/2H+ + 1/4SO472 + 1/2H20- Cu(OH)3/2(SO 4)l/4 3.56 -

24. 1/2Cu20 + H20 - CU(0H)3 /2Cll/2+ 1/2 H+ + e -6.60 -4.83

25. 1/2Cu2 + 20 - Cu(0R) 3/2 (SO4)1/4+ 1/2H+ + e -7.15 -

*(aq) means dissolved molecule.

35

-~ 4. , , * s

Table 5 Reactions Used in the Calculations for the Lead-Brine System

Reaction Log K

Number Equations of the Reactions 250C 1000C

1.2.3.4.5.6.7.8.9.

10.11.12.13.14.

15.16.

17.

18.

19.

20.

21.

22.

23.

24.25.

26.

PbO + 2He + 2e - Pb + H20Pb304 + 8H+ + 8e - 3Pb + 4H20Pb203 + 6H+ + 6e - 2Pb + 3H2 0PbO2 + 4H+ + 4e - Pb + 2H20Pb+Z + 2e PbHPbO2- + 3H+ + 2e Pb + 2H20Pb+4 + 4e - PbPbO3-2 + 6H+ + 4e - Pb + 3H20

Pb(OH)2 + 2H+ + 2e - Pb + 2H20PbC12 + 2e Pb + 2C1-Pb + S04-

2 + 8H+ + 6e - PbS + 4H20PbSO4 + 2e - Pb + S04-PbCO3 + H+ + 2e Pb + HC03 -Pb3 (OH)2 (CO3)2 + 4H+ + 6e

' 3Pb + 2H20 + 2HC03-PbI2 + 2e = Pb + 2I-PbO + 2Pb + 3H2 0- Pb304 + 6H+ + 6ePb304 + 4H+ + 4e= PbO2 + 2Pb + 2H20

PbO + 2H+ + S04-2. PbSO4 + H20

PbO + 2H+ + 2C1-- PbC1 2 + H2 0

Pb304 + 8H+ + S042 + 6e

- PbSO4 + 2Pb + 4H20Pb304 + H+ + 2C1- + 6e

- PbC12 + 2Pb + 4H2 0PbO2 + 4H+ + S04- + 2e

- PbSO4 + 2H20PbO2 + 4H+ + 2C1- + 2e

= PbC12 + 2H20PbCO3 + H20 = PbO + HCO3- + H+PbCO3 + 2Pb + 4H2 0

= Pb3 04 + HC03- + 7H+ + 6ePbCO3 + 2H20

- PbO2 + 3H+ + HC03- + 2e

8.38

57.9952.4944.71-4.25

23.7252.9475.9750.88-9.0452.68

-12.37-6.88

-11.06-12.32

-3.61-7.51

8.57

52.5546.2238.27-1.78

21.60

43.03-5.6343.96-9.42-4.08

-49.61 -43.98

13.28

20.75

17.42

70.36

67.03

57.08

53.75-15.26

14.28

17.99

14.20

61.97

58.18

47.69

43.90-12.65

-64.87 -56.63

-51.59 -42.35

36