anglo research a division of anglo operations limited johann steyl saimm hydrometallurgy conference...

Anglo Research

A Division of Anglo Operations Limited

Johann SteylSAIMM Hydrometallurgy Conference

26 February 2009

Thermodynamics & SpeciationH2SO4-Me(II)SO4-H2O, T 200C

2

Agenda

• Introduction

• Model Development- First principles perspective (infinite dilution)- Phenomenological description (real solutions)

• Application

3

Why solution chemistry model?

Introduction

• Kinetic processes influenced by solution species(entropy driven)

• Anticipate continuous circuit response to step change(incorporate into steady-state model of circuit)

• Thermodynamic properties indirectly influence kinetics, for example,− Solvent activity

4

Modelling Methodology

Introduction

• Interaction versus Speciation

• Predict speciation at high temperatures− Regress model to speciation data at room temperature− Regress model to thermodynamic data over full T & [Me] range− Take care in selecting K, ΔH, ΔCp at the reference state

• Combine interaction/speciation (modern approach)− Must be guided by minimum parameter space− Chemical kinetics (explicitly recognise only contact pairs, e.g. HSO4

−)− Pitzer interaction-type model provides strong enough framework − Surrogate salt approach (Mg)

5

Agenda

• Introduction

• Model Development- First principles perspective (infinite dilution)

6

Infinite Dilution

Model Development

• Gibbs-Helmholtz:

2

oo

TT

)K(

d

lndRg

− Heat capacity function known:

− Heat capacity small:

r

oTo

To

T

1

T

1HKK r

r

gRlnln

T

Tr

op

oT

o TCr

d

• Estimation methods:

− Density f :

)T(T

TT

1

T)/(T

C

T

1

T

1HKK r

rr

Prg

oTp,

rg

oTo

To

r

rr

rln

RRlnln

− BLCM:

rr

opr

oT

oT

oT T

TTTTΔC)T(TΔSΔGΔG

rrln

7

Model Development: Infinite Dilution

First-Principles: Methodology

DMol3/COSMO

1. Ek ?S ?

2. H ~ Ep

3. Static

8

Thermodynamics from QM Perspective


)( eHH gΔH

(g)ion

hydatΔHΔH

)( eHH aqΔH

2(g)21 red

H5O2+ H7O3

+H3O

+

H9O5+

(aq)22(g)(aq)75(aq)3 O3HH2eOHOH

Eabs = 4.65 V (calculated) vs. Eabs = 4.4 – 4.8 V (literature)

H2 - cycle:

9

[H2SO4]2[H2SO4]3

H2SO4


Define basis for the sulfate ion:

(aq)24(l)2(aq)n2

24(aq)75(aq)3 On)H(3SOHO)(HSOOHOH

H2SO4(l)

SO42-(2H2O)(3H2O)2

SO42-(H2O)8

(H2O)HSO4−(3H2O)

HSO4-(H2O)4 H2SO4(H2O)2

log(K) ~ 2 log(K) ~ -1

10


Define basis for Mg-SO42- interactions:

(aq)2(aq)n2

o4(aq)82

24(aq)62

2 On)H(14O)(HMgSOO)(HSOO)(HMg

(H2O)5MgSO4(H2O)4

log(K) ~ 1 - 2 (ΔS ~ 110 – 131 J/mol.K ?)

MgSO4(H2O)9

1st contact pair

11

(H2O)4MgSO4(H2O)5

(H2O)4Mg[SO4(H2O)4]22–


Define basis for Mg-SO42- interactions:

log(K) ~ -3.5 (ΔH~50 kJ/mol, ΔS~100 J/mol.K )

Mg(SO4)22-(H2O)12

2nd contact pair

(aq)2(aq)102242(aq)92

o4(aq)62

2 OH5O)(HSOMgO)(HMgSOO)(HMg

(aq)2(aq)122

224(aq)92

o4(aq)82

24 OH5O)(H Mg(SOO)(HMgSOO)(HSO )

Bidentate

12

Thermodynamic Values (ΔH, ΔS, ΔCp)

(aq) 42

(aq) 4(aq) HSOSOH

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 25 50 75 100 125 150 175 200Temperature (Celsius)

log(

K1º)

Dickson et al (1990)

Bale et al (1991)

HSC (2006)

Measured (Appendix)

H+ + SO42− = HSO4

−

1:


13

Thermodynamic Values (ΔH, ΔS, ΔCp)2: o

(aq) 42(aq) 4(aq) SOHHSOH

(aq)o

(aq) 42(aq)2(aq) 4 OHSOHOHHSOIsocoulombic:

-16

-15

-14

-13

-12

-11

-10

0.0015 0.0020 0.0025 0.0030 0.0035

1/T (1/Kelvin)

log(

Kº)

Rx7

5

Data

Linear Fit

80

85

90

95

100

105

110

115

120

-125 -100 -75 -50 -25 0 25 50(T - Tr)

∆G

º - f(

Cpº)

Data

Linear Fit

a b

-6

-5

-4

-3

-2

-1

0

1

0.0015 0.0020 0.0025 0.0030 0.00351/T (1/Kelvin)

log

K2º

Oscarson et al (1988)Density Model (∆Cp = 113 J/mol.K)BLCM (∆Cp = -120 J/mol.K)Isocoulombic Reaction (∆Cp = 0 J/mol.K)QM Simulation (this study)Atkins (1994)Perrin (1977)Young & Blatz (1948)Awakura et al (1990)

H+ + HSO4− = H2SO4º

log(K) vs 1/T

(∆Cpº = 0 J/mol.K)

f(Cpº) = ∆Cpºr∙[T-Tr-Tln(T/Tr)]vs. (T-Tr)

(∆Cpº = -120 J/mol.K @ 150C)


14


3:

f

CIP2stoic

CIPo3 m

α

)(γ

γβ

System Method a log(3º) Reference

MgSO4-H2O

FeSO4-H2O

CuSO4-H2O

ZnSO4-H2O

RS

DRS

RS

RS

RS

~1.5

~1.6

b ~l.5 c 1.0

~1.5

Rudolph et al (2003)

Akilan et al (2006a)

Rudolph et al (1997)

Akilan et al (2006b)

Rudolph et al (1999a)

(aq)2y

zo(aq) 4

o(aq) 4n2y

z2(aq) 4

2(aq)y

z O)Hn(MgSOSO))Mg(OH(}SO){Mg( 11

log(K) ~ 1.5

ΔH ~ 10 kJ/mol

ΔCp ~ ? J/mol.K

o(aq) 4(aq) 4(aq) MgSOSOMg 22


15


4:

ΔH ~ 50 kJ/mol

ΔS ~ 100 J/mol.K

ΔCp ~ ? J/mol.K


2(aq)24

o(aq) 4

2(aq) 4 )Mg(SOMgSOSO

16

Agenda

• Introduction

• Model Development- First principles perspective (infinite dilution) - Phenomenological description (real solutions)

17

Model Development: Real Solutions

H2SO4 - H2O System

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1(mol/kg)1/2

Mea

n A

ctiv

ity C

oeffi

cien

t

Covington et al (1965)

Pitzer et al (1977)

Rearson & Beckie (1987)

Holmes & Mesmer (1992)

Clegg et al (1994)

Pitzer et al (1977)

This study

25ºC

200ºC

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

0.0 0.2 0.4 0.6 0.8 1.0

(mol/kg)1/2lo

g (

)

Young et al (1959)Lindstrom & Wirth (1969)Chen & Irish (1971)Clegg & Brimblecombe (1995)Clegg et al (1994)Holmes & Mesmer (1992)This study

25ºC

200ºC

0

10

20

30

40

50

60

70

80

90

100

25 50 75 100 125 150 175 200Temperature (ºC)

Fra

ctio

n sp

ecie

s (%

)

Bisulfate

Sulfate

H2SO4º

1 mol/kg H2SO4

18

0.015

0.017

0.019

0.021

0.023

0.025

-45 -40 -35 -30 -25 -20 -15

β(2)MS (kg/mol)

Re

sid

ua

l su

m o

f sq

ua

res

Literature

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1(mol/kg)1/2

Me

an

Act

ivity

Co

effi

cie

nt

Harned & Owen (1958)

Robinson & Stokes (1959)Pitzer (1972)

Pitzer & Mayorga (1974)Snipes et al (1975)

Rard & Miller (1981)Holmes & Mesmer (1983)

Archer & Wood (1985)Phutela & Pitzer (1986)

Archer & Rard (1998)Guendouzi et al (2003)

This study

25ºC

80

125

150

200ºC

0.0

0.2

0.4

0.6

0.8

1.0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

(mol/kg)1/2

Me

an

Act

ivity

Co

effi

cie

nt CuSO4

ZnSO4

FeSO4

MgSO4

16

17

18

19

20

21

22

255 260 265 270 275280285290295

05

1015

2025

Res

idua

l sum

of

squa

res

Cpº(CIP1)

Cpº(CIP2)


MgSO4 - H2O System

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

(mol/kg)1/2

3 &

3+

4

Rudolph et al (2003, RS)

Akilan et al (2006a, DRS)

This study

25ºC

80ºC

125ºC

150ºC

200ºC

19


MgSO4 - H2O System

{SO42-↔MgSO4} interaction parameter

20

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0.00.10.20.30.40.50.60.7

0.00.1

0.20.3

0.40.5

0.60.7

Rel

ativ

e m

ean

activ

ity c

oeffi

cien

t

H2S

O4

H2SO4 (mol/kg) MeS

O4

(mol

/kg)

MgSO4 (Majima et al, 1988) MgSO4 (Rard & Clegg, 1999) CuSO4 (Majima et al, 1988) ZnSO4 (Majima et al, 1988) ZnSO4 (Tartar et al, 1941)


H2SO4 - MgSO4 - H2O System

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.0 0.1 0.2 0.3 0.4 0.5H2SO4 (mol/kg)

So

lub

ility

(m

ol/k

g)

Marshall & Slusher (1965)

This study

MgSO4.H2O(s) solubility (200C)

25C

21

Agenda

• Introduction

• Model Development- First principles perspective (infinite dilution) - Phenomenological description (real solutions)

• Application

22

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

MgSO4 (mol/kg)

Fra

ctio

n C

IP's

Fe(II) Oxidation (example)

Application

0.1 mol/kg H2SO4

100C

150C

200C

O2H4Fe4HO4Fe 23

22

Rate2 = -k2 (FeCIP)2 [O2]

Rate1 = -k1 (Fe2+)2 [O2]

Ea

23

Anglo American plcPaul Dempsey

Anglo ResearchDr. Maggie Burger

Acknowledgements

25

0.0

0.1

0.2

0.3

0.4

0.5

0.150.20

0.250.30

0.350.40

0.450.50

100

120

140

160

180

200

Fra

ctio

n C

IP's

H2SO4 (mol/kg)

Temperature (C)

0.5 mol/kg MgSO4

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