Anglo Research A Division of Anglo Operations Limited

Anglo Research A Division of Anglo Operations Limited Thermodynamics & Speciation H 2 SO 4 -Me(II)SO 4 -H 2 O, T 200 C Johann Steyl SAIMM Hydrometallurgy Conference 26 February 2009

Agenda • Introduction • Model Development - First principles perspective (infinite dilution) - Phenomenological description (real solutions) • Application 2

Introduction Why solution chemistry model? • Kinetic processes influenced by solution species (entropy driven) • Thermodynamic properties indirectly influence kinetics, for example, − Solvent activity • Anticipate continuous circuit response to step change (incorporate into steady-state model of circuit) 3

Introduction Modelling Methodology • Interaction versus Speciation • Combine interaction/speciation (modern approach) − Must be guided by minimum parameter space − Chemical kinetics (explicitly recognise only contact pairs, e. g. HSO 4−) − Pitzer interaction-type model provides strong enough framework − Surrogate salt approach (Mg) • 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 4

Agenda • Introduction • Model Development - First principles perspective (infinite dilution) 5

Model Development Infinite Dilution • Gibbs-Helmholtz: − Heat capacity function known: − Heat capacity small: • Estimation methods: − Density f : − BLCM: 6

Model Development: Infinite Dilution First-Principles: Methodology DMol 3/COSMO 1. Ek ? S ? 2. H ~ Ep 3. Static 7

Model Development: Infinite Dilution Thermodynamics from QM Perspective H 2 - cycle: Eabs = 4. 65 V (calculated) vs. Eabs = 4. 4 – 4. 8 V (literature) 8

Model Development: Infinite Dilution Define basis for the sulfate ion: H 2 SO 4(l) log(K ) ~ 2 log(K ) ~ -1 SO 42 -(H 2 O)8 9 HSO 4 -(H 2 O)4 H 2 SO 4 (H 2 O)2

Model Development: Infinite Dilution Define basis for Mg-SO 42 - interactions: 1 st contact pair log(K ) ~ 1 - 2 (ΔS ~ 110 – 131 J/mol. K ? ) Mg. SO 4 (H 2 O)9 10

Model Development: Infinite Dilution Define basis for Mg-SO 42 - interactions: 2 nd contact pair log(K ) ~ -3. 5 (ΔH ~50 k. J/mol, ΔS ~100 J/mol. K ) Bidentate Mg(SO 4)22 -(H 2 O)12 11

Model Development: Infinite Dilution Thermodynamic Values (ΔH , ΔS , ΔCp ) 1: 12

Model Development: Infinite Dilution Thermodynamic Values (ΔH , ΔS , ΔCp ) 2: Isocoulombic: log(K ) vs 1/T (∆Cpº = 0 J/mol. K) 13 f(Cpº) = ∆Cpºr∙[T-Tr-Tln(T/Tr)] vs. (T-Tr) (∆Cpº = -120 J/mol. K @ 150 C)

Model Development: Infinite Dilution Thermodynamic Values (ΔH , ΔS , ΔCp ) 3: log(K ) ~ 1. 5 ΔH ~ 10 k. J/mol ΔCp ~ ? J/mol. K 14

Model Development: Infinite Dilution Thermodynamic Values (ΔH , ΔS , ΔCp ) 4: ΔH ~ 50 k. J/mol ΔS ~ 100 J/mol. K ΔCp ~ ? J/mol. K 15

Agenda • Introduction • Model Development - First principles perspective (infinite dilution) - Phenomenological description (real solutions) 16

Model Development: Real Solutions H 2 SO 4 - H 2 O System 1 mol/kg H 2 SO 4 17

Model Development: Real Solutions Mg. SO 4 - H 2 O System era Lit e tur 18

Model Development: Real Solutions {SO 19 Mg. SO 4 - H 2 O System 4 2 -↔Mg. SO 4 } interaction parameter

Model Development: Real Solutions H 2 SO 4 - Mg. SO 4 - H 2 O System Mg. SO 4. H 2 O(s) solubility (200 C) 25 C 20

Agenda • Introduction • Model Development - First principles perspective (infinite dilution) - Phenomenological description (real solutions) • Application 21

Application Fe(II) Oxidation (example) 200 C 150 C Rate 1 = -k 1 (Fe 2+)2 [O 2] 100 C Rate 2 = -k 2 (Fe. CIP)2 [O 2] Ea 0. 1 mol/kg H 2 SO 4 22

Acknowledgements Anglo American plc Paul Dempsey Anglo Research Dr. Maggie Burger 23

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0. 5 mol/kg Mg. SO 4 25