SOLVENT EXTRACTION OF COPPER AND CYANIDE FROM WASTE CYANIDE SOLUTION by FENG XIE B. Sc., The Northeastern University (PRC), 1992 M. Sc., The Northeastern University (PRC), 1995 M. A. Sc., The University of British Columbia, 2005 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Materials Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April 2010 © Feng Xie, 2010 ABSTRACT The potential use of two commercial extractants, LIX 7950, a guanidine derivative, and LIX 7820, a solvent mixture of quaternary amine and nonylphenol, for recovery of copper and cyanide from waste cyanide solution has been investigated. Low equilibrium pH favors copper extraction while a high molar ratio of cyanide to copper depresses the copper loading. It is confirmed that Cu(CN)32 is preferentially extracted over Cu(CN)43 and CN by the extractants. Solvent extraction of the mixture of metal cyano complexes shows a selectivity order as follows: Zn > Ni > Cu > Fe. The presence of S042 or S203 shows an insignificant effect on copper extraction while SCN ions may potentially compete for the available extractant with copper cyanide species and thus depress copper extraction significantly. Both extractants exhibit an affinity sequence as SCN > CNO > CN> S203. The selectivity order of different anions with the extractants can be explained by the interrelated factors including anion hydration, charge density, compatibility of the formed complex with the organic phase and the geometry effect. The extraction of Cu(CN)32 with LIX 7950 is exothermic with an enthalpy change (AH°) of -191 kJ/mol. The copper extraction with LIX 7820 has little change when the temperature is varied from 25 °C to 45 °C. For both extractants, the loaded copper and cyanide can be stripped efficiently by a moderately strong NaOH solution. Further increase in NaOH concentration results in the formation of a third phase. The presence of NaCN can facilitate stripping of the loaded copper and cyanide by favoring the formation of Cu(CN)43 in the stripping solution. The important findings suggest a possible solution to the separation of metal cyanide species and free cyanide in the cyanide effluent. Both extractants can be used in a SX circuit for pre concentrating copper into a small volume of strip solution which can be further treated by electrowinning, AVR, SART or similar processes to recover copper products and cyanide. The free cyanide will remain in the raffinate solution from solvent extraction circuit which allows for the potential recycling of the barren solution to the gold cyanidation process. 11 TABLE OF CONTENTS ABSTRACT . ii TABLE OF CONTENTS iii LIST OFTABLES vi LISTOFFIGURES ix ACKNOWLEDGEMENTS xiv 1 Introduction 1 1.1 Cyanide classification 2 1.2 Free cyanide 3 1.3 Cyanate and thiocyanate 5 1.4 Metal cyanide complexes 7 1.4.1 Cyanide complex equilibrium 7 1.4.2 Copper cyanides 9 1.4.3 Zinc cyanides 12 1.4.4 Nickel cyanides 14 1.4.5 Iron cyanides 16 1.4.6 Gold and silver cyanide complexes 17 1.4.7 Mixtures of metal cyanide species 18 2 Cyanide Destruction and Recovery 19 2.1 Chemical destruction process 19 2.1.1 Inco S02/Air process 19 2.1.2 Hydrogen peroxide 20 2.1.3 Caro’s acid 21 2.2 Cyanide and metal recovery process 21 2.2.1 AVR/MNR/SART process 22 2.2.2 Activated carbon 24 2.2.3 Ion exchange resin 25 2.2.4 Solvent extraction 29 V 111 2.2.5 Miscellaneous . 33 2.3 Research objective 34 3 Experimental 36 3.1 Organic reagents and chemicals 36 3.2 Preparation of the extractant solvents 37 3.3 Preparation of aqueous solutions 37 3.4 Test procedure 39 3.5 Analysis 39 4 Extraction with LIX 7950 42 4.1 Terms and definitions 42 4.2 Equilibrium time 43 4.3 Organic formula 44 4.3.1 Effect of diluents 44 4.3.2 Effect of modifiers 46 4.3.3 Effect of the extractant concentration 49 4.4 Effect of temperature 51 4.5 Effect of CN/Cu ratio 55 4.5.1 Extraction results 55 4.5.2 FTIR analysis 57 4.5.3 Preferential extraction 58 4.6 Effect of phase ratio 63 4.7 Effect of other anions 67 4.7.1 Extraction of the mixture solution 67 4.7.2 Effect of S042 71 4.7.3 Effect of SCN, CNO and S203 73 5 Extraction by LIX 7820 78 5.1 Equilibrium time 78 5.2 Organic formula 79 5.2.1 Effect of the molar ratio of nonyiphenol to Aliquat 336 79 5.2.2 Effect of diluents 84 5.2.3 Effect of the extractant concentration 85 iv 5.3 Effect of CN/Cu ratio . 87 5.4 Effect of phase ratio 90 5.5 Effect of temperature 92 5.6 Co-extraction with other anions 94 5.6.1 Effect of non-metal anions 94 5.6.2 Extraction from a mixed solution of metal cyanides 96 6 Discussion 99 7 Stripping of the Loaded Copper and Cyanide 105 7.1 Effect of stripping reagents 105 7.1.1 Stripping with NaOH solution 105 7.1.2 Stripping with NaCN-NaOH solution 107 7.2 Effect of temperature 108 7.3 Effect of phase ratio 110 8 Conclusions and Recommendations 112 8.1 Conclusions 112 8.2 Recommendations 114 Bibliography 115 Appendix I Analysis Methods 126 Free Cyanide 126 Thiocyanate 127 V LIST OF TABLES Table 1-1 Simplified classification of cyanide compounds (modified from Flynn and McGill, 1995) 3 Table 1-2 Solubility of common copper minerals in 0.1 % NaCN solutions (after Hedley and Tabachnik, 1968) 10 Table 1-3 Some properties of copper(I) cyanide species (Flynn and McGill, 1995 and Sharpe, 1976) 12 Table 1-4 Some properties of zinc cyanide species (Flynn and McGill, 1995 and Sharpe, 1976) 14 Table 1-5 Some properties of nickel(II) cyanide species (Flynn and McGill, 1995 and Sharpe, 1976) 15 Table 1-6 Some properties of iron cyanide species (Flynn and McGill, 1995 and Sharpe, 1976) 16 Table 1-7 Some properties of gold and silver cyanide species (Flynn and McGill, 1995 and Sharpe, 1976) 18 Table 2-1 Some commercial base extractants for gold solvent extraction (Rydberg, et a!., 2004) 30 Table 3-1 Some information of LIX® 79 and Aliquat® 336 36 Table 3-2 Some information of diluents and modifiers used in the research 37 Table 3-3 Some information of inorganic chemicals used in the research 38 Table 3-4 The major components in the mixture solution of metal cyanides 39 Table 4-1 Comparison of the effect of diluent types on extraction of metal cyano complexes . .46 Table 4-2 The effect of modifier types on copper extraction with LIX 7950 (Org: 10% v/v LIX 7950, aq: [Cu] = 3.93 x i0 mol/L, CN/Cu = 5; A/O = 1; 25°C) 47 Table 4-3 The effect of temperature on copper extraction with LIX 7950 (Org: 10 % v/v 7950 and 50 g/L 1-dodecanol in n-dodecane; aq: [Cu] = i0 mol/L, CN/Cu=3,A/O=1) 52 Table 4-4 Comparison of 1G° and uS0 for different solvent extraction systems 54 vi Table 4-5 Copper extraction with LIX 7950 under pH uncontrolled conditions (Org: 10% v/v LIX 7950 and 50 gIL 1-dodecanol in n-dodecane, aq: [Cu] = 500 mg/L, CN/Cu = 5, initial pH 10.5; 20 °C) 65 Table 4-6 The separation factors for Zn, Ni, and Fe over Cu under different equilibrium pH (Org: 30% v/v LIX 7950 and 100 g/L 1-dodecanol in n-dodecane, initial aqueous solution as in Table 3-4; A/0=1; 25 °C) 70 Table 4-7 The effect of S042 on copper extraction with LIX 7950 (Org: 10%v/v 7950 and 50 g/L 1-dodecanol in n-dodecane, aq: [Cu] = 3.93 x i0 mol/L, CN/Cu = 3; AJO = 1; 20°C) 72 Table 4-8 The loaded anion content under different initial concentrations (Org: 10%v/v LIX 7950 and 50 g/L 1-dodecanol in n-dodecane; aq: [Cu] = 3.93 x 10 mol/L, CN/Cu = 3; PHeq = 10.50 ± 0.05; A/0 1; 25°C) 77 Table 5-1 The effect of 1-octanol concentration on copper extraction with Aliquat 336 (Org: 9.4 x i0 mol/L Aliquat 336 in n-octane, aq: [Cu] = 3.93 x i0 mol/L, CN/Cu=5;A/0=1;20°C) 83 Table 5-2 Copper extraction with LIX 7820 under pH uncontrolled conditions (Org: 2% v/v LIX 7820 in n-octane, aq: [Cu] = 500 mg/L, CN/Cu = 5, pH 10.5; 20°C) 90 Table 5-3 The loaded anions under different initial anion concentrations (Org: 2%v/v LIX 7820 in n-octane, aq: [Cu] = 3.93 x i0 mol/L, CN/Cu = 3; PHeq = 10.50 ± 0.05; A!0 = 1; 20°C) 95 Table 6-1 Summary of the selectivity orders with various extractants 100 Table 6-2 The hydration properties of some anions 102 Table 7-1 Stripping of copper and cyanide from the loaded LIX 7950 by NaOH solutions (Org: 10% v/v LIX 7950 and 50 g/L 1-dodecanol in n-dodecane, loaded Cu and CN are 3.68 x i0 mol/L and 1.11 x 102 mol/L, respectively; 0/A = 1; 20 °C) 106 Table 7-2 Stripping of copper and cyanide from the loaded LIX 7820 by NaOH solutions (Org: 2% v/v 7820 in n-octane, loaded Cu and CN are 2.17 x i0 mol/L and 6.50 x i0 mol/L, respectively; 0/A = 1; 20 °C) 106 Table 7-3 Stripping of copper and cyanide from LIX 7950 by NaOH-NaCN solutions (Org: 10% v/v LIX 7950 and 50 g/L 1-dodecanol in n-dodecane, Cu and CN are 3.68 x i0 mol/L and 1.11 x 102 mol/L, respectively; [NaOH] = 1 mol/L; 0/A = 1; 20°C) ....108 vii Table 7-4 Stripping of copper and cyanide from LIX 7820 by NaOH-NaCN solutions (Org: 2% v/v LIX 7820 in n-octane, loaded Cu and CN are 2.16 x 10-3 mol/L and 6.50 x 10-3 mol/L, respectively, [NaOHJ = lmol/L; 0/A = 1; 20 °C) 108 viii LIST OF FIGURES Figure 1-1 Plot of equilibrium distribution diagram for free cyanide vs pH at 25 °C 4 Figure 1-2 Eh-pH diagram of CN-H20 system ([CN] =102 mol/L, 25 °C) 6 Figure 1-3 Eh-pH diagram for S-CN-H20 system ([CN] = i0 mol/L, [S] = i0 mol/L, 25 °C) 7 Figure 1-4 Eli-pH diagram for Cu-CN-H20 system ([Cu] = 1 mol/L, [CN] = 1 mol/L, 25 °C) 11 Figure 1-5 Plot of mole fraction of copper cyanide species vs log [CN] ([Cu]= 0.1 mol/L, 25 °C) 11 Figure 1-6 Eh-pH diagram for Zn-CN-H20 system ([CN] = mol/L, [Zn] = i0 mol/L; 25 °C) 13 Figure 1-7 Eh-pH diagram for Ni-CN-H20