The effect of roasting temperature on arsenic volatilization for calcines produced in

183 Pages·2012·5.11 MB·English

by  Brandon Chambers

AN INVESTIGATION INTO THE SULPHATION ROASTING
OF ENARGITE CONCENTRATES

by

Brandon Tadashi Chambers

A thesis submitted to the Robert M. Buchan Department of Mining
In conformity with the requirements for
the degree of Master of Applied Science

Queen’s University
Kingston, Ontario, Canada
(August, 2012)

Copyright © Brandon Chambers, 2012
Abstract
Potential new ore deposits containing significant levels of enargite, a copper arsenic
sulphide mineral, are being considered for development. The processing of high arsenic
copper concentrates directly in copper smelters is difficult due to environmental
concerns. This thesis investigates a process using sulphation roasting as an alternative
method for processing enargite concentrates; copper is recovered from the calcine by acid
leaching, gold is extracted from the leach residue by conventional cyanidation and
arsenic is either fixed in the calcine or precipitated from process emissions. In this
research, sulphation roasting between the temperatures of 300-800oC, with varying
oxygen and sulphur dioxide partial pressures, was investigated.
Experiments indicated that high levels of copper extraction, as well as arsenic fixation,
could be achieved from the produced calcines through hydrometallurgical processes. At
operating temperatures between 400-550oC copper sulphate, copper arsenate, iron
sulphate, hematite and iron arsenate form in the calcine, as well as some arsenic being
volatilized as arsenic trioxide. At processing temperatures between 475-575oC, greater
than 80% of the arsenic was retained in the calcine as copper and iron arsenates. Copper
arsenate would be weak-acid soluble and fixed in an effluent treatment plant along with
arsenic captured in the wet-gas scrubber bleed solution. As operating temperatures
increase above 650oC copper sulphates were converted into oxysulphates, oxides and
ferrites, hematite production was favoured, and arsenic was primarily volatilized.
Increasing the sulphur dioxide addition in the reaction atmosphere resulted in additional
sulphate formation and increased sulphate stability at higher temperatures.
Sulphation roaster heat balances were developed for calcines produced at two
temperatures, 500 and 750oC. They indicated that while high copper extraction and
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arsenic fixation rates could be achieved, the sulphation roasting reactions are highly
exothermic and significant cooling water would need to be added. Due to these issues, it
is likely that partial roasting operations would be economically favourable in greenfield
operations. However, niche applications of this process in operations with existing
copper SX/EW facilities in good acid markets, have the potential to be economically
favourable.
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Acknowledgements
I would like to thank both of my supervisors Dr. John Peacey and Dr. Chris Pickles for
the opportunity to work with them during my time as a graduate student. Their
enthusiasm, guidance, patience, and advice, has not only positively impacted my
research, but also my personal development.
I would like to extend particular thanks to Dr. Chris Harris for his mentorship in the
mining laboratories. Maritza Bailey’s assistance, advice and friendship, has been a
critical component in my experimental research. Kathy Gholshani, Alan Grant, Brian Joy
and Jerzy Jurek are thanked for resources, support and guidance provided. Lastly, I
would like to thank my family and friends for their support and encouragement.
Funding for this research was provided by NSERC and Xstrata.
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Table of Contents
Abstract ......................................................................................................................................................... ii
Acknowledgements ...................................................................................................................................... iv
Chapter 1 : Introduction ................................................................................................................................ 1
1.1 General Overview ............................................................................................................................... 1
1.2 The Arsenic Problem .......................................................................................................................... 1
1.3 Arsenic Demand .................................................................................................................................. 2
1.4 Current Processing Options for Enargite Concentrates ...................................................................... 3
1.5 Proposed Alternative Method for the Processing of Enargite Concentrates ....................................... 4
Chapter 2 : Literature Review ....................................................................................................................... 8
2.1 Enargite Deposits ................................................................................................................................ 8
2.2 Physical Separation of Enargite .......................................................................................................... 8
2.3 Arsenic Stability .................................................................................................................................. 9
2.3.1 Arsenical Ferrihydrite ................................................................................................................ 12
2.3.2 Ferric Arsenate ........................................................................................................................... 13
2.3.3 Calcium Arsenate ....................................................................................................................... 14
2.3.4 Current Arsenic Treatment and Disposal Practices .................................................................... 14
2.4 Current Processing Methods for Arsenic-Rich Complex Copper Concentrates ............................... 15
2.4.1 Partial Roasting .......................................................................................................................... 16
2.4.2 High Temperature Pressure Oxidation ....................................................................................... 19
2.4.3 Bioleaching ................................................................................................................................ 21
2.4.4 Other Process Options for Treating Enargite Concentrates ....................................................... 22
2.4.5 Process Comparison of Current Methods for Treating Enargite Concentrates .......................... 23
2.5 Sulphation Roasting .......................................................................................................................... 25
2.5.1 Fundamental Theory .................................................................................................................. 25
2.5.1.1 Reaction Mechanism .......................................................................................................... 26
2.5.2 Previous Examples of Sulphation Roasting ............................................................................... 34
2.5.2.1 Lakeshore Mine .................................................................................................................. 35
2.5.2.2 Bagdad Copper Mine ......................................................................................................... 38
2.5.2.3 Other Chalcopyrite Concentrates and Ores ........................................................................ 40
2.5.2.4 New Brunswick SRL Process ............................................................................................ 42
2.5.2.5 Dead Roasting of Sulphide Concentrates ........................................................................... 42
2.6 Overview of the Proposed Sulphation Roast, Weak-Acid Leach, Electrowinning Process.............. 43
2.6.1 Sulphation Roasting ................................................................................................................... 43
2.6.2 Weak-Acid Leaching.................................................................................................................. 44
2.6.3 Production of Scorodite (FeAsO ·2H O) ................................................................................... 45
4 2
2.6.4 Solvent Extraction and Electrowinning (SX/EW) ...................................................................... 45
2.6.5 Gold and Silver Recovery through Cyanidation ........................................................................ 46
Chapter 3 : Thermodynamic Analysis ........................................................................................................ 47
3.1 Evaluation Method for the Sulphation Roasting of Enargite Concentrates ...................................... 47
3.2 The Effect of Temperature ................................................................................................................ 50
3.3 The Effect of Oxygen Addition ........................................................................................................ 54
3.4 The Effect of Gas/Solid Molar Ratio and Temperature .................................................................... 60
3.5 The Effect of the p /p Ratio ........................................................................................................ 66
SO2 O2
3.6 Summary of Thermodynamic Results ............................................................................................... 70
Chapter 4 : Materials and Methods ............................................................................................................. 72
4.1 General Overview ............................................................................................................................. 72
4.2 Sample Characterization ................................................................................................................... 72
4.3 Thermogravimetric and Differential Thermal Analysis with Evolved Gas Analysis ....................... 76
4.4 Static Bed Tube Furnace Studies ...................................................................................................... 77
4.5 Product Characterization and Analytical Techniques ....................................................................... 79
4.6 Diagnostic Leach Tests ..................................................................................................................... 81
4.7 Error Analysis ................................................................................................................................... 82
4.7.1 Thermogravimetric Differential Thermal Analysis with Evolved Gas Analysis ....................... 82
4.7.2 Bench Scale Experimentation .................................................................................................... 82
4.8 Mass Balance of the Roasting Tests and Proposed Calcine Compositions ....................................... 83
Chapter 5 : Results and Discussion ............................................................................................................. 84
5.1 Preliminary Studies and Variables .................................................................................................... 84
5.2 Effect of Temperature on Sulphation Roasting in Air ...................................................................... 91
5.2.1 Solubility of Copper, Iron, and Arsenic Species in the Calcine ............................................... 103
5.2.2 Mass Balance of the Proposed Reaction Mechanism and Calcine Composition ..................... 104
5.3 Effect of Processing Temperature on Sulphating Conditions with Sulphur Dioxide Addition ...... 106
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5.4 Calcine Amenability to Leaching ................................................................................................... 113
5.4.1 Investigation of the Leach Residue .......................................................................................... 119
5.5 Effect of Sulphur Dioxide (SO ) Partial Pressure ........................................................................... 120
2
5.6 Effect of Simultaneously Varying Sulphur Dioxide (SO ) and Oxygen (O ) Partial Pressure ....... 129
2 2
Chapter 6 : Industrial Implementation and Economic Analysis ............................................................... 132
6.1 Process Flowsheet ........................................................................................................................... 132
6.2 Heat Balance ................................................................................................................................... 134
6.3 Industrial Implementation of Sulphation Roasting ......................................................................... 137
6.4 Industrial Implementation of Dead Roasting .................................................................................. 138
Chapter 7 : Conclusions and Future Work ................................................................................................ 139
7.1 Conclusions ..................................................................................................................................... 139
7.2 Future Work .................................................................................................................................... 141
7.2.1 Fluidized Bed Roaster Experimentation................................................................................... 142
7.2.2 Investigation of Dead Roasting Conditions .............................................................................. 142
References ................................................................................................................................................. 143
Appendix A –Preliminary Experimental Results ...................................................................................... 151
A.1 Laser Particle Size Analysis ........................................................................................................... 151
A.2 Representative Sampling for Static Bed Roasting Experimentation .............................................. 152
A.3 Static Bed Roasting Retention Time Experimentation .................................................................. 153
A.4 Static Bed Roasting Sample Charge Experimentation ................................................................... 154
A.5 Additional Retention Time Data for Diagnostic Leach Tests ........................................................ 154
A.6 Statistical Analysis of the Raw Data .............................................................................................. 157
A.6.1 Simultaneous Thermal Analysis Error Analysis ..................................................................... 160
Appendix B - Raw Data Experimental Results ......................................................................................... 161
B.1 Bench Scale Experimentation Raw Data ........................................................................................ 161
B.2 Selected X-Ray Diffraction Results ............................................................................................... 163
Appendix C – Mass Balance ..................................................................................................................... 166
Appendix D – Heat Balance Calculations ................................................................................................. 169

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List of Figures
Figure 1: Industry average copper grade trends (Codelco, 2010) ................................................................. 3
Figure 2: Simplified process flowsheet for treating enargite or high arsenic containing concentrates
using a sulphation roast ................................................................................................................................. 5
Figure 3: Predominance area diagrams of the Cu-S-O and Fe-S-O systems at 527oC and 727oC
(Ferron & De Cuyper, 1992) ....................................................................................................................... 30
Figure 4: The effect of temperature and sulphur dioxide addition on product solubility for the
roasting of chalcopyrite concentrates (Shirts et al, 1975) ........................................................................... 39
Figure 5: The expected behaviour of the calcine with response to changes in temperature and partial
pressure ....................................................................................................................................................... 43
Figure 6: The effect of temperature on the equilibrium amounts of gaseous species in the S-O system
for the control conditions in the absence of calcine .................................................................................... 50
Figure 7: The effect of temperature on the equilibrium amounts of Cu-Fe-O species for the control
conditions .................................................................................................................................................... 51
Figure 8: The effect of temperature on the equilibrium amounts of arsenic-containing species for the
control conditions........................................................................................................................................ 52
Figure 9: The effect of temperature on the partial pressure of gaseous arsenic species in the As-O
system ......................................................................................................................................................... 53
Figure 10: The effect of oxygen addition on the equilibrium amounts of copper containing species at
750 K (477oC) for the control conditions .................................................................................................... 54
Figure 11: The effect of oxygen addition on the equilibrium amounts of iron species at 750 K
(477oC) for the control conditions .............................................................................................................. 55
Figure 12: The effect of oxygen additions on the equilibrium amounts of arsenic containing species
at 750 K (477oC) for the control conditions ................................................................................................ 56
Figure 13: The effect of oxygen additions on the equilibrium amounts of copper containing species at
1000 K (727oC) for the control conditions .................................................................................................. 57
Figure 14: The effect of oxygen additions on the equilibrium amounts of iron containing species at
1000 K (727oC) for the control conditions .................................................................................................. 58
Figure 15: The effect of oxygen additions on the equilibrium amounts of arsenic containing species
at 1000 K (727oC) for the control conditions .............................................................................................. 59
Figure 16: The effect of gas/solid molar ratio and temperature on the equilibrium amounts of SO ,
2(g)
SO , O and S in equilibrium with the calcine for the control conditions ......................................... 60
3(g) 2(g) 2(g)
Figure 17: The effect of gas/solid molar ratio and temperature on the equilibrium amounts of CuO,
CuSO , CuO·Fe O and Cu (AsO ) for the control conditions .................................................................. 61
4 2 3 3 4 2
Figure 18: The effect of gas/solid molar ratio and temperature on the equilibrium amounts of
Fe (SO ) , FeSO , Fe O , CuO·Fe O and FeAsO for the control conditions ........................................... 63
2 4 3 4 2 3 2 3 4
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Figure 19: The effect of gas/solid molar ratio and temperature on the equilibrium amounts of As O
4 6
, Cu (AsO ) , As O and FeAsO for the control conditions .................................................................... 65
(g) 3 4 2 2 5 4
Figure 20: The effect of pSO /pO and temperature on the equilibrium amounts of As O , As O ,
2 2 2 5 4 6(g)
FeAsO and Cu (AsO ) for the control conditions ..................................................................................... 66
4 3 4 2
Figure 21: The effect of p /p and temperature on the equilibrium amounts of CuO, CuO·Fe O ,
SO2 O2 2 3
CuSO and Cu (AsO ) for the control conditions ...................................................................................... 68
4 3 4 2
Figure 22: The effect of p /p and temperature on the equilibrium amounts of FeSO , Fe (SO ) ,
SO2 O2 4 2 4 3
Fe O , CuO·Fe O and FeAsO for the control conditions ......................................................................... 69
2 3 2 3 4
Figure 23: X-ray spectrum of the La Coipa concentrate ............................................................................. 74
Figure 24: Gold association in La Coipa Concentrate ................................................................................ 75
Figure 25: Schematic diagram of the static bed tube furnace ..................................................................... 78
Figure 26: Simultaneous thermal analysis at a heating rate of 10k/min in a nitrogen atmosphere ............. 85
Figure 27: Simultaneous thermal analysis at a heating rate of 10k/min in an air atmosphere .................... 86
Figure 28: The effect of temperature on mass loss for various particle sizes of an enargite
concentrate, in an air atmosphere, at a heating rate of 10k/min .................................................................. 88
Figure 29: The effect of temperature on mass loss for various heating rates in air an air atmosphere ....... 89
Figure 30: Preliminary studies for diagnostic leach experimentations ....................................................... 91
Figure 31: The effect of temperature on arsenic volatilization and sample mass in air .............................. 92
Figure 32: The XRD pattern of the volatilized arsenic product .................................................................. 94
Figure 33: The effect of roasting temperature on copper extraction, based on diagnostic leach tests of
a calcine produced in an air atmosphere ..................................................................................................... 95
Figure 34: The effect of roasting temperature on iron extraction, based on diagnostic leach tests of a
calcine produced in an air atmosphere ........................................................................................................ 97
Figure 35: The XRD pattern of a sample produced at 425oC in air ............................................................ 98
Figure 36: The effect of roasting temperature on arsenic extraction, based on diagnostic leach tests of
a calcine produced in an air atmosphere ..................................................................................................... 99
Figure 37: Electron microprobe analysis of an arsenic compound, as a thin section, in a calcine
processed at 700oC in a 16% O and 25% SO atmosphere. ..................................................................... 102
2 2
Figure 38: The effect of roasting temperature on arsenic volatilization and mass change of a calcine
produced in a 16% O and 25% SO atmosphere...................................................................................... 108
2 2
Figure 39: The effect of roasting temperature on copper extraction, based on diagnostic leach tests of
a calcine produced in a 16% O and 25% SO atmosphere ...................................................................... 109
2 2
Figure 40: The effect of roasting temperature on iron extraction, based on diagnostic leach tests of a
calcine produced in a 16% O and 25% SO atmosphere ......................................................................... 111
2 2
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Figure 41: The effect of roasting temperature on arsenic extraction, based on diagnostic leach tests of
a calcine produced in a 16% O and 25% SO atmosphere ...................................................................... 112
2 2
Figure 42: Thin-section SEM image of a calcine produced at 500oC in a 6% O and 70% SO
2 2
atmosphere ................................................................................................................................................ 113
Figure 43: SEM images of the as-received sample and calcines produced at 600, 700 and 800oC .......... 114
Figure 44: Thin-section SEM images of calcines produced at 600 and 700oC in a 16% O and 25%
2
SO atmosphere ......................................................................................................................................... 115
2
Figure 45: EMPA imaging and EDS analysis of a calcine produced at 600oC in a 16% O and 25%
2
SO atmosphere ......................................................................................................................................... 117
2
Figure 46: EMPA imaging and EDS analysis of a calcine produced at 700oC in a 16% O and 25%
2
SO atmosphere ......................................................................................................................................... 118
2
Figure 47: The XRD pattern of the leach residue of a calcine produced at 600oC in air .......................... 119
Figure 48: Scanning Electron Microscope imaging of gold and silver particles in the leach residue,
produced in a 16% O and 25% SO atmosphere at 400 and 500oC, respectively .................................... 120
2 2
Figure 49: The effect of roasting temperature on sample mass for calcines produced in various SO
2
partial pressures ........................................................................................................................................ 121
Figure 50: The effect of roasting temperature on arsenic volatilization for calcines produced in
various SO partial pressures .................................................................................................................... 122
2
Figure 51: The effect of temperature on water-soluble copper extraction for calcines produced in
various SO partial pressures .................................................................................................................... 123
2
Figure 52: The effect of temperature on water-soluble iron extraction for calcines produced in
various SO partial pressures .................................................................................................................... 124
2
Figure 53: The effect of temperature on the strong-acid soluble iron extraction for calcines produced
in various SO partial pressures ................................................................................................................ 125
2
Figure 54: The effect of temperature on weak-acid soluble arsenic extraction for calcines produced in
various SO partial pressures .................................................................................................................... 126
2
Figure 55: The effect of the p /p ratio on arsenic volatilization for calcines produced at 500 and
SO2 O2
600oC......................................................................................................................................................... 130
Figure 56: The effect of the p /p ratio on iron recovery, based on diagnostic leach tests of a
SO2 O2
calcine produced at 500oC ......................................................................................................................... 131
Figure 57: Detailed proposed process flowsheet ...................................................................................... 132

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