The Speciation of Gold in Mine Wastes and Natural Watersflex.flinders.edu.au › file ›...

The Speciation of Gold in Mine Wastes and

Natural Waters

A thesis submitted for fulfilment of the degree of Doctor of Philosophy

Christine Ta BTech (Forens&AnalytChem), BSc (Hons)

Faculty of Science and Engineering School of Chemical and Physical Sciences

May 2013

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Declaration 'I certify that this thesis does not incorporate without acknowledgment any material

previously submitted for a degree or diploma in any university; and that to the best of my

knowledge and belief it does not contain any material previously published or written by

another person except where due reference is made in the text’.

Christine Ta

____________________ on ____________

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Acknowledgements

Firstly, I would like to thank my remarkable supervisory team. Thank you all for your

guidance and inspiration. I’ve learnt a lot and I’m grateful to have worked with you all.

My sincerest thanks go to Assoc. Prof. Claire Lenehan, who has been a wonderful

mentor all these years. Your insightfulness and belief in my abilities have helped me

grow as a researcher (and cheers for getting us an ICP-MS!).

Thank you to Dr. Frank Reith for introducing me to the area of gold geochemistry.

Your experience and enthusiasm for my research was invaluable.

Thank you Dr. Joël Brugger for all your help with GWB and for making everything look

easy.

Thank you Prof. Allan Pring for all your sensible advice and kind words of

encouragement (I’ve kept the emails!).

Special thanks to Jason Young and Dr. Daniel Jardine from Flinders Analytical, where most

of this work has been carried out. Your efforts in setting up our ICP-MS for solvent work and

the help you provide students are much appreciated. Thank you to the laboratory teaching

department at Flinders University for sharing the HPLC, especially David Vincent for moving

the HPLC down to Flinders Analytical every time there was a break in teaching. Thank you to

Dr. Jason Kirby and Claire Wright (CSIRO Land & Water, Waite) for my initial introduction to

using HPLC-ICP-MS.

A big thank you to everyone who collected or provided water samples for this study,

especially Dr. Frank Reith, Dr. Joël Brugger, Dr. Carla Zammit, Roger Fidler and Jim Safta

(PIRSA), Dr. Susan Wilson (University of New England), Newmont Exploration Proprietary

Limited and Barrick Gold of Australia Limited, Straits Resources (Hillgrove Antimony/Gold

Mine), Paul Androvic and Andy Giles from (Dominion Mining, Challenger Gold Mine), Reece

Wilkie (Northgate Minerals, Stawell Gold Mines) and Dr. David Gray and Dr. Ryan Noble

(CSIRO, Perth). Thank you to Prof. Leone Spiccia and Dr. Rosalie Hocking (Monash

University) and the SA Museum for providing the manganese minerals and compounds for

this study.

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Many thanks to Julie Smith (CSIRO Land & Water, Waite) for the chemical analyses

conducted on the water samples and Dr. Barbara Etschmann (SA Museum) for the XRD

analyses on the manganese oxides.

Thank you to the ARC Linkage Grant (LP100102102) for funding this project and the

Australian Postgraduate Award for funding me!

Thank you to the Lenehan and Popelka-Filcoff Research Group. I am very grateful to have

been part of such an encouraging and diverse research group (and one that bakes!).

I must thank the many PhD students that have shared an office with me: Jessirie Dilag,

Owen Osborne, Lintern Fairbrother, Leigh Thredgold and Karen Bruce. Thank you for all the

laughs, support and long lunches. Being office-mates with you all has been a blast.

My biggest thank you goes to all my friends and family. Thank you for your patience, love

and unwavering support throughout this whole process. Thank you Mum and Dad for being

so proud of me and for all the food! Thank you to my sister Elle for proof-reading my thesis

and editing in bright pink. That was fun to read.

Finally, a big thank you my boyfriend David for his endless love and support (emotional and

financial ha-ha). You have always kept me smiling. Thank you.

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Summary

The geomicrobiological cycle of gold has been widely studied in an effort to improve gold

exploration techniques and gold recovery in mining processes. But these studies and the

basic understanding of how aqueous gold behaves are largely based on chemical speciation

modelling (indirect speciation), as current direct speciation techniques are limited by their

poor sensitivity and interferences from real matrices.

This study describes the development of a HPLC-ICP-MS method for the determination of

Au(I)-cyanide, Au(I)-thiosulfate, Au(III)-chloro-hydroxyl and Au(III)-bromo-hydroxyl

complexes in mine waters and groundwaters. A systematic study of the HPLC variables led

to the final mobile phase: a buffer of 1 mM tetrabutylammonium chloride and 5 mM sodium

dihydrogen phosphate/disodium hydrogen phosphate prepared in 6: 17.5: 76.5 v/v/v

isopropanol: acetonitrile: water. The detection limits for the gold species ranged from 0.081-

0.58 g L-1

.

Sixty two water samples (from mine waters, groundwaters and environmental monitoring

bores) were collected from around Australia and analysed with the developed method. Trace

amounts of Au(I)-cyanide were detected in a few environmental monitoring bores (~0.7 – 11

µg L-1

), of which the proximity to tailings dams and other mining processes suggests that the

Au(I)-cyanide arose from leached mining processes. Unexpectedly, Au(III) was detected in a

near-neutral, saline groundwater (~0.4 µg L-1

), even though Au(III) is predicted to be

thermodynamically unstable at those conditions. Chemical analysis of saline groundwater

samples revealed an apparent correlation between manganese and Au(III) and led to an

investigation into the effect of manganese on the speciation of gold.

Preliminary studies investigating the ability of various natural manganese oxides (pyrolusite,

birnessite, tokodorite, cryptomelane, lithiophorite/ vernadite/ goethite, chalcophanite/

hetaerolite and coronadite) and manganese complexes (Mn-1,4,7-triazacyclononane,

[(bpy)2MnIII(-O)2Mn

IV(bpy)2](NO3)3, (bpy = 2,2’-bipyridyl)) to oxidise Au(I) or Au(0) to form

aqueous Au(III) under non-acidic, surface conditions (similar to the saline groundwaters

collected). Synthetic analogues of manganese oxides (including pyrolusite and potassium

Page | v

permanganate) were also tested. These reactions comprised of stirring ~0.0001 M Mn-oxide

and 0.1 M Cl- with either Au(I)-thiosulfate ([Au] = 1 mg L

-1) or Au(0) powder ([Au] = 50 mg L

-1)

made up to 100 mL with water.

The formation of aqueous Au(III) from Au(I) was not observed with natural or synthetic

manganese minerals under circumneutral to alkaline conditions, but was observed for

permanganate (at pH 6.9) and [(bpy)2MnIII(-O)2Mn

IV(bpy)2]

3- (pH 4.7). Both compounds

were also observed to oxidise Au(0) powder to aqueous Au(III). These preliminary studies

support previous hypotheses by Boyle [1] and Emmons [2] that gold can be mobilised by

manganese in the environment, and may have provided further details on the mechanism for

the mobilisation of gold by manganese in the environment. We propose that the presence of

O2 is necessary for the oxidation of Au(0) to Au(I), and the reduction or disproportionation of

the manganese oxide followed by the adsorption of Au(I) appears to be necessary for the

oxidation of Au(I) to Au(III).

In summary, due to the limited techniques able to directly speciate gold at environmentally

relevant concentrations, the development of a sensitive and direct speciation method to

enhance current understanding of the geomicrobiological cycle of gold is required. The

research presented here may advance the use of HPLC-ICP-MS as a technique for mineral

exploration, in studies on the fate of gold in mine wastes and bioremediation processes, and

in studies on the effect of organic matter, microorganisms and minerals on the speciation of

gold.

Dedicated to

My Parents

Kuan and Mayling Ta

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Contents

Declaration i

Acknowledgements ii

Summary iv

Contents vii

Figures x

Tables xii

List Of Acronyms xiii

1. Introduction 1

1.1 Gold 2

1.2 Gold in the environment 2

1.2.1 Plants and organic matter 4

1.2.2 Microorganisms 6

1.2.3 Aqueous forms of gold 7

1.3 Previous gold speciation techniques 14

1.3.1 Overview 14

1.3.2 Ultraviolet-Visible Spectroscopy (UV-VIS) studies 14

1.3.3 Raman studies 16

1.3.4 X-ray absorption spectroscopy (XAS) 18

1.3.5 Extraction-photometric reagents 20

1.3.6 Chemical speciation modelling 21

1.3.7 HPLC-ICP-MS studies 21

1.4 Instrumentation 23

1.4.1 Separation by HPLC 23

1.4.2 Detection with ICP-MS 23

1.5 Software and modelling 25

1.5.1 The Geochemist’s Workbench® (GWB) 25

1.6 Conclusions & Project Premise 26

2. Method Development 27

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2.1 Introduction 28

2.2 Study Scope 29

2.3 Experimental 30

2.3.1 Reagents and Standards 30

2.3.2 HPLC-ICP-MS set up 31

2.3.3 HPLC-ICP-MS procedure 32

2.3.4 Modelling Studies 33

2.4 Results and Discussion 34

2.4.1 Preliminary work 34

2.4.2 Choice of ion-pairing agent 34

2.4.3 Choice of buffer 37

2.4.4 pH effect 40

2.4.5 Phosphate buffer effect 41

2.4.6 Choice of organic modifier 43

2.4.7 Isopropanol-acetonitrile system 44

2.4.8 Application of method to model solutions 45

2.4.9 Analytical figures of merit 52

2.5 Conclusions 53

3. Application to water samples 54

3.1 Introduction 55

3.2 Study Scope 56

3.3 Experimental 57


3.3.2 Water samples 57

3.3.3 ICP-MS set up 60

3.3.4 ICP-MS procedure 61

3.3.5 Water composition analysis 61

3.3.6 Modelling Studies 61


3.4.1 Determination of total Au by ICP-MS water samples 62

3.4.2 Application to water samples associated with gold mines 64

3.4.3 Application of method to groundwater samples 68

3.4.4 Thermodynamic modelling of groundwaters 71

3.4.5 Implications on gold mobility 77

3.5 Conclusions 79

4. Manganese and Gold 80

4.1 Introduction 81

4.1.1 Mn in the environment 81

4.1.2 Mn reacting with gold 82

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4.2 Study Scope 83

4.3 Experimental 84


4.3.2 Manganese compounds 84

4.3.3 Oxidation experiments procedure 85


4.4.1 Oxidation of Au(I) 87

4.4.2 Oxidation of Au(0) 92

4.4.3 Kinetic Au(I) Oxidation Studies with Potassium Permanganate and

[(bpy)2MnIII(-O)2Mn

IV(bpy)2]

3- 93

4.4.4 Kinetics of Au(0) Oxidation with [(bpy)2MnIII(-O)2Mn

IV(bpy)2]

3- 100

4.4.5 Implications for the mobility of gold 103

4.5 Conclusions 105

5. Conclusions and Future Work 106

5.1 Conclusions 107

5.2 Future work 108

5.2.1 Groundwater analysis 108

5.2.2 Remediation and Recovery Processes 109

5.2.3 Manganese and Gold 109

5.2.4 Thermodynamic models 110

6. Appendices 111

Appendix A 112

Appendix B 114

Appendix C 115

Appendix D 119

7. References 120

7.1 References 121

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Figures

Figure 1-1 The geomicrobiological cycle of gold in the environment. 4

Figure 1-2 Secondary electron micrographs of bacterioform gold. 7

Figure 1-3 Absorption spectra of 10-4

M Au(III) in 1 M NaCl solution at varying pH. 10

Figure 1-4 Absorbance spectra of Au(III)-Cl-OH complexes as a function of pH. 11

Figure 1-5 Absorbance spectra of 2.5 x 10-3

M HAuCl4 solutions. 12

Figure 1-6 Raman spectra of the Au-Cl stretching and Au-OH stretching ranges. 13

Figure 1-7 Absorbance spectra of [AuCl4]- and [AuBr4]

-. 15

Figure 1-8 Absorption spectra by gold particles of different radii. 16

Figure 1-9 Raman active vibrational modes of the [AuCl4]- complex. 17

Figure 1-10 Enhancement of the symmetric stretch of [AuCl4]- at ~347 cm

-1. 17

Figure 1-11 The two spectral regions in XAS: XANES and EXAFS. 18

Figure 1-12 Typical Au-LIII edge XANES spectra as taken from Berrodier et al. [111]. 19

Figure 1-13 Fourier transforms of EXAFS spectra of Au solutions. 19

Figure 1-14 TBAC structure. 23

Figure 1-15 Schematic of the Agilent ICP-MS set up. 24

Figure 1-16 Schematic of electron multiplier. 25

Figure 2-1 Effect of ion-pairing agent’s alkyl chain length on gold signal and separation. 36

Figure 2-2 Effect of ion-pairing agent alkyl chain length on [Au(CN)2]- retention time. 36

Figure 2-3 A comparison of the Au(III)-halides in an ammonium phosphate buffer. 37

Figure 2-4 Log-log activity-activity speciation diagram of Au(III)-halide species. 39

Figure 2-5 Effect of pH on the signal and retention times on the gold species. 40

Figure 2-6 Effect of phosphate buffer concentration on gold signal and separation. 42

Figure 2-7 Log-log activity-activity speciation diagram of Au(I) with H2PO4- and S2O3

2- ions. 42

Figure 2-8 Effects of cyanide impurities in acetonitrile on the gold species. 43

Figure 2-9 Effect of isopropanol/acetonitrile on the gold signal and separation. 44

Figure 2-10 Effect of dilution and aging time on Au(III)-chloride stability in water. 47

Figure 2-11 Effect of dilution and aging time on Au(III)-bromide stability in water. 49

Figure 2-12 Effect of dilution and aging time on Au(III)-chloride stability in mobile phase. 50

Figure 2-13 The interaction effect from mixing gold standards on the speciation of gold. 52

Figure 3-1 Log fO2-pH speciation plot of Au in the presence of various common ligands. 56

Figure 3-2 Detection of [Au(CN)2]- in water samples associated with gold mines. 64

Figure 3-3 Detection of high [Au(CN)2]- signals in samples associated with gold mines. 65

Figure 3-4 Measurement of Au in an unspiked Tanami monitoring bore water. 66

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Figure 3-5 Measurement of Au in spiked (7 mg L-1

) Tanami monitoring bore water. 67

Figure 3-6 Detection of Au(III)-chloride in groundwater samples. 69

Figure 3-7 Effect of HDTMAOH ion-pairing agent on the retention time of Au-chloride. 70

Figure 3-8 Effect of HDTMAOH on peak retention times in various waters. 71

Figure 3-9 Thermodynamically predicted gold species for Lake Way. 76

Figure 4-1 Effect of various Mn(III/IV) oxides on Au(I)-thiosulfate. 88

Figure 4-2 Effect of various Mn minerals on Au(I)-thiosulfate peak area over time. 89

Figure 4-3 Effect of synthetic manganese compounds on Au(I)-thiosulfate after 23 days. 91

Figure 4-4 Effect of synthetic manganese oxides on Au(0), t = 1 day. 92

Figure 4-5 Effect of permanganate on the speciation of Au(I)-thiosulfate. 95

Figure 4-6 Effect of permanganate on the speciation of Au(I)-thiosulfate over 24 hours. 96

Figure 4-7 Effect of [(bpy)2MnIII

(-O)2MnIV

(bpy)2]3-

on the speciation of Au(I) thiosulfate. 98


(-O)2MnIV

(bpy)2]3-

on Au(I)-thiosulfate over time. 99


(-O)2MnIV

(bpy)2]3-

on the speciation of Au(0). 101


(-O)2MnIV

(bpy)2]3-

on the speciation of Au(0) over time. 102

Figure 6-1 Effects of dilution and aging time on Au(I)-thiosulfate stability in water. 112

Figure 6-2 Effects of dilution and aging time on Au(I)-cyanide stability in water. 113

Figure 6-3 Effect of HDTMAOH on the unretained peak in Challenger mine wastes. 114

Figure 6-4 XRD pattern of G17606, birnessite. 115

Figure 6-5 XRD pattern of G18130, lithiophorite/vernadite/goethite. 116

Figure 6-6 XRD pattern of G13911, kutnahorite. 116

Figure 6-7 XRD pattern of G7678, Cryptomelane. 117

Figure 6-8 XRD pattern of G31991, hetaerolite/chalcophanite/hollandite. 117

Figure 6-9 XRD of G30226, Pyrolusite. 118

Figure 6-10 XRD of G30226, Coronadite. 118

Figure 6-11 Effect of Cl- ions on [(bpy)2Mn

III(-O)2Mn

IV(bpy)2]

3- and permanganate solutions. 119

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Tables

Table 1-1 Known gold minerals as listed by Boyle [1]. 3

Table 2-1 The chemicals used in this study. 30

Table 2-2 Final operational conditions for HPLC-ICP-MS. 32

Table 2-3 The tetra-ammonium-hydroxide ion-pairing agents investigated. 35

Table 2-4 Mass balance recovery of gold standards (n=1). 45

Table 2-5 Analytical figures of merit. 53


Table 3-2 List of water samples collected for this study. 58

Table 3-3 ICP-MS operating conditions and data acquisition parameters 60

Table 3-4 Water samples analysed in this chapter. 62

Table 3-5 Concentrations of [Au(CN)2]- determined with HPLC-ICP-MS. 66

Table 3-6 Cyanide concentrations of mine waters determined by a cyanide probe. 68

Table 3-7 Geochemical analysis of the groundwater from Fifield, Lake Way and British King. 73

Table 3-8 ICP-MS analysis of the groundwater from Fifield, Lake Way and British King. 74


Table 4-2 List of synthetic and natural manganese compounds in this study. 85

Table 4-3 The pH values of the natural Mn-oxide and Au(I)-thiosulfate reactions. 87

Table 4-4 The pH values of the Mn-oxide and Au(I)-thiosulfate reactions. 91

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List Of Acronyms

AAS Atomic Absorption Spectroscopy

APHA American Public Health Association

bpy 2,2’-bipyridyl

CSIRO Commonwealth Scientific and Industrial Research Organisation

DC Dissolved Carbon

DOC Dissolved Organic Carbon

EC Electrical Conductivity

EXAFS Extended X-ray Absorption Fine Structure

GNP Gold Nanoparticle

GWB The Geochemist’s Workbench®

HA Humic Acid

HDTMAOH Hexadecyltrimethylammonium Hydroxide

HPLC High Performance Liquid Chromatography

IC Inorganic Carbon

ICP-MS Inductively Coupled Plasma-Mass Spectrometry

ICP-OES Inductively Coupled Plasma-Optical Emission Spectrometry

ID Internal Diameter

LMCT Ligand-to-Metal Charge Transfer

LOD Limit of Detection

LOQ Limit of Quantitation

m/z Mass-to-Charge Ratio

PIRSA Department of Primary Industries and Resources of South Australia

PVDF Polyvinylidene Difluoride

QPC Quartz Pebble Conglomerate

RP-IPC Reversed Phase-Ion Pairing Chromatography

RR Resonance Raman

TACN Triazacyclononane

TBAC Tetrabutylammonium Chloride

TBAOH Tetrabutylammonium Hydroxide

TEAOH Tetraethylammonium Hydroxide

TN Total Nitrogen

TPAOH Tetrapropylammonium Hydroxide

UV-VIS Ultraviolet-Visible

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XANES X-ray Absorption Near Edge Structure

XAS X-ray Absorption Spectroscopy

XRD X-ray Diffraction

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