mercury in artisanal and small scale gold mining

200 Pages·2010·2.75 MB·English

MERCURY IN ARTISANAL AND SMALL SCALE GOLD MINING:
IDENTIFYING STRATEGIES TO REDUCE ENVIRONMENTAL
CONTAMINATION IN SOUTHERN ECUADOR

by

Patricio Colón Velásquez López
M.Sc. in Aquaculture, Agricultural Faculty of Bioscience Engineering, Ghent
University, Belgium, 1996
Engineer in Aquaculture, Faculty of Agricultural Sciences, Universidad Técnica
de Machala, Ecuador, 1987

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

in
The Faculty of Graduate Studies
(Mining Engineering)
THE UNIVERSITY OF BRITISH COLUMBIA
(Vancouver)

August 2010

© Patricio Colón Velásquez López, 2010
Abstract

This investigation builds on research about mercury use in custom processing
centers in Portovelo-Zaruma Southern Ecuador, where around 3000 people are
directly involved to produce around 9 tonnes/annum of gold. The lack of
understanding about mercury dynamics during gold processing reduces the
development of appropriate solutions to mitigate the environmental contamination.
The analysis of the amalgamation systems in 8 centers indicated that 12 to 40%
of the total mercury used in the process has been evaporated when amalgams are
burned, 40 to 60% of mercury has been recovered and 1 to 35% of mercury has
been lost with the tailings. The amalgamation of the whole ore in barrels
(―Chanchas‖) contributes to the highest concentrations of mercury in tailings (350
ppm Hg). Around 1.5 tonnes/annum of mercury has been likely released to the
environment in Portovelo from which 71% goes to the air and the remaining
mercury enters the cyanidation process. As amalgamation does not extract all the
gold present in the ore, the mercury rich-tailings are processed with cyanide
preferentially through Merrill-Crowe or Carbon in Pulp (CIP) system. The analysis
of 7 cyanidation processing plants revealed that 51% and 14% of mercury is
released as dissolved mercury from CIP and the Merrill-Crowe process
respectively. Approximately 27% of mercury is released to the atmosphere with the
Merrill-Crowe when zinc shavings are burned. The CIP process releases 3.72% of
mercury during carbon elution. A laboratory cyanidation test confirmed that
mercury dissolution from tailings is much slower than gold dissolution.
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The established division of labor in place among miners and owners of
processing centers forces the use of mercury in amalgamation combined with
cyanide leaching. As miners do not understand the actual process, they accept low
levels of gold recovery by amalgamation, leaving the rich tailings to the owners of
processing centers. This generates dependency on mercury and reduces the
opportunity to improve the system.
One lesson gleaned from this study is that a participatory integrated assessment
approach may contribute to learning, increasing awareness, and it can help identify
practical and effective options for reducing mercury contamination in artisanal gold
mining operations.
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Table of contents

Abstract .................................................................................................................. ii
Table of contents ................................................................................................... iv
List of tables ......................................................................................................... vii
List of figures ........................................................................................................viii
List of acronyms ..................................................................................................... ix
Acknowledgments .................................................................................................. x
Chapter 1 : General introduction ............................................................................. 1
1.1 Background ........................................................................................................... 1
1.2 Statement of the problem ...................................................................................... 8
1.3 Approach of the thesis ......................................................................................... 10
1.4 Research questions .............................................................................................. 11
1.5 Research objectives ............................................................................................. 12
1.6 Thesis outline ...................................................................................................... 12
1.7 Significance of the work ....................................................................................... 14
Chapter 2 : Methodological approach ................................................................... 16
2.1 Study design ........................................................................................................ 16
2.2 Data gathering ..................................................................................................... 18
2.3 Selection of ASGM processing centers .................................................................. 19
2.4 Integrated assessment of mercury use in processing centers ................................. 20
2.4.1 Assessing the amalgamation process ......................................................................... 22
2.4.2 Assessing the cyanidation process ............................................................................. 23
2.4.3 Assessment of mercury in the environment ............................................................... 26
2.5 Laboratory test of mercury dissolution in cyanide solutions .................................. 26
2.6 Quality control ..................................................................................................... 26
2.7 Data analysis ....................................................................................................... 27
2.8 Integrating knowledge ......................................................................................... 28
Chapter 3 : Artisanal and small scale gold mining in Southern Ecuador: development
and characterization ............................................................................................. 32
3.1 Geographical location of the study site ....................................................................... 32
3.2 Historical gold mining development in Southern Ecuador ...................................... 34
3.3 Previous work at the site ...................................................................................... 38
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3.4 The artisanal miner .............................................................................................. 41
3.5 Gold processing methods ..................................................................................... 44
3.6 The gold processing centers ................................................................................. 46
3.6.1 The “Chancha” processing center ............................................................................... 49
3.6.2 The Chilean mill processing center ............................................................................. 52
3.6.3 Cyanidation processing center ................................................................................... 55
3.6.4 Merrill-Crowe process ................................................................................................ 56
3.6.5 CIP process ................................................................................................................. 58
3.7 Organization of people and processing centers ..................................................... 60
3.8 Mercury contamination from ASGM ..................................................................... 61
Chapter 4 : Results and discussion about mercury in the amalgamation process .... 65
4.1 Balance approach ................................................................................................ 65
4.2 Mercury balance in amalgamation of concentrates ............................................... 65
4.3 Mercury balance in amalgamation of the left-over material .................................. 67
4.4 Mercury balance in amalgamation of the whole ore ............................................. 69
4.5 Mercury recovery and losses ................................................................................ 70
4.6 Hg –Au ratio ........................................................................................................ 74
4.7 Air mercury contamination during amalgam burning ............................................ 76
Chapter 5: Results and discussion about mercury in cyanidation process................ 77
5.1 Balance approach ................................................................................................ 78
5.2 Mercury balance in Merrill-Crowe process ............................................................ 78
5.3 Mercury balance in CIP process ............................................................................ 83
Chapter 6 : General discussion ............................................................................... 90
6.1 Alternative livelihood................................................................................................. 90
6.2 ASGM communities and mercury dynamics ................................................................ 93
6.3 Stakeholder perceptions and interests ....................................................................... 99
6.4 Reasons for the use of mercury in ASGM .................................................................. 104
6.5 Mercury releases to the environment ....................................................................... 107
6.6 Impacts of mercury contamination ........................................................................... 112
6.7 Mercury and cyanide in the aquatic environment ..................................................... 116
6.8 Strategies for reducing mercury contamination ........................................................ 122
6.9 Perspectives for the future to mitigate mercury contamination................................. 130
6.9.1 Governmental actions .............................................................................................. 130
6.9.2 Stakeholder participation and knowledge interchange ............................................ 137
Chapter 7 : Conclusions ....................................................................................... 152
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Chapter 8 : Claim to original research .................................................................. 156
Chapter 9 : Suggestions for further work ............................................................. 157
References .......................................................................................................... 159
Appendices ......................................................................................................... 173
APPENDIX I: Assessment of mercury during the whole ore amalgamation ....................... 173
APPENDIX II: Assessment of mercury during the left-over amalgamation ........................ 174
APPENDIX III: Assessment of mercury during the amalgamation of concentrates ............ 175
APPENDIX IV: Assessment of mercury during the cyanidation in Merrill-Crowe system ... 176
APPENDIX V: Distribution (%) of mercury in Merrill-Crowe cyanidation plants. ............... 177
APPENDIX VI: Assessment of mercury in one CIP cyanidation processing plant ................ 178
APPENDIX VII: Assessment of mercury during the 5 days of cyanide leaching. ................. 179
APPENDIX VIII: Mercury and gold leaching at different NaCN concentrations. ................. 180
APPENDIX IX: Elemental chemical composition of suspended solids (CIP process). .......... 181

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List of tables

Table 2.1: Methods for Measuring Hg during amalgamation process ............................... 22
Table 2.2: Workshops and meetings participation ............................................................ 31

Table 3.1: Concentration of mercury in sediment, water and biota. ................................. 62

Table 4.1: Average mercury distribution in Processing Centers ....................................... 72
Table 4.2: Estimated mercury releases in the Portovelo Zaruma area ............................. 74

Table 5.1: General conditions of Merrill-Crowe and Carbon in Pulp process. ....... 78
Table 5 2: Estimated mercury discharged during cyanidation ............................... 85

Table 6.1: Categories of problems of ASGM. ................................................................. 101
Table 6.2: Categories of opportunities associated with ASGM. ...................................... 103

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List of figures

Fig 2.1: Flow diagram of the study approach of mercury in ASGM system ....................... 17
Fig 2.2: Location of Portovelo-Zaruma and Ponce-Enriquez. ........................................... 20
Fig 2.3: Diagram of assessment of mercury in gold processing system ........................... 21

Fig 3.1: Location of processing centers. ........................................................................... 47
Fig 3.2: Flowchart of processing system of ASGM in Southern Ecuador. ......................... 49
Fig 3.3: Typical ―Chancha‖ processing center .................................................................. 50
Fig 3.4: ―Chanchas‖ or drums .......................................................................................... 52
Fig 3.5: The Chilean mill center for crushing and milling the ore. ..................................... 53
Fig 3.6: Diagram of cyanidation of Merrill-Crowe process ................................................ 57

Fig 4.1: Mercury balance during amalgamation of gravity concentrates. .......................... 66
Fig 4.2: Mercury balance during the amalgamation of left-over material .......................... 68
Fig 4.3: Mercury balance for the amalgamation of the whole ore. .................................... 69

Fig 5.1: Balance of mercury in Merrill Crowe process cyanidation plants . ....................... 79
Fig 5.2: Mercury and gold leached during five days in Merrill-Crowe system. .................. 80
Fig 5.3: Mercury and gold dissolution at different cyanide concentrations. ....................... 82
Fig 5.4: Balance of mercury (kg) in CIP process in one processing plant. ........................ 84
Fig 5.5: Metallic mercury in solid tailings after cyanidation. .............................................. 88

Fig 6.1: System dynamics of mercury from ASGM in Southern Ecuador. ........................ 94
Fig 6.2: Estimate of mercury discharges by ASGM in Portovelo–Zaruma. ..................... 109
Fig 6.3: Mercury and cyanide in aquatic ecosystems. .................................................... 118
Fig 6.4: Demonstration of the kitchen-bowl retort. .......................................................... 124

viii
List of acronyms

ASGM – Artisanal and small scale gold mining
APROPLASMIN – Asociación de Propietarios de Plantas de Beneficio Mineral
CIP – Carbon in Pulp
CIMA – Compañía Industrial Minera Asociada
EIA - Environmental Impact Assessment
ENSO – El Niño Southern Oscilation
FUNGEOMINE – Fundación Geologica Minera
FUNSAD – Fundación para la salud
GEF – Global Environmental Facility
Ha – Hectare
PRODEMINCA – Proyecto de Desarrrollo Minero y Control Ambiental
SADCO – South American Development Company
UN-COMTRADE – United Nations Commodity Trade Statistics
UNIDO – United Nations for Industrial Development Organization
UNEP – United Nations Environment Programme
USEPA – US Environmental Protection Agency
WHO – World Health Organization

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Acknowledgments

Firstly I would like to thank to my supervisor, Dr. Marcello Veiga and the co-
supervisor Dr. Ken Hall for the guidance and direction provided during this PhD. I
am heartily thankful to Marcello Veiga whose friendship, guidance and support
from the early to the final level enabled me to develop an understanding of the
subject of gold processing and foundations to apply research in mining
communities. Dr. Hall guidance has allowed me discerning complex issues which
also strength my capacity for this doctorate, and his suggestions pointed me in the
right direction to perform this thesis. Apart of my supervisors I would like to
recognize my appreciation to Margot Parkes for her preliminary assistance on the
road to achieve this thesis.
I am thankful to the University of British Columbia and especially to professors,
colleagues, and staff of the Norman B. Keevil Institute of mining engineering for
support received to achieve my studies.
My thanks to several funding sources for this achievement. I would like to
express my gratitude to Dr Jerry Spiegel, who in addition to serving on my thesis
committee, supported my PhD through the CIDA, University partnership of
Cooperation and Development TIER 1 ―Sustainable managing environmental and
health risk in Ecuador‖ project University Partnership. In addition I thank authorities
of the Technical University of Machala, from Ecuador for their support to
accomplish this goal. Additional funding was also received from The United
Nations Industrial Development Organization through the Global Mercury Project
under direction of Marcello Veiga for whom I also express my gratitude.
As I spent most of my office time at the Health Promotion Research (Global
Health Institute), I would like to thank my colleagues and friends for their help and
assistance provided in every moment I needed.
This thesis would not have been possible without the opportunity I found
through many people in Ecuador. Owners of processing centers, miners,
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