M. Adams – Gold Ore Processing (2016)

Автор: M. Adams
Название книги: Gold Ore Processing (2016)
Формат: PDF
Жанр: Геология
Страницы: 981
Качество: Изначально компьютерное, E-book

Gold Ore Processing: Project Development and Operations, Second Edition, brings together all the technical aspects relevant to modern gold ore processing, offering a practical perspective that is vital to the successful and responsible development, operation, and closure of any gold ore processing operation. This completely updated edition features coverage of established, newly implemented, and emerging technologies; updated case studies; and additional topics, including automated mineralogy and geometallurgy, cyanide code compliance, recovery of gold from e-waste, handling of gaseous emissions, mercury and arsenic, emerging non-cyanide leaching systems, hydro re-mining, water management, solid–liquid separation, and treatment of challenging ores such as double refractory carbonaceous sulfides. Outlining best practices in gold processing from a variety of perspectives, Gold Ore Processing: Project Development and Operations is a must-have reference for anyone working in the gold industry, including metallurgists, geologists, chemists, mining engineers, and many others.

Includes several new chapters presenting established, newly implemented, and emerging technologies in gold ore processing
Covers all aspects of gold ore processing, from feasibility and development stages through environmentally responsible operations, to the rehabilitation stage
Offers a mineralogy-based approach to gold ore process flowsheet development that has application to multiple ore types

The first edition of Advances in Gold Ore Processing arrived at a time when the gold price had increased from low values
of around US$270/troy oz in 2001 to an average of $444/troy oz in 2005. Since that time, the price has soared, reaching an
average of $1669/troy oz in 2012 before softening to the 2015 levels of $1100/troy oz. This remarkable performance has
led to a resurgence in primary gold production worldwide, as well as renewed interest in exploration, research, development,
and technological innovation throughout the industry. However, this has been tempered to a significant extent by a
near-threefold increase in cash operating costs from $269/troy oz in 2005 to $750/troy oz in 2014 and similar increased
ratios in capital costs for new (Greenfield) and expansion production capacity. Capital cost intensity for new gold production
capacity now ranges from $1500 to $4500/annual troy oz produced, depending on the ore feed grade, processing
method, byproducts, and ore complexity. This leaves much of the industry facing significant challenges to profitability for
existing operations and for adding new capacity. A key part of this story is that average ore grades have decreased
significantly from about 1.8 g/t in 2005 to approximately 1.3 g/t in 2014. Ore deposits are being developed with
increasingly complex mineralogy and metallurgical properties as the more easily treatable resources are depleted. This not
only adds to the cost of extraction, both capital and operating but also increases the development time for projects and adds
technical risk.
The global gold production profile was very different in 2005. South Africa was the top producer with 300 metric tons,
followed by Australia, United States, China, and Peru. Total global gold production increased from almost 2520 metric tons
in 2005 to over 3100 metric tons in 2014; however, China increased its production to take the top position, followed by
Australia, Russia, United States, and Peru. Much of China’s production comes from small, distributed deposits, using
conventional technology that can be applied effectively at a small scale e for example, gravity concentration, flotation,
amalgamation, cyanidation, and direct smelting/processing of concentrates. In parallel with this, production from many of the
major producing mines dropped off significantly, such as Yanacocha, Peru (Newmont Gold), and Driefontein, South Africa
(Gold Fields). This serves to underscore the dramatic changes that have occurred within the industry over the past 10 years.
Turning to the processing aspects of the industry, gold ore processing is dominated by the cyanidation process. Since
the inception of the process in the late 1800s, cyanide has been used widely to extract gold because of its relatively low
cost, great effectiveness for gold and silver dissolution, selectivity for gold and silver over other metals, as well as relative
ease and efficiency of metal recovery from solution. Also, despite some concerns over the toxicity of cyanide, it can be
applied with little risk to human health and the environment. The oxidant most commonly used in cyanide leaching is
oxygen, usually supplied from air, which contributes to the attractiveness of the process.
Since the mid-1970s, alternative leaching reagent schemes to cyanide have been investigated for any or combinations of
the following reasons:
l Environmental pressures, and in some cases restrictions or limitations, may make the application of cyanide difficult in
certain locations;
l Some alternative reagent schemes provide faster gold (and/or silver) leaching kinetics;
l Several can be applied in acidic media, which may be more suitable for refractory ore treatment, and
l Some are more selective than cyanide for gold and silver over other metals, such as copper and zinc.
Some of the more important reagent systems that have been investigated (or reinvestigated) are chlorineechloride,
thiosulfate, thiocyanate, thiourea, ammonia, ammoniaecyanide, alkaline sulfide, and other halide combinations. Aside
from the advantages listed here, all of the alternative reagent schemes have disadvantages compared with cyanide and, at
this time, none appear to be widely applicable, at least not without further significant advances in the technology. However,
thiosulfate has emerged as the front runner of the alternative schemes for niche applications, and Barrick Gold has
advanced and implemented the commercial development of thiosulfate technology to treat carbonaceous ‘preg-robbing’
material at Goldstrike in Nevada. Carbonaceous, preg-robbing ores are the primary potential application for this emerging
technology.
The application of ultrafine grinding to treat ores and concentrates by liberating gold and silver values from sulfides has
gained momentum following the development of efficient fine-milling equipment, including the Xstrata IsaMill, the Metso
SMD Detritor, and the Metprotech mill as options. These developments paved the way for more efficient grinding down to
finer sizes, around 80% passing 10e15 mm and below d hence, the term “ultrafine” grinding. Also, further development
of the Metso Vertimill following many successful tertiary grinding and regrinding installations has led to its consideration
for ultrafine grinding applications (down to about 80% less than 15 mm). Other fine grinding mills are in development. The
ability to economically grind to such fine sizes presented the opportunity to liberate precious metals from refractory sulfide
ores and concentrates without the need for more costly oxidative treatment, such as roasting, pressure oxidation, and
biological oxidation. While not the first to use ultrafine grinding to treat concentrates, the application at Kalgoorlie
Consolidated Gold Mines (KCGM, Western Australia) in 2001 to treat refractory sulfide gold ore to supplement the roaster
capacity opened up the technology to the industry. The ultrafine milled product was cyanide leached, achieving a gold
recovery of over 90%. This was a significant development as it was the first major commercial application to avoid the
need for oxidative pretreatment. Ultrafine grinding has subsequently been installed at Kumtor (Kyrgyzstan) in 2005, Pogo
(Alaska) in 2006, and Lake Cowal (Australia) in 2006. The product grind sizes were 80% less than 12 mm, 80% less than
10 mm, and 80% less than 15 mm, respectively, for these operations. In 2015, many other operations are considering or
using a similar processing approach, emphasizing the need for continued research and development in this area.
During the past 10 years or so, significant innovations have occurred in process mineralogy. At the forefront of this
work has been the development of automated scanning electron microscopy techniques (e.g., QEMSCAN, provided by
FEI, and the Mineral Liberation Analyzer, developed by the JK Institute of Technology, Australia). These techniques are
now well known to most in the industry, and the significance of being able to perform accurate, quantitative, mineralogical
analysis on representative samples of ore, intermediate processing products, and residues from projects and operations
cannot be overstated. The individual mineral grain identification and quantification, size-by-size analysis, and mineral
liberation/locking analyses that can be generated have revolutionized the approach to design and optimization of mineral
and metal extraction worldwide. Other advanced mineralogical techniques are also now available that provide important
diagnostics for gold and silver recovery optimization, troubleshooting, and process design.
Other key areas of process developments that are covered within this volume include the following:
l Centrifugal gravity concentration equipment, with increasing volume treatment rates
l Intensive leaching equipment and systems to most effectively treat high-grade gravity and flotation concentrates
l Enhanced heap-leaching technology, especially cold climate and dry climate operations and the potential use of
high-pressure grinding rolls to prepare heap leach feed material
l Refractory ore processing, including improved pressure oxidation and roasting technology
l Continued and improved application of biological oxidation to treat flotation concentrates
l Goldecopper and copperegold ore treatment, including the use of sulfidization, acidification, recycle, and thickening
(SART) technology and effective control of cyanide speciation
In parallel with these processing developments, a major effort with respect to the gold extraction industry was the
publication of the International Cyanide Management Code (2002), to which most of the major gold and silver producers
that use cyanide have committed to follow. This code was developed by the International Cyanide Management Institute
(ICMI), a nonprofit organization set up under the United Nations Environment Program (UNEP) and the International
Council on Metals and the Environment (ICME). All of this activity represented significantly increased emphasis on the
control and treatment of gold extraction byproducts and effluents, which should be considered as an integral part of gold
extraction processes. Detoxification of cyanide solutions and slurries is an important aspect of gold ore processing globally
and there are many alternatives for detoxification of cyanide-containing solutions. Where applicable, the preferred method
is to allow the cyanide concentration to decay naturally through the carbon-in-pulp/carbon-in-leach (CIP/CIL) circuit to the
point at which it reaches levels acceptable for discharge to the tailings containment facility. There are many operations that
are able to meet strict discharge limits to tailings facilities without the need for any form of cyanide destruction other than
natural degradation over time. However, these operations carefully manage cyanide concentrations down the leaching and
CIP/CIL circuit, as well as wash ratios in thickeners, using re-circulated, reclaimed or fresh water in the circuit. The
cyanide degrades further over time in the tailings facility, ultimately to non-toxic products, and the understanding of such
degradation processes has improved significantly over the past 25e30 years, including natural degradation of free, weak
acid-dissociable (WAD) and total cyanide species, thiocyanate, and cyanate. The use of tailings thickeners and, where
necessary, tailings filtration can assist with recovering and recycling cyanide-bearing solution. All of these practices help to
reduce cyanide naturally within the overall extraction circuit.
Where the above methods are not sufficient to meet the Cyanide Code guidelines (e.g.,
50 mg/L WAD cyanide
discharge to tailings storage facilities) and/or regulatory environmental requirements, other methods of detoxification must
be used, with the exception of some operations using the hypersaline process water in the Eastern Goldfields of Western
Australia, where natural processes provide a Code-certifiable protective mechanism. After almost 30 years of application at
operations throughout the world, the use of sulfur dioxideeair has become the preferred and most cost-effective method of
cyanide destruction where natural degradation is not adequate. Many other methods have been tested and used
commercially; for example, hydrogen peroxide and Caro’s acid (hydrogen peroxide and sulfuric acid) have both been used
successfully at a variety of operations in various configurations.
Water conservation is, and will continue to be, an area for innovation and this is highlighted in this second edition.
Dry-stacked tailing, such as used at La Coipa (Chile), has additional benefits of cyanide recycling and reduced environmental
concerns for groundwater contamination. Use of brackish and saline water is commonplace in Western Australia
and is currently extending to applications in Chile and Peru.
An important lesson from all of the major innovations in gold and silver extraction is that innovations are rarely
“eureka” moments, but rather they result from a sustained period of testing, investigating, modifying, and improving a
particular technological approach to a problem. In the case of cyanidation, carbon adsorption, heap leaching, and refractory
ore treatment processes, the technology had been known, and versions of each process had been patented, tested and tried
for several decades. Those who successfully commercialized these innovations learned from the prior versions of the
technology, borrowed from other branches of the industry (and in some cases from other industries), and improved the
application of the technology with often simple modifications. The first-user recognized the benefit of the emerging
technology over the incumbent process; they were persistent and relentless in their pursuit of successful commercialization;
and in all cases they relied on innovative and tenacious process operators (not necessarily the inventor or researcher) to
implement the technology effectively. Success was not intuitively obvious in these efforts, and in most cases there were
several failures or, at best, marginal and/or small applications of the technology that preceded widespread
commercialization.
As such, this second edition is particularly timely and valued. The format used in the first edition has been retained, but
the number of chapters has been expanded to cover important issues such as geometallurgical developments, Cyanide Code
compliance, alternative lixiviants, water management, arsenic and mercury management, gold recovery from e-waste, and
emerging and transformational gold processing technologies d a significant enhancement and update to the previous
edition. The contributing authors represent an excellent global cross section of gold metallurgists, researchers, developers,
and experts in related fields. Mike D. Adams is to be congratulated on bringing together this valuable contribution to the
literature on gold extraction and processing.

This second edition of Gold Ore Processing arrives a decade after the first edition was published in 2005 and has
established itself as a widespread reference work in the gold processing and mining industry. A revised and extended
edition was therefore timely. The 55 chapters in this second edition volume bring together many technical aspects of
relevance to gold ore processing, from project feasibility study stage, through operations stage to the closure and rehabilitation
stage. The various process flowsheet unit operations that may be applicable to any particular ore type are covered,
along with new emerging trends and potentially transformational technologies. In addition to updates of the existing
chapters, advances in several fields have necessitated extensive rewrites, sometimes with new authors. On the other hand,
scant developments in several mature areas meant that revision was not warranted, with editorial comments providing some
measure of update.
This edition incorporates 13 new chapters, including some 90 contributing authors, spanning environmental considerations,
modern instrumental techniques, and emerging technologies. Additional topics covered are as diverse as the
evaluation and funding of capital projects, solideliquid separation, alternative lixiviants, gold refining, tailings treatment,
and recycling of electronic waste in the circular economy. A new chapter on geometallurgy and automated mineralogy has
been included. Increasing emphasis on environmental aspects in gold mining has resulted in additional chapters covering
management of arsenic and mercury, as well as water management. At the time of the first edition, the International
Cyanide Management Code was in its infancydafter a decade of progress, two new chapters have now been contributed,
covering perspectives from both regulator and auditor.
Existing chapters have been updated to include relevant new processes, flowsheets, technologies, and philosophies.
Examples and indicative data, as well as industry profiles for particular technologies, have been reviewed and revised for
currency and relevancy. Some chapters have additional co-authors or lead authors. Sadly, first edition contributors André
Laplante, David Muir, Rong-Yu Wan, and Martin Millard have passed on in the intervening 10 years since the first edition
was published.
This book should be of use across the gold industry, and it is hoped that metallurgists, geologists, chemists, mining
engineers, managers, financiers, operations, projects, and research staff alike will find the content both useful and
stimulating.