a global leader in mineral and metallurgical innovation
Issue No. 148
September 2009
Mintek-designed resin for Azerbaijan gold project
ANGLO ASIAN MINING PLC has selected the Mintek-developed DOWEX™ MINIX™ ion-exchange resin
for gold recovery at its Gedabek (Gädäbäy) gold-copper project in Azerbaijan.
Gedabek, which is the first operating
gold mine in the south-west Asian
country, was officially opened and
produced its first gold in May 2009.
The operation consists of an open
pit mine and heap-leach facility, with
gold recovery by resin-in-solution and
electrowinning. Copper production will
begin shortly. The mine is expected to
produce more than 300 000 ounces of
gold during its initial six-year mine life.
Owing to the substantial copper grade
of the ore, the copper concentration
in the leach solution is about 100
times that of gold. “An ordinary ionexchange resin would become loaded
with copper, with very little capacity
remaining for gold,” said Dr Roger
Paul, Mintek’s General Manager:
Technology, who visited the mine in
June to assist with optimising the
gold recovery circuit. “The DOWEX
MINIX strong-base resin, however, is
extremely selective for gold over all
other metal cyanide complexes, and
is able to achieve high gold loadings
under these conditions, resulting in a
greatly improved gold recovery. The
Gedabek plant is the first application of
the resin in a leach solution containing
such high copper concentrations,
and we are very pleased with its
performance.”
Several important classes of gold
deposit contain appreciable quantities
of cyanide-soluble copper minerals
that can build up in the metallurgical
process solutions, resulting in gold
lock-up in the circuit and reduced
recoveries. “The DOWEX-MINIX
resin makes low-cost heap leaching
viable where, due to technological
or economic considerations, it is not
practicable to remove the copper
by flotation or acid leaching prior to
cyanidation,” said Dr Paul.
Gold recovery from cyanide leach
solutions with anion exchange resins
is commonly practiced in the CIS
countries, and western gold mining
companies are now beginning to
realise the economic benefits of ion
exchange. Resins are more versatile
than activated carbon because they
can be customised to improve features
such as selectivity, loading capacity,
Gedabek, the first operating gold mine in Azerbaijan, began production in May 2009.
and resistance to poisoning. They
can also be eluted at much lower
temperatures, and unlike activated
carbon do not require thermal
regeneration.
RUSSIA
GEORGIA
AR
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NI
A
Gedabek goldBAKU
copper mine
AZERBAIJAN
IRAN
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50
100 km
Originally envisaged as an alternative to
granular active carbon for gold recovery,
the DOWEX-MINIX resin found its
first niche application in recovering
gold from carbonaceous preg-robbing
ores. It is used in this role at Avocet
Mining’s Penjom mine in Malaysia, and
formerly at the Barbrook gold plant near
Barberton in South Africa. The resin,
designated XZ 91419, is manufactured
and supplied under licence by the Dow
Chemical Company.
In this issue...
Mintek/Azerbaijan gold project.....page 1
NIMCIX expertise.........................page 2
Advanced gold leach facility.........page 2
The mine is situated in the Middle East Tertiary
fold belt, which extends from Pakistan to the
Balkans and contains a number of gold and
copper deposits including Sarcheshmeh in
Iran, Madneuli in Georgia, and Kişladağ in
Turkey.
Mintek gold catalysts distributed..page 3
New Biotech Manager..................page 3
Minfurn for water treatment..........page 4
Mintek re-establishes NIMCIX
expertise
Advanced gold leach facility
WITH THE REVIVAL OF INTEREST IN URANIUM PROJECTS
over the past few years, Mintek has re-established and updated
its expertise in NIMCIX ion exchange technology.
The NIMCIX contactor is a
continuous ion-exchange
(CIX) column developed by
Mintek (then the National
Institute for Metallurgy - NIM)
during the uranium boom
of the 1970s and 1980s.
A notable breakthrough,
it enabled uranium to be
recovered from unclarified
solutions. A number of
commercial plants were built
and operated successfully –
the Vaal River South plant,
commissioned in 1978, is
still in operation and was
recently upgraded with glassreinforced plastic (GRP)
columns. Two new plants,
Ezulweni and Trekkopje (in
demonstration phase), have
been commissioned in the
past 18 months.
The major variables in a NIMCIX
operation include the diameter
of the column, the resin flowrate,
and the number and height of the
stages. To assist in the design and
optimisation of these variables,
a spreadsheet-based model has
been developed that simulates
the performance of a column for
specific applications. Using the
model, it is easy to manipulate
the variables in order to arrive at
the most efficient and economical
design. Mintek is currently
undertaking pilot plant trials to
confirm the accuracy and reliability
of its current model for the
adsorption circuit, and also plans
to validate the model against an
industrial-scale operation.
NIMCIX-type designs were
also used for resin elution on
several past commercial plants,
although the principles were
somewhat different to the columns
used for extraction. Mintek is
evaluating a novel countercurrent
elution design that would allow
continuous resin transfer, and
hence a more efficient elution
and a higher eluate uranium
concentration. This would allow
direct precipitation of uranium
from the eluate, thus avoiding the
extra capital and operating costs
associated with a downstream
solvent-extraction purification
stage.
Page 2
The advanced leach facility, showing (from the left) the
leach reactor, sampling circuit and cell for online solution measurements such as pH, Eh, and dissolved oxygen.
Samples can also be taken manually for metals and cyanide
analysis. The Cynoprobe online cyanide analyser is on the
far right.
MINTEK HAS COMMISSIONED A NEW
ADVANCED GOLD LEACH FACILITY aimed at
NIMCIX columns at the VaalRiver
uranium plant (courtesy AngloGold
Ashanti Ltd.).
A NIMCIX column consists
of between 10 and 14 stages
separated by perforated plates.
Unclarified pregnant leach solution
is passed upwards through
the column, fluidising the resin
in each stage. Eluted resin is
transferred into the top of the
column, while loaded resin is
withdrawn periodically from the
bottom of the column during a
period of backflow. The NIMCIX
column has several advantages
over conventional fixed-bed ionexchange columns:
• It can treat solutions that contain
up to about 300 milligrams per
litre suspended solids;
• Construction and operation
are simple, and capital and
operating costs relatively low;
• Operation is efficient and stable
over a wide range of feed rates
and concentrations;
• Efficiency of recovery is high,
and resin losses are relatively
low;
• The contactor can be
successfully scaled-up to large
diameter units;
• The plant is highly automated,
and start-up and shut-down are
effected with ease; and,
• Plant reliability and availability
are high.
optimising the design and operation of gold recovery circuits
from both the environmental and economic standpoints.
The fully instrumented mini-plant is designed to supplement
the widely-used bottle roll technique for gold amenability
testwork by allowing the leaching kinetics of the target
metal and the environmental parameters to be monitored
in relation to the process conditions. The environmentally
harmful elements such as cyanide, arsenic, and heavy
metals are tracked in “real time” as the leach progresses.
“Understanding how the chemistry of the process changes in
response to variations in the controllable leach parameters
will enable us to improve leach plant designs to meet
environmental protection standards without compromising
gold recovery,“ explained Sonestie Janse van Rensburg,
senior scientist in Mintek’s Hydrometallurgy division.
The facility makes it possible to modify and evaluate the
process parameters that can be realistically changed on
an operating gold plant, such as pH, Eh, oxidant addition,
pulp viscosity, and cyanide concentration, and to gauge the
effectiveness of staged addition of cyanide, pre-oxidation
(with detailed dissolved oxygen measurements), and the
addition of supporting reagents such as lead nitrate. Cyanide
consumption and the concentrations of free and weak-acid
dissociable (WAD) cyanide are monitored using Mintek’s
Cynoprobe online analyser. Total cyanide and thiocyanate as
well as cyanate can be quantified using standard laboratory
methods such as Segmented Flow Injection analysis. The
gold dissolution kinetics can also be evaluated in conjunction
with other elements, for example iron, sulphur, copper, and
nickel, during the leach.
The advanced leach facility bridges the knowledge gap
between the gold leach process and the observable
environmental impacts when residues are discharged,”
said Peter Lotz, head of Mintek’s cyanide services group.
“Better operational and management strategies help to avoid
regulatory fines or plant closures, and reduce remediation
costs either during operation or at the decommissioning
stage. Waste minimisation is also an important part of
operational sustainability.
Instead of applying the conservative, reactive approach
to ameliorate environmental problems once they become
apparent, it is preferable to identify up-stream process
modifications that avoid the problems in the first place.
“Experience has shown that this sort of pro-active
management is better dealt with by metallurgical staff during
the design phase or at the operational level rather than by
on-site environmental personnel - hence Mintek’s approach
to integrate it into the process metallurgy,” concluded Lotz.
Issue No. 148
September 2009
Strem Chemicals to distribute Mintek gold catalysts
STREM CHEMICALS INC., a USA-based manufacturer of specialty chemicals for research and
development, has entered into a distribution agreement with Mintek for the AUROliteTM gold catalysts
developed through Project AuTEK of Mintek’s Advanced Materials Division (AMD).
“Gold catalysis has had a recent
resurgence,” said Dr. Ephraim S.
Honig, COO at Strem Chemicals,”
so we are pleased to be extending
our line of gold homogeneous
catalysts with Project AuTEK’s
heterogeneous line.”
AUROlite gold catalysts perform
in a variety of applications, such
as gas phase CO oxidation,
and may be used in respiratory
protection devices. “In terms of
low temperature CO oxidation
our catalysts outperform the
currently employed Hopcalite
and PGM catalyst technologies,”
said Jason McPherson, head
of the AuTEK Catalysis scaleup and commercialisation unit.
“Furthermore, we see a bright
future for their use in liquid phase
oxidations and other industrial
reactions.”
Through Strem, AuTEK is offering
three varieties of the AUROlite
line of gold catalysts, with a 1 per
cent loading of gold on aluminium
oxide, titanium dioxide, and zinc
oxide supports. The gold itself is
deposited on the support via a
proprietary process that yields gold
nanocrystallites of about 2-3 nm.
Each catalyst is of “commercial
grade”, as AuTEK has already
scaled up its production capacity.
Mintek and Strem, together with
Nanostellar Inc., exhibited their
technologies at the World Gold
Council stand at the 21st North
micro-electronics, chemicals and
petrochemicals industries. Strem
also provides custom synthesis,
process development and GMP
manufacturing services. For more
information visit www.strem.com
Gold chloride solution - the starting material for
the manufacture of AUROliteTM catalysts.
American Catalysis Society Meeting
in San Francisco in June 2009.
This meeting, which is a premier
scientific event in the field of
catalysis research and development,
attracted more than 1 000 of the
world’s leading scientists, chemists,
and engineers involved in the
use of catalysts in the petroleum,
chemical, pharmaceutical energy,
and environmental industries.
AuTEK is a joint venture between
Mintek, and three major South
African gold mining houses Anglogold Ashanti, Gold Fields, and
Harmony Gold - the main focus of
which is to develop novel industrial
applications for gold. R&D is
carried out in the fields of catalysis,
biomedical, and nanotechnology.
The AuTEK catalysis R&D unit
was formed in 2000. Since
AuTEK is trying to bridge the gap
between research and industrial
implementation, a scale-up and
commercialisation unit specifically
focusing on the research outcomes
of project AuTEK catalysis
was created in 2004. For more
information visit www.autek.org
For more information and to order
please see www.autek.org
Strem Chemicals, Inc., based in
Newburyport, Maryland, USA, is
a privately held manufacturer and
marketer of high-purity specialty
chemicals, including catalysts,
ligands, organometallics, metal
carbonyls and nanomaterials. The
company’s products are used for
research and development and
commercial scale applications,
particularly in the pharmaceutical,
CO oxidation testwork using gold-based catalysts.
New Manager: Biotechnology
PETRUS VAN STADEN has been appointed as Manager: Biotechnology.
He succeeds Dr Tony Pinches, who retired at the end of 2008.
Petrus, who holds a M.Sc. in Chemical Engineering from the University of the Witwatersrand, began
his career in 1986 in Mintek’s Hydrometallurgy division. In 1996 he joined the Biotechnology division
as Project Manager: Bioleach Processes, subsequently becoming Head of Process Design.
He has taken a leading role in a number of major Mintek projects, including the development of
the Minfurn carbon regeneration furnace, the Peñoles bioleaching project on complex basemetal concentrates in Mexico, and most recently the NICICO copper heap bioleaching
project in Iran.
Issue No. 148
September 2009
Page 3
First Minfurn in water-purification industry
A MINFURN CARBON-REGENERATION FURNACE has been commissioned at the Rietvlei water
treatment plant near Tshwane in South Africa’s Gauteng Province.
The furnace, which has a capacity
of 25 kilograms of dry regenerated
product per hour, restores the
efficiency of the granular activated
carbon (GAC) that the plant uses
to adsorb dissolved organic matter
before the final chlorination step in
the treatment process.
This is the first adaptation of the
unique direct resistive heating
technology to an area outside the
gold industry.
The Minfurn was originally designed
and developed by Mintek
specifically for the regeneration
of GAC used to adsorb gold
from solution in the carbon in
pulp (CIP) and carbon in solution
(CIS) recovery processes. The
furnace employs a technique of
direct resistive heating by means
of an electrical current passed
directly through the carbon bed.
This results in a high degree of
regeneration efficiency, with
significant advantages over
other regeneration technologies,
including low consumption of
electricity, ease of operation,
minimal moving parts, and low
maintenance.
About 30 Minfurns have been
installed in industry, mainly at small
and medium-sized gold mines in
Latin America. Recently, further
opportunities were identified for
the application of the technology
in two new industry sectors –
potable water treatment and food
processing.
Since GAC has an affinity for
organic substances and repels
water, it represents and effective
way of separating traces of
organic matter from water. “This is
particularly important in the light
of recent changes in raw water
quality and supply in the southern
African region,” says Hylton Gidish,
Mintek’s product manager for the
Minfurn. “Locally, acceptable final
organics levels are 20 nanograms
per litre. Previously, this level was
relatively easily maintained by most
water works in South Africa, but with
recent deterioration in both quality
and supply of raw water, increasing
organic matter has begun to be a
problem, particularly
at the smaller plants.”
Page 4
The Rietvlei water purification plant.
The Rietvlei plant, which produces
40 million litres of drinking water a
day (about 6 per cent of Tshwane’s
daily requirements), was the first
plant in South Africa to apply a GAC
filtration system for drinking water
treatment. The project, which was
completed in 1999, was awarded
the SA Association of Consulting
Engineers’ national award for
technical excellence in 2000. The
plant was recently singled out as the
best medium-sized water purification
facility in South Africa.
The Minfurn installation at Rietvlei
presents an ideal opportunity for
commercial demonstration of the
technology in the potable water
treatment industry. Similarly, a foodprocessing company in the USA
has successfully tested a Minfurn for
regenerating spent GCA used in the
removal of unwanted colour from
their lactic acid product.
“The GAC used in the water
treatment and food industries is
typically finer-grained and softer
than the material used for gold
recovery,” explained Gidish. “The
Minfurn is ideally suited for these
applications, since it results in
minimal abrasion of the carbon, and
hence fewer losses of fine material.”
Development work is ongoing at
Mintek to adapt the Minfurn and
the operating procedure to GAC
samples with different physical and
electrical characteristics, as well
as in unexplored areas of GAC
application.
Tinus Botha (left), acting foreman, and Carel
Taljaard, Deputy Director Purifiactions and
Maintenance at Rietvlei.
Produced by the Information and Communications
division at Mintek
200 Malibongwe Drive, Randburg, South Africa
Private Bag X3015, Randburg 2125, South Africa
Tel: +27 11 709 4111
Fax: +27 11 793 2413
ISBN 1012-5299
Website: http://www.mintek.co.za
E-mail: [email protected]
Write to the Editor, Mintek Bulletin, for further
information on any of the articles in this issue.
Issue No. 148
September 2009