GOLD EXTRACTION_proof 19/07/2016 14:53 Page 4
GOLD EXTRACTION
n Smaller plant and site
n No need of costly tailings pond facilities
There are reduced site rehabilitation costs due
to smaller site footprint and fewer environmental
liabilities.
Enhanced CIL/CIP
DST Process chlorination circuit overview
under its supervision. Samples were submitted
for analysis to SGS Canada - Mineral Services.
All solid residues met environmental norms
and DST's chlorination circuit delivered the
anticipated gold recoveries which were higher on
average than cyanide yields on same samples. In
addition, the process successfully demonstrated
its closed circuit operation with the recycling and
regeneration of the reagents.
John W. Mercer, President and CEO of DST
stated: “We consider this an important
endorsement of the DST Gold Process;
demonstrating its potential as an interesting
alternative to cyanide.”
DST is currently working on projects for the
commercialisation of its technologies in Canada,
Argentina, Bulgaria, Chile, Ireland, Namibia and
Peru.
With several mining jurisdictions around the
world banning or restricting the use of cyanide,
some mining companies struggle with good
projects due to increasing environmental and
social concerns related to the use of cyanide.
This alternative process from DST uses
chlorination in order to extract precious metals
from refractory minerals. It operates in a closed
loop circuit, which implies that no liquid effluents
are generated, eliminating the need for costly
tailings ponds. The chemistry and process design
is also viable for treating precious metal deposits
containing base metals. The tailings from the
process are inert from toxic substances, sulphide
depleted and not acid generating, and as a
result, meet environmental norms. The efficiency
of the process has demonstrated high gold
recoveries within a fraction of the time needed
for cyanidation to obtain similar results.
The efficiency of the process, coupled with its
operating conditions, plant size and construction
material allow for competitive operating and
capital costs as confirmed by technical and economic
validation by recognised engineering firms.
DST has a 15 t/d demonstration plan located in
Thetford Mines, Quebec, that processes material
on a commercial basis. The plant can extract gold
and silver using DST’s chlorination technology.
In May DST entered into an agreement with
Empresa Nacional de Minería, Chile (ENAMI) for
the purchase of 125 t of gold concentrate to be
processed using DST's technology. This is part of
a phased plan to establish a commercial
processing facility, using DST's patented
technology, in Chile.
The concentrate contains an estimated 115 g/t
of gold, 9.0% Cu and mercury content in excess
of 600 g/t. This complex material is difficult to
process using conventional processing methods
without the associated environmental liabilities
and metallurgical challenges. An earlier piloting
campaign successfully removed 99.7% of the
sulphide and 99.6% of the mercury content. The
calcine material was then submitted to acid and
water leaching where 99% of the copper was
recovered as copper sulphate. DST's chlorination
process that followed achieved a gold recovery of
98.8% and a final gold deposition over silica
recovery of 99.8%.
DST says the operating costs of its process are
similar to cyanidation on a $/oz basis. However,
there are lower capital costs due to:
n Reaction time, gold extraction in hours
instead of days (shorter process time)
Chlorination chemistry involved in the DST
process. Chlorine, along with a catalytic amount
of bromine, are used as oxidising agents
because of the particularly fast reaction of
bromine with gold
Huntsman has been looking at addressing the
operational challenge of processing ores
containing problematic gangues to help
customers achieve target mineral recoveries and
concentrate grade. Drawing on its polymer
technologies, and its recently commissioned
metallurgical facility in Melbourne, Australia,
Huntsman has been focused on developing
dispersants and depressants that offer benefit for
the treatment of ores bearing fibrous, micaceous
and carbonaceous gangues. This includes ores
from most of the world’s major mining regions.
Huntsman’s new POLYMAX®K50 &
POLYMAX®K55 polymer dispersants have
demonstrated beneficial effect on ores containing
fibrous and mixed mica/carbonaceous gangues.
Fibrous gangues i.e. asbestos, manifest in higher
pulp viscosities, poor froth characteristics and
drainage leading to lower grades, recoveries and
process interruptions from fibre build up.
K50 dispersant, added at typically 50-70 g/t
into the conditioning tank ahead of rougher
flotation, has been shown to inhibit fibre build
up, restore froth mobility and improve drainage.
As well as improved recovery and grade, plant
down time was reduced from the observed
reduction in fibre build up rate.
Mica and carbonaceous gangues can inhibit
flotation recovery and grade, leading to
inconsistent and high reagent consumption and
lower process efficiencies. K55 dispersant can
enhance the performance of natural polymers,
such as starch and dextrin, resulting in
noticeable improvement in copper recovery,
grade, and an overall reduced reagent demand.
Graphite and carbonaceous gangues can be
seen to cause a distinct increase in reagent
demand and poor froth mobility leading to a loss
in recovery and grade. POLYMAX®G30 and
POLYMAX®G35 dispersants preferentially bind
with active carbon sites and when added to the
conditioning stage at a range of 25-50 g/t, can
reduce reagent demand and enhance recovery
and grade.
In addition to their use in flotation, POLYMAX
K50, POLYMAX G30 and G35 dispersants can also
improve the performance of CIP/CIL processes.
K50 dispersant can assist with modifying the
viscosity of ores containing high talc that causes
issues with high viscosity slurry. At a dosage of
50-70 g/t, POLYMAX K50 dispersant can be
added in the mill or leach conditioning tank to
aid pumping and slurry rheology for improved
activated carbon/leachant contact.
AUGUST 2016 | International Mining 71