GOLD EXTRACTION
hours, with cyanide providing similar recoveries in 30 hours, EnviroLeach
said
The company currently estimates its process is applicable to over 80% of
mining/extraction methods, yet it is working on a new in-situ leaching
application that could expand this further.
Kell progress
In this same feature two years ago, we reported on developments of Kell
Process’ hydrometallurgical process, a treatment option for the recovery of
platinum group metals (PGMs), gold, silver and base metals from flotation
concentrates to refined products on site.
Since then, the process, which is cyanide-free and can eliminate
emissions of sulphur dioxide, arsenic trioxide and other toxic elements
often emitted by smelters and roasters, has been demonstrated in a nine-
week pilot program at Simulus Laboratories in Perth, Australia.
This 1:1,000 scale campaign supported a bankable feasibility study for a
110,000 t/y plant treating a UG2 Meresky concentrate at the Pilanesberg
platinum mine, owned by Sedibelo Platinum. Sedibelo, along with the
South African Industrial Development Corp, are investors in Kell Process.
At the same time as this, Zimbabwean Mining Development Corp has
signed an agreement with the company for a centralised PGM concentrate
processing plant.
Kell is a patented four step process involving aqueous pressure
oxidation, atmospheric leaching, heat treatment and atmospheric oxidative
leaching. It typically recovers a higher percentage of value metals (around
94-99% for platinum, palladium, rhodium, gold, nickel, cobalt and copper)
than smelter refining or cyanide leaching, according to the company.
In addition to the two agreements Kell Process has in place, further test
work and engineering studies for Kell applications at several other
producers and development projects are being progressed, according to the
company. This is for a range of concentrates, including PGMs, refractory
gold and silver, copper-gold and polymetallic.
Grind down your
maintenance costs
Efficient cyanide use
While there are several trends pushing miners away from the use of cyanide,
there is still a reluctance to completely move away from using the lixiviant.
Still, whether it be for financial or environmental reasons, all companies
using cyanide are keen to reduce the amount they are using: a tricky
proposition considering the gold-bearing ores coming into the market are
increasing in complexity.
The presence of cyanide-soluble base metals such as copper and zinc in
gold concentrates are becoming much more commonplace, according to
BQE Water. These metals form weak acid dissociable (WAD) complexes with
the cyanide and preferentially compete for cyanide, the company said. This
typically means that, in order to effectively extract gold from the
concentrate, more cyanide must be added to the solution – bringing about
financial and environmental costs.
BQE Water has taken the SART process, developed and commercialised
by Lakefield Research (now SGS Canada), and is applying it to mining
projects suffering such problems.
As Kratochvil explains, “SART comes in because it avoids the negative
interference of base metals in the extraction of precious metals.”
SART, specifically, breaks the base metal bond from the WAD complex
and precipitates the metal as a commercial-grade concentrate. The cyanide
is regenerated as free cyanide and recycled to the gold extraction circuit.
Kratochvil provided two examples that best displayed the results of
BQE’s SART work to date:
“The SART at the Mastra mine, in Turkey, where the process permitted
gold production from the part of the orebody, which helped access cleaner
gold mineralisation while achieving a payback of less than six months on
the SART plant investment.
Köppern roller presses have been proven successful
throughout the world in plants specializing in the cost-
saving high pressure comminution of various ores like
iron, copper, gold, diamond, molybdenum and lithium ore.
The Köppern Hybridur® tires feature an extremely
wear-resistant surface that provides enhanced roller
protection when grinding abrasive ores.
Köppern – Quality made in Germany.
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Process technology know-how
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[email protected]
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AUGUST 2019 | International Mining 51