HEAP LEACH – SX-EW_proof 26/10/2016 10:02 Page 8
HEAP LEACH – SX/EW
silica with POLYSIL, these particles can be grown
in size to the point where they can be flocculated
and removed from leach liquors. The removal of
these fine colloidal particles can reduce
flocculent demand, enhance settling r ates and
improve TSS and solution clarity of overflow
liquors from CCD/clarifiers reporting to SX.
New leaching ideas
In July 2016 Iberian Minerals filed a patent in the
US for its Enviroleach, a proprietary,
environmentally-friendly, non-cyanide based
leach formula for the extraction of precious
metals from ores, concentrates and tailings. A
new 100% owned subsidiary, Enviroleach
Technologies has been created to pursue
commercial opportunities for this product. The
past 12 months have seen extensive testing of
the unique Enviroleach formula on a number of
different ores, concentrates and tailings. Iberian
notes; “the sustainability of the gold industry is
being challenged by reduced grades, more
complex ores and increasingly stringent
environmental conditions. Within industry both
the use and disposal of cyanide present
significant safety and environmental challenges”.
Enviroleach Technologies is helping reduce the
risks and environmental impact of current
processing operations and developing alternative
processes that use less-toxic alternatives to
cyanide.The primary challenge in devising a
suitable substitute for cyanide in gold processing
lies in developing an equally effective, stable and
degradable leach reagent, which is not a
persistent environmental toxin. As gold
cyanidation rates are relatively slow, the industry
has been searching for faster gold leaching reactions
capable of facilitating high metal recovery rates.
Alternative lixiviants or leaching agents should
also be inexpensive, recyclable, selective, nontoxic and compatible with existing downstream
recovery processes. There is an increasing
interest in finding new alternatives or improving
previously tried processes. Numerous other
chemicals have been tested to leach gold,
including; thiosulphate, thiocyanate, ammonia,
bromine, chlorine, bisulphides, and thiourea but
no-one has come up with a more cost effective
and productive method than leaching with
cyanide until now, reports Iberian.
The following table compares the applicability
26 International Mining | NOVEMBER 2016
spectrum, costs, consumptions and sensitivities
of the Enviroleach formula to cyanide and some
of the more prominent alternatives to cyanide.
Gold and other precious metals are readily
recovered from the Enviroleach solution through
a number of well-known and proven extraction
methods including; EW, carbon adsorption and
precipitation.
Duane Nelson, CEO of Enviroleach
Technologies, states: “we are very excited with
the results of the Enviroleach formula. We have
now completed over 2,000 tests and it has been
proven by independent analysis to be safer, and
it provides faster dissolution rates and much
broader operational parameters than typical and
high intensive cyanide solutions on a number of
different ores, concentrates and tailings.
Enviroleach can potentially offer an effective
alternative to cyanide worldwide and help to
reduce the risks and environmental impact of
mineral processing. It may even open up
opportunities in areas where the use of cyanide
is banned including several European countries,
South American countries and some American
states. We will continue testing the formula on a
broad selection of ores, concentrates and tailings
and report the results over the next few months.”
Recently, Iberian engaged the services of MetSolve Laboratories to oversee the development
and independent testing of the formula. Ish
Grewal, President of Met-Solve Laboratories,
states; “I have had the opportunity to test,
review and analyse numerous lixiviants for gold.
Having spent extensive time studying the results
of the Enviroleach reagent, we are very
impressed with this formula. We are delighted to
be working with the Iberian team to advance this
exciting non-toxic technology.”
Last year, Mining and Process Solutions (MPS)
was awarded an exclusive licence to the
GlyLeach™ process. This is a novel leaching
technology that was developed by Curtin
University for leaching of base and precious
metals. It is an alkaline based process that will
leach copper from copper oxide, mixed oxide and
supergene sulphide ores, and even primary
copper sulphide ores. It will also leach gold when
the temperature of the glycine is raised to 60°C.
In signing the agreement, the process inventor,
Professor Jacques Eksteen, from Curtin
University’s Department of Mining Engineering
and Metallurgical Engineering commented: “the
process has a number of immediate applications
including leaching of low grade ores,
differentially leaching of copper and gold ores,
upgrading concentrates, and tailings retreatment.”
The major reagent in the process is glycine
which is the simplest and cheapest of the amino
acids, and is available in bulk ranging from food
grade to technical grade. It has a number of
attractive chemical and physical properties that
gives it significant advantages over any other
copper or gold lixiviant:
n It is an environmentally safe and stable
reagent. It is biodegradable and is easily
metabolised in most living organisms
n It is active as a selective leach agent only
when used in an alkaline-based circuit
between pH 8 and 12
n It provides a step change in copper leaching
with enhanced solubility of copper ions in
aqueous solutions and forms stable
complexes with copper. It is a very effective
leaching agent for almost all copper minerals
apart from chrysocolla, a copper silicate
mineral
n It is easily recovered and recycled. Apart from
normal process losses (usually expected to
be less than 5%), +99% of the glycine is
recoverable