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HEAP LEACH – SX/EW
and stripping. Field data showed 89% extraction
efficiency using 42% less organic and minimal
organic entrainment – “all in less than 15 seconds
for extracting and 30 seconds for stripping,”
reports Finfrock. “We also found that optimising
O/A and V/O ratios will further enhance
extraction efficiency and max loading, and
redesigning minor internal parts of the centrifuge
will improve net transfer and phase separation.
That’s when we engaged the DOE lab to
customise a proprietary CSX centrifuge for
copper SX – the first of its kind on the market.
“In another study, we compared holdup
volumes of an MSX plant to a conventional SX
plant of equal capacity, and found that the MSX
plant requires over 95% less initial organic
inventory to load the plant. Since MSX is a fullyenclosed loop system, it also requires over 95%
less makeup organic to replace losses due to
evaporation and entrainment.”
RRT’s BFX ceramic membrane solution is ideal
for reclaiming entrained organic. BFX (byproduct
filtration extraction) plants recover organic entrained
in raffinate or rich electrolyte for reuse. RRT uses
ceramic membranes since they are resistant to
concentrated caustic, acidic, and organic solvents.
Ceramic material enables high mechanical strength,
chemical compatibility, thermal stability, and flux for
a longer operational life.
RRT is also developing a nanofiltration solution
with a copper producer for treating pregnant
leach solution prior to entering the SX plant to
improve the quality of the PLS and reduce the
size of the stream.
Phil Morton, Mining Business Development
Manager at Genesys International, a leading
provider of chemicals for reverse osmosis,
nanofiltration and ultrafiltration systems, notes
that one of the earliest large-scale examples of
reverse osmosis membranes being used to both
clean up wastewater and recover metals was at
Mexicana de Cananea mine in northern Mexico.
The mine was facing closure due to an ironic
combination of insufficient water and the threat
of the operational parts of the mine becoming
flooded. 17 million m3 of wastewater had
accumulated in the pit, which had been used as a
pregnant leach reservoir since the 1980s.
Following successful pilot plant tests the
management team decided to install a full-scale
reverse osmosis membrane plant in 1997,
working with Harrison Western.
The plant was used to:
n Remove water from the pit
n Increase the copper concentration in the acid
leach water fed to the copper extraction plant
n Remove excess water from the leach circuits
n Recover water from the tailings thickener
n Produce clean water for ongoing production.
It was designed to treat a feed water flow of
900 m³/h (4,000 US gal/min) operating at 50%
30 International Mining | NOVEMBER 2016
recovery and producing a 450 m³/h concentrate
stream at 1.6 g/litre of copper and 450 m³/h of
clean permeate water for reuse.
The key objective was to increase the copper
concentration in the feed to the SX/EW plant.
Copper deposited on the cathodes increased
by more than 14%, creating savings of $212,000
in process water cost and $27,000 in sulphuric
acid costs. The level of water in t he pit also dropped
and was predicted to continue dropping by about 3.5
m/y, equating to around a billion gallons.
According to Harrison Western, the typical
capital cost for the membrane plant was $1.5$2.5/US gal/d. The typical operating costs were
$1-$2/1,000 US gal of water recovered, giving a
payback period of one to three years.
The operating costs included:
n Power consumption
n Prefiltration and pretreatment
n Antiscalant and cleaning chemicals
n Membrane cleaning and replacement.
The combined capital and operating costs of
an alternative solution, a lime precipitation system
to account for the loss of copper, would have been
around $5/1,000 US gal of water recovered.
“Despite the success of this first example,
adoption of the technology in the mining industry
was slow to take off. This may have been due to
the operational and capital costs involved as well
as a shroud of secrecy, which resulted in a lack of
published reference material,” Morton says.
“Most of the operational membrane plants in
the industry have been commissioned in the last
five years, thanks to a drop in the price of membrane
elements and more reliable plant designs. Mining
companies Barrick and Newmont in particular have
established several successful plants around the world
during this time.
“At Genesys International we have identified
just 70 operational membrane plants in the
mining sector globally. Of these, 51 of these were
commissioned within the last decade, 69% are
located at gold and copper mines and nearly a
quarter are registered for use to recover metal.
This is because, in precious metal mines,
membrane plants can be used to concentrate
waste water, making it possible to recover
additional metal from ‘barren’ liquor.”
The Genesys International team can advise on
the most appropriate cleaning regime to
maximise the efficiency of membrane plants for
metal recovery. IM
References
1. Copper Heap Leach Development – Not as Easy as it
Looks, Alan Taylor, ALTA MetBytes
2.COPPER LEACHING: 2014-2015 GLOBAL OPERATING
DATA, by R. Washnock, G. Zarate and R. Scheffel, SME
Annual Meeting, February 2016, Phoenix, Arizona
3.Geophysical Heap Characterization throughout
Construction and Operations of the Carlota Mine, Brian
Cubbage, Dale F. Rucker, Bob Zaebst, Jim Gillis, Joseph
Cain, Proceedings of Heap Leach Mining Solutions, 2016,
October 2016, Lima, Peru
4.SX IMPURITY TRANSFER AND WASH STAGE
CONSIDERATIONS, T. Bednarski, A. McCallum and T.
McCallum, Cytec Industries
5.POLYSIL® COAGULANTS TO IMPROVE SX CONDITIONS
– A PRACTICAL WAY TO REDUCE COLLOIDAL SILICA AND
CRUD FORMATION, A. Smethurst, S. Hearn, S. Boskovic,
Huntsman, SME Annual Meeting, February 2015, Denver,
Colorado