LEACHING & SX/EW
with on-site cyanide production, may make
the use of cyanide acceptable, at least in
some jurisdictions
n It is imperative to continue to work on
developing alternative leaching systems in
case a widespread cyanide ban should
eventuate
n Alternatives to cyanide could play an
important role if research work on improving
ore permeability makes it feasible to apply in-
situ leaching to gold ores
The use of oxygenated sulphuric acid leaching
with added sodium chloride was pioneered in the
copper matte leach plant at Port Pirie in South
Australia (now owned and operated by Nyrstar) in
the 1980s. This plant produces 4,500 t/y of EW
copper cathode. Some earlier attempts were
made to adapt the process to the leaching of
chalcopyrite and mixed copper sulphide
concentrates. Leaching of chalcopyrite was
successfully achieved, but the process has never
been extended beyond the Port Pirie site, due to
a variety of commercial reasons.
The ALTA 2017 paper Acid Chloride-Sulphate
Leaching of Magnetite Hosted Chalcopyrite
Concentrates from the Viscaria Copper Project In
Sweden by Nigel Ricketts of Altrius Engineering
Services and Ray Robinson of Avalon Minerals
outlines the successful leaching trials using this
leaching system to leach magnetite hosted
chalcopyrite mineralisation from Viscaria. “The
mineralisation contains both talc and magnetite,
with very little pyrite. The chalcopyrite was able
to be leached to up to 96% recovery within eight
hours from a variety of flotation concentrates.
The rapid dissolution of magnetite means that
the flotation should be taken to a cleaner
concentrate before leaching in order to minimise
the acid consumption. It was also found to be
possible to precipitate the iron dissolved from
both the magnetite and chalcopyrite during the
leach as a jarosite, potentially eliminating the
need for a dedicated iron removal step in the
flowsheet.”
The leaching regime followed on from the
findings of the Port Pirie researchers and
consisted of the following variables:
n Acid addition as 98% sulphuric acid – 80-90
g/litre
n Copper sulphate – added to 5 g/litre to
minimise H 2 S formation on start-up
n Sodium chloride – added to 30 g/litre
chloride
n Pulp density – usually 10% solids by weight
n Oxygen addition – 0.25 litre/min
n Temperature - 95°C aim
n Agitation – 1,000 rpm on the Rushton impeller
Jack Bender, Mining Solutions, BASF Corp,
reported on large-scale column testing
performed in An Effective New Leaching Aid
Successfully Tested with Oxide and Mixed
38 International Mining | NOVEMBER 2017
Sulphide Copper Ores. Some 90 kg of an
agglomerated ore was leached for 60-120 days in
batches of 16 columns, at which point roughly
75% of the total copper was leached for oxide
ores and 60% of the sulphide ores. The leaching
aid candidate achieved a 5-20% increase in
copper recovery over columns without leaching
aids with an overall standard deviation of less
than 1% for the data between columns.
In addition to the column testing, the leaching
aids were subjected to bacteriological
compatibility testing to ensure no adverse effect
to the existing microorganisms in the ore. Results
of the testing showed little overall negative effect
on the micro-organisms. Surface-active surfactant
type leaching aids tend to have a negative effect
on SX and can have a negative effect on the EW
system. Leaching aid SX compatibility was
accomplished by batch and continuous processes.
The testing included extraction/stripping kinetics,
selectivity, phase disengagement, loading and
organic solubility testing.
It was determined that the concentration of
chloride/nitrate can influence the efficiency of
the leaching aid, with a slightly negative effect at
very high concentrations. In addition to the
column testing, the leaching aids were subjected
to chemical compatibility testing to ensure that
there are no negative effects on downstream
processes. Based on the results of the current
column testing, BASF is moving forward with
customer trials.
HeapS