Market Survey on Copper - Indian Bureau of Mines

d) Agitation Leaching: It is rapid leaching of fine particles (usually 90% -
75 microns) of oxide copper concentrates/roaster calcines in strong acid
solutions. It requires only 2-5 hours leaching time.
The leaching usually takes place continuously in a series of 3-4 tanks
with agitation being provided by air or mechanical means. Rapid leaching is
encouraged by high temperature (60 o C) operation. Existing plant use co-current
or counter current leaching. Counter current washing is also practiced to ensure
that pregnant solution is entirely recovered from the leach residue. This process
yields the highest metal recovery in shortest possible time but requires the
highest capital investment.
e) Bacterial Leaching: In certain cases, microbial leaching can be used
for profitable copper recovery from low grade sulphide ore in heaps, dumps or
in-situ in mines or deposits. The process is attractive because relatively little
labour and capital investment are required compared with conventional
techniques and commercial leaching operations.
f) Copper Recovery from Leach Solution: Pregnant solutions from
leaching contain copper at sufficient concentration for direct electro-winning of
high purity copper whereas solutions from in situ, dump and heavy leaching
being weak, need additional treatment for copper extraction. Cementation and
solvent extraction are important for recovering copper from weak solutions.
Both strong and weak pregnant solutions contain impurities (iron, cadmium,
lead and zinc) inherited from the ore and they require purification prior to
further treatment. This is achieved by precipitating ferric iron from aerated
solution with burnt lime at pH: 3-3.5 and by bleeding a portion of electrolyte
from the circuit for decopperising the discard.
ii) Cementation: As practiced in copper industry, the pregnant solution
flows through a pile of scrap steel and copper precipitates on the iron surfaces
as per the following reaction
Fe + Cu 2+ � Cu + Fe 2+
(Scrap) (Solution) (Cement Copper) (Solution)
The copper precipitate detaches in flake or powder form under the
influence of the solution flow. It is invariably contaminated with iron upon
which it precipitates (typical analysis: 85-90% Cu, 0.2-2% Fe, 0.5% SiO2 +
Al2O3 and remainder oxygen). The cement copper is purified by melting in
smelting furnaces/converters and therefore subjected to electro-refining.
iii) Electro Winning
Leaching operation and leaching solvent extraction produce solution
with dissolved copper. The copper from these solutions is recovered in the form
of copper cathode by electrowinning. This process involves application of an
electrical potential between an inert anode (antimonial lead) and a copper
cathode both immersed in copper-bearing solution. The electrowinning cathode
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