CESL Gold Technology
CESL Gold Process Description
CESL technology has been adapted to treat
leach residue from the CESL Copper
Process to produce a doré product.
Washed and filtered copper plant residue is
sent to Pressure Cyanidation where it is
mixed with recycled barren solution to form
slurry. Simultaneously, lime is added to
neutralize any remaining acid components
in the residue and increase the pH to 10.5,
in preparation for cyanidation. The repulped
and neutralized residue is then leached with
cyanide solution, under high pressure
oxygen, at 3500 kpag, (500 psig). The
retention time of 60 to 90 minutes is
comparatively short compared to
conventional atmospheric cyanidation. The
short retention time minimizes the formation
of thiocyanate during cyanidation.
Thiocyanate production can thus be
drastically reduced, compared to
atmospheric cyanidation using the typical
long retention times. The major by-products
of cyanidation of the Copper Process
residue are copper cyanides, as well as
some thiocyanate and cyanate.
CESL Limited
12380 Horseshoe Way
Richmond, BC
Canada, V7A 4Z1
+1 778 296 4900 Tel
+1 778 296 4908 Fax
[email protected]
www.cesl.com
Pressure cyanidation is followed by filtration
of cyanidation slurry to produce pregnant
solution and washed residue. The pregnant
solution is treated first for precious metal
recovery, by carbon absorption in carbon
columns, and then the barren solution is
treated for cyanide recovery, before
recycling back to the pressure cyanidation
vessel. Loaded carbon is washed with acid
to remove inorganic fouling and then
reneutralized with caustic prior to stripping.
The gold and silver in loaded carbon is
stripped in a strip vessel at elevated
temperature and pressure into a pure
electrolyte, providing feed to gold
electrowinning. Stripped carbon is
regenerated by removing organic fouling via
kiln which improves gold adsorption onto the
carbon.
The copper removal process is designed to
remove copper and thiocyanate. Copper
cyanides are treated primarily by a variation
of the Acid Volatilization Reneutralization
process, in which most of the cyanide in the
copper cyanide complex is recovered as
sodium cyanide, and recycled back for more
gold and silver leaching. The copper is
precipitated as solid copper thiocyanate with
minor solid copper cyanide, with the solids
recycled back to the CESL Copper Process
for additional copper recovery in Pressure
Oxidation. The acidified slurry is separated
to remove the copper solids, leaving both
gaseous and aqueous phases together in the
liquid. This stream is split into two streams.
One stream goes to Neutralization and the
other to hydrogen cyanide Stripping and
Absorption. The split is determined by the
need for water balance (the bleed stream
sent to Stripping is sent to Cyanide
Destruction), and by the need to limit the
overall cyanide tenor in the recycled barren
(to limit hydrogen cyanide vapour losses
throughout the circuit). At the pH 2-4, the
acidification product is stripped of its
hydrogen cyanide gas phase by air stream
contact in a packed tower. The gas product
now containing hydrogen cyanide is then
recovered in an absorption tower using
caustic solution at pH 11, and is recycled as
cyanide liquor to Pressure Cyanidation.
Cyanide Destruction is used to treat the bleed
stream from the process in order to maintain
a water balance and bleed out minor
impurities from the process. The product
slurry from the cyanide destruct reactors is
then filtered to produce a filtrate and a filter
cake; the filtrate may be recycled to the
Copper Plant or discharged to an effluent or
the tailings pond. The filter cake consists
largely of gypsum (>95%) with trace amounts
of copper and iron. This cake is
environmentally stable and can be managed
effectively or co-stored with tailings.
CESL Gold Process Flowsheet
Cyanide
Oxygen
Acid
Cyanide
Recovery
Gold Recovery
Copper Plant
Residue
Pressure
Cyanidation
Hydrated
Lime
Caustic
Air & HCN
Loaded
Carbon
Cyanide
Filtration
Stripped
Carbon
Strip
Filtration
Cyanide
Destruct
4
Final Residue
(To Tailings)
Air
Electrowinning
Copper Solids
(To Copper Plant)
Gold / Silver Dore
Bleed
(To Tailings)
CESL Gold Process Technology Advantages
CESL has developed an efficient process for recovering gold and silver from copper sulphide
concentrates, using cyanide to leach residue from the CESL Copper Process.
•
Add value by recovering precious metals on-site economically in comparison to
conventional smelting and refining where gold and silver are recovered effectively at very
low cost.
•
Low cyanide consumption can be achieved by combining process innovations: These
include pressure cyanidation for short retention times to minimize thiocyanate, partial
suppression of copper cyanide formation, and finally by recovering cyanide as efficiently as Precious metals are
possible from the (reduced) copper cyanide complexes. Total cyanide consumption with the recovered as doré in the
CESL process
new process is low at about 2 kg NaCN/tonne concentrate, net of cyanide recovery.
Whereas precious metals recovery by simple cyanidation consume large amounts of
cyanide, due to formation of both thiocyanate and also copper cyanides, typically consuming >30 kg NaCN / tonne
residue.
•
Gold and silver recovery is consistently 90%.
•
Cyanide consumption due to thiocyanate is expected to be between 0.5 – 1.3 kg NaCN / tonne residue, accounting for
about half of the known consumption. This low cyanide consumption enables the CESL Copper Process to efficiently
process copper-gold-silver concentrates in competition with conventional smelters.
To learn more, please visit our website at www.cesl.com