GENERAL47956

• Permit No: M1988112
• IBM Index Class Name: General Documents
• Doc Name: THE RECOVERY OF CYANIDE FROM SLURRIES
• Media Type: D
• Archive: No

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Fourth, the capital costs of cyanide recovery systems are less than for either chemical or bidogkal
treatment facliftles. Incorporation of s cyanide recovery system Into the metallurgical clrcut reduces
downstream cyanide and metals levels, and thereby further reduces the capital and operating costs of
treatment by reducing the size d the treatment facOtry and the pedod of time treatment is requred fdlowing
mine dosure. The economic advantages are in addHlon to the environmental advantages discussed {n the
previous section..
Examination of the proposed Golden Cross cyanide recovery system provides an excellent example of the
economics of the process (it). The anticipated capital cost for the G~ranisorb Process Is about S(NZ)
2,200,000. There are several direct caphal cost benefits due to incorporation of cyanide rec ovary. First,
there Ls no need for the backfill wash plant which would have cost about S(NZ) 600,000. Second, there are
substantial reductions In downstream treatment requirements associated with the hydrogen peroxde
treatment fac~ity.
The excess process water accumulating in the decant pond will be treated and discharged to a local river.
By Incorporating cyanide recovery, there Is a slgnHlcant decrease In untreated cyanide concentrations,
thereby decreasing chemical costs. The reduction In cyankfe minimizes the ammonia tormtd via natu2l
attenuation and chemical treatment to such an extent that nitrHication is not required. These modifications
in treatment capacity reduce the original capital cost estimate for cyanide, metals, and ammonia treatment
from about S(NZ) 6,300,000 to 5(NZ) 3,700,000. The overall capital cost savings Is S(NZ) 3,200,000
compared to the S(NZ) 2,200,000 cost of the cyanide recovery system.
Based on the pilot plant results, estimates of the cost of cyanide recovery have been prepa~ed on a per
tonne basis. The cost per day to operate the cyanide recovery process including sulfuric acd, power for
the air supply, caustic, and lime Is S(NZ) 1.10/tonne. The cost assumes a power requirement of 150 kw at
a cost of S(NZ) 0.08/kw-hr, and chemical costs 3 to 5 times higher than In the United States.
In terms of operating cost credits, there Is a return for recovered cyanide and caustic contained In the
scrubber sdution. Assuming a 90 percent recovery from a 200 mg/I WAD cyanide slurry, the operating cost
credit is S(NZ) 2.17/tonne. The calculations assumed a sodium cyanide Cost of S(NZ) 3.30/kg. The cyanide
usage rate Is low and assuming a more realistic cyanide concentration of 300 mg/I and a 90 percent
recovery, the operating cost credit Increases to S(NZ) 3.23/tonne of ore processed.
introduction of the cyanide recovery system reduces the downstream WAD cyanide concentrat on requiring
treatment from about 45.0 mg/I to 4.0 mg/I. On the basis of hydrogen peroxide consumption alone, there
is a decrease In operating chemical costs of S(NZJ 1.08/tonne, assuming a peroxide cost of S(NZ) 1.56/kg . .
for 50 percent sdution, and a 250 percent theoretical excess of peroxide.
;.. _... The net operating Cost benefit for the cyanide recovery process Is S(NZ) 2.15/tonne of ore li.e. 52.17 +
51.08 - 51.10) or 5(NZ) 1,550,000 (or a 720,000-ton-per-year operation. The net operating r:ost savings
amounts to over 5(NZ) 12,000,000 during the eight-year life of the mine.
There are additional cost savings due to decreases In operating staff and other chemicals utilized (f.e.
copper sulfate) In the hydrogen peroxide treatment facility. Furthermore, there Is no need to line the
impoundment as would be case In many Installations In the U.S. Uning of an Impoundment cieslgned for
the Goden Cross Mine would require a several million ddlar expenditure, and would be very diNicult to
Install due to the terrain. The anticipated capital operating cost savings are significant In an a{~plicatlon of
low cyanide containing slurries and high chemical and power costs, with greater benefits realised fn more
typical mining installations.
The operating costs associated with Golconda C.R.P. Including chemicals, power, and labor were S(AUS)
1.07/tonne, with a cost recovery of 5(AUS) 2.13/tonne of sdution treated. Nearly 70 percent of the cost