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1 1 1 1 1 1 ~... ~ ... Page 18 Fourth, the capial costs of cyanide recovery systems are less than for ehher chem[cal ar bldogical treatment facilhies. Incorporation of a cyanide recovery system Into the metallurgical circuR reduces downstream cyanide and metals levels, and thereby further reduces the rapttal and operatl~g costs of treatment by reducing the size of the treatment facility and the period of time treatment Is required fdlowing mine closure. The economic advantages are In addftlon to the environmental advantages dlscUssed In the previous section. ~ : ' Examination of the proposed Gdden Cross cyanide recovery system provides an excellent a mple of the economics of the process (1i). The anticipated capital cost for the Cyanisorb Process Is~bout S(NZ) 2,200,000. There are several direct capital cost benefits due to Incorporation d cyanide recovery. First, there is no need for the bacMill wash plant which would have cost about S(NZ) 600,000. Second, there are substantial reductions In downstream treatment requirements associated wRh the hydrogen peroxide treatment facility. 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 significant decrease In untreated cyanide concentrations, thereby decreasing chemical costs. The reduction In cyanide minimizes the ammonia formed via natural attenuation and chemical treatment to such an extent that nftrification is not required. These modrfications in treatment capacRy reduce the original capital cost estimate for cyanide, metals, and ammonia treatment from about S(NZ) 6,300,000 to $(NZ) 3,700,000. The overall cap'rtat cost savings Is S(N 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 prepar@d on a per tonne basis. The cost per day to operate the cyanide recovery process Including sulfuric acid, power for the air supply, caustic, and lime Is S(NZ) 1.10/tonne. The cost assumes a power requirement bf 150 kw at a cost of $(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/1 WAD cyanide slurry, the operating cost credit is S(NZ) 2.17/tonne. The calculations assumed a sodium cyanide cost of $(NZ) 3.30/kg. the cyanide usage rate Is low end assuming a more realistic cyanide concentration o1 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 concentratipn requiring treatment from about 45.0 mg/I to 4.0 mg/I. On the basis of hydrogen peroxide consumption >tione, there is a decrease In operating chemical costs of S(NZ) 1.08/tonne, assuming a peroxide cost of S(NZ) 1.56/kg for 50 percent sdutlon, 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 (Ke. 52.17 + 3t.08 - E1.10) or S(NZ) 1,550,000 fora 720,000-ton-per-year operation. The net operating cbst savings amounts to over S(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 (I.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. Llning of an Impoundment designed for the Gdden Cross Mine would require a several million ddlar expenditure, and would be very difficult to Install due to the terrain. The anticipated capital operating cost savings are significant In an application o1 low cyanide containing slurries and high chemical and power costs, with greater benefits realized In more typical mining Installations. The operating costs associated with Gdconda C.R.P. Including chemicals, power, and labor wlere E(AUS) 1.07/tonne, with a cost recovery of $(AUS) 2.i3/tonne of sdution treated. Neady 70 percent iof the cost