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It Is Important to note that although laboratory testwork Indicates that the taiings slurry at the San Luis ske is amenable to cyanide treatment using the INCO SOZ/Air process, conclusions are based on bench-sale tests. Results may deviate somewhat under full-scale operating condkions. Addkional test data indicate that the optimum sulfur dioxide dose is 3.5 gm S0,/gm WAD cyanide ~ ~ and that the best resuts are obtained at a pH of 8 to 8.5. Copper in sduNon is essential as a ,f ~ 't • catalyst for cyanide oxidation using the INCO SOz/Air process. However, given the existing copper (~''~ ~rw ~,~• ~ concentrations in the San Luis tailings slurry, addkion of copper sulfate for catalysis should not be i r4 ~ _ ~w necessary as discussed below. -- _ - z 14 BMR recently completed acyanide-sduble copper evaluation for the San Luis ore body. Exploration drilling composke samples were agitated wkh a sodium cyanide solution, filtered, and analyzed for copper. Cyanide-sduble copper was evaluated as these complexes will be sdubllized during the carbon-in-leach process. Wet chemistry methods were employed to mimic plant operating condkions. All tdd, 943 samples from 80 drill hdes were evaluated (Battle Mountain Resources, 1992). Assay data were used to develop grade estimates of cyanide-sduble copper associated wkh gdd reserves. The results of the cyanide-sduble copper reserve calculations Indicate that a welghted- average copper concentration of 52 ppm copper is associated wkh the presently~efined ore body at the San Luis ske (Battle Mountain Resources, 1992). A copper concentraton of approximately 50 ppm is required to catalyze the sulfur dioxide cyanide oxidation reaction (Devuyst etal, 1964). Therefore, the addkion of copper sulfate should not be necessary. However, the INCO SOZ/Air system for the San Luis ske is being designed so that a copper sulfate distribution system can easily PJ~ ~ ~ be installed at a future date,rf needed. During upset condkions, the addkion of copper sulfate may ~~ J ~ be necessary to catalyze batch treatment. In these skuations, copper sulfate will be manually added ~ o-o-o-~~~ to the reactor by operating personnel. '" ~Q~~ l J ~ Design Considerations y~r,/ ~~ ~ Based on laboratory results, INCO has developed process design crkeria for the San Luis ske. ~S~a~ N" Design criteria and spec'rfications developed by INCO are included in their entirety in Attachment ~~,` A and discussed below. Documentation induded in Attachment A sets forth INCO's ~ recommendations for equipment sizing, as well as types and quantkies of reagents needed to Lv~ 25301/RN0510.RPT INCA SO~/Air Technical Revision Page 5 June 16, 7992 San Wia Mins