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<br />Other strong metalcyanide complexes inducting gdd cyanide, silver cyanide, and mercury cyanide <br />are not oxkfized in the INCO S02/Air process. <br />Thiocyanate will be partially oxidized by sulfur dioxide and air, although the reaction is inhibked until <br />most free cyanide and weaklycomplexed metallic cyanide forms are removed and excess sulfur <br />dioxide Is added to the reactor. <br />Sulfuric acid (HZSO~) generated during cyanide and other oxfdatlon reactions Is neutralized wkh lime <br />to form calcium sulfate according to the fdlowing reaction: <br />i~w~ <br />Ca(OH)2 + HzSO, -> CaS0~~2HZ0 ~' I I' <br />~, Jv~ <br />cr <br />c <br />a <br />INC.O SOZ/AIR CASE HISTORY <br />INCOSOz/Airisademonstratedcyanidedestructiontechndogy. Approximatelythirty-fourlndustrlal <br />sties in the United States and Canada currently are licensed to use the INCO SOZ/Air process <br />(INCO 6cploration and Technical SeMces Incorporated, undated). Representative sties employing <br />the INCO SOz/Air process are presented in Table t along wkh pertonnance data. <br />As shown in Table 1, the INCO SO,/Afr process has been successfully implemented at a number <br />of mining facilkles. Total cyanide concentrations have been effectively reduced on a continuous <br />basis to concentrations as low as t mg/I. <br />IMPLEMENTATION OFTHE INCO SOZ/AIR PROCESS AT THE SAN LUIS SITE <br />Laboratory Studies <br />Laboratory studies were undertaken by INCO F~cploration and Technical Services Incorporated <br />(INCO) to evaluate the feasibility of using the INCO SO,/Air process as a method of cyanide <br />destruction at the San Luis ske. Tailings slurry samples from the San Luis Mine were successfully <br />treated using the INCO SOZ/Air process. ~ <br />-\~ <br />Tailings slurry samples, characteristic of the slurry leaving the sbkh carbon-in-leach (CIL) tank at San <br />Luis, were collected and analyzed for cyanide by INCO. The slurry samples exhibked WAD and <br />total cyanide concentrations d 345 mg/I and 352 mg/I, respectively. Following treatment, WAD and <br />total cyanide concentrations were reduced to less than 5 mg/I (INCO Exploration and Technical <br />Services Incorporated, 1992). <br />25301/RN0610.RPT INCO S02/Air Technical Revision Page 3 <br />June 16, 1992 San Luis Mins <br />