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<br />Dr. James A. Pendleton <br />May 26, 1992 <br />Page 3 <br />cyanate and metallic hydroxide precipitates. Cyanate is then hydrolyzed to form <br />ammonia and carbonate as shown above. For example: <br />Cu(CN) + H2O2 + OH- ----> OCN~ + Cu(OH) + H2O <br />Hydrogen peroxide treatment has been demonstrated to be one of the most effective <br />methods for detoxifying cyanide containing solutions. It is relatively easy to use, <br />requires relatively unsophisticated equipment and allows for imprecise operational <br />conditions (Denton, etal, 1991; Mudder, 1989). <br />LABORATORY STUDIES CONDUCTED FOR THE SAN LUIS SI~'E <br />Laboratory studies to investigate the feasibility of using hydrogen peroxide to reduce <br />WAD cyanide levels at the San Luis Mine have been conducted by FMC Corporation and <br />Degussa Corporation (Castrantas, 1992; Norcross, 1992). Results of the studies are <br />summarized below and included in their entirety in Attachment B. <br />FMC Corporation <br />In April 1992, FMC evaluated the effect of weight ratios of peroxide to cyanide on <br />cyanide detoxication efficiency of the method. Experiments were carried out by reacting <br />clear water and slurry samples from the San Luis impoundment with 50 percent FMC <br />standard-grade hydrogen peroxide. Liquid and slurry samples were analyzed for WAD <br />cyanide before and after detoxification. In addition, liquid samples were analyzed for <br />copper before and after detoxification, <br />Results of FMC's study are included in Attachment B and summarized below. Hydrogen <br />peroxide effectively detoxified WAD cyanide in both clear pond and tailings slurry <br />samples taken from the San Luis facility under laboratory conditions. Substantial levels <br />of cyanide destruction were achieved using 1.5:1 and 4:1 weight ratios of hydrogen <br />peroxide to cyanide in clear pond water and in slurries under stirred and/or unstirred <br />conditions at 1:1, 2.5:1, and 5:1 weight ratios of hydrogen peroxide to cyartide. Copper <br />concentrations in the liquid samples also were reduced (Castrantas, 1992). <br />Degussa Corporation <br />In May 1992, Degussa evaluated the feasibility of using hydrogen peroxide to treat the <br />liquid pools in the San Luis tailings impoundment. Tests of varying hydrogen peroxide <br />concentrations were conducted on samples taken from the impoundmeht in agitated <br />beakers using 50 percent Degussa standard-grade hydrogen peroxide. Liquid samples <br />