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<br />Dr. James A. Pendleton <br />May 26, 1992 <br />Page 2 <br />As proposed, the hydrogen peroxide destruction method will be used in conjunction with <br />the existing CYTOX system on a continuous, but interim, basis until the INCO process <br />is installed and functioning properly. BMR estimates that the INCO process will be <br />installed and ready to commence operation by late September 1992. <br />This technical revision is limited to a discussion of the hydrogen per4zide treatment <br />method as applied to the San Luis tailings impoundment. Proposed operations of the <br />INCO process will be addressed under a separate technical revision. As currently <br />planned, the technical revision for the incorporation of the INCO process will be <br />submitted to your department no later than June 15, 1992. <br />BACKGROUND <br />Hydrogen peroxide has been widely used for the destruction of cyanide in mill tailings <br />and other cyanide-containing streams. FMC Corporation (FMC), one of the major <br />hydrogen peroxide producers in the United States, currently provides hydrogen peroxide <br />to mining operations in several states including South Dakota, where operating conditions <br />are stringent. These facilities are effectively using hydrogen peroxide reduce cyanide <br />concentrations in their barren leaching solutions (personal communic8tion with W. <br />Wayne Sigle, FMC Corporation, May 22, 1992). In addition, Degussa Corporation <br />(Degussa), another large producer of hydrogen peroxide, has been conducting hydrogen <br />peroxide research for nearly 15 years and currently provides technical assistance to a <br />number of mining operations in the United States (Personal Communication with Earnest <br />W., Haug, Degussa Corporation, May 21, 1992). A short list of representative mine <br />sites currently using hydrogen peroxide for cyanide detoxification and contacts for further <br />information is included in Attachment A. <br />Under alkaline conditions, hydrogen peroxide has been demonstrated to oxidize both free <br />and WAD cyanide species. Free cyanide is oxidized by hydrogen peroxide to form <br />cyanate (OCN-), according to the following reaction: <br />CN~ + HZOZ ----> OCN- + HZO <br />cyanate subsequently hydrolyzes to yield ammonia and carbonate under alkaline <br />conditions: <br />OCN- + OH' + HZO ----> CO,2- + NHr <br />Weakly-complexed metals cyanides oxidized by hydrogen peroxide include copper, zinc, <br />and nickel. Hydrogen peroxide oxidizes these weakly-complexed metal cyanides to form <br />