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<br />Dr. James A. Pendleton <br />May 26, 1992 <br />Page 4 <br />were analyzed for total cyanide, WAD cyanide, capper and pH before and after <br />detoxification. In addition, reaction times were assessed. <br />Results of Degussa's study are included in Attachment B and summarized below. <br />Hydrogen peroxide effectively detoxified WAD cyanide in liquid tailings samples under <br />laboratory conditions. Substantial levels of cyanide destruction were achieved using 3,400 <br />to 6,000 pounds of hydrogen peroxide (50 percent solution) per acre foot of liquid. <br />Copper concentrations in the liquid samples also were reduced (Norcross, 1992). <br />IMPLEMENTATION OF THE HYDROGEN PEROXIDE DTG,STRUCTION <br />PROCESS AT THE SAN LUIS SITE <br />Performance history and laboratory testwork conducted by FMC and Degussa indicate <br />that hydrogen peroxide will be a successful WAD cyanide detoxification system for the <br />San Luis tailings impoundment (Castrantas, 1992; Norcross, 1992). 'T'herefore, BMR <br />proposes to install and commence operation of an interim hydrogen peroxide system as <br />soon as possible. <br />Existing WAD cyanide concentrations in the tailings impoundment will be reduced to less <br />than 50 ppm by adding hydrogen peroxide (HZOZ) directly to the liquid pools in the <br />tailings impoundment. Polyethylene pipes will be floated on the surfaces of the upper <br />and lower liquid pools in the impoundment and hydrogen peroxide will be pumped <br />through the pipes from a truck located on the splitter berm, as shown in Figure 1. <br />In addition to detoxifying the liquid pools in the impoundment, tailings added to the <br />impoundment from the mill will be detoxified on a continuous basis. 'Lrhe continuous <br />hydrogen peroxide distribution system will be installed along the edges of the <br />impoundment in close proximity to the tailings distribution lines (see Figure 1). <br />Hydrogen peroxide will be pumped from a tanker wck through polyethylene pipes and <br />added to the clear water as the slurry is deposited and beaches are formed. <br />Sufficient quantities of hydrogen peroxide, approximately 2.5 to 3.0 ratio of peroxide to <br />WAD cyanide, will be added directly to the liquid pools in the tailings Impoundment. <br />The actual amount of hydrogen peroxide added to the impoundment will be a function <br />of field conditions. Peroxide will continue to be added directly to the liquid pools until <br />the WAD cyanide concentration drops below 50 ppm. At that time, addition of peroxide <br />directly to the pools and likely will not be required; however, operation of the continuous <br />system will continue. <br />Cyanide and copper concentrations will be monitored on a regular basis during <br />detoxification of the existing liquid pools in the impoundment. The amount of peroxide <br />