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iii iuiiiiiiiiii iii , <br />P,1!`i_~ LA`;D RcCLA~dAT10N DIV1S10N <br />Department of Natural Resources <br />t 3 t 3 Sherman St.. Room 2 i 5 <br />Denver, CO 80203 <br />303 866-366. <br />FA x: 303 832 8106 <br />s~r~~r~~~ L; ~~ ~~;~~ <br />Jt= W~ <br />1~ 9 <br />F.,. ,..;~l~i ll~^~~O <br />~~ ~j: <br />~ 18 T6 <br />Roy Romer. <br />Governor <br />MEMORANDUM Michael B. Long, <br />^ /b~ Division Director <br />I <br />T0: Jim Pendleton <br />FROM: v Harry Posey <br />RE: Disposition of WAD cyanide in tailings; Battle Mountain <br />Gold; San Luis Project; Permit No. M-88-112 <br />August 7, 1992 <br />To answer your request for information regarding the disposition of <br />WAD cyanide in the tailings at Battle Mountain, please consider the <br />following. <br />WAD cyanide will break down in virtually any acid med$um. Upon <br />failure of the AVR, we have had to consider two acids: hydrogen <br />peroxide and sulfur dioxide. Either of these components will react <br />to break down the WAD cyanide molecules creating any of several <br />stable, relatively benign reaction products. <br />The key to destroying WAD cyanide is simply that the reaatants come <br />into contact. Whether by adding HZOZ to the ponds or Si02 and air <br />to the process stream, the physical process of mixing the reactants <br />is relatively straightforward. Because the reaction is <br />spontaneous, cyanide breaks down almost immediately after mixing is <br />achieved. (The blue sheen that reportedly spread across the <br />tailings ponds after H2O2 was added is indicative of the speed of <br />the reaction.) <br />The rate of the reaction within the tailings depends on the <br />hydraulic conductivity of the tailings. Consider the simple case, <br />a density-stratified system consisting of: <br />1. WAD-free process water at the top, <br />2. H2O2-bearing process water below that, <br />3. mixed Hz02- and WAD-bearing process water farther <br />down, <br />4. WAD-bearing process water even deeper, ahd <br />5. tailings solids with interstitial WAD-bearing <br />process water at the base. <br />Upon adding H2O2 to a static column consisting of WAD-laden process <br />water overlying tailings with interstitial WAD-bearing Water, the <br />H2oz ;•~ill sink - owing to its higher density - through the column, <br />ar,d react with FTAD cyanide en route. Provided the column remains <br />