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• sulfate concentration than anticipated. As a result, the excess organic cazbon may have acted to <br />enhance manganese and iron solubility by chelating and solubilizing these elements. <br />Within 6 weeks, the sulfate in the columns was entirely transformed (to below detection limits) <br />to reduced sulfur compounds, with >95% of the sulfur precipitating within the columns. The. <br />sulfur that remained in the solution occurred as aqueous sulfide. The columns also released lazge <br />quantities of manganese, resulting in initial concentrations that were above the original input <br />values. Total dissolved solids also increased initially, primarily as a result of the formation of <br />bicazbonate that results from the oxidation of organic matter during the reduction of sulfate. <br />The column filled with West Pit backfill rock showed a slow decrease from the initial elevated <br />concentrations of manganese, bicazbonate, and other constituents, probably as a result of <br />precipitation of solid phases within the column. After 18 weeks of reaction, manganese <br />concentrations decreased to values that were below those initially present in the pit water that <br />was used to charge the column. In a full-scale treatment within the West Pit the precipitation of <br />i manganese as sulfides or carbonates may take many months or even yeazs to reach steady-state <br />concentratton. <br />A single oxidative column was operated to demonstrate manganese removal. Effluent from the <br />flow-through sulfate reduction column (manganese concentration between 60 and 80 mg/L) was <br />passed through a column that contained pebble-sized limestone, feldspar, and quartz rocks. <br />Oxygen was supplied to this column by aspirating air from the bottom of the column. This <br />column was inoculated with streambed sediments from the Rito Seco. As microbes grew on the <br />rock surfaces, concentrations of iron, manganese, fluoride, silica, and calcium decreased. <br />Reports from other similaz systems indicate manganese removal will become more efficient with <br />time, because the iron and manganese oxides formed during oxidation become catalysts for the <br />formation of additional metal oxides, and effectively scavenge these dissolved metals to very low <br />aqueous concentrations. The oxidative column served two additional purposes: (1) excess <br />sulfide that was not precipitated in the reductive column was rapidly oxidized (back to sulfate), <br /> <br />Battle Mountain Resources Shepherd Miller, fnc <br />Ilgranirelpdrive1f00I67lrepor[sldmglarrochmrnrAdoc 3 June 8, 1999 <br />