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• 4.3.3.1 Process Chemistry <br />Sulfate reduction process chemistry has been previously described in the in-situ treatment section <br />(4.3.1.2). The primary modification of sulfate reduction in a passive anaerobic cell would be that <br />the chemical transformations occur within a rock matrix. The rock matrix in the pit contains <br />manganese, whereas the anaerobic cell would be constructed with material containing low <br />concentrations of manganese to reduce soluble manganese formed by the reductive dissolution of <br />minerals in the rock matrix. The rock matrix would be chosen to provide a source of iron for <br />long-term precipitation of sulfide as iron sulfides (e.g., greigite, pyrite). Some co-precipitation of <br />manganese with these iron sulfides would be expected to occur in the anaerobic cell (Huerta- <br />Diaz and Morse, 1992). <br />Manganese oxidation by microorganisms in passive aerobic cells is commonly employed for <br />treatment of coal mine effluent in the eastern U.S. (Brant and Ziemkiewicz, 1997). Passive <br />aerobic cells are typically constructed with pebble-sized limestone or quartz rocks and aze <br />• designed to maximize oxygen transfer into the water. Microorganisms such as Leptorhrix <br />discophora grow and coat these rocks with a dazk slime. The activity of these microorganisms is <br />stimulated by the presence of some short-chain cazbon compounds and iron (Nelson et al., 1999). <br />After atwo- to six-month acclimation period, manganese removal remains active as long as <br />oxygen is available according to the following reaction: <br />MnZ' + O, ~ MnO, + 2H' <br />Manganese oxides aze stable as long as oxidizing conditions are maintained. <br />4.4 Approach to Treatment Option Selection <br />The approach used in the selection of the treatment options was based on: (1) the establishment <br />of performance criteria and (2) evaluating bench-scale and pilot-scale studies and process related <br />literature for effectiveness and operability. <br /> <br />Bau[e Mounmm Resources. /nc. <br />palOOI671reportslmarchrp11v26n1rmnglmarch.doc 47 March?2, /999 <br />