Microcosm experiments were conducted to evaluate the ability of sugarcane bagasse to immobilize metals and buffer pH of acid mine drainage (AMD). An AMD solution was created using de-ionized water and mine tailings at a water:tailings ratio of 30:1 (wt. basis) to produce an effluent with a pH and total metals concentration of 2.32 and 169.05 mg/L, respectively. Bagasse was subsequently immersed in AMD filtrate at AMD:bagasse ratios ranging from 5:1 to 20:1. Using microcosms, four combinations of treatments were considered using the aforementioned AMD:bagasse ratios; pure bagasse and bagasse amended with glucose (0.1g) and/or digester sludge (5 mL). Pure bagasse did not significantly impact pH or metals concentrations (Al, As, Cu, Fe, Mn, Zn) after 180 days. Active microcosms produced near neutral pH conditions (4–6.5) and very high reductions (>95%) in dissolved Cu, Pb and Zn concentrations including many nondetectable concentrations. Significant Pb reductions were also measured in several non-sludge amended samples indicating that bagasse can help immobilize Pb without amendments. Comparison of the sludge amended bagasse with (BSG) and without (BS) glucose indicated that glucose may delay or inhibit sulfide reducing conditions on the basis of measured sulfide concentrations and pH. The BS microcosms produced the largest reductions in Pb and Zn concentrations which further suggests labile carbon addition to bagasse is not necessary for AMD treatment.
Materials such as limestone, soil, cow manure, straw and haybales, sawdust, mushroom compost, peat, clay, turkey litter and dolomitic tailings have been at least partially successful as passive treatment systems for attenuating AMD (Gazea et al. 1996). A unifying theme between these varied and low-cost materials is the provision of labile organic matter to sustain iron and sulfate reducing bacteria coupled with the promotion of anaerobic, reducing and neutral to alkaline conditions.