Evaluation of in situ layers for treatment of acid mine drainage: A field comparison

Reactive treatment layers, containing labile organic carbon, were evaluated to determine their ability to promote sulfate reduction and metal sulfide precipitation within a tailings impoundment, thereby treating tailings effluent prior to discharge. Organic carbon materials, including woodchips and pulp waste, were mixed with the upper meter of tailings in two separate test cells, a third control cell contained only tailings. In the woodchip cell sulfate reduction rates were 500 mg L −1 a −1, (5.2 mmol L −1 a −1) this was coupled with the gradual removal of 350 mg L −1 Zn (5.4 mmol L −1). Decreased δ 13C DIC values from −3‰ to as low as −12‰ indicated that sulfate reduction was coupled with organic carbon oxidation. In the pulp waste cell the most dramatic change was observed near the interface between the pulp waste amended tailings and the underlying undisturbed tailings. Sulfate reduction rates were 5000 mg L −1 a −1 (52 mmol L −1 a −1), Fe concentrations decreased by 80–99.5% (148 mmol L −1) and Zn was consistently