Evaluation of Phosphate Materials for Control of Acid Production in Pyritic Mine Overburden

Abstract

AbstractAcid mine drainage is a serious and pervasive threat to surface and groundwater quality in the USA. Recent research has indicated that phosphate can be effective at immobilizing Fe and inhibiting the production of acid associated with the oxidation of pyritic mine wastes. Four phosphate materials were replicate tested for their ability to inhibit acid production from pyritic coal overburden using a soxhlet humidity cell leaching technique. These materials included two apatite ores (Comineo ore and Texas Gulf ore) at an application rate of 30 g kg−1 by weight apatite [Ca5(PO4)3OH] and two byproducts of the phosphate industry (Cominco waste and Stauffer sludge) at rates of 10, 30, and 50 g kg−1 apatite by weight. Results of leachate analyses indicate that all phosphate sources at all rates of application resulted in significant (P ≤ 0.05) decreases in titratable acidity vs. a control Acidity reductions ranged from a low of 7% for samples treated with Cominco waste (10 g kg−1) to a high of 67% for Texas Gulf ore‐treated samples. Texas Gulf ore, Stauffer sludge (10, 30, and 50 g kg−1) and Cominco waste (10, 30, and 50 g kg−1) significantly reduced dissolved total Fe concentrations in leachate, with Stauffer sludge (50 g kg−1) and Texas Gulf ore producing the most notable diminutions (62 and 63%, respectively). Maximum decreases in sulfate (SO2−4) concentrations of 26, 20, and 25% were achieved by applications of Texas Gulf ore and Stauffer sludge (30 and 50 g kg−1), respectively. The more effective overall performance of the Stauffer sludge and Texas Gulf ore was attributed to the considerably greater relative surface area and P solubility of these amendments. Results of a scanning electron microscope examination of amendments corroborate these findings.