Evaluation of Phosphate Sources for Control of Acid Production in Coal Overburden

摘要

Acid mine drainage (AMD) is a serious and pervasive threat to surface and groundwater quality in the eastern Appalachian coal regions and at large surface area coal mines in the western United States. Recent research has indicated that the use of phosphate materials can be an effective treatment for the amelioration of AMD. Phosphate is effective at immobilizing iron and inhibiting the production of acid associated with the oxidation of FeS2. A preliminary simulated weathering study was performed to evaluate the potential of several regional phosphate sources for controlling the production of acid from pyritic coal overburden. Sources deemed most effective were tested further for application rate determination utilizing a replicated soxhlet leaching technique described by Renton et al (1988a). Phosphate sources tested in this part of the study included two apatite ores (Cominco ore and Texas Gulf ore) at an application rate of 3% by weight apatite and two byproducts of the phosphate industry (Cominco waste and Stauffer sludge) at rates of 1%, 3% and 5% apatite by weight. Results of leachate analyses indicate that all sources at all rates of application resulted in significant decreases in titratable acidity versus a control. Acidity reductions ranged from a low of 7% for samples treated with Cominco waste (1%) to a high of 67% for Texas Gulf ore-treated samples. Texas Gulf ore, Stauffer sludge (1%, 3% and 5%) and Cominco waste (1%, 3% and 5%) significantly reduced iron (Fe) concentrations in leachate, with Stauffer sludge (5%) and Texas Gulf ore producing the most notable diminutions (62% and 63%, respectively). Decreases in Fe and acidity levels appear to be primarily attributable to the precipitation by PO4 of Fe derived from the dissolution of FeS2 oxidation products and not necessarily a decrease in FeS2 oxidation. Maximum decreases in sulfate concentrations of 26%, 20% and 25% were achieved by applications of Texas Gulf ore and Stauffer sludge (3% and 5%), respectively. The more effective overall performance of the Stauffer sludge and Texas Gulf ore can be attributed to the considerably greater relative surface area and P solubility of these amendments. Results of a scanning electron microscope examination of amendments corroborates these findings.