Acid 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.

Remediation of mining waste deposited along the margins of Silver Bow Creek as a result of historic mining was evaluated in a multi-year research project funded cooperatively by the State of Montana, EPA, and ARCO Coal. The objective of the Streambank Tailings and Revegetation Study (STARS) was to evaluate the environmental performance of base addition, deep mixing techniques, and revegetation relative to the fate and transport of key metals of concern at the site. This paper summarizes the effect of lime amendments and revegetation on potential leaching of metals into groundwater, and runoff and erosion from streambank areas contaminated with tailings. Water flux in the unreclaimed and revegetated tailings was simulated using UNSAT2. Results of modeling water flux in the vadose zone indicated that 3 to 8 cm of groundwater recharge occurs in an average year in untreated tailings. Revegetation alters the site water balance so that groundwater recharge is unlikely. The amount of metals that migrate into surface water during high-intensity summer thunderstorms was predicted for existing conditions and for lime-treated and revegetated tailings. The US Department of Agriculture GLEAMS model was used to predict long-term runoff and erosion from the site. A three-year GLEAMS simulation indicated that STARS treatments would decrease runoff by 2 to 3-fold, and would change the timing of runoff. On the existing tailings, runoff was predicted intermittently from March through September. On reclaimed areas, runoff was predicted only in March and April when Silver Bow Creek provides more dilution. Substantial reductions in metal loading could be achieved due to reduction in runoff from midsummer thunderstorms which are historically associated with fish kills.

During mining and processing of precious metals it is often necessary to dispose of treated process solutions to manage the on-site water balance. The solutions typically have elevated levels of trace metals and possibly cyanide. Land application, where solution is applied to soils at a controlled rate, can be an effective means of treatment and disposal. Treatment of the solution occurs as metals are attenuated by soils. Important mechanisms of removal include adsorption by clays, organic matter, and hydroxide and oxide minerals. Adsorption batch tests using synthetic treated mine process solution were performed on a O to 6 inch loam soil from a proposed land application area at a western U.S. precious metals mine to characterize the adsorption behavior of silver, cadmium and copper. Results of testing were used to construct adsorption isotherms to predict the maximum adsorptive potential of, and metal loads to, the soil. The results indicate that the soils were effective at reducing silver, cadmium and copper levels in the process solution and that soil had ample adsorption capacity for these metals, suggesting periodic land application of treated mining process solutions can be a safe, effective management tool.