Abstract: Acid mine drainage (AMD) is a widespread environmental problem associated with both working and abandoned mining operations. As part of an overall strategy to determine a long-term treatment option for AMD, a pilot passive treatment plant was constructed in 1994 at Wheat Jane Mine in Cornwall, UK. The plant consists of three separate systems; each containing aerobic reed beds, anaerobic cell and rock filters, and represents the largest European experimental facility of its kind. The systems only differ by the type of pre-treatment utilised to increase the pH of the influent minewater (pH<4): lime-dosed (LD), anoxic limestone drain (ALD) and lime free (LF), which receives no form of pre-treatment. The Wheal Jane pilot plant offered a unique facility and a major research project was established to evaluate the pilot plant and study in detail the biological mechanisms and the geochemical and physical processes that control passive treatment systems. The project has led to data, knowledge, models and design criteria for the future design, planning and sustainable management of passive treatment systems. A multidisciplinary team of scientists and managers from the U.K. universities, the Environment Agency and the Mining Industry has been put together to obtain the maximum advantage from the excellent facilities facility at Wheal Jane. (C) 2004 Elseaier B.V All rights reserved.

Abstract: Flooding partially oxidized mine tailings for the purpose of mitigating further oxidation of sulfide minerals and generation of acid drainage is generally preceded by treatment with alkaline amendments to prevent releasing previously accumulated acidity to the water cover. This work compares the ability of calcite (CaCO3) and quicklime (CaO), two common amendments, to establish and maintain pH conditions and dissolved metal concentrations within environmentally acceptable ranges over long time periods. Although higher initial pH values were obtained with quicklime, the pH of quicklime treated tailings decreased over time. This was attributed to the low buffering capacity of quicklime treated tailings and to the consumption of hydroxide ions by incongruent dissolution of water-insoluble iron oxyhydroxysulfate minerals. In contrast, the pH of tailings treated with calcite increased initially and then remained stable at pH approximate to 6.7. This pH behavior was due to the lower reactivity of iron oxyhydroxysulfates with calcite, the increased buffering capacity provided by bicarbonate ions, and the incomplete dissolution of calcite. Overall, calcite was found preferable to quicklime for maintaining long-term neutral pH conditions in the treated tailings. With the exception of zinc, acceptable dissolved metal concentrations were achieved with calcite treated tailings.