Abstract: Acid drainage waters generated in the copper ore deposit Elshitza. Central Bulgaria, were treated by a natural wetland located in the deposit. The waters had a pH in the range of about 2.5 – 3.5 and contained copper, cadmium, arsenic, iron, manganese and sulphates as main pollutants. The watercourse through the wetland covered a distance of about 100 in and the water flow rate varied in the range of about 0.5 – 2.0 1/s. The wetland was characterized by an abundant water and emergent vegetation and a diverse microflora. Phragmites communis was the prevalent plant species in the wetland but species of the genera Scirpus, Typha, Juncus, Carex and Poa as well as different algae were also well present. It was found that an efficient removal of the pollutants was achieved and their residual concentrations in the wetland effluents were decreased below the relevant permissible levels for water intended for use in the agriculture and/or industry. The removal was clue to different processes but the microbial dissimilatory sulphate reduction and the sorption of pollutants by the organic matter and clay minerals present in the wetland played the main role. Negative effects of the pollutants on the growth and activity of the indigenous plant and microbial communities were not observed.

Abstract: Contact of oxygen contained in air and water with mining materials can increase the solubility of metals. In heaps leached by cyanide, metals can also be made soluble through complexation with cyanide. During closure, water in heaps, and water collected in mine workings and pit lakes may require treatment to remove these metals. In situ microbiological treatment to create reductive conditions and to precipitate metals as sulfides or elemental metal has been applied at several sites with good success. Treatment by adding organic carbon to stimulate in situ microbial reduction has been successful in removing arsenic, cadmium, chromium, copper, iron, lead, manganese, mercury, nickel, selenium, silver, tin, uranium, and zinc to a solid phase. Closure practices can affect the success of in situ treatment at mining sites, and affect the stability of treated materials. This paper defines factors that determine the cost and permanence of in situ treatment.

Abstract: The Gilt Edge gold mine is an acid drainage site that has been put on an accelerated closure schedule. The mine ceased activities in 1999 when Dakota Mining Corporation declared bankruptcy forcing the State of South Dakota to immediatly assume water treatment operations. Evaluation of conceptual closure plan options and cost estimates led the State of South Dakota to a decision to seek Federal assistance. The site has quickly moved into reclamation mode for the principal contamination source, the Ruby waste-rock dump. Designs and specifications for capping the Ruby waste-rock dump were prepared while Superfund listing was pursued. In October of 2000, mobilization of the first reclamation contractor began and by December the site was added to the National Priorities List. Capping the waste-rock dump will address a major acid drainage source. Water treatment requirements are expected to decline as conventional methods such as diverting clean water, backfilling, grading, capping, limestone neutralization, and revegetation are implemented. Acid seepage from underground workings, steep highwalls, and some pit backfills will remain. Major field trials of emerging technologies are nearing completion and some are showing promising results. Carbon reduction in a pit lake, and pyrite microencapsulation on simulated waste dumps, are showing initial success. Their application may minimize or eliminate the need for long-term active water treatment which has been a long sought goal for major acid rock drainage sites.