Biological cycling of arsenic in sediments impacted by gold mill effluents.

Abstract

Effluent treatment from gold milling requires the removal of heavy metals, cyanide and arsenic. The waters are generally alkaline and hence this presents a technical problem regarding the choice of a removal process. Conventional water treatment processes for arsenic removal include chemical oxidation (chlorination), coagulation - flocculation, liming, filtration, activated carbon adsorption and, ultimately, processes such as demineralizing by reverse osmosis or ion exchange. In principal, therefore, it is possible to select a treatment technology which will produce the desired effluent quality; however, the costs associated with the treatment technology are frequently prohibitive. The cost effectiveness of a treatment process is therefore equally important. With increasing environmental awareness, the treatment technologies do not only have to be economic and technically effective, but consideration has to be given to the long term stability of the resultant sludge. In addition, the decommissioning of the these facilities, along with the disturbed areas, has to be considered. The CREM task force has evaluated these technologies for their effectiveness. For arsenic, liming or softening was considered the most effective method which also removes any heavy metals. These methods produce sludges which represent an environmental problem. Therefore, better and more environmentally acceptable treatment processes have to be developed.