Microbial Treatment of Cyanide and Heavy Metals Containing Waste Water from Gold Mining

Cyanide-bearing waste water from'gold mining is usually decontaminated by oxidation so that the dissolved metals are precipitated as hydroxides. The disadvantages of this method are high consumption of chemicals and the formation and liberation of toxic compounds. Various bacterial and fungal strains capable of degrading cyanides or having a high potential for metal adsorption were isolated from water and sediment samples from a wastewater deposit in Romania. Some of the isolates were characterised and identified. For those strains showing the most rapid degradation or the greatest adsorption capacity, important parameters were analysed using synthetic media and process water and waste water from the cyanidation plant. Optimum pH and temperature levels, maximum tolerable cyanide and metal concentrations, as well as possibilities for the addition of required substances, such as hydrocarbon sources or phosphate, were determined. With a view towards the development of a pilot plant, the immobilisation of microorganisms was achieved on a natural zeolite. With a view to a technical application, further improvements are to follow as part of the development of a pilot plant.