Abstract
Industries like electroplating, printed circuit board manufacturing and jewellery units situated in urban areas originate large-volume low-tenor effluents containing gold-cyanide. Since cyanide is toxic and gold being precious metal, non-renewable and finite resource; their complete removal from effluents is the key. The author in present paper, explores the possibility of treating gold-cyanide using an integrated biosorption-biodetoxification technologies. Rice husk, a low-cost biomass was selected from an exhaustive screening programme for the sorption of gold-cyanide. The optimum sorption conditions were: pH 4.0, biomass quantity 1% (w/v) and contact time 30-40min. Uptake of gold-cyanide was found to increase as a function of initial gold-cyanide concentration. The data obtained obeyed the basic principles of Langmuir and Freundlich isotherm models. L-cysteine enhanced the biosorption ability of Rice husk. Adsorbed gold-cyanide on Rice husk could be desorbed using caustic soda with >90% efficiency. Traces of gold-cyanide remained after biosorption was then completely biodegraded using live bacterial consortium. The treated effluent conformed to statutory disposal standards in India.
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