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Bioremediation of cyanide leaching residues

Abstract:

Bioremediation is an economic and effective technique to detoxify cyanide leaching residues. This treatment technique was investigated to determine its applicability to effluents and solid wastes from Ecuadorian cyanidation plants. Tailings from different cyanide leaching plants that utilized different types of ore were used to isolated native strains of bacteria using several nutrient media. These tests were carried out on a laboratory scale in Erlenmeyer flasks with a solid/liquid ratio of 1/10 in a rotating shaker at 150 rpm and 30°C. The pH of the pulp and the bacterial population were measured daily by standard plate counting. The obtained colonies were characterized for Pseudomonas-type bacteria. The obtained cultures were progressively conditioned for higher concentrations of free cyanide at an initial pH of 11 in nutrient media. Pseudomonas population, pH and free cyanide were measured daily. The results show that bacteria levels higher than 104 cells/ml were able to resist a concentration of 100 ppm free cyanide, while 108 cells/ml were required to resist a concentration of 750 ppm free cyanide in the media. At concentration levels higher than 750 ppm free cyanide, the toxicity of the media did not allow bacterial survival. The cultures adapted to 750 ppm of free cyanide were able to detoxify a fresh cyanide residue containing more than 3000 ppm of total cyanide. Blank tests (without bacteria) were also carried out. The results showed a reduction of total cyanide content between 200 and 390 ppm/day, in the first 3-4 days for the solid and liquid residue, respectively. The total cyanide remediation rate in the blank controls was constant at approximately 45 ppm/day. © 1999 Elsevier B.V. All rights reserved.