Cyanide degradation and the biosorption of heavy metals in waste waters from ore mining and treatment works

Principles for bacterial cyanide degradation and the use of fungi for the sorption of heavy metals have been established on a laboratory scale. On the basis of results obtained, the operation of a biotechnical plant would appear to be a cost-effective option. Potential applications include gold extraction plants, electroplating works and general industrial operations involving cyanide-bearing waste waters.

Hydrogen cyanide (hydrocyanic acid) and its salts (cyanides) are highly toxic compounds which are produced e.g. during gold extraction. On the grounds of their toxic effects on fish and other aquatic organisms, cyanide-bearing waste waters must be decontaminated. The oxidation processes applied for this purpose, which involve the use of hypochloride, consume large quantities of chemicals and are also associated with the release of toxic compounds.

This project involved the development of principles for a biotechnical process involving the use of micro-organisms for the degradation of cyanide and the sorption of heavy metals.

Results:

• The best results for cyanide degradation have been achieved by the bacteria Burkholderia cepacia and Pseudomonas spec..  Under optimum degradation conditions (20 - 30C, pH 8), the degradation of cyanide in concentrations up to 520 mg/l (20 mmol/l) is possible.  Ammonia is generated as an intermediate product, which can then be assimilated by bacteria.  Natural zeolite is a suitable carrier material for a fixed bed reactor.
  
  
• The fungus Aspergillus fumigatus has proved its worth for the biosorption of heavy metals. The sorption capacity of this fungus is dependent upon the cultivation method applied and ranges from 65 – 80 mg of metal per gram of dry material weight.

Conclusion:

The advantages of this process are low operating costs, the removal of metals by biosorption and the prevention of the accumulation of toxic intermediate and end products.




Source Of Supply: The final report (call number F 00 B 491, in German) can be borrowed from:
Technische Informationsbibliothek (TIB) Hannover




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