Biotechnology process for the treatment of gold mill effluent

Symposium Rouyn-Noranda 2002
Abstract Gold mill effluents contain toxic pollutants such as cyanide, thiocyanide, ammonia, and heavy metals. Various practical and economical technologies are in use for the removal of cyanide and heavy metals from gold mill effluents, however, the removal of thiocyanide and ammonia is quite challenging for the industry. Both thiocyanide and ammonia if present in the effluents are toxic to aquatic life. The new Canadian Metal Mining Effluent Regulations will require mine effluents to be non-toxic. Thus there is a need to develop practical and economical technology for thiocyanide and ammonia removal.

The Mine Effluents program in the Environment Group is presently evaluating biotechnology processes for the removal of thiocyanide and ammonia from gold mill effluents. Chemical processes, although effective may not be economical and also may not produce non-toxic effluents. The processes being evaluated are attached growth systems (such as Rotating Biological Contactor) and completely mixed suspended growth systems. In attached growth systems the microorganisms attach to the available surfaces in the reactor and provide the necessary treatment. In suspended growth systems, microorganisms remain in suspension to provide necessary water treatment and are subsequently removed by gravity settling. The microorganisms that are used in such treatment systems for the degradation of thiocyanide and ammonia are commonly found in the soils at gold mine sites. The microorganisms convert thiocyanide and ammonia to a relatively non-toxic nitrate. The biotechnology also offers additional advantage of degrading nitrates to nitrogen gas, if required, at little additional costs. The research to date at MMSL has shown that the biotechnology is effective in treating gold mill effluents for the removal of thiocyanide and ammonia down to temperatures as low as 10 oC. This research, focused on developing biotechnology for the treatment of gold mill effluents, will offer the Canadian gold industry with an innovative technology to assist the industry in complying with new Canadian Metal Mining Effluent Regulations.
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