Cyanide treatment: Physical, chemical and biological processes

There are several water and tailings treatment processes that have been successfully used worldwide for cyanide removal at mining operations. The key to successful implementation of these processes involves consideration of the following:•Site water and cyanide balances under both average and extreme climate conditions.•Goals to be adopted for cyanide levels in treated effluent, including the form of cyanide to be regulated (free vs. WAD vs. total cyanide).•The range of cyanide treatment processes available and their ability to be used individually or in combination to achieve treatment objectives.•Proper treatability testing, design, construction, maintenance and monitoring of both water- and cyanide-management facilities.By carefully considering these aspects of water and cyanide management before, during and after mine operation, operators can reduce the potential for environmental impacts associated with the use of cyanide. Another aspect of cyanide treatment to be considered is the potential environmental impact of the cyanide-related compounds - cyanate, thiocyanate, ammonia, nitrate and nitrite. These compounds may be present in mining solutions to varying extents and may require treatment if water is to be discharged. Each of these cyanide-related compounds is affected differently in the treatment processes discussed, and this should be considered when evaluating cyanide-treatment alternatives for a given site. Table 13 provides a simplified summary of the general applications of various treatment technologies for the removal of iron cyanide and WAD cyanide. This table represents a very simplified summary, but can be used as a conceptual screening tool when evaluating cyanide-treatment processes.