Detoxification processes are used to reduce the concentrations of toxic constituents in tailings streams and process solutions, either by dilution, removal, or conversion to a less toxic chemical form (sometimes referred to as“destruction” or “degradation” in the case of toxic cyanide species). The objective is to produce an effluent that meets limits or guidelines that have been set to conform with the environmental and/or metallurgical requirements of the project. This section discusses methods of detoxification which may be applied individually or as combinations of processes (e.g., with reagent and metal recovery processes) to achieve the detoxification objectives.
The most important constituents are cyanide species and heavy metal ions, which are considered in the following sections. The control of other solution components and conditions (e.g., sulfate, chloride, and nitrate concentrations, pH, conductivity, turbidity, etc.) may also be important under particular circumstances; however, specific methods for their control are not considered further here.
The methods available for cyanide detoxification can be grouped in the following categories: