Design and analysis of an experiment for assessing cyanide in gold mining wastes

Gold mining wastes treated by heap leaching cyanidization typically contain several metallo-cyanide species. Accurate measurement of total cyanide by the most common methods in such a case may be hampered by the inadequate recoveries that occur for certain cyanide compounds (e.g., gold cyanide). Accurate measurement may be further hampered by the presence of other substances in the waste that act as interferences. A laboratory experiment using the EPA-approved ‘MIDI method’ was executed to assess the accuracy of the method when faced with various cyanide mixtures coupled with varying concentrations of several potential interferences. The mixture constituents and the particular interferences were chosen to simulate those that occur in gold mining wastes. This paper describes the statistical aspects of the design, which involves crossing a mixture experiment with variations in several process variables (total cyanide amount and concentrations of three potential interferences). The paper also describes the strategy used to arrive at the final prediction models.