Abstract:

Cyanide has been used by the precious metals industry since the 1890s to extract metals of economic interest such as gold and silver from mineralized ore placed on leach pads or processed through a mill. In addition to forming complexes with metals of economic interest, cyanide also complexes other metals including iron, copper, and cobalt, increasing their solubility with a circumneutral pH. These complexes may pose challenges for discharges from the process water circuit, including point source and non-point source discharges from tailings management infrastructure. The direct measurement of cyanometallic complexes is challenging, and while total cyanide measurement is common, the accuracy of that assessment depends upon the ability of the method to promote non-destructive dissociation of the complexes. For especially strong cyanometallic complexes, like those of cobalt, being able to detect the presence of the cyanide complex is critical to understanding performance against low-level standards for the protection of beneficial uses, such as aquatic life, where otherwise inconsequential amounts of cyanide can limit the effectiveness of conventional treatment approaches. In this paper, we describe factors affecting cobalt cyanide complexation, analytical methods that have been developed to identify cobalt in a cyanide complex, passive sampling and active extraction methods that use the cobalt cyanide as a tracer to detect the presence of process water, the effect of ultraviolet light on complex stability, and treatment options for management of process water containing cobalt cyanide.

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John Moynihan