Cyanide, pH and acid drainage
The word ‘cyanide’ can stir people’s emotions. This is not surprising, given the less desirable aspects of its historical use, and the many myths and misconceptions relating to cyanide.
The term pH is the standard measure of acidity. The maintenance of a desired pH range has important implications for life processes, agriculture, industry and the environment. Within the mining industry, maintenance of a desired pH range has important implications for many of the processes that take place.
Acid formation in rock is a natural process. This can be seen over much of the Coromandel Peninsula on road cuttings in the area as iron coloured stainings on the surface of excavations and in open drainage channels. Excavation can accelerate the process of acid formation because it exposes rock to atmospheric oxygen. Groundwater, rivers and streams can potentially be adversely affected by acid drainage, and the associated increase in the solubility and leaching of metals. There are examples around the world where this has happened, and a local example exists at the old Tui mine near Te Aroha, about 60 kilometres southeast of Waihi.