New research into reducing acid rock drainage

Pyritic waste rock piles generate acid rock drainage, which damages the environment and gives headaches to mining companies. Different methods such as subaqueous deposition and perpetual treatment of effluent have been employed to try to reduce the problem.

An entirely different tactic has been investigated by Margarete Kalin of Toronto-based Boojum Research and Bryn Harris, a metallurgical consultant in Montreal. They based their work on the knowledge that phosphate as it is used for rust protection can also control or reduce pyrite oxidation, that not all rock in a pile is exposed to water (and thus to oxidation), and that it appears that microbes can form a microfilm on mineral surfaces, protecting them from oxidation.

Their long-term experiment involved treating 17 drums of variously fresh and weathered, high-and low-pyrite ore and waste rock by adding phosphate mine wastes, and included the appropriate controls. The 3.5 tonnes of rock came from BHP Billiton’s Selbaie polymetallic mine in northern Quebec. The drums were weathered for 2.7 years, stored indoors for 4.5 years and then re-exposed outdoors for 1.3 years. Discharge was collected and analyzed.

The results were not conclusive, but are laying the groundwork for a better way to understand and reduce acid rock drainage. The experiment and its results will be released shortly in the journal Hydrometallurgy (www.elsevier.com/locate/hydromet). For more information contact Ms. Kalin at margarete.kalin@utoronto.ca