Kinetic Testing for Oxidation Acceleration and Passivation of Sulfides in Waste Rock Piles to Reduce Contaminated Neutral Drainage Generation Potential

Contaminated neutral drainage (CND), generated when metals are leached and enough neutralizing minerals are present to keep a near-neutral pH, is a growing environmental concern related to mine waste management. There is a need to find ways to reduce CND generation from mine waste to avoid perpetual effluent treatment. Nickel concentrations at the Lac Tio mine effluent have been sporadically higher than provincial environmental standards. In this project, three different treatment solutions were applied to Lac Tio mine waste rock samples in 70 kg waste rock columns in an attempt to reduce nickel CND generation potential by forcing sulfide oxidation and/or passivation. Following the applications, kinetic tests were used to determine any reduction in sulfide oxidation and nickel leaching. Hydrogen peroxide and sodium silicate were the main products tested, alone and in combination with a sodium bicarbonate buffer. Buffered hydrogen peroxide showed the best potential to reduce CND generation, with nickel release reduced from 1.4 x 10(-3) mg/kg/day (untreated) to 4.0 x 10(-5) mg/kg/day (treated) and near-neutral pH values. This passivation treatment also reduced the sulfur release rate by more than 50%. Optical and scanning electron microscopy observations supported the laboratory results. To conclude, this research project proposes a new way to reduce the CND generation potential of low sulfide waste rock.