Sulfide mineral oxidation in freshly processed tailings: batch experiments

This work focuses on sulfide mineral oxidation rates under oxic conditions in freshly processed pyrite-rich tailings from the ore concentrator in Boliden, northern Sweden. Freshly processed tailings are chemically treated in the plant to kill bacteria and to obtain increased metal yields, resulting in a high pH level of 10-12 in the process water. Different oxidation experiments (abiotic oxidation in untreated tailings, acid abiotic oxidation and acid microbial oxidation), containing the Boliden tailings, were performed at room temperature with dissolved oxygen (0.21 atm O-2) for 3 months. The different pyrite oxidation rates given from the study were 2.4 x 10(-10) mol m(-2) s(-1) for the microbial, 5.9 x 10(-11) mol m(-2) s(-1) for the acidic abiotic and 3.6 x 10(-11) mol m(-2) s(-1) for the untreated experiments. Because of the potential precipitation of gypsum in the batch solutions, these oxidation rates are considered minimum values. The release rates for copper and zinc from chalcopyrite and sphalerite in the acid experiments were also investigated. These rates were normalized to the metal concentration in the tailings, and then compared to the release rate for iron from pyrite. These normalized results indicated that metal release decreased in the order Cu>Zn>Fe, demonstrating that pyrite is more resistant to oxidation than sphalerite and chalcopyrite. Pyrite was also more resistant to acidic dissolution than to microbial dissolution, while a significant fraction of sphalerite and chalcopyrite dissolved in the acid abiotic solutions. (C) 2002 Published by Elsevier Science B.V.