Sulfide oxidation in unweathered mine tailings from the Skellefte ore district, Northern Sweden
Licentiate thesis, Stockholm university
This thesis focuses on sulfide oxidation in freshly processed tailings from the ore concentrator in Boliden, and in 50 years old tailings from Impoundment 1 in Kristineberg, northern Sweden. Sulfide oxidation rates were quantified in sulfide-rich unweathered mine tailings under different conditions, reflecting primarily variations in tailings composition, and oxygen availability. Batch experiments on freshly processed tailings (abiotic oxidation in untreated tailings, acid abiotic oxidation and acid microbial oxidation) were performed with full access to dissolved oxygen for 3 months, while column experiments on old tailings (one coarse grained and one fine grained) were performed under oxygen limitation and water saturation for 11 months. It could be concluded based on the column experiments that the sulfide oxidation continues in the interior of soil covered tailings deposits, even though the oxidation rates are extremely low. While pyrrhotite oxidation rates are usually greater than the rates for pyrite under the same conditions, pyrite oxidation rates were greater in the batch experiments because of the lower pH, greater oxygen availability, and probably a more active population of iron- and sulfur-oxidizing bacteria.