Modelling of sulfide oxidation with reactive transport at a mine drainage site

A plume of groundwater affected by sulfide oxidation extends 160 m downgrad ient from the Nickel Rim Mine tailings impoundment and discharges to a smal l lake. The plume water has near neutral pH, but contains high concentratio ns of Fe and SO4. Field observations indicate that the release of SO4, H+, Fe2+ and other metals and their distribution in the aquifer is controlled b y the rate of sulfide oxidation in the vadose zone of the tailings and by s ubsequent dissolution and precipitation of carbonate and oxyhydroxide miner al phases in the tailings and aquifer. Using field-determined aqueous and s olid geochemistry, a conceptual geochemical model for the site was develope d. This model accounts for trends in pH and in the concentrations of Fe and SO4. The numerical model MINTOX was used in conjunction with this conceptu al model to simulate sulfide oxidation and two-dimensional reactive transpo rt of dissolved sulfide oxidation products. Simulated sulfide oxidation and transport are compared to trends observed in the field after 35 years of o xidation. Similarity between observed and simulated concentrations demonstr ates that, when used with a well-developed conceptual geochemical model, MI NTOX is capable of simulating sulfide oxidation and plume evolution at mine drainage sites. (C) 2000 Elsevier Science B.V. All rights reserved.