John Wiley & Sons, Ltd.

Geochemical control processes and potential sediment toxicity in a mine‐impacted lake

Geochemical parameters and major ion concentrations from sediments of a freshwater lake in the town of Åtvidaberg, south‐eastern, Sweden, were used to identify the geochemical processes that control the water chemistry. The lake sediments are anoxic, characterized by reduced sulphur and sulphidic minerals. The hypothesis tested is that in sulphidic‐anaerobic contaminated sediments, the presence of redox potential changes creates a favourable condition for sulphide oxidation, resulting in the release of potentially toxic metals. The acid volatile sulphide (AVS) contents ranged from 5.5µmol/g to 16µmol/g of dry sediment. Comparison of total mine tailing metals (∑MTM) to simultaneously extracted metals (SEM) in sediments indicates that up to 20% of the ∑MTM are bound to the solid phase as AVS. Consequently, the AVS/SEM analysis classified all sediment samples as potentially toxic in terms of heavy metal concentrations (i.e ∑SEM/AVS > 1). Evaluation of hydrogeochemical data suggests that calcite dissolution, iron (III) oxyhydroxysulphate mineral jarosite (H‐Jarosite) precipitation, hematite precipitation and siderite precipitation are the most prevailing geochemical processes that control the geochemical interactions between the water column and sediment in a mine‐impacted lake. The geochemical processes were verified and quantified using a chemical equilibrium modeling program, Visual MINTEQ model version 3.1, beta. The identified geochemical processes create an environment where the characteristics of sulphate‐rich waters and acidic‐iron produce the geochemical conditions for acid mine drainage (AMD) and mobilization of toxic metals. This article is protected by copyright. All rights reserved

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