Evaluating the Efficacy of Shrimp Shells and Demolished Concrete in Reducing Mine Drainage in South Greenland: Column Leaching Test Results

Abstract

Immobilization of Pb and Zn leached from waste rock (WR) using shrimp shells, waste concrete, and sea water was investigated in continuous flow column leaching tests. To evaluate dynamic long-term leaching behaviors, leachate was collected at different liquid/solid (L/S) ratios up to 10 L/kg (≈ 12 weeks). The results showed that the leached content of Pb, Zn, Ni, Cu, Cd, and As from the WR control treatments generally decreased over the experimental period. The shrimp shell treatment further decreased the release of Pb (0.4–0.5%), Zn (19%), Cu (140–150%), and Cd (20–24%), possibly caused by a change in pH. In contrast, the concrete treatment increased the release of Pb (110–150%) and Zn (200–250%) in the leachate, while the leaching of Cu and Cd remained basically unaffected, reflecting a weaker pH effect than that of the shrimp shell treatment. Multi-variate data analysis further confirmed the experimental data and suggested that the release of arsenic, and to some extent also Cu, originated from the shrimp shells. The mechanisms behind the immobilization of these elements are likely biological sulfate reduction caused by the shrimp shell amendment raising the pH, which increased the precipitation of secondary minerals. The results suggest that these amendments carry the potential for bringing new elements into the system and any future remediation plans for these mine sites should be tailored with that in mind. The results suggest that this mitigation could be effective and should be further investigated.

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