Pilot-scale Studies of Different Covers on Unoxidised Sulphide-rich Tailings in Northern Sweden: the Geochemistry of Leachate Waters |
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Authors: | Lena Alakangas Björn Öhlander |
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Affiliation: | 1. Div of Applied Geology, Lule? University of Technology, SE-97187, Lule?, Sweden
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Abstract: | Abstract. Leachate water quality from covered and uncovered unoxidised sulphide-rich tailings in six pilot-scale (5x5x3 m3) test cells was monitored during 2004 and 2005. The covers consisted of a layer of clayey till, sewage sludge, apatite or
Trisoplast (a commercial mixture of tailings, bentonite, and a polymer). All layers were protected by an unspecified till
except in one reference cell, where the tailings were left open. All leachate waters showed near-neutral pH as a result of
neutralization by calcite in the tailings and by Ca(OH)2 added prior to deposition. Average dissolved sulphur concentrations in the leachates were ≈ 600 mg L-1, except in the cell with sewage sludge (300 mg L-1). The source of sulphur was mainly pyrite oxidation, but residual sulphur probably remained from the enrichment process.
The near-neutral pH favoured precipitation of metal-(oxy)hydroxides with subsequent removal of trace elements such as Cd,
Cu and Pb (< 15 μg L-1) from the solutions. High concentrations of Co, Mn, Ni, and Zn were found in leachates from the apatite, Trisoplast, and
uncovered tailings cells. High As concentrations were found in the leachates in the sewage sludge and clayey till cells. The
lowest metal concentrations, redox potential, and highest pH were found in the sewage sludge cell. Decreased elemental metal
concentrations during 2004 suggest improved performance over time. |
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Keywords: | :" target="_blank">: Dry cover mine water remediation sulphide tailings |
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