Abstract
At the Kristineberg mine, northern Sweden, sulphidic mine tailings were remediated in an 8-year pilot-scale experiment using sewage sludge to evaluate its applicability as a sealing layer in a composite dry cover. Sediment, leachate water, and pore gas geochemistry were collected in the aim of determining if the sludge was an effective barrier material to mitigate acid rock drainage (ARD) formation. The sludge was an effective barrier to oxygen influx as it formed both a physical obstruction and functioned as an organic reactive barrier to prevent oxygen to the underlying tailings. Sulphide oxidation and consequential ARD formation did not occur. Sludge-borne trace elements accumulated in a reductive, alkaline environment in the underlying tailings, resulting in an effluent drainage geochemistry of Cd, Cu, Pb and Zn below 10 μg/L, high alkalinity (810 mg/L) and low sulphate (38 mg/L). In contrast, the uncovered reference tailings received a 0.35-m deep oxidation front and typical ARD, with dissolved concentrations of Cd, Zn and sulphate, 20.8 μg/L, 16,100 μg/L and 1,390 mg/L, respectively. Organic matter degradation in the sludge may be a limiting factor to the function of the sealing layer over time as 85 % loss of the organic fraction occurred over the 8-year experimental period due to aerobic and anaerobic degradation. Though the cover may function in the short to medium term (100 years), it is unlikely to meet the demands of a long-term remedial solution.
Highlights
Preventative remedial measures against acid rock drainage (ARD) formation in tailings repositories have been extensively studied globally (INAP 2009; Lottermoser 2010) and within Sweden (Hoglund et al 2005)
At the Kristineberg mine, northern Sweden, sulphidic mine tailings were remediated in an 8-year pilotscale experiment using sewage sludge to evaluate its applicability as a sealing layer in a composite dry cover
Composite covers used in Sweden have resulted in a 99 % (Lundgren and Lindahl 1993) and 95 % reduction in oxygen diffusion and water infiltration, respectively, compared to pre-remedial conditions, reducing 99.8 % of metals transported from tailings repositories (Carlsson 2002b)
Summary
Preventative remedial measures against acid rock drainage (ARD) formation in tailings repositories have been extensively studied globally (INAP 2009; Lottermoser 2010) and within Sweden (Hoglund et al 2005). In Sweden, composite dry cover designs are considered a successful long-term, low maintenance remediation solution (INAP 2009) They consist of a protective layer (PL) and a sealing layer (SL). Composite covers used in Sweden have resulted in a 99 % (Lundgren and Lindahl 1993) and 95 % reduction in oxygen diffusion and water infiltration, respectively, compared to pre-remedial conditions, reducing 99.8 % of metals transported from tailings repositories (Carlsson 2002b). There is a lack of research focusing on sub-surface SS-SL’s buried beneath an overlying protective cover as part of an engineered composite dry cover used for the abatement of ARD It is the aim of this study to determine if an application of SS as a SL in a composite cover is a viable long-term remedial solution to prevent ARD formation in sulphidic mine tailings. The tailings in the SSC were covered with a composite cover containing a sewage sludge sealing layer (SS-SL) (0.25 m), an (m)
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