Abstract
The mobility of contaminants from mine waste can be assessed using different extraction methods. Aqua regia (AR) extraction is the most commonly used method in Finland. Another method is the analysis of leachate from net acid generation (NAG) tests, which is primarily designed for acid production potential assessment. We investigated the performance of single-addition NAG test leachate analysis and AR extraction in drainage quality prediction, using waste rock and drainage water samples from several Finnish waste rock sites. Our objective was to improve interpretation of the AR and single-addition NAG test leachate analysis results in drainage quality prediction. The AR extraction effectively reflected elements that occurred in elevated concentrations in drainage water, though it over-predicted Al, As, Cd, Co, Cu, and Ni in some circumneutral drainages, and Cr in general. The single-addition NAG test leachate analysis also performed well in assessing the mobility of contaminants including Al and Cr at acid mine drainage sites. As the contaminants tend to precipitate in neutral NAG test solution, the usability of the method in neutral mine drainage cases should be further investigated. Furthermore, the conclusions presented in this study are limited to waste rock samples collected from the surface of piles; future work will examine waste rock history, dump cores, drainage quality changes, etc. in more detail.
Highlights
One of the main environmental issues associated with metal sulfide mining is generation of contaminated acid rock drainage (ARD) or neutral rock drainage (NRD) (e.g. Dold 2014; Heikkinen and Räisänen 2009; MEND 1991; Nieva et al 2018; Price 2003; Singer and Stumm 1970)
The acid production potential of mine waste is usually determined based on different acid–base accounting (ABA) tests (Price 2009; Sobek et al 1978), with the standardised method SFSEN 15875 (SFS-EN 2012) being widely used in Europe
Samples 101–111 were those used in Karlsson et al (2018b) and consisted of ≈ 15–20 kg of heterogeneous rock material of particle size of ≈ 5–10 cm randomly collected from the surface of waste rock piles above drainage points, where water samples were collected for comparison
Summary
One of the main environmental issues associated with metal sulfide mining is generation of contaminated acid rock drainage (ARD) or neutral rock drainage (NRD) (e.g. Dold 2014; Heikkinen and Räisänen 2009; MEND 1991; Nieva et al 2018; Price 2003; Singer and Stumm 1970). Dold 2014; Heikkinen and Räisänen 2009; MEND 1991; Nieva et al 2018; Price 2003; Singer and Stumm 1970) Mine waste facilities such as waste rock piles and tailings impoundments are the main sources of ARD and NRD (MEND 1991; Price 2003). The acid production potential of mine waste is usually determined based on different acid–base accounting (ABA) tests (Price 2009; Sobek et al 1978), with the standardised method SFSEN 15875 (SFS-EN 2012) being widely used in Europe Another commonly used method is the single-addition net acid generation (NAG) test (AMIRA 2002; Miller et al 1997), which involves the reaction of a sample with hydrogen peroxide (H2O2) to rapidly oxidise any sulfide minerals present.
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