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Introduction
Coal mining and beneficiation operations generate a considerable amount of industrial solid waste in terms of production, accumulation volume, occupied area, and acid rock drainage (ARD) generation (Bell et al. 2001; Bian et al. 2010; Komnitsas et al. 2001; Simate and Ndlovu 2014). The ARD can contaminate regional surface and groundwater or the land, with toxicity levels depending on discharge volume, pH, total acidity, concentration of dissolved metals, and buffering capacity of the receiving streams (Akcil and Koldas 2006; Kontopoulos 1998).
Approximately 6.5 million tonnes (t) a year of coal waste were generated in Brazil during the years 2008–2014, almost 80% of which was in the state of Santa Catarina (SIECESC 2014). The grade of coal deposits in Brazil is relatively low, and approximately 65% of the run-of-mine (ROM) coal extracted from underground mines in the carboniferous region of Santa Catarina is discarded in waste dump deposits. In addition, inadequate waste management in the past has left a devastating legacy in this region, with pollution plumes extending more than 6000 ha over several catchment areas. Local studies have indicated considerable contamination of the Araranguá, Tubarão and Urussanga river basins, with reduced pH and high concentrations of metals and sulfate (Gomes et al. 2011; SIECESC 2014).
Currently, Brazilian coal mining operations emphasize an end-of-pipe treatment approach to coal waste and ARD management (Silva and Rubio 2009; Silveira et al. 2009). Chemical ARD treatment techniques such as lime neutralization typically consume large amounts of expensive reagents, generate significant quantities of sludge, and are only effective in reducing ARD risks in the short term. As pointed out by Kontopoulos (1998), many of these shortcomings can be overcome by implementing preventative techniques that minimize the generation and the subsequent dispersion of ARD from waste dump deposits. One such approach entails the pre-disposal removal of ARD-generating sulfide minerals by means of physical separation techniques such as flotation and density separation. Apart from reducing ARD risk, integration of a sulfide removal step into the beneficiation circuit also offers opportunity for additional value recovery (Amaral Filho et al. 2013; Benzaazoua et al. 2008; Hesketh et al. 2010; Hilson 2000; Kazadi Mbamba et al. 2012).
The ability to accurately predict the ARD-generating potential of wastes plays an important and essential role in...