Abstract
Acid mine drainage is generated when mining activities expose sulphidic rock to water and oxygen leading to generation of sulphuric acid effluents rich in Fe, Al, SO4 and Mn with minor concentrations of Zn, Cu, Mg, Ca, Pb depending on the geology of the rock hosting the minerals. These effluents must be collected and treated before release into surface water bodies. Mining companies are in constant search for cheaper, effective and efficient mine water treatment technologies. This study assessed the potential of applying magnesite as an initial remediation step in an integrated acid mine drainage (AMD) management system. Neutralization and metal attenuation was evaluated using batch laboratory experiments and simulations using geochemical modelling. Contact of AMD with cryptocrystalline magnesite for 60 min at 1 g: 100 m. S/L ratio led to an increase in pH, and a significant increase in metals attenuation. Sulphate concentration was reduced to .1 910 mg/.. PH redox equilibrium (in C language) (PHREEQC) geochemical modelling results showed that metals precipitated out of solution to form complex mineral phases of oxy-hydroxysulphates, hydroxides, gypsum and dolomite. The results of this study showed that magnesite has potential to neutralize AMD, leading to the reduction of sulphate and precipitation of metals. Keywords: acid mine drainage, cryptocrystalline magnesite, toxic metals, geochemical modelling, water treatment
Highlights
The aftermath of gold and coal mining has triggered serious environmental problems that need urgent attention prior to degradation of terrestrial and aquatic ecosystems and their ability to foster life (Jooste et al, 1999; Luís et al, 2009; Raymond et al, 2009; Equeenuddin et al, 2010)
During rainfall and underground working, sulphide minerals react with water and oxygen leading to the formation of highly acidic mine eff luent known as acid mine drainage (AMD)
This study has shown that magnesite can be used to remediate AMD
Summary
The aftermath of gold and coal mining has triggered serious environmental problems that need urgent attention prior to degradation of terrestrial and aquatic ecosystems and their ability to foster life (Jooste et al, 1999; Luís et al, 2009; Raymond et al, 2009; Equeenuddin et al, 2010). Mining of the aforementioned minerals exposes sulphidebearing minerals to oxidising conditions. The acidity in AMD promotes the leaching of heavy metals from the surrounding geology (Johnson et al, 2005; Sheoran et al, 2006; Cheng et al, 2009; Simate et al, 2014; Amos et al, 2015; Delkash et al, 2015). Numerous technologies have been developed for remediation of acid mine drainage (Gitari et al, 2008; Delkash et al, 2015; Lakovleva et al, 2015). The commonly used technologies include ion exchange (Buzzi et al, 2013), reverse osmosis (Johnson et al, 2005), adsorption (Gitari, 2014; Lakovleva et al, 2015), biosorption (Sheoran et al, 2006) and precipitation (Bologo et al, 2012; Maree et al, 2013). Generation of secondary sludge, toxicity, high operation costs, poor efficiency and demand for large expanses of land limit the application of the majority of developed technologies (Johnson et al, 2005; Kalin et al, 2006; Sheoran et al, 2006, Simate et al, 2014)
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