Remediation of acid mine drainage using magnesite and its bentonite clay composite

Abstract

Wastewaters originating from mining activities are usually acidic and often contain high concentrations of Fe, Mn, Al and SO 2 in addition to traces of Pb, Co, Ni, Cu, Zn, Mg, Ca and Na. This wastewater impacts surface and subsurface water resources negatively and has to be treated before release to receiving aquatic ecosystems. Numerous wastewater treatment technologies have been developed and implemented. However, cost implications, ineffectiveness, selective treatment capabilities and generation of secondary sludge that is toxic and expensive to dispose-off to the environment due to stringent environmental regulations often limit their application. As such, mining companies are in a search for cheaper, brine free, effective and efficient mine water treatment technology. This study assessed the potential of applying mechanochemically modified cryptocrystalline magnesite-bentonite clay composite for acid mine drainage (AMD) treatment. To accomplish this, neutralization of acidity and removal of inorganic contaminants from mine effluents were studied using batch laboratory experiments and precipitation of chemical species was determined using pH Redox Equilibrium (in C language) (PHREEQC) geochemical modelling. The present study was divided into three parts which includes: (1) the application of magnesite for remediation of AMD, (2) the application of ball milled bentonite clay for remediation of AMD and (3) the application of magnesite-bentonite clay composite for remediation of AMD.