Sulfate removal from mine drainage by electrocoagulation as a stand-alone treatment or polishing step

Abstract

Conventional chemical precipitation methods of salinity removal from mine drainage (MD) are ineffective to deal with sulfate concentrations lower than the solubility of gypsum (CaSO4·2H2O). As the standards of sulfate concentrations become more stringent, this limitation of conventional methods of precipitation drives the need for complementary or alternative solutions. In this context, this study evaluates the efficiency of electrocoagulation (EC) as a stand-alone treatment or as a polishing step following chemical precipitation. The best performance in batch of synthetic MD was obtained at the lowest current density tested of 20 mA/cm2 and at the lowest initial sulfate concentration of 1.3 ± 0.1 g/L. The role of pH was also deemed essential, with acidic pH favouring the coagulation process. Despite EC proving rather inefficient at removing sulfates on its own (in the range of 6 to 31% in 30 min) relative to hydrated lime (Ca(OH)2, 17% removal) and mostly high density sludge (HDS, 45% removal), the combination of EC with the above-mentioned chemical precipitation methods allowed substantial improvement in sulfate removal (up to 35% with Ca(OH)2 and 52% with HDS) much faster (in 30 min instead of 120 min).