Sulfate removal from mine drainage by Ettringite precipitation

Abstract

The research was studied the optimum conditions for sulfate removal from lignite coal mine drainage in Thailand by ettringite precipitation using Central Composite Design (CCD). The effects of Ca/S and Al/S ratio (mole basis) and reaction time on the sulfate removal efficiency were investigated. The full factorial statistical analysis showed that the Al/'S ratio and reaction time had a significant effect on sulfate removal efficiency, which the sulfate removal efficiency increases when Al/S ratio and reaction time are increased. The Ca/S ratio in the range of 1-7 had been found no significant effect on sulfate removal efficiency. The optimal reaction time obtain from the predicted equation from CCD was equal to 6.14 h, while CalS and Al/S ratio were fixed at 4 and 4.5, respectively, at ambient temperature. At the optimum condition, the sulfate removal of 99.6 and 99.0% were achieved from Lamphun and Lampang mine drainage, respectively, which is very close to the predicted value (100%). The research also found that, sulfate removal efficiency reduces from 99.6% to 64.2%, when sodium aluminate was used as aluminium source. The increasing of speed and time of rapidly stirring were not significantly effect on sulfate removal efficiency.