A concrete reactive barrier for acid mine drainage treatment

Abstract

Pervious concrete was investigated for potential use as a permeable reactive barrier (PRB) for treatment of acid mine drainage (AMD). Pervious concrete mixtures of various water/cement ratios (0·50, 0·40, 0·35, 0·30, 0·27) and cement contents (300, 360, 380, 400 kg/m3) were prepared. Dolomite and granite aggregate types, size 9·5 mm, were employed. The tests performed were density, compressive strength and porosity. Water treatment was determined by analysis of the influent and effluent AMD after passage through the pervious concrete. It was found that a filter thickness of at least 500 mm was required to increase the pH of acidic mine water from 2·8 to between 5 and 7, and achieve a corresponding reduction in electrical conductivity. When used in the filter mix design, the granite aggregate gave better treatment performance in comparison with the dolomite aggregate. The concrete PRB treatment led to the effective removal of major metals from the AMD. The treatment reduced the metals in the AMD by 30% sulfate, 99% iron, 50–83% manganese, 85% calcium and 30% total dissolved solids. There was, however, a noticeable increase in magnesium concentration in the water effluent 49–66%. These results are short-term tests and further work is in progress to investigate the system's life expectancy.