Treatment of acidic groundwater in acid sulfate soil terrain using recycled concrete: column experiments

Acidic groundwater generated from pyrite oxidation in acid sulphate soil (ASS) is a major geoenvironmental problem in Australia. This study aims to evaluate recycled concrete as a reactive material in permeable reactive barriers (PRBs) for the remediation of acidic groundwater in lowlying ASS floodplains. Laboratory experiments were systematically conducted to investigate the acid neutralisation behaviour of recycled concrete and its potential to remove dissolved Al and Fe. The results confirmed that recycled concrete could effectively treat acidic groundwater from an ASS terrain, resulting in near-neutral effluent over a long period with complete removal of Al and Fe. The major mechanisms involved in neutralising acidic groundwater are thought to be the precipitation of Al and Fe as oxides, oxy-hydroxides and hydroxides. However, the accumulation of secondary minerals could decrease the reactivity of the recycled concrete. Indeed, chemical armouring could decrease the neutralising capacity of recycled concrete by up to 50% compared to the theoretical acid neutralisation capacity of this material. The results reported here also show that the neutralisation capacity and reactive efficiency of recycled concrete are dependent on not only the initial pH value but also the concentration of both Al and Fe in the acidic groundwater.