From highly polluted Zn-rich acid mine drainage to non-metallic waters: Implementation of a multi-step alkaline passive treatment system to remediate metal pollution

Abstract

Complete metal removal from highly-polluted acid mine drainage was attained by the use of a pilot multistep passive remediation system. The remediation strategy employed can conceptually be subdivided into a first section where the complete trivalent metal removal was achieved by the employment of a previously tested limestone-based passive remediation technology followed by the use of a novel reactive substrate (caustic magnesia powder dispersed in a wood shavings matrix) obtaining a total divalent metal precipitation. This MgO-step was capable to abate high concentrations of Zn together with Mn, Cd, Co and Ni below the recommended limits for drinking waters. A reactive transport model anticipates that 1 m3 of MgO-DAS (1 m thick×1 m2 section) would be able to treat a flow of 0.5 L/min of a highly acidic water (total acidity of 788 mg/L CaCO3) for more than 3 years.