In situ reactive zone with modified Mg(OH) for remediation of heavy metal polluted groundwater: Immobilization and interaction of Cr(III), Pb(II) and Cd(II).

Mg(OH) dissolves slowly and can provide a long-term source of alkalinity, thus a promising alternative reagent for the in situ remediation of heavy metal polluted groundwater. However, the application of Mg(OH) on in situ reactive zone (IRZ) for heavy metal polluted groundwater has never been investigated. In this study, the behaviors of heavy metals in a Mg(OH) IRZ were monitored for 45d. The heavy metals show a sequential precipitation by modified Mg(OH) due to the difference of K. Column tests were conducted to investigate the temporal and spatial distribution of heavy metals in Mg(OH) IRZ and evaluate the stabilization effect for multi-heavy metal polluted groundwater. Experimental results indicate that there exist interactions between different heavy metals, and their zoning distribution is attributed either to the competitive adsorption onto porous media (control column) or to the sequential precipitation of heavy metal ions (IRZ column). In contrast with the control column, heavy metal contaminated area in Mg(OH) IRZ significantly shrinks. According to the chemical speciation analysis, when water containing Pb(II), Cd(II) and Cr(III) flows through Mg(OH) IRZ, exchangeable fraction of total concentration significantly reduce and the proportion of carbonate and Fe/Mn oxides fraction increase, indicating the decrease of their mobility and toxicity.