In Situ Layered Double Hydroxide for Efficient Remediation of Acidic Water

Abstract

The efficient and sustainable in situ remediation of high-strength acidic groundwater contaminated by complex micropollutants with minimal use of chemicals is a challenge. Here it is reported that MgAl alloy achieves neutralization and a complete removal of 20 mg L⁻¹ Cd²⁺, Cr(VI), Cu²⁺, Ni²⁺, and Zn²⁺ in 15 min from acidic water free of chemicals. The removal rate of heavy metals and nitrate increases with decreasing pH and is not significantly reduced after 5 cycles of treating acidic water. The excellent performance of MgAl alloy in reactivity, durability, and efficiency is attributed to a synergistic effect of chemical reduction and eutectic reactions, which is catalyzed by intermetallic compound Mg₁₇Al₁₂ and in situ layered double hydroxide (iLDH). The pH 2.47 of an acid mine drainage sample from copper ore mines is raised to 7.4 ± 0.4 and the concentrations of Al, Cr, Cu, Fe, Mn, Ni, and Zn ions are reduced to <0.55 mg L⁻¹ from 5–559 mg L⁻¹. In contrast, quick lime treatment increases the pH to 12.45, whereas activated carbon, zerovalent iron, and conventional LDH are not able to neutralize or remove Al³⁺ and heavy metals. The findings of this study provide new insights into the efficient, green, and sustainable approach for acidic water remediation.