Chemical stabilization of mercury in contaminated soil using Mg2Al layered double hydroxide supported iron sulfide composite

Mercury (Hg) contamination in soil has been a worldwide environmental concern. We prepared and investigated a novel Mg2Al layered double hydroxide supported iron sulfide composite (FeS@Mg2Al-LDH) for immobilization of mercury in two high-profile Hg-contaminated field soils (TJ soil represents freshly Hg-contaminated soil and GY soil represents historically aged Hg-contaminated soil). Amending the two soils with FeS@Mg2Al-LDH effectively immobilized mercury. The addition of 0.02% of FeS@Mg2Al-LDH immobilized 97.0% of mercury in TJ soil within 80 d. Similarly, the addition of 0.05% of FeS@Mg2Al-LDH immobilized 84.9% of mercury in GY soil. Increasing the FeS@Mg2Al-LDH dosage enhanced the immobilization efficiency. Increasing the dosage from 0.02% to 1% boosted the Hg immobilization efficiency in TJ soil from 97.0% to 99.4%. Increasing the dosage from 0.05% to 1% enhanced the Hg immobilization efficiency in GY soil from 84.9% to 86.2%. FeS@Mg2Al-LDH reacted with Hg via chemical precipitation and surface complexation, and transformed Hg from more available Hg fractions (exchangeable and carbonate bound fractions) into less available forms (organic and residual fractions), thus, reducing the environmental risk of mercury. The addition of FeS@Mg2Al-LDH inhibited the production of methylmercury while enhanced the soil enzyme activities. This study proves the potential and feasibility of FeS@Mg2Al-LDH to effectively immobilize mercury in soil.