Immobilization of Pb, Cd, and Cr in contaminated soil around mining areas using Mg/Al LDH-zeolite and evaluation of maize growth

Abstract

This study conducted simultaneous adsorption of Pb, Cd, and Cr ions using Mg/Al LDH-zeolite on contaminated soils from lead-zinc and tin mining areas. The optimal conditions were a 3% adsorbent-to-soil ratio, a 30-day incubation period, and 70% soil moisture. Characterization of the materials revealed that Mg/Al LDH-zeolite has superior physicochemical properties to natural zeolite, with a higher surface area and better adsorption capacity. Results indicated significant reductions in exchangeable heavy metal content: in lead-zinc mining area soil, exchangeable Pb decreased from 139.79 mg/kg to 10.95 mg/kg, Cd from 1.518 mg/kg to 0.533 mg/kg, and Cr from 2.636 mg/kg to 0.461 mg/kg using Mg/Al LDH-zeolite. In tin mining area soil, exchangeable Pb decreased from 583.97 mg/kg to 48.22 mg/kg, Cd from 0.498 mg/kg to 0.122 mg/kg, and Cr from 106.095 mg/kg to 38.038 mg/kg. Maize cultivation on post-adsorption soil showed improved growth performance, with plants exhibiting increased height and ear and reduced heavy metal accumulation in roots, shoots, and grains. Pb, Cd, and Cr concentrations in maize roots decreased significantly, with Pb reducing to 0.113 mg/kg in the lead-zinc area and 0.203 mg/kg in the tin area, Cd reducing to 0.061 mg/kg and 0.037 mg/kg, respectively, and Cr reducing to 0.036 mg/kg and 0.243 mg/kg respectively. Mg/Al LDH-zeolite consistently demonstrated higher efficiency in reducing the bioavailability and translocation of heavy metals in maize tissues, confirming its potential as an effective adsorbent for soil remediation. Key mechanisms, including adsorption, surface complexation, ion exchange, precipitation, and structural incorporation, reduce metal mobility and bioavailability.