Optimized immobilization of lead and cadmium in soil using dithiocarboxy functionalized silica: A long-term...

The efficient immobilization of heavy metals often requires a high dosage of remediation material, resulting in increased remediation costs and potential ecological risks. In this study, we developed a novel silica-based material, RNS-TS, characterized by a high density of dithiocarboxy groups, aimed at remediating Pb and Cd contaminated soils and evaluating the long-term efficacy via aging experiments. The synthesized RNS-TS achieved a functional group density of 2.59 mmol/g. At a concentration of 1 %, it effectively reduced the content of bioaccessibility Pb, Cd, and Cu in slightly contaminated soil by 86 %, 82 %, and 100 %; in moderately contaminated soil by 94 %, 75 %, and 100 %; and in heavily contaminated soil by 68 %, 60 %, and 100 %. Furthermore, the remediation process was relatively fast, with equilibrium achieved within one day after adding the RNS-TS. Aging experiments revealed that the remediated products exhibited excellent stability under simulated climate conditions such as extreme temperatures, freeze-thaw cycles and dry-wet cycles etc. Field experiments demonstrated that a 0.2 wt% application of RNS-TS reduced the content of bioaccessible Cd from 0.6 mg/kg to 0.3 mg/kg (approximately 50.8 % reduction), while Cd content in wheat grains decreased from 0.18 mg/kg to 0.08 mg/kg (approximately 54.4 % reduction). This successful application ensured safe wheat production. This material shows great promise as a risk element stabilization agent for heavy metal-contaminated soils.