[Remediation of Antimony-polluted Soil Using Iron Sulfide-modified Biochar and Stability Assessment After...

To investigate the remediation effects and mechanisms of iron sulfide-modified biochar （FeS-BC） on polluted soil surrounding an antimony smelting plant, soil from around a decommissioned antimony smelting plant in the Qinglong County, Guizhou Province, was used as the research subject. Through soil cultivation experiments, the effects of raw biochar （BC） and iron sulfide-modified biochar （FeS-BC） on the leaching toxicity, bioavailability, and speciation of antimony （Sb） in the soil were compared. The results showed that with an FeS∶BC mass ratio of 1∶5 and an addition rate of 7%, the average stabilization efficiency of Sb in soils with varying degrees of Sb pollution （G1-G6） reached 66.85%. FeS-BC maintained high Sb stabilization efficiency across a wide pH range （2.0-10.0）. In soils treated with a certain proportion of BC, the leaching concentration and bioavailable content of Sb fluctuated during the remediation process, decreasing by 5.89%±3.04% （1.44%-9.08%） and 20.49%±17.74% （4.83%-58.39%）, respectively, after 60 days of remediation. In contrast, FeS-BC effectively reduced the leaching concentration and bioavailable content of Sb throughout the remediation period, with reductions of 35.80%±13.80% （17.78%-55.05%） and 34.84%±2.28% （31.60%-37.64%）, respectively, after 60 days of remediation. The stabilization mechanisms of Sb in soil by FeS-BC included electrostatic attraction, ion exchange, redox reactions, complexation, and precipitation. After 14 days of remediation with BC and FeS-BC, soils with varying Sb pollution levels （G1-G6） were subjected to alternating wet and dry conditions and freeze-thaw cycles. The leachate concentration and bioavailable content of Sb in soils remediated with BC increased, indicating a certain release risk. In contrast, in soils remediated with FeS-BC, while the leachate concentration of Sb increased, the bioavailable content decreased.