Mercury removal from contaminated soil by thermal treatment with FeCl3 at reduced temperature

Thermal treatment has been used to remediate mercury-contaminated soils; however, existing thermal technologies use high temperatures (e.g., 600-800 °C) and require high energy costs. Moreover, the treated soil is unfavorable for agricultural reuse. To address these issues, the present study developed a method for the thermal treatment of mercury-contaminated soils at a reduced temperature (400 °C) by adding FeCl3. A FeCl3/Hg molar ratio of 100:1 in the soil was adopted as the optimum dosage of FeCl3 required to achieve maximum reduction of mercury. The mercury concentration in soils was successfully reduced to 0.8 mg kg−1 when treated at 400 °C for 60 min and the treated soil retained most of its original soil properties. FeCl3 addition during thermal treatment not only accelerated the volatilization of mercury in the easily removed fraction but also reduced the volatilization temperature of mercury in the hardly removed fraction. The adsorbable organic halogens and PCDD/Fs formed during thermal treatment with FeCl3 would not affect the soil reuse in agriculture. The thermal decontamination method reduces energy costs and leads to agricultural soil reuse, thus providing a greener and more sustainable remediation method for treating mercury-contaminated soil in future engineering applications.