Na₂S Leaching Assisting Thermal Desorption for Thoroughly and Mildly Remediating Severely Hg-Contaminated Soil

Abstract

Thermal desorption has been widely used as an efficient method for remediating Hg-contaminated, whereas the current thermal treatment approach generally needed a high temperature (above 600°C), which negatively affected the soil composition and consumed energy. For the challenge, this study developed a novel Na₂S leaching assisting thermal desorption method for thoroughly repairing the severely Hg-polluted (168 mg/kg Hg) soil with a declined temperature (350°C). The results of this study indicate that Hg content could only be reduced from 168 mg/kg to 32.4 mg/kg by directly heating the soil at 550°C for 60 min. However, the Na₂S leaching assisting thermal desorption method could realize the low temperature and thorough remediation for highly Hg-polluted soil. When the thermal desorption temperature was reduced to 350°C and the thermal desorption time was kept at 60 min, the Hg content was decreased to 1.0 mg/kg, which was less than the Chinese National Standard. This should be ascribed to the fact that high-temperature volatile Hg compounds in the soil were first removed by Na₂S leaching pretreatment. This new collaborative remediation method could not only realize mild thermal desorption but also provide useful guidance for the severely Hg-contaminated soil.