Na₂S Solution Remediation for Heavy Mercury Contaminated Soil

Abstract

The Na₂S solution was adopted to extract mercury, especially the mobile Hg from heavy mercury contaminated soil. The mercury species in soil were determined by using US EPA3200 sequential extraction procedure. The Hg extraction ratio, which depended on process parameters, such as liquid [mL]/solid [g] ratio of the solution and soil (5 : 1–20 : 1), the Na₂S solution concentration (0.1–0.7 mol/L), leaching time (2–24 h) and heating temperature (25–80°C) were systematically investigated. It was shown that the total content of Hg in the soil was about 168 mg/kg, including mobile Hg 104 mg/kg, semi-mobile Hg 17 mg/kg and non-mobile Hg 47 mg/kg. Mobile Hg exhibited high toxicity and bioactivity accounted for 62% of total Hg. According to the extraction experiments, it was indicated that Na₂S solution could effectively extract Hg from heavy mercury contaminated soil. Under the optimal conditions, namely, liquid [mL]/solid [g] ratio of 10 : 1, the Na₂S solution concentration of 0.7 mol/L, the leaching time of 4 h and the heating temperature of 25°C, the Hg extraction ratio of total Hg reached 72%. The mobile Hg, in particular, was removed as high as 86%.