Removal of mercury from soil by photochemical vapor generation with dielectric barrier discharge trap

Most forms of Mercury (Hg) in soil have significant destructive effect on ecosystems and food safety because of enormous toxicity. The existing treatment methods have drawbacks such as high energy consumption, complex operation, long remediation cycle, and secondary pollution. Therefore, this study aims to develop a governance method with low energy consumption, simple operation, short execution cycle, and no secondary pollution.

A new system was set up to remove leachable Hg²⁺ from soil and its performance was evaluated. The system consisted of photochemical vapor generator (PVG, for Hg²⁺ removal), dielectric barrier discharge (DBD) trapping reactor (for collection of removed Hg⁰). In the presence of organic acids, leachable Hg²⁺ was converted to gaseous Hg⁰ by UV irradiation in the PVG, and transported to the DBD trap by air for collection of the removed Hg²⁺. Soil samples in PVG were taken into glass tubes at specific time and then added aqua regia, analyzed using ICP-MS after digested in a boiling water bath. The performance of DBD trap was analyzed by connecting with ICP-MS.

This study achieved the removal of leachable Hg²⁺ from soil under the UV excitation, the subsequent conversion of escaped gaseous Hg⁰ to solid and enrichment in DBD trap. The factors affecting the efficiencies of photochemical reaction, transport and collection were carefully investigated. Under the optimized conditions, the removal efficiency of 2.00 mg L⁻¹ leachable Hg²⁺ in soil reached 95.0% within 1 h. Even in the presence of 15 interfering ions separately containing 50 mg L⁻¹, good remediation effects can still be achieved. The capture rate of gaseous Hg⁰ by DBD trap is close to 100%. The system can achieve Hg pollution control in 10 types of soil, demonstrating great promotion value.

This system utilizes PVG theory and DBD low-temperature plasma device to construct a safe, green, simple, and inexpensive method for removing leachable Hg²⁺ from soil.