Study on the Remediation of Cadmium/Mercury Contaminated Soil by Leaching: Effectiveness, Conditions, and Ecological Risks

• Published in: Water, air, and soil pollution air, and soil pollution, 2023, Vol.234 (1), p.45, Article 45
• Main Authors: Li, Yinghua, Sun, Jiaru, Qian, Jie, Huang, Tianci, Su, Fei
• Format: Article
• Language: English
• Subjects: Acid leaching; Acids; Atmospheric Protection/Air Quality Control/Air Pollution; Cadmium; Chemical tests and reagents; Citric acid; Climate Change/Climate Change Impacts; Contamination; Earth and Environmental Science; Ecological effects; Edetic acid; Eluents; Elution; Environment; Environmental impact; Environmental monitoring; Ethylenediaminetetraacetic acids; Heavy metals; Hydrogeology; Leaching; Machining; Mercury; Mercury (metal); Organic acids; Oxalates; Oxalic acid; Parameters; Physicochemical processes; Physicochemical properties; Reagents; Remediation; Removal; Response surface methodology; Risk assessment; Soil; Soil conditions; Soil contamination; Soil improvement; Soil pollution; Soil properties; Soil remediation; Soil Science & Conservation; Soil stability; Soils; Stability analysis; Tartaric acid; Technology; Water Quality/Water Pollution
• ISSN: 0049-6979; 1573-2932
• DOI: 10.1007/s11270-023-06060-x

Soil leaching is a viable technology to achieve rapid remediation and reuse of contaminated sites. However, there is still a need to find leaching reagents that can achieve high removal rates of heavy metals with low environmental impact. Based on this, single and combined reagents were used to leach contaminated soil. In this study, three types of single leaching reagents, rhamnolipid, citric acid, and EDTA, were selected, and their leaching characteristics for cadmium (Cd) and mercury (Hg) were investigated. The effect of different factors on the elution rate was investigated by applying EDTA in combination with organic acids (citric acid, tartaric acid, and oxalic acid), and the operating parameters of EDTA-citric acid were optimized by using the response surface methodology. In addition, changes in the physicochemical properties of the soil before and after leaching, as well as the stability and mobility of heavy metals, were evaluated using I R and M F indices. The results showed that the mixture of 2% EDTA and 5% citric acid was the most effective for heavy metal removal. The optimum eluent parameters for S1 (light contamination level) were: EDTA/citric acid volume ratio:1:1, liquid/soil ratio:20:1, and leaching time:120 min; under these operating conditions, the Cd and Hg removal rates were 88.7% and 66.3%, respectively. The optimum eluent parameters for S2 (heavy contamination level) were: EDTA/citric acid volume ratio:1.5:1, liquid/soil ratio:30:1, and leaching time:120 min; under these operating conditions, the Cd and Hg removal rates were 91.2% and 71.5%, respectively. Both S1 and S2 could meet the soil standard after leaching with this composite reagent (Cd: 65 mg/kg; Hg: 38 mg/kg). In the risk assessment, the physicochemical properties of the soil did not change significantly after EDTA-organic acid leaching. The content of residual heavy metals in effective form was greatly reduced, and the stability was significantly improved, indicating that the composite leaching reagents could effectively reduce the ecological risk of contaminated soil. Therefore, combining EDTA with organic acids was an advisable method to improve soil leaching technology.