Photoinduced Self-Organized Precipitation in Leachate for Remediation of Heavy Metal Contaminated Soils

Soil pollution by heavy metals has become an urgent environmental problem worldwide. However, existing remediation technologies have various deficiencies such as high energy consumption, long operation time, and secondary pollution, which largely limit their practical engineering application. Here, we propose an environmentally friendly method combining citrate washing and subsequent light irradiation for rapid and simultaneous removal of toxic heavy metals from soils. At initial concentrations of 1601 and 104 mg kg–1 in the soil, the As and Cd percentage removal reached 73.0% and 67.3%, respectively. The ligand-to-metal charge transfer in Fe(III)-citrate complexes and formation of reactive intermediate HO2•/O2•– contributed to the citrate degradation and high-efficiency heavy metal removal (above 97.0% after 60 h) via coagulation and precipitation in the leachate under ultraviolet irradiation. For the soil with a low content of Fe, the photochemical removal efficiency of heavy metals could be significantly improved by the addition of Fe3+ in leachate. Pakchoi cultivation showed an obvious reduction in biotoxicity of the contaminated soil after remediation. Solar irradiation experiments demonstrated the potential applicability of the green and efficient approach for remediation of heavy metal contaminated soils.