In situ plant bionic remediation of cadmium-contaminated soil caused by a high geological background in Kaihua, Zhejiang Province, China.

A plant bionic in situ soil remediation system was designed to rehabilitate acidic cadmium (Cd)-contaminated soil in a high geological background area, Kaihua County of Zhejiang Province in China. In this system, citric acid, an environmental-friendly organic compound, was adopted to activate soil Cd. The soil solution was driven into the plant bionic root using a solar powered simulated transpiration system. Activated Cd in the soil solution was adsorbed by the modified polyurethane foam (DTC-LPEI-PUF) in the bionic root. Under the acidic conditions caused by citric acid (pH = 4.5), DTC-LPEI-PUF could effectively adsorb Cd, and the adsorption rate reached equilibrium after 5 h. Theoretical calculations suggested that the absorption behavior followed pseudo -second order kinetics, and the saturated adsorption capacity of Cd by DTC-LPEI-PUF was 89.05 mg/g, obeying Langmuir isothermal adsorption models. In addition, the main ions in soil, such as calcium (Ca) and magnesium (Mg), had little effect on the adsorption by DTC-LPEI-PUF. However, iron ions (Fe3+) significantly influenced the adsorption of Cd by DTC-LPEI-PUF. After 28 d of an in situ remediation, the total contents of Cd in contaminated soil declined from 3.63 mg/kg to 2.69 mg/kg, i.e., 26% of the total Cd was removed. In addition, after remediation, the removal of available Cd reached 47%. Our results demonstrate that the proposed plant bionic in situ remediation system has a promising prospect for application to rehabilitate Cd-contaminated soil in a high geological background area, although the technology needs further improvement.