Electrokinetic Remediation of Cadmium-Spiked Soil Using Tea Saponins Powered by Solar Energy

Abstract

To reduce energy consumption and secondary contamination of soil, using natural biosurfactants-tea saponins as enhancement agent was studied on electrokinetic remediation (EKR) of cadmium (Cd)-spiked soil powered by solar energy. The current during EKR, the pH of soil before and after remediation, the initial and the residual Cd in the soil, Cd collected in the electrolyte, the mass balance of Cd, and cost analysis and energy consumption were investigated. Analytical methods such as Fourier Transform Infrared Spectrometer (FTIR), Scanning Electron Microscope (SEM), and Energy Dispersive Spectroscopy (EDS) were applied. Experimental results showed that tea saponins could increase the removal of Cd from the soil by promoting Cd desorption and its complexation that increased its mobility. There was a significant positive correlation between the concentration of tea saponins and Cd removal efficiency, but this positive correlation gradually decreased and the most suitable concentration of tea saponins was 2 g/L under the conditions of this experiment. EKR driven by solar power (Treatment time: 180 h) can achieve the Cd removal efficiency of approximately 90% which was a promising technology for soil remediation, especially in regions with abundant sunshine year-round. FTIR analysis indicates that tea saponins can be quickly and naturally degraded without resulting in secondary pollution to the soil. According to SEM and EDS analysis, most of the Cd pollutants in the soil were removed by EKR, but some pore clogging still existed.