Physico-Chemico and Thermally Enhanced Soil Washing for Heavy Metal Contaminated Site at Yongsan Railroad Area

Abstract

A series of soil washing tests was conducted on railroad site soil with high concentration of copper (Cu), lead (Pb), and zinc (Zn). The initial heavy metal concentration of soil was varied from 1069 mg/kg to 2870 mg/kr for Cu, 873 mg/kg to 3300 mg/kg for Pb, and 279 mg/kg to 829 mg/kg for Zn. Since the soil was heavily contaminated, optimization and enhancement for soil washing was needed. In this study, enhancement performance of soil was conducted based on optimization in chemical aspect and addition of physical and thermal effect in the system. It was found that the proper condition in chemical aspects was using sequential washing by 0.2 M Na2-EDTA solution followed by 0.5 M HCl, 1:5 g/ml of solid liquid ratio, and 30 minutes of contact time. In addition, physical effect affected in breakage soil aggregation, which was found effectively enhance the performance by changing stirring speed to 120 rpm and using dispersing agent 2% in this experiment. Furthermore, more increment of removal efficiency occurred by increasing temperature up to 70 ℃ because it favoured molecular movement and collision between contaminant and washing solution. Nevertheless raising higher temperature would decrease in performance for Cu. Compared to conventional chemically soil washing only, adding physical and thermal effect into the system will enhance performance from 30.0% to 62.5% for Cu, 53.7% to 79.8% for Pb, and 40.7% to 66.5% for Zn.