Optimizing extraction procedures for better removal of potentially toxic elements during EDTA-assisted soil washing

Purpose: Ethylenediaminetetraacetic acid (EDTA)-enhanced soil washing is an important technique of removing potentially toxic elements (PTEs) from contaminated soils. Conventional mechanical shaking (CMS) method is widely adopted in soil washing. However, it consumes a considerable amount of time and energy. Extraction methods which need less contact time or power, such as static equilibrium extraction (SEE) and ultrasound-assisted extraction (UAE), are potential to replace CMS in industrial application. Methods: The washing process of the soil from a contaminated site was optimized by investigating various extraction conditions, including EDTA concentration, contact time, and different extraction methods, such as CMS, SEE, and UAE, in this study. Results: The results indicated that EDTA greatly enhanced the removal of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) from the soil. The EDTA was more effective in removing Pb and Cu than Cd and Zn, regardless of the extraction method. This might be mainly attributed to the strong complexation capacity of EDTA with Pb and Cu and geochemical distribution of the target PTEs. The three extraction methods were almost equally efficient, while SEE required less energy and UAE needed shortened contact time compared with CMS. Conclusion: Based on the above results, SEE and UAE are promising alternatives to CMS for cleaning up PTEs-contaminated soils.