Advanced Oxidation for Treatment of Aqueous Extracts from EDTA Extraction of Pb and Zn Contaminated Soil

The feasibility of using advanced oxidation processes (AOPs): ozone, ozone/sonification, and ozone/ultraviolet (UV) irradiation in treatment to remove heavy metals and ethylenediamine tetraacetate (EDTA) from aqueous extracts, obtained after soil extraction with EDTA, was examined. Extraction of soil contaminated with $\mathrm{1,243}\mathrm{mg}{\mathrm{kg}}^{-1}$ Pb and $\mathrm{1,190}\mathrm{mg}{\mathrm{kg}}^{-1}$ Zn with $40\mathrm{mmol}{\mathrm{kg}}^{-1}$ EDTA removed $41.8\pm 0.9$ and $7.2\pm \mathrm{.0.2}\%$ of Pb and Zn. Of the AOPs tested, only the use of ozone/UV enabled the decomposition of EDTA–heavy metals complexes in aqueous soil extracts, and recovery of released Pb and Zn by sorption on a commercial sorbent Slovakite. After treatment, the concentration of Pb, Zn, and EDTA in the extracts was fairly low ( $2.87\pm 1.15\mathrm{mg}{\mathrm{L}}^{-1}$ , $7.58\pm 2.12\mathrm{mg}{\mathrm{L}}^{-1}$ , and $0.012\pm 0.002\mathrm{mmol}{\mathrm{L}}^{-1}$ , respectively), and could presumably be reduced even further with a continuation of treatment. The treated extract was used for subsequent soil rinsing, which removed an additional $12.7\pm 1.6$ and $2.7\pm 0.1\%$ of soil Pb and Zn. The results of our study indicate that the use of ozone/UV is a feasible option for treatment of aqueous soil extracts from EDTA extraction. Treated extracts could be safely discharged or reused to lower requirements for process water.