Efficient removal of thallium and EDTA from aqueous solution via the Fenton process

As a common chelating agent, ethylenediaminetetraacetic acid (EDTA) can form stable chelates with toxic metals. Such metal-EDTA complexes are of chemical stability, which poses a challenge to their removal from contaminated water/wastewater. In this study, simultaneous removal of toxic heavy metal thallium (Tl) and EDTA using the Fenton process was investigated for the first time. Influencing factors including the molar ratio of [Fe2+]/[H2O2], H2O2 dosage, pH and reaction time on the removal performance of Tl and EDTA were examined. Over 98% of Tl and 62% of total organic carbon (TOC) can be removed under optimized conditions: [Fe2+] of 21.6 mM, [H2O2] of 54.0 mM, reaction pH of 2.5, reaction time of 5 h and flocculation pH of 10.0. After treatment, an increase in ammonium nitrogen was clearly observed, which was mainly due to the cleavage of C-N and N-N bonds of EDTA. The single-factor experiments and the analyses of FT-IR, SEM-EDS and X-ray photoelectron spectroscopy spectra reveal that the removal of Tl and EDTA was mainly attributed to the synergistic effects of Fenton oxidation, surface complexation, coagulation, precipitation and co-precipitation. The findings of this study indicate that the Fenton process is a facile, effective and promising technique for Tl and EDTA removal from water/wastewater.