Oxidation of aqueous EDTA and associated organics and coprecipitation of inorganics by ambient iron-mediated aeration

Cationic metal and radionuclide contaminants can be extracted from soils to groundwater with sequestering agents such as EDTA. However, EDTA must then be removed from the groundwater, by advanced oxidation or specialized biological treatment. In this work, aqueous individual metal-EDTA solutions were aerated with steel wool for 25 h, at ambient pH, temperature, and pressure. Removal of approximately 99% of EDTA (0.09-1.78 m M); glyoxylic acid (0.153 mM); chelated Cd²⁺ (0.94 and 0.0952 mM), Pb²⁺ (0.0502 mM), and Hg ²⁺ (0.0419 mM); and free chromate and vanadate was shown. EDTA was oxidized to glyoxylic acid and formaldehyde, and metals/metalloids were coprecipitated together with iron oxyhydroxide floe. Free arsenite and arsenate were each removed at 99.97%. Free Sr²⁺, and chelated Ni²⁺ were removed at 92% and 63%, respectively. Similar removals were obtained from mixtures, including 99.996 ± 0.004% removal of total arsenic (95% confidence). Traces of iminodiacetic acid, nitrilotriacetic acid, and ethylenediaminetriacetic acid were detected after 25 h. Results are consistent with first-order, solution-phase oxidation of EDTA and glyoxylic acid by ferryl ion and H₂O₂, respectively, with inhibition due to sludge accumulation, and equilibrium metal coprecipitation. This ambient process, to our knowledge previously unknown, agrees with recently reported findings and shows promise for remediation of metals, metalloids, and radionuclides in wastewater, soil, and sediment.