Oxidation of Aqueous EDTA and Associated Organics and Coprecipitation of Inorganics by Ambient Iron-Mediated Aeration

Abstract

Cationic metal and radionuclide contaminants can be extracted from soils to groundwater with sequestering agents such as EDTA. However, EDTA must then be removed fromthe 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 mM); glyoxylic acid (0.153 mM); chelated Cd2+ (0.94 and 0.0952 mM), Pb2+ (0.0502 mM), and Hg2+ (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 floc. 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 H202, 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.

Hydrogen peroxide-enhanced iron-mediated aeration for the treatment of mature landfill leachate

“…The H 2 O 2 -enhanced iron-mediated aeration (IMA) process using fibrous media was tested in fixed bed reactors developed by Englehardt et al [13,14], as shown in Fig. 1.…”

“…For example, in the case of activated sludge treatment, corrosion of the pump station, unstable chlorine residual in the treatment plant effluent, and sludge bulking the mechanism of organics oxidation at neutral-weakly basic pH has not been known to be general. Englehardt et al [14] suggested production of other reactive species such as ferryl under such conditions, which involves Fe II -mediated H 2 O 2 formation. Furthermore, iron oxyhydroxides produced can precipitate a number of heavy metals such as Cd 2+ and Pb 2+ .…”

The EDTA Complex of Oxidoiron(IV) as Realisation of an Optimal Ligand Environment for High Activity of FeO2+

“…[47] The involvement of a high valent ferryl (Fe IV ) or perferryl (Fe V ) species has been invoked in recent studies on the autoxidation reaction of Fe II in the presence of ethylenediaminetetraacetate (EDTA) and other chelating ligands. [48][49][50] Experimental evidence has been put forward for the generation of a strong oxidant, responsible for the degradation of the ligand and the associated organics, whose reactivity differs from the one of a hydroxyl radical. It has been proposed that [FeO(H 2 O) 5 ] 2+ may be generated in experimental conditions as a by-product of the Fe II -to-Fe III oxidation.…”

Oxidation of organic contaminants in water by iron-induced oxygen activation: A short review

“…Chemical oxidation by the nZVI/O2 system can enhance the biodegradability of wastewater containing toxic biocides, improving the efficiency of the secondary biological treatment [51]. Englehardt et al [52] showed the ZVI/O2 system can simultaneously treat ligands and heavy metals in wastewater; organic ligands were oxidized by reactive oxidants, and heavy metals were removed by co-precipitation with Fe(III)-oxyhydoroxides. Fu et al [53] also demonstrated a dye compound and Cr(VI) can be simultaneously removed in the ZVI/O2 system via oxidation and reduction/co-precipitation, respectively.…”