Sequestration of chelated copper by structural Fe(II): Reductive decomplexation and transformation of CuII-EDTA

Chelated coppers, such as Cu-II-EDTA, are characteristically refractory and difficult to break down because of their high stability and solubility. Cu-II-EDTA sequestration by structural Fe(II) (=Fe(II)) was investigated intensively in this study. Up to 101.21 mgCu(II)/gFe(II) was obtained by =Fe(II) in chelated copper sequestration under near neutral pH condition (pH 7.70). The mechanism of Cu-II-EDTA sequestration by =Fe(II) was concluded as follows: 3Cu(II)-EDTA+7=Fe(II)+9H(2)O -> Cu(0) + Cu2O down arrow (the major product)+2Fe(2)O(3)center dot H2O down arrow+3Fe(II)-EDTA+14H(+) Novel results strongly indicate that Cu-II reductive transformation induced by surface =Fe(II) was mainly responsible for chelated copper sequestration. Cu(0) generation was initially facilitated, and subsequent reduction of Cu(II) into Cu(I) was closely combined with the gradual increase of ORP (Oxidation-Reduction Potential). Cu-containing products were inherently stable, but Cu2O would be reoxidized to Cu(II) with extra-aeration, resulting in the release of copper, which was beneficial to Cu reclamation. Concentration diminution of Cu-II-EDTA within the electric double layer and competitive adsorption were responsible for the negative effects of Ca2+, Mg2+. By generating vivianite, PO43- was found to decrease surface =Fe(II) content. This study is among the first ones to identify the indispensible role of reductive decomplexation in chelated copper sequestration. Given the high feasibility and reactivity, =Fe(II) may provide a potential alternative in chelated metals pollution controlling. (C) 2016 Elsevier B.v. All rights reserved.