Complete Cu removal through Fe(II) mediated decoupling of CuEDTA complexes from simulated industrial wastewater with simultaneous precipitation

Abstract

A complete removal of Cu from CuEDTA complexes by replacement/precipitation reactions using ferrous ions was realized. The effects of pH, iron dosage and reactions time on Cu removal were evaluated. The results were explained with the aid of chemical equilibrium modeling. Fe(III) ions effectively liberate Cu(II) ions from CuEDTA complexes by the replacement reaction at an acidic pH region, but the precipitation of ferric hydroxides at elevated pH levels renders a negative effect on Cu removal. In contrast, Fe(II) ions replace Cu(II) effectively at an alkaline pH region, where both replacement and precipitation of Cu can take place simultaneously. Cu removal was enhanced and was independent of the precipitation time when Fe(II) was dosed instead of Fe(III), reaching 100% removal of Cu at Cu:EDTA:Fe molar ratio of 1:1:5. The treatment efficacy of the replacement/precipitation processes for Cu removal followed by Fenton process for COD removal was compared with that of Fenton process for COD removal followed by alkaline precipitation for Cu removal. A complete Cu removal was achieved by the former, whereas only 40%–66% of Cu was removed by the latter.