Outstanding performance of electro-Fenton process for efficient decontamination of Cr(III) complexes via alkaline precipitation with no accumulation of Cr(VI): Important roles of iron species

The oxidation-precipitation processes has been considered as the feasible strategy for the decontamination of Cr(III) complexes. However, the priority of this strategy was seriously deteriorated by the formation of toxic Cr (VI). In this study, dual oxidation and reduction functions of electro-Fenton process were exploited as the pretreatment unit of alkaline precipitation for Cr(III) complexes decontamination. Highly oxidant species hydroxyl radicals ((OH)-O-center dot) formed in electro-Fenton system led to the enhanced mineralization of Cr(III)-citrate attaining 71 % TOC removal in 60 min releasing free Cr(III) or Cr(VI) ions into the solution. Notably, Cr(VI) was hardly accumulated because of the formation of highly reductive Fe(II) complexes. The local basic environment at the cathode created by H2O reduction resulted in electro-precipitation of Cr(III) species. Moreover, Fe3+, a widely used flocculant, generated during the process from the oxidation of Fe-2 rendered residual amount of Cr (total) below 1.5 mg L-1 after the subsequent alkaline precipitation.