Precise decomplexation of Cr(III)-EDTA and in-situ Cr(III) removal with oxalated zero-valent iron

Cr(III)-organic complexes removal from wastewater is challenging to decompose the complexes without pro-ducing toxic Cr(VI). Herein we demonstrated that oxalated zero-valent iron (Ox-ZVI) could one-step decomplex 95.4% of Cr(III)-EDTA with 94.2% removal of total Cr and 60.5% removal of TOC without generating Cr(VI) at pH 6.0. Ox-ZVI with FeC2O4 shell preferred to adsorb and activate O2 to produce more reactive species than ZVI with iron oxide shell, while the generated 1O2 could selectively break the Cr-O and Cr-N bond to precisely decomplex Cr(III)-EDTA without producing Cr(VI). The released Cr(III) was in-situ precipitated on the surface of ZVI in Cr(OH)3 form. Interestingly, & BULL;OH preferred the effective degradation of the released EDTA ligand to the oxidation of the chelated Cr(III) at pH 6.0. This study offers a green and facile method for the Cr(III)-organic complexes treatment, and also sheds light on the importance of reactive species adjustment for the precise pollutant control.

Automated summary

Oxalated zero-valent iron (Ox-ZVI) efficiently removes Cr(III)-organic complexes without producing toxic Cr(VI). It selectively breaks the Cr-O and Cr-N bonds of Cr(III)-EDTA complexes without generating Cr(VI), achieving 95.4% decomplexation and 94.2% removal of total Cr. The study highlights the importance of adjusting reactive species for precise pollutant control and provides a green and facile method for Cr(III)-organic complexes treatment.