Continuous treatment of chromium picolinate and efficient chromium removal without hexavalent chromium accumulation using the modified Fe-C micro-electrolysis process

Abstract

Cr(pic)3, an emerging contaminant, is easily degraded to hexavalent chromium (Cr(VI)) in environment, which exacerbates its risk. Because of the complexing structure, removal of this organic chromium is rather difficult through the simple adsorption and precipitation. Herein, disposal of Cr(pic)3 via the modified iron-carbon (Fe-C) micro-electrolysis (abbreviated as Fe-C) process (H2O2 was added simultaneously as the reactant) was first developed in this work. The modified process could accelerate the de-complexation of Cr(pic)3 and promote Cr removal at a lower H2O2 dosage than the Fenton process. Cr(VI) was not accumulated in the process. Almost all the Cr(pic)3 could be degraded and the residual chromium (all was trivalent chromium Cr(III)) was decreased from 520 to 52.7 μg/L within 30 min under optimized conditions in batch experiments (i.e., pHinitial = 3.0, pHfinal = 7.0, [H2O2]0 = 0.3 mM, [Fe-C fillers]0 = 0.1 g/L, respectively). Mechanisms of Cr(pic)3 de-complexation and Cr removal were elucidated based on the products detected and characteristics of the precipitates. Adsorption was the main mechanism for Cr(III) removal. It exchanged the hydroxyl ligand with the iron hydro(oxides) to form inner sphere complex. Factors that potentially affected the performance of the modified Fe-C process were investigated, including the operational parameters and the composition of water matrix. Moreover, the feasibility and stability of the established method were further confirmed by the column test, which realized the continuous operation and maintained the residual Cr in the effluent constant below 10.0 μg/L. Collectively, these findings consistently indicated that the modified Fe-C process is a robust and promising approach for the industrial disposal of Cr(pic)3.