Selective removal of total Cr from a complex water matrix by chitosan and biochar modified-FeS: Kinetics and underlying mechanisms.

Cr(VI) is difficult to remove from wastewater via a one-step method because it is a type of oxyanion. Developing ARPs to selectively remove total Cr is critical for Cr(VI) remediation, including Cr(VI) adsorption-reduction and Cr(III) complexation. Hereon, chitosan and biochar modified-FeS (CTS-FeS@BC) was prepared to apply in the selective removal of total Cr from wastewaters. The results showed that the activity of amorphous FeS on CTS-FeS@BC for Cr(VI) removal (110.0 mg/g FeS) was significantly enhanced by CTS and BC, and efficiency was inhibited slightly by many anions and humic acid (HA). Meanwhile, the removal of total Cr by CTS-FeS@BC (99.1 mg/g FeS) via ARPs was improved by 1.2 and 40.3 times when compared with CTS-FeS and raw FeS, respectively. Besides, CTS-FeS@BC exhibited an outstanding selectivity for total Cr removal in metal cations-Cr binary solutions and in a complex water matrix. The mechanism of ARPs on CTS-FeS@BC demonstrated by the results of the 1,10-phenanthroline experiment and the distribution of Cr species was that Cr(VI) was first adsorbed by outer-sphere complexation for reduction, and then adsorbed Cr(III) combined with Fe(III) species to generate Fe(III)-Cr(III) complex for total Cr removal. Overall, this study provides an ARP to effectively solve Cr pollution in wastewaters.