A ferric chloride/sodium alginate/biochar composite as a filler for a permeable reactive barrier for removing Cr(VI) from groundwater
Haihua Li, Xinyi Wang, Hongyu Nie, Ya-Hui Xu, Xuehui Pei, Haozu Cheng, Gaojie Chai
Abstract
Chromium is regarded as one of the most hazardous heavy metals due to its potent and pervasive toxicity to the ecosystems and human beings. In this study, a ferric chloride (FeCl 3 ), sodium alginate (SA) and biochar (BC) composite in a 3D network structure was obtained via pyrolysis and co-impregnation. Subsequently, it was used as a filler for permeable reaction barrier (PRB) to remove Cr(VI) pollution from groundwater. The results indicate that the Cr(VI) removal rate by FeCl 3 /SA/BC exceeded 63 % at pH values ranging from 2 to 8, exhibiting a broader pH adaptation range. The presence of Fe 3 + and Mn 2+ facilitated the uptake and elimination of Cr(VI) by FeCl 3 /SA/BC, whereas the presence of Mg 2+ , Ca 2+ , Cl − , SO 4 2− , HCO 3 − and PO 4 3− inhibited the adsorption of Cr(VI). A low flow rate proved advantageous in enhancing the removal efficiency of Cr(VI). Specifically, the adsorption capacity of FeCl 3 /SA/BC for Cr(VI) was 12.50 mg·g −1 at an influent flow rate of 1.0 mL·min −1 . The penetration time and depletion point were 14 days and 40 days, respectively. This material used as a filler for PRBs demonstrated good permeability with a permeability coefficient of 12.66 m·d −1 . Furthermore, a thorough investigation of the structural, chemical and physicochemical properties of FeCl 3 /SA/BC, coupled with an investigation into the occurrence of chromium species in the reaction medium, revealed that its mechanism of action on Cr(VI) including electrostatic adsorption, redox and co-precipitation. Thus, FeCl 3 /SA/BC provides a cost-effective and efficient Cr(VI)-remediating filler for PRBs by exploiting agricultural waste resources. • Novel PRB filling materials were prepared using FeCl 3 , sodium alginate and biochar. • The material exhibited higher Cr(VI) removal rate and broader pH range. • Fe 3+ and Mn 2+ facilitated the uptake and elimination of Cr(VI) by FeCl 3 /SA/BC. • The material displayed favourable permeability and anti-clogging characteristics. • The removal mechanism of Cr(VI) by FeCl 3 /SA/BC were systematically investigated.