The Ce-Fe loaded biochar for efficient removal of hexavalent chromium: Broad pH adaptation and mechanisms

The adsorption as a convenient, effective and economical method has been widely used for the removal of highly toxic Cr(VI) from aqueous solution in recent years. However, the adsorption for Cr(VI) was usually more effective under acidic conditions and less effective in neutral and alkaline environments, and there are few studies on the response sequence of the functional groups on the biochar participating in the Cr(VI) removal process. The biochar CeFe-SPBC prepared in this work not only showed a great removal efficiency (85.7%) for Cr(VI) at pH= 3, but also exhibited a removal efficiency close to 70% for Cr(VI) at pH= 9, which reflected that the CeFe-SPBC had an excellent adaptability to changes in pH. The characterization results displayed the large specific surface area (296 m2/g) and various functional groups as well as metal oxides of CeFe-SPBC. And, the response sequence of the main functional groups was identified as follows: Ce-O > Fe-O > aromatic CC > C-OH > -COO-. On this basis, the adsorption-enhanced reduction-immobilization mechanisms of Cr(VI) on the surface of the CeFe-SPBC were discussed in detail. •The response priority of M-O bonds (Ce-O, Fe-O) was the highest.•CeFe-SPBC exhibited a great adaptability to the wide changes of system pH (2−9).•The CO and Fe(II) could act as the intermediate in the process of electron transport between CeFe-SPBC and Cr(VI).•The removal of Cr(VI) involved the adsorption-enhanced reduction-immobilization mechanisms.