Microwave-assisted magnetic biochar for removal of hexavalent chromium from aqueous solution

In this study, biochars were prepared by pyrolysis of tea waste and rice husk and hexavalent chromium (Cr(VI) sorption was obtained after post-modification of biochars with magnetic iron nano/micro-particles. The maximum sorption of Cr(VI) by magnetic tea waste biochar (MTWB) was 99.9% followed by 97.36% for magnetic rice husk biochar (MTRHB) at pH 5.2. Among studied competing ions, sulfate ions (SO42-) considerably reduced the sorption of Cr(VI) up to ~66.5% for both biochars. The surface functional groups such as – OH, C-H, Fe-O and porous biochars structure loaded with iron nanoparticles helped in Cr(VI) adsorption by ion exchange and electrostatic interactions as indicated by FTIR, XPS and SEM-EDS data. Both Cr(III) and Cr(VI) species were observed on biochars surface confirming the Cr(VI) removal process by reduction and direct adsorption of Cr(VI) ions. Hence, this study provides an excellent option for the application of magnetic biochars to treat Cr(VI) containing wastewater.