Microwave-assisted torrefaction of biomass Kappaphycus alvarezii-based biochar and magnetic biochar for removal of hexavalent chromium [Cr(VI)] from aqueous solution

The present study investigates the isotherm and kinetics of aqueous hexavalent chromium [Cr(VI)] removal using biochar (Ka-BC) and magnetic biochar (Ka-MBC) derived from seaweed biomass, Kappaphycus alvarezii. Characteristics of prepared Ka-BC and Ka-MBC were explored by FT-IR, XRD, SEM, EDAX, and surface area analysis. The effects of initial pH, contact time, and chromium concentration were investigated based on batch adsorption experiments. The maximum chromium adsorption was 64.8% and 82.5% using Ka-BC and Ka-MBC, respectively, corresponding to 500 mg/L loading at pH 3 with initial chromium concentration of 1 mg/L after 150 min of sorption reaction. The removal of chromium is mainly dependent on pH and follows a pseudo-second-order kinetic model. The adsorption experiments showed that Ka-MBC has better removal capacity than the Ka-BC due to multi-layer mechanism and surface roughness phenomenon in Ka-MBC. The chromium adsorption on Ka-MBC followed Langmuir isotherm. The current study demonstrates the utilization of seaweed-derived magnetic biochar composite as an efficient sorbent and low-cost alternative for the removal of Cr(VI) from the environment.