A mechanistic insight into chromium (VI) ion adsorption onto pristine, UCB as well as Al-modified Neolamarckia cadamba wood biochar, MCB

In this study, unmodified and modified wood biochar of Neolamarckia cadamba was used as an adsorbent for the removal of hexavalent chromium from an aqueous solution. The biochar material was characterized by different analytical techniques like SEM, BET-N₂, FT-IR, and LIBS. The EDX and recorded LIBS spectra demonstrated a fingerprint of the elemental composition of biochar. The presence of peaks of chromium (Cr) showed the adsorption of chromium ions onto the biochar. BET-N2 analysis indicated the pore size (210 nm) and pore volume (0.004 cm³/g) of the biochar. The batch adsorption experiments revealed the optimum values of pH (4.0), adsorbent doses (0.2 g/L), initial Cr(VI) concentration (10 mg/L), and contact time (45 min) in the adsorption process. The adsorption isotherm and kinetic models were used to explain the nature and rate of adsorption. The Langmuir isothermal models showed better compliance with adsorption capacity: 86.95 mg/g for modified biochar (MCB) and 34.72 mg/g for unmodified biochar. Chemisorption and exchange of negatively charged chromate ions by chloride ions, i.e., anion-exchange reactions, have been considered ideal reactions that regenerate the spent UCB and MCB biochars during a series of sorption and desorption reactions. The special attribute, e.g., its low cost and simple regeneration using common salt, can be seen as a promising factor for the biochar in the removal of chromate ions from the liquid solution. Graphical Abstract: (Figure presented.)