Potential of Bauhinia Racemosa Sawdust for Chromium (VI) Removal: Adsorption Optimization and Mechanistic Insights

The purpose of the present study was to assess the effectiveness of Bauhinia racemosa sawdust powder (BRSP) for its potential use as a low-cost ligno-cellulosic adsorbent for the removal of hexavalent chromium [Cr(VI)] from aqueous solution. Adsoprtion study based batch experiments were conducted to study the various factors affecting adsorption, such as Cr(VI) concentration, initial pH, biosorbent particle size, contact time, and solution volume. The biosorbent was also characterized by FTIR, BET analysis, and SEM-EDX. The surface area, proximate analysis, Boehm titration, and point of zero charge estimation (pHPZC) were measured to determine the surface characteristics and functional group interactions. Maximum Cr(VI) removal was 99.78% and maximum Cr(VI) adsorption was 106.86 mg/g under optimal conditions (pH 4.0, dose of 0.4 g of grains in 100 mL of solution for a particle size of 75 µm with 100 mg/L concentration and a contact time of one h). The Langmuir isotherm model effectively fits the adsorption equilibrium data, indicating monolayer adsorption. Nevertheless, kinetic runs based on the pseudo-second-order model indicated that chemisorption was the predominant process. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) suggested that the process was spontaneous and endothermic. These results indicated that BRSP is a promising sustainable biosorbent for removing Cr(VI) from polluted water, offering a green strategy for resource recycling and effluent treatment in diverse industries. The driving forces are van der Waals interaction, π-π stacking, hydrophobic, and electrostatic interactions.