Hexavalent Chromium Adsorption on Adsorbent Derived From Biomass of Fabaceae Plant in Vietnam: Effect of Preparation Conditions on Equilibrium Adsorption Capacity

Abstract

The present work is devoted to examining the potential of Sesbania sesban biochar produced through slow pyrolysis for 120 min at 300°C in removing hexavalent chromium from the aqueous phase. The physicochemical characteristics of biochar were analyzed utilizing a variety of analytical tools including SEM, BET, and FTIR. Results revealed that the biochar had a smooth surface, an even stacking pattern with a porous texture, a large BET surface area equal to 562 m²/g, and a pH_pzc of 6.9. The biochar efficiency in eliminating Cr (VI) was investigated through several variables, including biochar dosage (0.1–0.4 g), pH (2–8), initial chromium ion concentration (10–40 mg/L), and adsorption time (15–120) min. The results identified the best conditions for adsorbing Cr (VI): an initial concentration of 10 mg/L, an absorbent dosage of 0.3 g, a pH solution of 2, and a reaction time of 90 min. The experiment achieved a Cr (VI) removal efficiency of over 90% by applying these conditions. The adsorption isotherm data were analyzed and showed a strong correlation coefficient (R² = 0.985) for Langmuir monolayer model, in which the maximum adsorption capacity achieved was 5.3 mg/g. According to the kinetic investigation, the adsorption of Cr (VI) was adapted to a pseudo-second-order model having a high R² value of 0.998. These results demonstrate that Sesbania sesban biochar has excellent potential as a cost-effective and highly efficient adsorbent for removing hexavalent chromium and improving water quality.