Biosorption of hexavalent chromium by biochar prepared from the Ceratonia siliqua pod: Kinetic, equilibrium, and thermodynamics studies

Ceratonia siliqua pod biochar sample (CBC) was generated in this work from C. siliqua (carob pod waste) biomass (CBM) by slow pyrolysis for 5h at 400°C as an alternative low-cost biosorbent for the removal of Cr(VI). The biosorption parameters that were adjusted were the initial pH (2.0–10.0), temperature (30°C, 40°C, and 50°C), biosorbent dose (0.01–0.03 g/50 mL), initial Cr(VI) concentration (10–100 mg/L), and contact period (0–360 min). The interaction between the surface functional groups on the CBM and CBC and the Cr(VI) ions was found to be the primary mechanism for Cr(VI) sorption via surface complexation and electrostatic interactions, according to the investigation of the pH influence. The Langmuir isotherm was shown to be more well-fitting than the Freundlich and Dubinin-Radushkevich isotherms for the concentration range of 10 to 100 mg/L. The testing results indicated a sorption capacity of 90.909 mg/g of CBM and 131.579 mg/g of CBC. According to kinetic investigations, the absorption of Cr(VI) ions onto CBM and CBC was defined in pseudo-second order. The findings of thermodynamic investigations showed that the biosorption of Cr(VI) ions onto CBM and CBC was an exothermic, spontaneous process. These findings demonstrated that, even for high concentrations of Cr(VI) in industrial wastewater, CBM and CBC could be viable, affordable alternatives as adsorbents.