Exploring the synergistic effects of calcium chloride modification on stem bark eucalyptus biochar for Cr(VI) and Pb(II) ions removal: Kinetics, isotherm, thermodynamic and optimization studies

In this study, stem bark eucalyptus was subjected to pyrolysis modification to produce modified biochar. The modified biochar (MSBEB) was characterized using Fourier Transform Infrared Spectroscopy (FTIR), Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray Diffraction (XRD), and Brunauer–Emmett–Teller (BET) techniques. The impact of adsorption process variables such as temperature, adsorbent dosage, pH and contact time on the metals ion removal efficiency were investigated. The optimum conditions for maximum removal of Cr(VI) and Pb(II) ions were determined as 45.20 °C, 0.12 g/L, and 120.5 min through optimization process. The excellent performance of the modified biochar can be attributed to its porous structure, surface area, surface chemistry and crystallinity as supported by SEM, BET, FTIR and XRD analysis. However, based on the high correlation coefficient (R2), low values of chi square (χ2) and sum of square error (SSE), the Freundlich isotherm and Pseudo-second order kinetics provided the best fit, suggesting chemisorption as the dominant mechanism. Thermodynamic analysis indicated an endothermic, spontaneous, and feasible reaction.