Treatment of chromium-laden aqueous solution using CaCl₂-modified Sargassum oligocystum biomass: Characteristics, equilibrium, kinetic, and thermodynamic studies

Biosorption properties of a CaCl₂-modified Sargassum oligocystum algae biomass for removal of Cr(VI) from aqueous solutions were investigated. Experimental parameters affecting the biosorption process such as pH, contact time, biosorbent dosage, and temperature were studied. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), mapping test, energy-dispersive X-ray spectroscopy (EDX), and specific surface area were used to assess the physico-chemical properties the biosorbent. The surface area of biosorbent was found to be 35.64 m²/g. FTIR test revealed that the active groups of -OH, -NH₂, -C-H, C-O, -C-N, and S=O were present on the surface of CaCl₂-modified S. oligocystum biomass. The kinetic behavior of the chromium biosorption by modified S. oligocystum biomass followed well pseudo-second order kinetic (R²>0.999). The biosorption equilibrium occurred at 100^th min of contact time. The Langmuir, Freundlich, and Dubinin-Radushkevich models were applied to describe the biosorption isotherm of Cr(VI) onto modified S. oligocystum biomass. According to the R_L and n parameters of the studied isotherms, the Cr(VI) biosorption process was physical and desirable. The chromium biosorption capacity of modified S. oligocystum biomass was found to be 34.46mg/g. The calculated thermodynamic parameters (ΔG^o, ΔH^o, and ΔS^o) indicated that the biosorption of Cr(VI) onto modified S. oligocystum biomass algae was feasible, spontaneous, and exothermic under examined conditions.