Characterization of modified sawdust, kinetic and equilibrium study about methylene blue adsorption in batch mode

Methylene blue (MB) biosorption by citric acid modified pine sawdust (Pinus tabulaeformis) was studied from aqueous solutions. Batch experiments were conducted to determine the biosorption properties of the biomass. The Langmuir isotherm equation could fit the equilibrium data. The maximal equilibrium quantity of MB from Langmuir model was 111.46 mg g^?1 at 293 K. The Elovich model adequately described the kinetic data in comparison to the pseudo-first-order model and pseudo-second-order model; the process involving rate-controlling step is very complex involving both boundary layer and intra-particle diffusion processes. The effective diffusion parameter D _i and D _f values were estimated at different initial concentration, and the average values were determined to be 5.76×10^?8 and 2.12× 10^?7 cm² s^?1. Thermodynamic parameters showed that the adsorption of methylene blue onto pine sawdust biomass was feasible, spontaneous and endothermic under studied conditions. The physical and chemical properties of the biosorbent were determined by SEM, TG-DSC, XRD, and the point of zero charge (pH _pzc ) and the nature of biomass-dye interactions were evaluated by FTIR analysis, which showed the participation of COOH, OH and NH₂ groups in the biosorption process. Biosorbents could be regenerated using 0.01 mol L^?1 HCl solution at least three cycles, with up to 90% recovery. Thus, the biomass used in this work proved to be effective for the treatment of MB bearing aqueous solutions.