Abstract
We investigated chemical composition and sorption properties of lignocellulosic complexes of wastes of agroindustrial complex, namely crushed shells of apricot, cherry and peach seeds, and walnut shells. Chemical analysis revealed that walnut shells show the highest content of polysaccharide components. Cherry and peach seed shells are characterized by a higher content of aromatic components (lignin). Based on the results of sorption of benzene vapor, the following sequence of the volumes of adsorption pores was found: walnut shells (0.03 cm3 g–1)=apricot seed shells (0.03 cm3 g–1)>peach seed shells (0.02 cm3 g–1)>cherry seed shells (0.01 cm3 g–1). The sorption capacity of biosorbents towards methylene blue was investigated as a function of pH of an aqueous solution, process duration, and initial dye concentration. It was established that the maximum efficiency of sorption is achieved at pH 6, while the minimum value corresponds to low pH values. Probably, an increase in pH value leads to deprotonation of carboxyl groups of biosorbents followed by changes in their surface charge into negative. This causes a decrease in electrostatic repulsion forces between the positively charged dye cation and the surface of the biosorbents. Therefore, the sorption centers are formed. The data on kinetics of sorption showed that during the first 30 min of contact the absorption of 55–60% of the dye cations occurs on the biosorbents, whereas complete sorption equilibrium is achieved within 120–180 min. The following sequence of the sorption capacity of lignocellulosic materials towards methylene blue was established: apricot seed shells (43.9 mg g–1)>walnut shells (37.8 mg g–1)>peach seed shells (30.1 mg g–1)>cherry seed shells (26.5 mg g–1). The Freundlich isotherm is the most suitable for describing the cationic dye absorption by biosorbents, and the calculated values are in good agreement with the experimental data.
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