Adsorptive removal of rhodamine B from textile wastewater using water chestnut (<i>Trapa natans L.</i>) peel: adsorption dynamics and kinetic studies

Abstract

Water chestnut peel, an agricultural bio-waste, was used as a biosorbent for removal of rhodamine B (RhB), basic textile dye, from an aqueous solution. The effects of various experimental parameters were studied. The equilibrium data correlated well with a Freundlich isotherm (R2 = 0.98–0.99) followed by a Halsey isotherm model (R2 = 0.98–0.99) which indicated heterogeneity of the adsorbent surface and multilayer adsorption of RhB dye onto the water chestnut peel waste (WCPW). High correlation coefficients (R2 = 0.99) together with close agreement between experimental qe (0.4–1.7 mg g−1) and calculated qe (0.4–2.5 mg g−1) suggested that the adsorption process followed pseudo-second-order kinetics, with k2 values in the range of 52–3.4 × 10−1 g mg−1 min−1 at different concentrations. The overall mechanism of adsorption was controlled by both liquid-film and intra-particle diffusions. The negative values of change in Gibb's free energy (−ΔG0 = 19.2–29.2 kJ mol−1) and positive values of change in enthalpy (ΔH0 = 30.9–117.6 kJ mol−1) revealed the process to be spontaneous and endothermic. WCPW was found to be an effective adsorbent for removal of RhB, a cationic dye, from an aqueous solution.