Thermodynamics of Cr(VI) adsorption on strong alkaline anion exchange fiber

Removal of Cr(VI) from aqueous solution by strong alkaline anion exchange fiber (SAAEF) was achieved using batch adsorption experiments. The effect of contact time, initial Cr(VI) concentration and pH was investigated. The results showed that the maximum adsorption capacity of SAAEF was 187.7 mg/g at pH=1.0. The adsorption capacity increased with Cr(VI) concentration but decreased with pH value when pH>1.0. Adsorption isotherms at various temperatures were obtained. Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models were adopted and the equilibrium data fitted best with the Langmuir isotherm. The constants of these models indicated that the adsorption process involved both chemisorption and physisorption. The values of thermodynamic parameters, including ΔH, ΔG and ΔS, suggested that the adsorption of Cr(VI) on SAAEF was a spontaneous, entropy-driven and endothermic process. Q(iso) was not a constant value, which indicated an inhomogenous energy distribution on SAAEF.