Abstract:The Cr(III) desorption experiments of Gaomiaozi (GMZ) bentonite in aqueous solutions were performed. The variables affecting the desorption behaviors, such as contact time, concentration of the desorbent, pH value of the solution, temperature and desorption isotherms, were investigated by the batch experiments. The results show that the adsorbed Cr(III) on GMZ bentonite can be easily extracted by the desorbent. Kinetics examination shows that desorption is slower than adsorption, and the desorption rate increases with time and reaches the equilibrium after 3 h. The final desorption ratios of Cr(III) are 89.4%, 56.5% and 77.2% in the desorption solution with 0.1 mol/L HCl, 1 mol/L NaCl, and 1 mol/L CaCl₂, respectively, and the concentration can promote the desorption progress. Furthermore, the results of successive regeneration cycles indicate that the bentonite has a good regeneration ability and reusability. The pH value is an important factor in the Cr(III) desorption from the GMZ bentonite. The results of adsorption and desorption isotherms show that both adsorption and desorption isotherms are consistent with the Freundlich equation. The comparison of adsorption and desorption isotherms implies that the adsorption/desorption hysteresis is negligible and the transport of Cr(III) in bentonite can be described by a reversible adsorption process.

Key words: GMZ bentonite; Cr(III); desorption; isotherms