Removal of Cd(II) from aqueous solution by a composite hydrogel based on attapulgite

Chitosan-g-poly(acrylic acid)/attapulgite composite with 30 wt% attapulgite content was used to remove Cd(II) from aqueous solutions. The parameters influencing the adsorption were investigated. When Cd(CH3COO)2 was used as the solute of the solution, the equilibrium adsorption capacity was evidently larger than that of the other three cadmium salts (Cd(NO3)2, CdCl2, CdSO4). Results from kinetic experiments showed that the rate of Cd(II) adsorption on the composite was quite fast, more than 90% of Cd(II) adsorption occurred within the initial 3 min, and the adsorption equilibrium may be reached within 10 min. The adsorption process can be well described by the pseudo-second-order kinetic model. The equilibrium adsorption isotherm was fitted for not only the Langmuir model but also the Freundlich model. Fourier transform infrared spectra before and after adsorption of Cd(II) on the composite showed that complexation was considered as the main mechanism. To evaluate the reuse value of the composite, a consecutive adsorption-desorption process was performed five times, and the results implied that the composite has the potential for regeneration and reuse.