ADSORPTION BEHAVIOR OF Cd, Pb, AND Ni FROM AQUEOUS SOLUTIONS ON CELLULOSE-BASED HYDROGELS

Removal of Cd 2+ , Pb 2+ , and Ni 2+ from aqueous solutions using cellulosegraft-acrylic acid (C-g-AA) hydrogels was investigated. Various factors affecting the adsorption capacity, such as pH, time, initial ions concentration, and competitive ions, were tested. The results showed that the adsorption of hydrogels was very pH dependent, and maximum adsorption was obtained at a pH of 5.0. The adsorption capacities of hydrogels for the heavy metal ions were 562.7 mg/g (Cd 2+ ), 825.7 mg/g (Pb 2+ ), and 380.1 mg/g (Ni 2+ ), respectively. The adsorption behavior can be very well described by the pseudo-second-order kinetic model and the Langmuir isotherm model. The observed affinity order of competitive ions adsorption is Pb 2+ >Ni 2+ >Cd 2+ in mmol/g. The hydrogels can be regenerated after releasing heavy metal ions and reused three times with 15% loss of adsorption capacity. Scanning electron microscope (SEM) images and Fourier transform infrared spectroscopy (FTIR) spectra before and after ion adsorption on the hydrogels revealed that the complexation between heavy metal ions and carboxyl groups on hydrogels was the main adsorption mechanism.