Removal of Cu2+ ions from aqueous solutions using starch-g-poly(acrylic acid)/rice husk ash: adsorption kinetics

A series of superabsorbent hydrogels composites based on the biopolymer starch (St) grafted poly(acrylic acid) and rice hull ash (RHA) were synthesized by solution polymerization according to the procedure described Azevedo et al.1, with the interest in the study of these systems as alternative adsorbents the of metal ions from aqueous solutions. The hydrogels were characterized by evaluated for adsorption kinetics for the Cu2+ ions. In order to examine the controlling mechanism of adsorption processes such as mass transfer and chemical reaction, the pseudo first order and pseudo-second order equations were used to test the experimental data. Table 1 presents results obtained for the pseudo first-order and pseudo second-order model. The correlation coefficients R2 for the pseudo-second-order kinetic plots for all the hydrogels studied are above 0.997, suggest that the pseudo-second-order kinetic model can describe well the experimental data, and meaning that the adsorption process of Cu2+ onto these adsorbents is probably controlled by the chimisorption phenomenon2. Moreover, the calculated equilibrium adsorption capacities qe,cal also agree with the experimental data in the case of pseudo-second order kinetics. In addition, it is obvious that when 10 wt% RHA is introduced into the hydrogel, the resulting adsorbent has faster initial adsorption rate and higher final adsorption capacity. That is, an appropriate addition of RHA into the polymeric networks can promote the adsorption of Cu2+ onto the hydrogels.