Adsorption characteristics of Cu(II) from aqueous solution onto poly(acrylamide)/attapulgite composite

Batch adsorption experiments were carried out to remove Cu(II) ions from its aqueous solutions using a poly(acrylamide)/attapulgite composite. The different parameters effecting on the adsorption capacity such as contact time, initial metal ion concentration, temperature and pH of the solution have been investigated. The adsorption kinetic experiments revealed that there are three stages in the whole adsorption process. It was found that Cu(II) adsorption onto the composite followed pseudo-second-order kinetics and were mainly controlled by the film diffusion mechanism, along with a considerable contribution of the intra-particle diffusion mechanism. Analysis of adsorption results obtained at different temperatures showed that the adsorption pattern on the composite well followed the Langmuir, Freundlih and D-R isotherms, and the characteristic parameters for each adsorption isotherm were also determined. The adsorption process has been found endothermic in nature and thermodynamic parameters have been calculated. The analysis for variations of IR spectra and the values of the mean free energies of adsorption (Ea) demonstrated that the chelation model should be the dominating adsorption mechanism. The species of copper salts can affect the adsorption capacity of the composite, which are in the order of CuSO4 > CuCl2 > Cu(NO3)2 ≫ Cu(CH3COO)2.