Studies of the adsorption thermodynamics and kinetics of Cr(III) and Ni(II) removal by polyacrylamide

Polyacrylamide (PAA) was investigated as an adsorbent for the removal of Ni(II) and Cr(III) metal ions from synthetic aqueous solutions. Different variables affecting the adsorption capacity of the adsorbent, i.e., contact time, pH of the sorption medium, metal ion concentration and temperature of the solution, were investigated by batch sorption experiments. The adsorption equilibrium data was best fitted by the Langmuir isotherm model. The maximum adsorption capacities were found to be 84.03 and 32.67 mg g(-1) polyacrylamide for Cr(III) and Ni(II), respectively. Three kinetic models, i.e., the pseudo-first-order, pseudo-second-order and intra-particle diffusion equations, were selected to follow the adsorption process. The kinetic parameters, i.e., rate constants, equilibrium adsorption capacities and related correlation coefficients, for each kinetic model were calculated and are discussed. It was indicated that the adsorption of both ions onto polyacrylamide could be described by the pseudo-second-order kinetic model. Various thermodynamic parameters, such as Delta H, Delta S and Delta G, were also evaluated and it was found that the sorption was feasible, spontaneous and exothermic.