Efficient removal of chromium (III) ions from aqueous solutions using sodium polyacrylate hydrogel powder: Characterization, kinetics, and regeneration studies

In this study, sodium polyacrylate hydrogels in powder form (PANa) were prepared by swelling in distilled water and then were used to remove chromium (III) ions from aqueous solution. The characterization of PANa powder before and after adsorption was carried out by FTIR, MEB and EDAX techniques. The effect of physicochemical conditions of adsorption medium such as contact time, initial pH, initial Cr (III) concentration, adsorbent mass and temperature on the adsorption capacity of PANa powder was examined. The adsorption equilibrium was reached at about 60 min giving an adsorption rate equal to 94 %. The maximum PANa adsorption capacity (the adsorbent mass 0.035 g, heavy metal concentration 150 ppm and pH = 5) is 269 mg / g. The study of adsorption kinetics was found to follow Lagergren pseudo second order while the experimental data obey Langmuir model. The acquired thermodynamic parameters ( Delta G degrees , Delta H degrees and Delta S degrees ) have indicated that the nature of adsorption process is spontaneous and endothermic. Finally, the regeneration study has revealed that PANa powder can be recycled for six cycles by desorption in a nitric acid solution (0.01 M).