Removal of Cr(VI) oxy-anions from aqueous solution by sorption into poly(acrylamide-co-maleic acid) hydrogels

The dynamic removal of hexavalent chromiuim by poly(acrylamide-co-maleic acid) hydrogels was studied by a batch equilibrium technique at 35 degrees C. Various kinetic and adsorption parameters such as rate constant for sorption, intraparticle diffusion rate constant, Langmuir constant, and adsorption capacity have been evaluated. The sorption process follows the Langmuir-type behavior and extent of sorption of Cr(VI) ions depends upon the composition of co-polymeric gels, presence of other ions in the solution, and temperature of the system. Relatively higher temperature favors the sorption process. The activation energy was found to be -20.369 kJ mol(-1). Finally, various thermodynamic parameters have also been calculated to elucidate the mechanism involved in the sorption process. The positive enthalpy change indicates the endothermic nature of the process. The presence of fluoride ions causes a decrease in the degree of sorption of Cr(VI). Finally, the sorption of Cr(VI) into the copolymeric sorbent has been explained on the basis of coordination between electron rich O and N atoms of sorbent molecules and the Cr(III) molecules. Moreover, H-bonding interactions also seem to contribute to the sorption process.