Chromium (VI) removal from aqueous solutions by purolite base anion-exchange resins with gel structure

The removal of Cr (VI) from aqueous solution using two strong base anionic resins with gel structure, Purolite A-400 (styrene-divinylbenzene matrix) and Purolite A-850 (acrylic matrix) was investigated in batch technique. The sorption efficiency was determined as a function of phases contact time, solution pH, resin dose, temperature and initial Cr (VI) concentration. The percentage of Cr (VI) removed reaches maximum values (up to 99 %) in the pH range 4 - 5.3 under a resin dose of 6 g/L and of Cr (VI) concentration up to 100 mg/L. An increase in temperature has a positive effect on the Cr (VI) sorption process. The equilibrium sorption data were fitted with the Freundlich, Langmuir and Dubinin-Radushkevich isotherm models, using both linear and nonlinear regression method. The Langmuir model very well verifies the experimental data and gives the maximum sorption capacity of 120.55 mg Cr (VI)/g and 95.82 mg Cr (VI)/g for A-400 and A-850 resins, respectively. The thermodynamic study and mean free energy of sorption values calculated using Dubinin-Radushkevich equation indicated the sorption is a chemical endothermic process. The kinetic data were well described by pseudo-second order kinetic equation and the sorption process is controlled by external (film) diffusion and intraparticle diffusion.