SELECTIVITY REVERSAL AND DIMERIZATION OF CHROMATE IN THE EXCHANGER AMBERLITE IRA-400

Chromate sorption on the strong basic anion exchanger, Amberlite IRA-4 00 is studied as function of pH (2-11), temperature (20-40 degrees C) and different initial concentrations (1.030-15.449 mmol/l). The sorpti on increases with the decrease in pH and increase in temperature. The ratios of chloride released/chromate sorbed are determined, which are found to decrease with the decrease in pH of the solution, while the e ffect of temperature on mole ratios is negligible. It is suggested tha t the chromate sorption takes place initially as CrO42- followed by HC rO4-. The differential isosteric heats of adsorption, <Delta(H)over ba r>, are also computed which show the process to be endothermic in natu re. IR spectra of chromate sorption on the chloride form of the resins have been studied as a function of pH at 20 degrees C. These spectra reveal the dimerization of HCrO4- to Cr2O72- at lower pH inside the ex changer.