Selective removal of chromates by macroporous exchanger Amberlyst A-21

Sorption studies of chromate on weakly basic macroporous anion exchanger Amberlyst A-21 were performed as a function of pH (2 - 9), temperature (20 - 40 degrees C) and concentration (0.4 - 80 mmol.l(-1)). Chromate sorption was observed to decrease with the increase in initial pH of the solution, with a sorption maxima at pH 2 and increased with the increase in temperature. The changes in pH and in the ratio of choride ions released to chromate ions sorbed suggested that the anion exchange process was accomanied by hydrolysis and Donnan invasion. The FTIR spectra and isoeteric heat of sorption besides showing the hydrolysis / Donnan invasion of resin under different experimental conditions of concentration, pH and temperature also showed the dimerization of the chromate species inside the resin phase.