Chromate ion-exchange process at alkaline pH

Abstract

The chromate ion-exchange recovery process is always carried out at acidic pH because of its much higher chromate removal capacity at acidic pH as opposed to alkaline pH. However, acidic pH operation always gives rise to early, gradual chromate breakthrough during conventional fixed-bed column runs. Possibility of alkaline pH operation, which gives self-sharpening type chromate breakthrough during column runs, has been studied in detail. A new polystyrene matrix resin with relatively high degree of crosslinking was found to have high chromate selectivity at alkaline pH. This enhanced chromate selectivity is due to the resin's increased hydrophobicity. Particularly at low ionic strength of cooling water, alkaline pH operation with this new resin may offer higher chromate selectivity compared to conventional acidic pH operation.