Separation of iron from zirconium in concentrated hydrochloric acid solutions by solvent extraction

Abstract

In order to produce high purity zirconium by removing iron by liquid-liquid extraction, several types of commercial extractants have been chosen, examined and compared. The extraction of iron by extractants involving compound formation, such as di(2-ethylhexyl)phosphoric acid (D2EHPA), is effective only in dilute acid solutions (pH > 0). However, a synergistic effect is obtained using a mixture of an acidic extractant (D2EHPA) and a chelating extractant (Kelex 100), which extracts iron effectively at high hydrochloric acid concentrations. For extractants involving solvation, such as tributyl phosphate (TBP), the percentage extraction of iron increases with increasing hydrochloric acid concentrations. However, the separation factor of iron to zirconium is poor for the extractants involving compound formation and solvation. The extraction of iron by extractants involving ion association, such as Aliquat 336, has therefore been studied. Excellent results have been obtained in separating iron from zirconium, and the stripping of iron can easily be achieved using dilute HCl as the stripping solution. A continuous mixer-settler operation comprising one extraction stage and two stripping stages has been performed using 5% Aliquat 336 in toluene as the solvent. Iron is removed from 1 g/l to a few milligrammes per litre and the zirconium concentration in the aqueous phase remains unchanged.