Removal of Zinc(II) and Iron(II) from Spent Hydrochloric Acid by Means of Anionic Resins

Anion exchange removed Zn(II) effectively from a spent hydrochloric acid with the practical exchange capacity of 0.62-0.76 mol/L Zn(II). The main species retained was monovalent ZnCl3- (80-90%) in the case of strongly basic anion exchangers, whereas in the case of weakly basic anion exchanger, its contribution was only 40%. Regeneration with water gave only dilute (15-20 g/L) Zn(II) solution contaminated with Fe(II). Improved regeneration with 6 M HCl and 25% ammonia solution eluted a Zn(II) solution of 42-100 g/L with iron(II) content below 0.1 g/L. Acid retardation provided effective separation of HCl and Fe (II) using the strongly basic Lewatit VP OC 1071. The productivity of the separation column amounted to 50-60 kg/(m^3 h) of iron(II) with a reasonable separation factor of Fe(II)/HCl equal to about 10. A new idea of acid retardation mechanism is proposed, in which two Donnan equilibria are considered: normal FeCl2 exclusion and HCl partition due to the membrane potential and salting-out effect.