Removal of zinc(II) from spent hydrochloric acid solutions from zinc hot galvanizing plants

The extraction of zinc(II) from spent pickling hydrochloric acid solutions obtained in zinc hot-dip galvanizing plants was studied. Tributyl phosphate and its mixtures with di(2-ethylhexyl)-phosphoric acid (DEHPA), HOE F 2562, ALIQUAT 336, ALAMINE 304, ALAMINE 308, ALAMINE 310, ALAMINE 336, and CYANEX 301 were used as extractants. The acidic extractants (CYANEX 301 and DEHPA) did not extract both zinc(II) and iron(III) from 10% HCl. Precipitation occurred or stable emulsions were formed when ALAMINE 304, ALAMINE 308, and ALAMINE 310 were used. Each of the other reagents coextracted both zinc(II) and iron(III). The latter had to be reduced to iron(II) prior to extraction. Tributyl phosphate and HOE F 2562 showed the best extraction performance. ALAMINE 336 and ALIQUAT 336 induced the oxidation of iron(II) to iron(III), thus enhancing the coextraction of iron. Zinc(II) could be effectively stripped from the loaded phases containing TBP and HOE F 2562 with water. A higher efficiency of stripping was observed in the second stage.