Separation of iron from zinc sulfate sol

It is necessary to remove Fe3+ from zinc solution in zinc production before proceeding to electrowinning, otherwise the purity of the zinc product will descend because of the iron impurity. D2EHPA does not effectively extract Fe3+ in the presence of zinc; therefore extraction of iron from zinc sulfate solution by synergetic extraction of D2EHPA mixed with LIX984N was investigated. The effects of pH, temperatures, and various extractant ratios (D2EHPA to LIX 984N ratios) on iron extraction were examined. The synergetic effects of two extractants were discussed with regard to the extraction diagrams, full factorial statistical design, selectivity function and thermodynamic study. Based on these investigations, it is found that at a temperature of 60°, D2EHPA to LIX 984N ratio of 1.5%: 95% and pH of 2, maximum value for separation factor of zinc and iron (about 2500) was obtained. The apparent standard molar enthalpies ( ∆H) for extraction of iron(III) by D2EHPA, D2EHPA with LIX 984N and LIX 984N were found to be +111.40, -35.39, +45.49 kJ/mol, respectively, which indicate that the extraction of iron species is intensified by tendency to react with a mixture of D2EHPA and LIX 984N. Finally, with respect to the McCabe-Thiele diagram, at the A:O ratio of 1:1, 2, two theoretical counter current extraction stages are sufficient to reduce the iron concentration in the aqueous solution from 1.3 g/L to less than 10 ppm.