Development of a process for the recovery of zinc sulphate from hot-dip galvanizing spent pickling liquor via two solvent extraction steps

A process for zinc sulphate recovery from the spent pickling liquor of a hot-dip galvanizing plant is developed. Two solvent extraction steps are used, the first with tributyl phosphate to selectively extract zinc chloride from the spent liquor and the second with di-2-ethylhexyl phosphoric acid (D2EHPA) to transfer zinc from a chloride to sulphate media. The final product of the process is found to meet the specification of low chloride concentration required for electrowinning when the loaded D2EHPA was washed with water. Mathematical simulation was used to further develop the process. Based on a feed concentration of 120 g/L Zn, 60 g/L Fe(II) and 1 mol/L HCl, the simulation predicts that 99.2% zinc can be recovered, yielding a product with 106 g/L Zn.