The Efficiency Improvement of Electrodeposition of High-Purity Zn by a Proper Electrolyte Solution Preparation from Spent Pickling Liquor by Anion-Exchange Separation

A better procedure for recovering high-purity Zn from the SPL solution has been devised. To provide a suitable electrolyte for the efficient cathodic deposition of high-purity Zn, complete anion-exchange purification had been done by chromatographic technique. The process was then continued by galvanostatic electrodeposition to determine the efficiencies. As the SPL needs to be neutralized before any attempts of Zn electrodeposition, NaCl may provide the required source of Cl- ions for complex formation. The equilibrium studies of the anion-exchange distribution in such solutions showed similar tendencies to those already known in HCl media. The anion-exchange chromatographic separation was devised – with the finer tuning of the parameters – according to the equilibrium result, but other physical parameters were also examined for improving the efficiency of separation and the recovery of Zn. The devised anion-exchange separation in chloride media can purify the SPL, containing Zn as the valuable component and higher concentrations of Fe as the main impurity. The most important impurities (Fe, Mn, Ni, Al and Co) can be efficiently separated in a dissolved state. At the same time, Zn is sorbed in the strongly basic anion[1]exchange resin at a moderate Cl- ion concentration (~ 2 M). Stirring with Fe chips provides a reduction of iron to the Fe(II) state. The remaining problem is minor copper contamination in the same effluent fraction as Zn, which however can be eliminated by a simple additional step of cementation or directly by pre-electrolysis.