Simultaneous Determination Of Cadmium, Cobalt, Copper, Lead, Mercury and Nickel in Zinc Sulfate Plant Electrolyte Using Liquid Chromatography with Electrochemical and Spectrophotometric Detection

The current efficiency (cost) of electrolytic production of high purity metallic zinc from zinc sulfate plant electrolyte is critically dependent on the concentration of a number of trace elements. The matrix, containing a very large concentration excess of zinc sulfate in concentrated sulfuric acid presents difficulties for determining low concentrations of other metals with many analytical methods. In this work it is shown that Cd, Co, Cu, Pb, Hg and Ni impurities may be simultaneously determined at concentrations less than or equal to 1 ppm using a combination of solvent extraction, high performance liquid chromatography and electrochemical or spectrophotometric detection. Solvent extraction utilizes the formation of pyrrolidine dithiocarbamate complexes, which after removal of zinc complexes and excess ligand on an anion exchange column can be separated on a C-I8 reverse phase chromatographic column and detected by UV/Visible spectrophotometric or electrochemical detection. Other combinations of chromatographic and detection procedures were thwarted by the very large concentration excess of zinc and other problems.