The effects of certain impurities and their interactions on zinc electrowinning

“The effects of germanium, antimony, arsenic, cobalt, glue, and free acid concentration were studied on both commercial and synthetic electrolytes. The effects of a single factor and the combined effects of multiple factors were elucidated. The temperature, zinc concentration, and current density were also varied. It was found that the acid concentration was the most critical factor when impurity levels were at normal plant solution concentrations. The ranges where the effect of the impurity became apparent were: greater than 20 ppb for antimony; 40 ppb for germanium; 120 ppb for arsenic; and 7-8 mg/l for cobalt for a solution containing 65 g/l zinc and 100 g/l free sulfuric acid. At higher levels of acid, the acceptable level of impurity declined markedly. Glue additions were found to counteract the effects of antimony and germanium, but did little to counteract the effects of cobalt and arsenic. The level of acid was found to be especially critical when cobalt and arsenic were in the electrolyte. Cobalt and arsenic exhibited synergism and lower current efficiencies were obtained for arsenic- cobalt combinations than expected. A factorially designed experiment was conducted to quantify the effects observed by one factor at a time testing. The effects of the various factors on electrode polarization were examined using cyclic voltammetry. Levels as low as 0.02 mg/l Ge and Sb and 0.1 mg/l Co cause measurable changes in polarization. The polarization characteristics of combinations of impurities and glue can be used to determine the optimum levels of glue addition. The structure of the deposits was examined using x-ray diffraction and scanning electron microscopy”--Synopsis, page iii