Precipitation of impurity ions from zinc leach solutions with high iron contents - A special emphasis on cobalt precipitation

The precipitation of iron from zinc leach solutions using ammonium peroxodisulfate (APS) as an oxidant was studied and evaluated. The effects of important process parameters, such as pH, temperature and concentration of oxidant, on the precipitation of impurity ions and on zinc loss were investigated. The results indicated that pH and temperature primarily affected the compositions of the iron precipitates and that the concentration of oxidant affected the amount of iron and other impurity ions that were removed. Under process conditions of pH 1.5, 90 °C and a 30% volume of APS/leach solution (0.5 M), the removals of Fe, Mn and As were 99.95%, 100% and 99.87%, respectively. Notably, cobalt was also precipitated as cobalt oxy-hydroxide (CoO·OH) under suitable precipitation conditions. It is possible to precipitate Co with rates between 70% and 90% depending on the concentration of APS. The Co precipitation tests revealed that higher Co concentrations in the pregnant solution help to precipitate Co at higher rates using this method.