Cadmium is most often found in nature in zinc compounds. These zinc compounds commonly occur in sulfide ores. Cadmium is collected, and isolated, as a by product of zinc processing. The first step of cadmium isolation is to remove the zinc and cadmium compound from the ores. The compounds are isolated by smelting zinc oxide with carbon, through electrolysis, or through treatment with sulfuric acid. The cadmium ‘contaminant’ can then be removed from the zinc metal through the process of vacuum distillation. During this process the distillation procedure uses pressure above the liquid mixture, and the volatile liquids are evaporated. The principle of vacuum distillation is based on the fact that when the vapor pressure of a liquid exceeds the ambient pressure, the liquid will begin to boil. If the zinc has undergone smelting, and cadmium sulfate is formed, then the cadmium is precipitated out of the solution through electrolysis.
