|Name: cadmium||Group number: 12|
|Symbol: Cd||Group name: (none)|
|Atomic number: 48||Period number: 5|
|Atomic weight: 112.411 (8) g||Block: d-block|
|CAS Registry ID: 7440-43-9||Voice: |
|Standard state: solid at 298 K||Colour: silvery grey metallic|
|Classification: Metallic||Availability: |
Nearing Zero cartoon included by kind permission of Nick Kim.
IsolationHere is a brief summary of the isolation of cadmium.
It is rare that preparation of cadmium in the laboratory should be required bacause of environmental concerns about cadmium. The isolation of cadmium is associated with zinc recovery as cadmium is an impurity in zinc ores. Most zinc production is based upon sulphide ores. These are roasted in industrial plants to form zinc oxide, ZnO. This may be reduced with carbon to form zinc metal, but in practice ingenious technology is required to ensure that the resulting zinc does not contain oxide impurities.
ZnO + C Zn + CO
ZnO + CO Zn + CO2
CO2 + C 2CO
After this process, zinc may be refined by distillation under vacuum and this process also allows the separation of any cadmium present in the crude zinc.
The other type of extraction of zinc is electrolytic. Dissolution of crude zinc oxide, ZnO, in sulphuric acid gives zinc sulphate, ZnSO4 in solution. Before electrolysis to produce zinc, the cadmium impurity and is removed as a precipitate by the addition of zinc dust as cadmium sulphate.