Cadmium is one of the byproducts from zinc hydrometallurgy process. The cadmium and other impurities are replaced by zinc powder during zinc electrolyte purification, getting purification residue. This cadmium material, cadmium sponge we call it, contains about 1-3% impurities like lead, copper, thallium and zinc, etc. Cadmium from spent cadmium-nickel battery is also an important source. Wherever the cadmium is from, the cadmium material has to be refined for recycling due to its hypertoxicity, either in oxide or salts.

The sponge cadmium gets oxidized in air easily. It can be reduced by coal at low temperature reduction atmosphere (500-550 °C). The reduction process produces crude cadmium and reduction slag containing cadmium less than 2%. The reduction slag can be quenched or be sliced by disc slicer to cadmium recovery. The crude cadmium is then refined by vacuum distillation furnace to high purity cadmium (≥99.995%). The distillation residue is regularly discharged through furnace bottom and collected for secondary treatment by the distillation furnace.

Characteristics

1.   Electricity consumption of distillation furnace, 500-600kW·h/ ton cadmium.

2.   High purity (≥99.995%) cadmium is produced by distillation, no emission of waste gas/water/residue.