Cadmium occurs as a minor component in most zinc ores and therefore is a byproduct of zinc production. Cadmium was used for a long time as a pigment and for corrosion resistant plating on steel. Cadmium compounds were used to stabilize plastic. With the exception of its use in nickel-cadmium batteries and cadmium telluride solar panels, the use of cadmium is generally decreasing in its other applications. These declines have been due to competing technologies, cadmium’s toxicity in certain forms and concentration and resulting regulations . Although cadmium is toxic, one enzyme, a carbonic anhydrase with cadmium as reactive center has been discovered.
Most cadmium used in industry is recovered from sphalerite (zinc sulfide), the principle ore of zinc where cadmium atoms replace some of zinc atoms in the sphalerite. On a worldwide basis, zinc ores around the world average about 1/400th as much cadmium as zinc. Although some zinc deposits have a higher cadmium/zinc ratio than others, those countries producing zinc from zinc ores also have the potential to produce significant quantities of cadmium. The cadmium is removed when zinc metal is purified in a refinery.
Cadmium ore beneficiation is therefore produced in countries where zinc is refined, not necessarily in the countries where zinc ore is mined. China, Japan, and Korea are the world’s largest producers, with Mexico, the United States, the Netherlands, India, the United Kingdom, Peru, and Germany next. About 15 other countries produce smaller amounts.
Cadmium is useful in a small number of other applications. Cadmium sulfide (also called cadmium yellow) is used as a paint pigment. Cadmium is used to make low-temperature melting alloys, such as solder and Wood’s Metal for indoor sprinkler systems. The latter is an alloy of 50%Bi, 25%Pb, 12.5% Sn, and 12.5%Cd which melts at about 160 degrees Fahrenheit, the temperature of a very hot shower. Cadmium ore flotation compounds are used both in black and white and color television tubes. It is used as a stabilizing compound in plastics.
Cadmium is mainly a byproduct of the production of zinc metal from sulfide ore concentrates. So typical cadmium ore crushing is also the crushing of zinc ores. The mined zinc ores are crushed and ground by cadmium ore crushers and cadmium mills to liberate the zinc sulfide particles from the waste host rock. The ground ore is usually treated by a differential flotation process to separate the zinc-bearing particles from the waste rock, yielding a high-grade zinc concentrate and waste tailings.