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Cadmium

cadmium

When the MMTA was formed in 1973 Cadmium was one of the first seven minor metals for which a norm was devised. Supply generally falls into two main categories –  4N (Cd 99.99% min.) and 3N5 (Cd 99.95% min).

Notice – you can read our new article investigating the latest uses of Cadmium here.

The majority of supply arises when Cadmium is cleaned from Zinc concentrates and thus typical large producers are found in South America (Peñoles of Mexico). Perhaps the largest supplier from CIS is Kazzinc (Kazakhstan), but good material recuperated from residues originates from Almalyk in Uzbekistan. We have illustrated some of this in the photos attached and this usually grades at 4N7 or better in the form of 10-12 kg net bars.

Of late the main swing buyers have been from China for their growing Nickel – Cadmium (Nicad) battery production. Meanwhile Cadmium – despite its bad press in terms of toxicity – is still virtually unsubstitutable for the yellow colour in indelible paints (e.g. car paint).

Cadmium facts

Cadmium was discovered in Germany in 1817 by Friedrich Strohmeyer.  He found the new element within an impurity in zinc carbonate (calamine) and for 100 years Germany remained the only important producer of the metal.

Cadmium is a silvery metal that tarnishes in air, and is soluble in acids but not alkalis. Cadmium-containing ores are rare and when found they occur in small quantities.  Greenockite (CdS), the only cadmium mineral of importance, is nearly always associated with sphalerite (ZnS). Consequently, cadmium is produced mainly as a by-product from mining, smelting, and refining sulfide ores of zinc, and to a lesser degree, lead and copper. Small amounts of cadmium are produced from secondary sources, mainly from dust generated by recycling iron and steel scrap.  Production in the United States began in 1907 but it was not until after World War I that cadmium came into wide use.

Cadmium also has the physical property of being able to absorb neutrons. As a result, it is used in nuclear reactor control rods to dampen the nuclear reaction and keep the fission reactions under control.

It is used in rechargeable batteries, alloys, pigments, coatings, plating and as stabilizers for plastics, but because of its toxicity these uses are being phased out wherever possible.  It is used in some of the lowest melting alloys and due to a low coefficient of friction and very good fatigue resistance, it is used in bearing alloys.

Cadmium finds use in electroplating and many kinds of solder contain this metal. Compounds containing cadmium are used in black and white television phosphors and also in the blue and green phosphors for colour television picture tubes.

Cadmium is 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 forms various salts, with cadmium sulfide being the most common. This sulfide is used as a yellow pigment. The metal itself as use in some semiconductors such as cadmium sulfide, cadmium selenide, and cadmium telluride, which can be used for light detection or solar cells. Also, HgCdTe is sensitive to infrared.  Another mass use of Cadmium is in Nickel-Cadmium batteries

Cadmium is well recovered via the recycling of nickel-cadmium batteries, which is required by law in some countries so that the cadmium is not discarded into the environment.

Atomic no.
Relative atomic mass
Melting point
Boiling point
Density
Electrical resistivity
Young’s modulus
Heat capacity
Abundance
Thermal conductivity
48
112.411
321.0 °C
767 °C
8650 Kgm-3
72.7 nΩm
50 GPa
26.020 J/K/mol
0.11 ppm
96.8 W/m/K