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Article updated on 03/03/20 by Priyom Bose
In 1817, German chemist Friedrich Strohmeyer discovered cadmium from an impurity of zinc carbonate (ZnCO3). Cadmium derives from the Latin term ‘cadmia’ and the Greek word ‘kadmeia’, which are ancient names for calamine.
Cadmium is a soft ductile metal with a bluish-silvery white crystalline physical appearance. It is easily cut with a knife and small additions of zinc make it very brittle. It resembles tin and is like zinc in many respects.
Electrolytic cadmium is 99.95% pure and is obtained primarily as a by-product of the zinc industry by treating the flue dust and fumes from the roasting of the ores. As an example, flue dust on average can contain approximately 600 kg of cadmium per metric ton of dust. Half the world’s production of cadmium is carried out in the United States.
Industrial Applications of Cadmium
- Cadmium is implemented as an alloying element in soft solders and fusible alloys.
- Adding small quantities of cadmium to copper gives higher strength, improved hardness and wear resistance, however, decreases the electrical conductivity. Copper containing 0.5 to 1.2% cadmium is commonly referred to as cadmium copper or cadmium bronze. Hitenso is a commercially available cadmium bronze and exhibits 35% greater strength than hard-drawn copper and 85% the conductivity of copper. Conductivity bronze another commercially available copper used extensively for electric wires, contains 0.8% cadmium and 0.6% tin and exhibits a conductivity 50% that of copper.
- Cadmium is employed in bearing alloys with low coefficients of friction
- Cadmium is used as a white corrosion-resistant plating metal (as an anode).
- Cadmium is used as a shield against neutrons in atomic equipment. However, gamma rays are emitted when the neutrons are absorbed, and these rays require an additional shielding of lead.
- Electronic applications requiring high corrosion resistance.
- Electroplating for the corrosion resistance coating for iron or steel, where a 0.008 mm (0.0003 in) is equivalent in effect of a zinc coating 0.025 mm (0.001 in). Cadmium electroplated in this application is denser than zinc and harder than tin. However electroplated coatings are subject to hydrogen embrittlement. For this reason, aircraft parts are generally coated by the vacuum process.
Commercial Uses of Cadmium Compounds
- Cadmium nitrate Cd(NO3)2 (a white powder) is used for making cadmium yellow and fluorescent pigments. It can also be used as a catalyst.
- Cadmium compounds are used in black and white television phosphors and the blue and green phosphors for color television tubes.
- Cadmium sulfide (CdS) is used for yellow pigment and when mixed with cadmium selenide (CdSe) (a red powder) gives a bright-orange pigment.
- In the semiconductor industry, sulfate in conjunction with cadmium is used to grow cadmium sulfate crystals in plate and rod form.
Impacts of Cadmium on Human Body and Environment
Cadmium is a known carcinogen. Cadmium and solutions of its compounds are extremely toxic and caution is required to not create dust or fumes. Cadmium can cause several health issues, including:
- Stomach pains
- Severe vomiting
- Bone fracture
- Psychological disorders
- Damage to reproductive systems, central nervous system, immune system, and possibly DNA.
Cadmium waste from industries contaminates the soil, air (burning of fossil fuels) and water. Cadmium can also enter the food supply when plants take in the element through the soil. Organisms that live in soil such as earthworms are highly vulnerable to cadmium poisoning, which can harshly affect the entire soil ecosystem. Marine life, especially organisms that live in freshwater, including mussels, oysters, shrimp, lobsters, and fish tend to be vulnerable to cadmium poisoning.
Sources of Cadmium
Cadmium does not abundantly occur naturally. Cadmium (Cd) is often associated in small quantities (0.1–1%) with zinc ores such as sphalerite (ZnS), however, the only commercially viable ore of the metal is greenockite (CdS), which theoretically contains 77.7% cadmium. Greenockite occurs as a yellow powdery form in the zinc ores of Missouri.
Cadmium mineral deposits are also found in Colorado, Illinois, Washington, Utah, Bolivia, Guatemala, Hungary and Kazakhstan. Mostly, cadmium in use is a by-product of treating zinc, copper and lead ores. The Minerals Education Coalition has explained that cadmium is mainly produced in places where zinc is refined as opposed to mined. Producers of cadmium include:
- The United States
- The Netherlands
- The United Kingdom