Cadmium bearing metals

Cadmium (2 x 10- % of the earth s crust) is derived exclusively from zinc ores the mineral greenockite, CdS, is without economic importance. Its lower b.p. enables cadmium metal, which may amount to 0.5% of crude zinc, to be separated by distillation. It is used in electroplating, in bearing metals, in fusible alloys, and in atomic reactors to absorb neutrons. 

Cadmium kad-me-om [NL, ff. L cadmia zinc oxide, ff. Gk kadmeia, ff. feminine of kadmeios Theban, from Kadmos] (1822) n. A bluish white malleable ductile toxic bivalent metallic element used in protective platings and in bearing metals. 

Activators. Activators are chemicals that increase the rate of vulcanization by reacting first with the accelerators to form mbber soluble complexes. These complexes then react with the sulfur to achieve vulcanization. The most common activators are combinations of zinc oxide and stearic acid. Other metal oxides have been used for specific purposes, ie, lead, cadmium, etc, and other fatty acids used include lauric, oleic, and propionic acids. Soluble zinc salts of fatty acid such as zinc 2-ethyIhexanoate are also used, and these mbber-soluble activators are effective in natural mbber to produce low set, low creep compounds used in load-bearing appHcations. Weak amines and amino alcohols have also been used as activators in combination with the metal oxides. 

Attack on metals can be a function of fuel components as well as of water and oxygen. Organic acids react with cadmium plating and 2inc coatings. Traces of H2S and free sulfur react with silver used in older piston pumps and with copper used in bearings and brass fittings. Specification limits by copper and silver strip corrosion tests are requited for fuels to forestall these reactions. 

Other Metals. Materials employed for hydrodynamic oil film bearings are primarily those covered above, but silver, 2inc, and cadmium find some use. 

Cadmium, as cadmium oxide, is obtained mainly as a by-product during the processing of zinc-bearing ores and also from the refining of lead and copper from sulfide ores (USPHS 1993). In 1989, the United States produced 1.4 million kg of cadmium (usually 0.6 to 1.8 million kg) and imported an additional 2.7 million kg (usually 1.8 to 3.2 million kg). Cadmium is used mainly for the production of nickel-cadmium batteries (35%), in metal plating (30%), and for the manufacture of pigments (15%), plastics and synthetics (10%), and alloys and miscellaneous uses (10%) (USPHS 1993). 

In mammals, cadmium inhibits copper absorption across the intestinal mucosa (Aaseth and Norseth 1986). Intercorrelations of copper with cadmium and zinc in livers of polar bears (Ursus maritimus) are probably mediated by metallothioneins, which may contain all three metals (Braune etal. 1991). In rats, copper protects against nephrotoxicity induced by cadmium, provided that copper is administered 24 h prior to cadmium insult. Specifically, rats given 12.5 mg Cu/kg BW by way of subcutaneous injection 24 h before receiving 0.4 mg Cd/kg BW — when compared to a group receiving Cd alone — did not have excessive calcium in urine and renal cortex or excessive protein in urine. Thus, 2.8 mg Cu/kg BW protects against 0.25 mg Cd/kg BW (Liu et al. 1992). 

Babbit metal. A soft alloy of metals such as tin, silver, arsenic, and cadmium combined with a lead base. It can be cast or used as a coating on steel bearings to form an oil-hke coating that reduces friction. Used to make oil-less bearings. 

Lubricant-film bearings primarily employ the white-metal babbitts, and a variety of copper and aluminum alloys. Since steel and cast iron structural parts are frequently used as oil-film bearing materials, they are also briefly covered along with silver, zinc, and cadmium which find limited use. For small bearings and bushings in light-duty and intermittent service, materials with self-lubricating properties are commonly used. 

A general lack of effectiveness has been noted for several MCAs in the suppression of GI-uptake of cadmium in mice. In this study the MCAs, the metal-binding capacity was 2-6.8 mM g 1, ranged from DTPA immobilized via amide bond formation to finely divided aminopropyl-silica, xanthates of polyvinylalcohol and various polysaccharides, and a dextran bearing ethylthiol moieties produced by action of ethylenesulphide on dextran209. ... 

Uses Cadmium (Cd) (L. cadmia Gr. kadmeia, ancient name for calamine, zinc carbonate) was discovered by Stromeyer in 1817 through an impurity in zinc carbonate. Cadmium most often occurs in small quantities associated with zinc ores, such as sphalerite (ZnS). The important compounds used in industry are cadmium oxide (CdO), cadmium chloride (CdCl2), cadmium nitrate (CdfNCRh), cadmium sulfide (CdS), and cadmium sulfate (CdSC>4). Greenockite (CdS) is the only mineral of any consequence bearing cadmium. Cadmium is also obtained as a by-product in the treatment of zinc, copper, nonferrous metal industry, and lead ores. Cadmium is a highly toxic heavy metal that forms complex compounds with other metals and elements. 

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