This chapter discusses iron and cobalt and other selected compounds that exist with these specific elements. Elemental iron has been known since prehistoric times. Around 1200
B.C.
, iron was obtained from its ores; this achievement marks the beginning of the Iron Age. Even with the development of other materials, iron and its alloys remain crucial in the economies of modern countries. Iron is also critical to life. It is an essential element and a component of hemoglobin. Cobalt was known to be used by early civilizations. Minerals containing cobalt were of value to early Egyptians and Mesoptamia for coloring glass deep blue.
Iron is the fourth most abundant element (5.1%) in the earth's crust. The molten core of the earth is primarily elemental iron. Iron occasionally occurs in its pure form; however, it is abundant in combination with other elements as oxides, sulfides, carbonates, and silicates. The physical properties of iron, the metal, are profoundly affected by impurities and by changes in temperature and treatment. Iron is superior to all other elements in magnetic properties.
Iron forms a large group of materials known as ferroalloys that are important as addition agents in steelmaking. Iron is also a major constituent of many special‐purpose alloys developed for characteristics related to magnetic properties, electrical resistance, heat resistance, corrosion resistance, and thermal expansion. Other compounds and then uses are discussed.
Mining and handling of iron ores provide exposure to dusts of SiO
2
and iron oxides. Carbon monoxide is a hazard in the operation of blast furnaces for the production of pig iron. The use of fluorspar (CaF
2
) in steelmaking gives rise to gases containing SiF
4
and other fluorine‐containing substances. The manufacture of alloy steels introduces hazards attendant on the use of metals such as chromium, manganese, nickel, vanadium, tungsten, molybdenum, and copper. “Pickling” of iron containing arsenic and phosphorus liberates arsine and phosphine. Certain grades of ferrosilicon used in steelmaking decompose with explosive violence on contact with moist air, evolving various toxic gases such as acetylene, H
2
S, SiH
4
, AsH
3
, and PH
3
. Fatal intoxications have occurred from such accidents during transportation, particularly at sea.
Because iron is essential to health, iron supplements are frequently used in the treatment of iron deficiency or iron malabsorption syndromes. Iron dextran is a complex of ferric hydroxide with dextran. It is injected to treat iron‐deficiency anemia in humans and in baby pigs. Exposure occurs in manufacturing and repacking, and use is limited. Slightly more than 1000 workers may be also exposed; about half are women. A great many more workers are exposed in the manufacture of oral iron preparations.
Cobalt is a hard, silver metal with a blue sheen. Physical and chemical properties of cobalt and some of its compounds are listed.
Cobalt is a hard magnetic metal, resembling nickel in appearance, but with a pinkish tinge.
In the glass and ceramic industries small quantities of cobalt oxide are used to neutralize the yellow tint resulting from the presence of iron in glass, pottery, and enamels. Larger quantities are used to impart a blue color to these products. Cobalt oxide is used in enamel coatings on steel to improve the adherence of the enamel to the metal.
Carbonyls are prepared by direct combination of metal, generally in finely divided form, with carbon monoxide. Cobalt hydrocarbonyl may be used as a catalyst in organic reactions. There is no mention of cobalt carbonyl use for any industrial purpose.
Cobalt linoleates, naphthenates, resinates, and ethylhexoates are excellent driers for paints, varnishes, and inks. Cobalt catalysts are used for many industrial reactions.
Cobaltous sulfate is sometimes added to nickel plating baths to improve smoothness, brightness, hardness, and ductility of deposits.
Cobalt compounds, such as the chloride, are added in very small amounts to livestock feeds, salt licks, and fertilizers in many parts of the world where a cobalt deficiency exists in the soil and natural vegetation.
An important, naturally occurring cobalt coordination compound is vitamin B
12
, the anti‐pernicious anemia factor.
Hazardous exposures to cobalt fume and dust from powder falls in the electric furnace and fume from melting and pouring of cobalt metal prior to pelleting may be sustained in the milling of cobalt.
In the production of cemented tungsten carbides (carballoy), exposures are to dust and fume of cobalt, in combination with dusts of WC, TiC, and TaC. Weighed charges of cobalt metal powder, tungsten metal powder, and lampblack, together with small additions of tantalum and titanium, are ground in ball mills. The charging and emptying of the containers cause dust exposures. After pressing, the material is put through a presintering process, following which it is cut and ground. This also presents a dust exposure. The material is given a final sintering, and the tips are brazed into holders (e.g., drills, lathe tools, sawteeth); some fume may be produced in these operations. The tools are then given a final (wet) grinding.
Cobalt is a common trace element in food. It is a component of vitamin B
12
and is, therefore, an essential element.
