Valahia University

Cobalt and its compounds

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Cobalt is a compound that occurs in nature. It occurs in many different chemical forms. Pure cobalt is a steel-gray, shiny, hard metal. Cobalt used in industry is imported or obtained by recycling scrap metal that contains cobalt. It is used to make alloys (mixtures of metals), colored pigments, and as a drier for paint and porcelain enamel used on steel bathroom fixtures, large appliances, and kitchenwares. Small amounts naturally occur in food. Vitamin B12 is a cobalt-containing compound that is essential for good health.. Some natural sources of cobalt in the environment are soil, dust, and seawater. Cobalt is also released from burning coal and oil, and from car and truck exhaust. Cobalt enters the environment from natural sources and from the burning of coal and oil. Cobalt stays in the air for a few days. Pure cobalt does not dissolve in water, but some of its compounds do. Everyone is exposed to cobalt at low levels in air, water, and food. People who live near hazardous waste sites containing cobalt may be exposed to higher levels of this chemical. Food is another source of exposure to cobalt.

Key words: cobalt, air, water, soil, food

Cobalt is a brittle, hard metal, resembling iron and nickel in appearance. It has a metallic permeability of about two thirds that of iron. Cobalt tends to exist as a mixture of two allotropes over a wide temperature range. The transformation is sluggish and accounts in part for the wide variation in reported data on physical properties of cobalt. Cobalt has also been used as a treatment for anemia, as it causes red blood cell production

Cobalt can stay for years in water and soil. It can move from the soil to underground water. Plants take up cobalt from the soil. OSHA exposure limit: 0.1 0.1mg/m³ for cobalt in workplace air for an 8-hour workday, 40-hour work week. American Conference on General and Industrial Hygiene (ACGIH) occupational exposure limit: 0.02 mg/m³ for cobalt for an 8-hour workday, 40-hour workweek. National Institute for Occupational Safety and Health (NIOSH) occupational exposure limit: 0.05 mg/m³ for cobalt for a 10-hour workday, 40-hour workweek.

Cobalt does not occur naturally as a base metal, but is a component of more than 70 naturally occurring minerals, including various sulfides, arsenides, sulfoarsenides, hydrates, and oxides. The most common cobalt minerals are the arsenide CoAs2–3 (smeltite), the arsenosulfide CoAsS (cobaltine), and the sulfide Co3S4 (linneite) (IARC, 1991).

Sources of environmental cobalt are both natural and anthropogenic (Barceloux, 1999). Natural sources include erosion (wind-blown continental dusts), weathering of rocks and soil, seawater spray, volcanoes, forest fires, extraction by plants, and continental and marine biogenic emissions. The worldwide estimate for atmospheric cobalt emissions is 5350–6170 tonnes per year (Lantzy & Mackenzie, 1979, Nriagu, 1989). Cobalt compounds have been found to occur naturally in seawater, surface water, spring water, and groundwater (Smith & Carson, 1981).

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