During the past two decades, technological advances have allowed considerable interchangeability among the various grades, particularly the so-called chemical grade which can be utilized in all three industries. It has been classified into three general grades associated with their use and chromic oxide content: metallurgical (greater than 46%), chemical (40–46%) and refractory (less than 40%) grades ( Papp, 1985). Compounds with solubilities towards the middle of this range are not easily classified, and technical-grade compounds, such as the various zinc chromates, can have a wide range of solubilities.Ĭhromite ore consists of varying percentages of chromium, iron, aluminium and magnesium oxides as the major components. Hexavalent chromium compounds classed as insoluble include barium chromate (4.4 mg/l at 28☌) and lead chromate (0.58 mg/l at 25☌) ( Windholz, 1983 Weast, 1985). Examples of soluble hexavalent chromium compounds are sodium chromate (873 g/l at 30☌) and potassium chromate (629 g/l at 20☌). In laboratory studies, solubilization depends on, e.g., the medium used in in-vitro tests for human exposures, solubility is related to the chemical environment in the respiratory tract. There is thus no general agreement on the definition of solubility: in practice, the aqueous solubility of Cr compounds has been classified as prompt (1 min) and short-term (30 min) ( Van Bemst et al., 1983).

Hexavalent chromium compounds are customarily classed as soluble or insoluble in water such a classification is useful in industry but might not be relevant to determining the biological properties of a compound. Data on solubility refer to saturated solutions in water or other specified solvents. Known physical properties of some of the chromium compounds considered in this monograph are given in Table 2.

Chemical and physical properties of pure substances

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