Trivalent Chromium Compounds

One concern is that Cr(III) and Al(III) compounds are both capable of forming octahedral complexes, and the introduction of these ions into an aqueous electrolyte will interfere with conversion of the hydrous alumina into the aluminum hydroxide film by bonding to the active film sites. Therefore, similar to their application in hexavalent chromate conversion coatings, fluoride ions are used to remove aluminum oxide and hydroxide films on the substrate surface before forming trivalent chromium conversion coatings.  

Other likely candidates to replace chromates are reducible hypervalent transition metals similar to chromium, which are 

Oxides of heavier elements, such as Mb, Hf, Ti, Zr, and Ta are very stable in their highest oxidation state. The mechanism for rare-earth inhibition seems to originate from the alkaline precipitation of protective oxide films at active cathodes. However, soluble and mobile precursors of these oxides remain difficult to stabilize in aqueous solution with the slight exception of Ce, which is the only lanthanide element that exhibits a tetra-valent oxidation state that is stable as a complex in aqueous 

The most recent Threshold Limit Value (TLV) published by the American Conference of Government Industrial Hygienists 1984-1985 show the time-weighted average TLV for soluble molybdenum particulates to be 5 mg/m and for insoluble particulates to be 10 mg/m. For comparison, the TLV for total particulates in the nuisance dust category is 10 mg/m. Molybdenum has long been identified as a micronutrient essential to plant life, and as playing a major biochemical role in animal health as a constituent of several important enzyme systems. Several studies have indicate that molybdenum-deficient diets may be associated with the incidence of various forms of cancer.  

Chemical Abstract Service number of 7631-95-0, for instance, but has not been selected for toxicity testing. Under RCRA, Mo is neither listed as a hazardous waste nor a hazardous constituent. Section 311 of the CWA lists 299 substances as hazardous if spilled in waterways no Mo compound is included. In summary, sodium molybdate and other molybdates are free of accompanying toxic elements or compounds and exhibit an environmental compatibility within the framework of their commercial utilization as a corrosion inhibitor. 

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Ghromium(III) Compounds. Chromium (ITT) is the most stable and most important oxidation state of the element. The E° values (Table 2) show that both the oxidation of Cr(II) to Cr(III) and the reduction of Cr(VI) to Cr(III) are favored in acidic aqueous solutions. The preparation of trivalent chromium compounds from either state presents few difficulties and does not require special conditions. In basic solutions, the oxidation of Cr(II) to Cr(III) is still favored. However, the oxidation of Cr(III) to Cr(VI) by oxidants such as peroxides and hypohaUtes occurs with ease. The preparation of Cr(III) from Cr(VI) ia basic solutions requires the use of powerful reducing agents such as hydra2ine, hydrosulfite, and borohydrides, but Fe(II), thiosulfate, and sugars can be employed in acid solution. Cr(III) compounds having identical counterions but very different chemical and physical properties can be produced by controlling the conditions of synthesis. 

Water-Soluble Trivalent Chromium Compounds. Most water-soluble Cr(III) compounds are produced from the reduction of sodium dichromate or chromic acid solutions. This route is less expensive than dissolving pure chromium metal, it uses high quaHty raw materials that are readily available, and there is more processing fiexibiHty. Finished products from this manufacturing method are marketed as crystals, powders, and Hquid concentrates. 

Reproductive Toxicity. No data are available that impHcate either hexavalent or trivalent chromium compounds as reproductive toxins, unless exposure is by way of injection. The observed teratogenic effects of sodium dichromate(VI), chromic acid, and chromium (HI) chloride, adininistered by injection, as measured by dose-response relationships are close to the amount that would be lethal to the embryo, a common trait of many compounds (111). Reported teratogenic studies on hamsters (117,118), the mouse (119—121), and rabbits (122) have shown increased incidence of cleft palate, no effect, and testicular degeneration, respectively. Although the exposures for these experiments were provided by injections, in the final study (122) oral, inhalation, and dermal routes were also tried, and no testicular degeneration was found by these paths. 

Among warm-blooded organisms, hexavalent chromium was fatal to dogs in 3 months at 100 mg/kg in their food and killed most mammalian experimental animals at injected doses of 1 to 5 mg Cr/kg body weight, but it had no measurable effect on chickens at dietary levels of 100 mg/kg over a 32-day period. Trivalent chromium compounds were generally less toxic than hexavalent chromium compounds, but significant differences may occur in uptake of anionic and cationic CL3 species, and this difference may affect survival. 

Water-soluble divalent and trivalent chromium compounds <0.5 7... 

Chromium and certain chromium compounds are classified as substances known to be carcinogenic. ERA classifies chromium as a de minimis carcinogen, meaning that the minimum amount of the chemical set by the U.S. Occupational Safety and Health Administration (OSHA) is considered to be carcinogenic. Chromium compounds vary greatly in their toxic and carcinogenic effects. Trivalent chromium compounds are considerably less toxic than the hexavalent compounds and are neither irritating nor corrosive. 

Trivalent chromium compounds (Cr )(chromic compounds) including chromic oxide (Cr203), chromic sulfate (Ct2[S04]3), chromic chloride (CrCb), chromic potassium sulfate (KCr[S04]2), and chromite ore (FeOCdCr203). 

In afterchroming the dye is allowed to go onto the fiber from an acid bath, and this is followed by treatment with dissolved alkali metal dichromate, which is reduced by the cystine group of the wool to trivalent chromium compounds. The chromium complex formed on the wool fiber contains two azo dye radicals for each metal atom (1 2 complex). 

Trivalent chromium compounds, except for acetate, nitrate, and chromium(III) chloride-hexahydrate salts, are generally insoluble in water. Some hexavalent compounds, such as chromium trioxide (or chromic acid) and the ammonium and alkali metal (e.g., sodium, potassium) salts of chromic acid are readily soluble in water. The alkaline metal (e.g., calcium, strontium) salts of chromic acid are less soluble in water. The zinc and lead salts of chromic acid are practically insoluble in cold water. Chromium(VI) compounds are reduced to chromium(III) in the presence of oxidizable organic matter. However, in natural waters where there is a low concentration of reducing materials, chromium(VI) compounds are more stable (EPA 1984a). For more information on the physical and chemical properties of chromium, see Chapter 3. 

Administration of inorganic trivalent chromium compounds or extracts of brewers yeast resulted in decreased blood glucose levels and cholesterol levels and regression of atherosclerotic plaques (Pi-Sunyer and Offenbacher 1984). Improved insulin sensitivity also resulted in an increased incorporation of amino acids into proteins and cell transport of amino acid in rats receiving supplemental chromium (Roginski and Mertz 1969). 

There is inadequate evidence for the carcinogenicity of elemental chromium and trivalent chromium compounds in experimental animals (IARC 1990 NTP 1998). IARC (1990) classifies chromium(O) and chromium(III) in Group C, that is, not classifiable as to carcinogenic potential. EPA has classified chromium(III) in Group D, not classifiable as to its human carcinogenicity (IRIS 2000a). 

Fregert S, Rorsman H. 1966. Allergic reactions to trivalent chromium compounds. Arch Dermatol 93 711-713. 

Korallus U, Ehrlicher H, Wustefeld E, et al. 1974a. [Trivalent chromium compounds - results of a study in occupational medicine]. Arb Soz Prev 9 51-54. (German)... 

Samitz MH, Shrager J. 1966. Patch test reactions to hexavalent and trivalent chromium compounds. Arch Dermatol 94 304-306. 

Trivalent chromium compounds (chromium chloride, chromium nicotinate, and chromium picohnate) are used by patients to enhance weight loss, to increase lean body mass, or to improve glycemic control. Drug histories should include attention to the use of over-the-counter nutritional supplements often regarded as harmless by the pubhc and lay media. The recommended daily allowance of chromium picolinate is 50-200 micrograms, but information about its toxicity is limited. 

In the late 1970s, however, Cr(VI) became identified as a suspected carcinogen. Therefore, to minimize worker exposure, trivalent chromium compounds were used instead. Many Cr(III) salts can substitute for Cr03 because they oxidize to Cr(VI) during calcination, and the anion is also burned away. For example, Cr(III) nitrate, acetate, acetylacetonate, chloride, or sulfate can be used. Basic chromic(III) acetate is currently the most common commercial source of chromium used in catalyst manufacture [32-38]. 

Mineral Tannages. The effects of chromium salts on skins were first investigated during the mid-nineteenth century and by the 1870s, leather was being produced commercially with these materials. Today over 90% of leather is manufactured using trivalent chromium compounds. 

Most trivalent chromium compounds exist as oxides, sulfides, or halides and are soluble in water only at low pH values, but acetate, chloride and nitrate salts are more soluble. At pH values above 5 to 6, chromiu-m(III) hydroxide precipitates. However, stable trivalent chromium complexes can be formed with sulfite ions (SOj ") at pH 9 and above, provided that an excess of sulfite is present in the solution. Complexes of chromium are also formed with amino acids and proteins, which is the reason why trivalent chromium compounds are... 

In related work, Williams and Feist (148) showed that a trivalent chromium compound was capable of adhering to wood to produce nearly the same weathering protection and water repellency as hexavalent chromium compounds. The critical factor was the ability of the chromium to fix or become unleachable, not the oxidative action of the hexavalent chromium ion on the wood. A further study by Williams and Feist (152) proved that Cr03 fixes to both wood and pure cellulose. With both materials, complete fixation of chromium resulted in a highly water-repellent surface. The similarity between treated wood and treated cellulose indicated that chromium-cellulose interactions should be included in defining the mechanism for wood surfaces stabilized with Cr and that previously proposed chro-... 

Chromium is the seventh most abundant element on earth with more than 2108 million tons of chromium metal, most of it residing in the core and mantle. The annual world production of chromium is estimated at 9 million metric tons most of the ore, in the form of chromite (Fe0Cr203), is produced by the Former Soviet Union and the Republic of South Africa. In the United States, trivalent chromium compounds are used as pigments and in leather tanning, and hexavalent chromium compounds are used principally in the ferrochrome and chemical industries. The combined production of chromium ferroalloys and chromium metal in the United States in 1988 was 119,645 metric tons from producers in West Virginia, South Carolina, New Jersey, Ohio, Kentucky, New York, Indiana, Utah, Peimsylvania, California, Texas, and North Carolina. Export of chromium materials from the United States in 1988 was 39,887 tons, mostly to Mexico, Canada, the Netherlands, Japan, and Germany. In 1990, the United States produced 150,600 tons of sodium dichromate and 53,300 tons of chromic acid. 

A number of metal salts have been found to induce delayed hypersensitivity, mainly of the contact type, in humans or in laboratory animals. Sensitivity to ions of chromium, mercury, platinum, nickel, beryllium, and others seem well established and Table 2 shows some recent findings. The best studied metal sensitizers are the chromium salts, since chromium eczema due to cement is the most important occupational dermatosis (Polak et al. 1973). Hexavalent chromium, in the form of potassium dichromate, is a better sensitizer than trivalent chromium. This seems related to the much better skin penetrating capacity of the dichromate, since numerous studies have shown that trivalent chromium compounds as opposed to hexavalent salt are the actual sensitizers (Polak et al. 1973). The same authors conclude that chromium is probably a component of the determinants formed with autologous carriers and does not produce autoantigens without further participation of the metal ion. In particular, oxidation reactions as generators of determinants seem inoperative in chromium hypersensitivity, since other strong oxidizers like... 

In mineral acid solution, hexavalent chromium compounds form with diphenyl carbazide an intensely red-purple coloured complex with an absorption maximum at 540 nm ( = 34,200). The measurement is performed in the aqueous phase. The complex forms instantaneously and is stable in sulphuric acid solution. The colour intensity of the solution is proportional to the concentration of chromate ions in the water sample. Trivalent chromium compounds are oxidized to chromate before complex formation and as such are also included in the measurement. 

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