Chromium occurrence

Kotas, J. and Z. Stasicka. 2000. Chromium occurrence in the environment and methods of its speciation. Environ. Pollut. 107 263-283. 

MertzW. 1969. Chromium occurrence and function in biological systems. Physiol Rev 49(2) 163-239. 

MacKenzie RD, Byerrum RU, Decker CF, Hoppert CA, Langham RF (1958) Chronic toxicity studies. II. Hexavalent and trivalent chromium administered in drinking water to rats. AMA Arch Ind Health 18 232-234 MacKenzie RD, Anwar RA, Byerrum RU, Hoppert CA (1959) Absorption and distribution of Cr in the albino rat. Arch Biochem Biophys 79 200-205 Mertz W (1969) Chromium occurrence and function in biological systems. Physiol Rev 49 163-239... 

Continued exposure of the nickel-chromium alloy to more severely sulphurising and reducing atmospheres results in local depletion of chromium to such an extent that nickel sulphide and the eutectic are formed internally. The latter constituents are not often observed in service failures, but the relative instability of nickel sulphide in the presence of chromium sulphide can result in its reduction to nickel during slow cooling on shut down. That nickel sulphide is formed is suggested by the frequent occurrence of blisters, associated with the formation of molten eutectic on the surface of sulphur-attacked specimens . 

The occurrence of stress-corrosion cracking in the martensitic steels is very sensitive to the magnitude of the applied stress. For instance, a 13% chromium martensitic steel tested in boiling 35% magnesium chloride solution (125.5°C) indicated times to failure that decreased abruptly from more than 25(X)h to less than 0.1 h as the applied stress was increased from 620 MPa to about 650 MPa (Fig. 8.25). However, the effects of stress on time to failure are not always so dramatic. For instance, in the same set of experiments times to failure for a 17Cr-2Ni martensitic steel gradually decreased from more than 800 h to about 8 h as the applied stress was increased from 500 MPa to 800 MPa. 

The last reaction is the most favored of these three. The actual occurrence of the reactions with elemental phosphorus or phosphorous trichloride as products has been explained to be due to kinetic reasons. The thorium present in the ore volatilizes in the form of thorium tetrachloride (ThCl4) vapor other metallic impurities such as iron, chromium, aluminum, and titanium also form chlorides and vaporize. The product obtained after chlorination at 900 °C is virtually free from thorium chloride and phosphorous compounds, and also from the metals iron, aluminum, chromium, and titanium. 

A literature method for preparation of chromyl acetate by interaction of chromium trioxide and acetic anhydride was modified by omission of cooling and agitation. The warm mixture exploded violently when moved [1], A later publication emphasised the need for cooling, and summarised several such previous occurrences [2], An earlier reference attributes the cause of chromium trioxide-acetic anhydride oxidation mixtures going out of control to presence of nitric acid or nitrates in the chromium trioxide, and a simple test to check this point is given [3], Mixtures used as a reagent for the remote oxidation of carboxylic esters are potentially explosive, and must be made up and used at below 25 °C under controlled conditions [4], An attempt to purify the anhydride by warming with 2% w/v of trioxide led to an explosion at 30°C [5],... 

Occurrence. The ore of Cr of higher commercial importance is chromite (FeCr204). Other minerals are crocoite PbCr04 and chrome ochre Cr203. About 2% Cr in emerald Be3Al2Si6018 is the source of its green colour. Chromium is comparable in abundance in the earth s crustal rocks with V and Cl. 

Mayer LM (1988) Geochemistry of chromium in the oceans. In Chromium in the Natural and Human Environments. Nriagu JO, Nieboer E (eds), Wiley Sons, New York, p 173-187 McNeal JM, Balishieri LS (1989) Geochemishy and occurrence of seleniimi an overview. In Seleniimi in Agriculture and the Environment. SSSA Special Publication. Jacobs LW (ed). Soil Science Society of America, Madison, WI, p 1-13... 

The NMRD profile of chromium(III) aqua ion (Fig. 18) is characterized by slow exchanging water protons, as clearly shown by the fact that the solvent proton relaxivity at low fields increases with increasing the temperature. The occurrence of slow exchange hinders any increase in relaxivity below 300 K, thus explaining the fact that the contact dispersion disappears in the low temperature profiles, whereas it is well shown in the high temperature profiles, as already discussed in Section I.C.8. 

Burns R. G. (1975). On the occurrence and stability of divalent chromium in olivines included in diamonds. Contrih. Mineral. Petrol, 51 213-221. 

Baskerville, Charles, The occurrence of vanadium, chromium, and titanium... 

The SSM sample was spiked with seven different heavy metals. The concentrations of each spike were followed arsenic - 500 mg/kg, cadmium-1000 mg/kg, chromium - 1500 mg/kg, copper - 9500 mg/kg, lead - 14,000 mg/kg, nickel - 1000 mg/kg, and zinc - 22,500 mg/kg. The concentrations used were based on the occurrence, frequency and concentration of contaminants commonly found in Superfund soils. 

Jhe distribution of beryllium, boron, titanium, vanadium, chromium, cobalt, nickel, copper, zinc, gallium, germanium, tin, molybdenum, yttrium, and lanthanum in the principal coal-producing beds of the Interior Province has been studied by the U. S. Geological Survey. Data, methods of sampling, and analyses are discussed by Zubovic and others (II, 12). This chapter discusses the occurrence of 13 of these elements with respect to geological and geochemical environments of coal deposition and chemical properties of the elements. Zinc and tin are not included in this study because they were detected in only a few samples. 

The retention of zinc in the lake sediments appears to be efficient under botlToxic and anoxic conditions no indication of a release of zinc from the sediments into the water column was found. In a similar way, the retention of chromium in the sediments appears to be efficient. Under anoxic conditions Cr(III) is formed, which is strongly bound to particles and is thus retained in the sediments.The occurrence of anoxic conditions favors the retention in the sediments of chromium and of zinc, in contrast to the release of manganese and of iron. 

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