Chromium chrome alum

Chromate of soda. See Sodium chromate Chrome. See Chromium Chrome alum. See Chromium potassium sulfate... 

The dichromate ion oxidises iron(II) to iron(III), sulphite to sulphate ion, iodide ion to iodine and arsenic(III) to arsenic(V) (arsenate). Reduction of dichromate by sulphite can be used to prepare chrome alum, since, if sulphur dioxide is passed into potassium dichromate acidified with sulphuric acid, potassium and chromium(III) ions formed are in the correct ratio to form the alum, which appears on crystallisation ... 

All compounds of chromium are colored the most important are the chromates of sodium and potassium and the dichromates and the potassium and ammonium chrome alums. The dichromates are used as oxidizing agents in quantitative analysis, also in tanning leather. 

Sodium thiosulfate is still used in chrome leather tanning as a reducing agent in two-bath processes to reduce dichromate (hexavalent chromium) to chrome alum (trivalent chromium) (see Leather). 

Ohio, high carbon ferrochromium is leached with a hot solution of reduced anolyte plus chrome alum mother Hquor and makeup sulfuric acid. The slurry is then cooled to 80°C by the addition of cold mother Hquor from the ferrous ammonium sulfate circuit, and the undissolved soHds, mostiy siHca, are separated by filtration. The chromium in the filtrate is then converted to the nonalum form by conditioning treatment for several hours at elevated temperature. 

Fig. 2. Flow sheet for production of electrolytic chromium by the chrome alum process at the Marietta Plant, Flkem Metals Co., Marietta, Ohio.

The mother Hquor from the cmde ferrous sulfate crystallisation contains neady all the chromium. It is clarified and aged with agitation at 30°C for a considerable period to reverse the reactions of the conditioning step. Hydrolysis reactions are being reversed therefore, the pH increases. Also, sulfate ions are released from complexes and the chromium is converted largely to the hexaaquo ion. Ammonium chrome alum then precipitates as a fine crystal slurry. It is filtered and washed and the filtrate sent to the leach circuit the chrome alum is dissolved in hot water, and the solution is used as cell feed. 

Fig. 3. Principal electrolytic ceU reactions and electrolyte concentrations in chromium production by the chrome alum process.

Table 6. Operating Parameters for Electrowinning of Chromium from Chrome Alum...

The reaction is cataly2ed by all but the weakest acids. In the dehydration of ethanol over heterogeneous catalysts, such as alumina (342—346), ether is the main product below 260°C at higher temperatures both ether and ethylene are produced. Other catalysts used include siUca—alumina (347,348), copper sulfate, tin chloride, manganous chloride, aluminum chloride, chrome alum, and chromium sulfate (349,350). 

Chrom, n. chromium chrome, -alauii, m. chrome alum. 

If more than simple atoms are bound to a central atom, then the coordination number still refers to the number of near neighbors. For example, in solid potassium chrome alum, KCr(S04)2- 12H20, and also in its fresh aqueous solutions, the chromium-containing cation is... 

Probably the most common compound of +3 chromium is potassium chrome alum, KCr(SOi)r 12H20. We know that the twelve water molecules are distributed equally, six around Cr+a and six around K+. Potassium chrome alum is just one example of the general class of solids called alums which have a 4-1 ion, a +3 ion, two sulfates, and twelve molecules of water. In the dyeing industry chrome alum is used for fixing dyes to fabrics. 

The formation of rnonodisperse amorphous, spherical particles of chromium hydroxide is offered here as an example. These dispersions are readily obtained by simply heating chrome alum solutions (35). It was established experimentally that the sulfate ion was essential in order to obtain uniform dispersions thus, when chromium nitrate solutions were aged, monodispersed particles were produced only if a sulfate salt was introduced into the reaction. 

Fig. 1.1.7 Complex solutes present in solutions of chrome alum, which on aging yield monodispersed amphorous spherical chromium hydroxide panicles. A labeled solution initially 4.0 X 10 4 mol dm-3 in chrome alum was heated at 75°C for 9 days. After cooling and filtering off the particles, the filtrate was subjected to paper electrophoresis. The corresponding solutes are (A) Cr1+, (B) Cr,(0H)2S042+. (C) Cr(OH)2, (D) Cr(0H)S04 and Cr(OH).,. (From Ref. 36.)...

Figure 1.1.19 illustrates such hematite particles coated with chromium hydroxide in which the latter was produced by the hydrolysis of a chrome alum solution in the presence of a-Fe203 cores on aging the dispersion at 85°C. For greater efficiency the chromium salt solution was either preheated or preheated with KOH (but avoiding precipitation of chromium hydroxide) (144). 

Fig. 1.1.19 (A) TEM of ellipsoidal hematite (a-Fci03) particles and (B) of the same particles coated by chromium hydrous oxide obtained by aging at 85°C for 6 h 40 cm3 of a dispersion containing 30 mg dm-3 of the cores in the presence of 5.0 X 10-4 mol dm-3 chrome alum. (From Ref. 144.)...

The halogenates of chromium, uranium, and manganese.—The double decomposition of chrome alum and barium chlorate, or a soln. of chromic sulphate and potassium chlorate, furnishes a violet liquid containing chromium chlorate,134 which becomes green at 65°. Even at ordinary temp, the soln. smells of chlorine at 100°, chlorine gas is given off and the liquid becomes reddish-yellow—it contains chromic... 

One hundred grams of very finely powdered potassium chromium (III) sulfate (chrome alum) are mixed in a flask... 

Chromium Ammonium Alum of Chromium Ammonium Sulfate. See Ammonium-Chrome Alum in Vol 1, pA156-L... 

Synonyms Chrome alum, Chromium and potassium sulfate, Potassium chromium sulfate. Appearance Dark violet-red crystals (ruby red by transmitted light) or light violet powder. Uses Preparation of chrome alum fixing bath as hardening agent for gelatin. 

Human lymphocytes Chromosomal aberrations — Hamamy et al. 1987 (IN) Chrome alum (primarily chromium sulfate)... 

SYNS CHROME ALUM CHROME POTASH ALUM CHROMIC POTASSIUM SULFATE CHROMIC POTASSIUM SULPHATE CHROMIUM POTASSIUM SULFATE (1 1 2) CHROMIUM POTASSIUM SULPHATE CRYSTAL CHROME ALUM POTASSIUM CHROMIC SULPHATE POTASSIUM CHROMIUM ALUM POTASSIUM DISULPHATOCHROMATE(III) SULFURIC ACID, CHROMIUM (3+) POTASSIUM SALT (2 1 1)... 

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