Chromium sulfate, decomposition

Different trivalent chromium products, chromium oxide, chromium hydroxide and chromium sulfate, are made by reduction of dichromate. Chromium sulfate is used in leather tanning. Skins are mainly derived from animals that are butchered for the food industry. To protect the skin from putrefaction it is transformed to leather by the tanning process. The tanning agent is fixed to the reactive groups of collagen, the protein in the sldn. That stops the spontaneous decomposition of collagen. 

Reduction of Ammonium Dichromate. Chromium(III) oxide can be obtained by thermal decomposition of ammonium dichromate. Above ca. 200 °C, a highly voluminous product is formed with elimination of nitrogen [3.48]. The pigment is obtained after addition of alkali salts (e.g., sodium sulfate) and subsequent calcination [3.49]. 

Chromium oxides with a minimal sulfur content are preferred for metallurgical applications. These are obtained by reacting sodium dichromate with ammonium chloride or sulfate in a deficiency of 10 mol% [3.51]. Chromium (III) oxides with a low sulfur content can also be obtained by thermal aftertreatment [3.52], Thermal decomposition of chromic acid anhydride (Cr03) yields high-purity chromium(III) oxide [3.53],... 

No reaction was observed when 86.5g of anhydrous di-propylenetriamine were heated with 27g of dehydrated chromium (III) sulfate on the steam bath. There was no sign of decomposition even after 4 hours at 2G0°C. A drop of water added as catalyst made no difference. 

Crude material prepared in glass on 3 g mol scale was distilled uneventfully at 40°C/ 0.067 mbar from a bath at 70—80°C. A 30 mol batch prepared in a glass-lined vessel with a stainless steel thermo-probe (and later found to contain 15 ppm of iron) decomposed very violently during distillation at 75°C/13 mbar from a bath at 130°C. Thermal analysis showed that the stability of the methyl (and ethyl) ester was very sensitive to traces of heavy metals (iron, copper, chromium, etc.) and was greatly reduced. Addition of traces of hydrated iron(II) sulfate led to explosive decomposition at 25°C. 

OSHA PEL CL 0.1 mg(Cr03)/m3 ACGIH TLV TWA 0.05 mg(Cr)/m3 Confirmed Human Carcinogen NIOSH REL (Chromium(VI)) TWA 25 ng(Cr(VI))/m3 CL 50 g/m3/15M SAFETY PROFILE A confirmed carcinogen. Poison. See also CHROMIUM COMPOUNDS and SULFATES. When heated to decomposition it emits toxic fumes of NH3, NOx, and SOx. 

HIDROXILAMINA (Spanish) (7803-49-8) A powerful reducing agent. Aqueous solution is a base. Contact with water or steam causes decomposition to ammonium hydroxide, nitrogen, and hydrogen. Contaminants and/or elevated temperatures above (reported at 158°F/70°C and 265°F/129°C) can cause explosive decomposition. Moisture in air or carbon dioxide may cause decomposition. Violent reaction with oxidizers, strong acids, copper(II) sulfate, chromium trioxide, potassium dichromate, phosphorus chlorides, metals calcium, sodium, zinc. Incompatible with carbonyls, pyridine. Forms heat-sensitive explosive mixtures with calcium, zinc powder, and possibly other finely divided metals. Aqueous solution incompatible with organic anhydrides, acrylates, alcohols, aldehydes, alkylene oxides, substituted allyls, carbonyls, cellulose nitrate, cresols, caprolactam solution, epichlorohydrin, ethylene dichloride, glycols, isocyanates, ketones, nitrates, phenols, pyridine, vinyl acetate. Attacks aluminum, copper, tin, and zinc. 

External sample decomposition procedures, such as ashing or acid digestion, not only eliminate the matrix but also convert the analyte to some specific salt suitable for HVAA analyses. For example, the ashing used to obtain data in Table 3.II converted the nickel to its sulfate. In the Project, indirect HVAA procedures were successfully applied to six elements. The application of these procedures, however, may be restricted by contamination or by reagent blanks. For example, exposure to nichrome heating elements affects chromium (see p. 19). Although destruction techniques eliminate the hydrocarbon matrix, they do not compensate for interelement interferences. 

Potassium or sodium-potassium alloy mixed with ammonium nitrate and ammonium sulfate results in explosion (NFPA 1986). Violent reactions may occur when a metal such as aluminum, magnesium, copper, cadmium, zinc, cobalt, nickel, lead, chromium, bismuth, or antimony in powdered form is mixed with fused ammonium nitrate. An explosion may occur when the mixture above is subjected to shock. A mixture with white phosphorus or sulfur explodes by percussion or shock. It explodes when heated with carbon. Mixture with concentrated acetic acid ignites on warming. Many metal salts, especially the chromates, dichromates, and chlorides, can lower the decomposition temperature of ammonium nitrate. For example, presence of 0.1% CaCb, NH4CI, AICI3, or FeCb can cause explosive decomposition at 175°C (347°F). Also, the presence of acid can further catalyze the decomposition of ammonium nitrate in presence of metal sulfides. 

The decomposition step is carried out in a mixture of 0.5 M sulfuric acid and 100 volume hydrogen peroxide. The copper(II) sulfate, potassium/sodium dichromate and arsenic pentoxide in CCA preservatives undergo fixation to form potassium/sodium sulfate by-products. Any potential interference in the chromium and arsenic signals from these compounds in the leachate is overcome by an excess of sodium... 

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