Leather chromate

Chromates and dichromates are used in industry as oxidising agents, for example in the coal tar industry, in the leather industry (chrome taiming), and in the dye industry as mordants. Some chromates are used as pigments, for example those of zinc and lead. Chromates and dichromates are poisonous. 

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. 

Around 1800, the attack of chromite [53293-42-8] ore by lime and alkaU carbonate oxidation was developed as an economic process for the production of chromate compounds, which were primarily used for the manufacture of pigments (qv). Other commercially developed uses were the development of mordant dyeing using chromates in 1820, chrome tanning in 1828 (2), and chromium plating in 1926 (3) (see Dyes and dye intermediates Electroplating Leather). In 1824, the first chromyl compounds were synthesized followed by the discovery of chromous compounds 20 years later. Organochromium compounds were produced in 1919, and chromium carbonyl was made in 1927 (1,2). 

Chrom-kali, n. (rotes) potassium dichromate (gelbes) potassium chromate, -karbid, n. chromium carbide, -lack, m. chrome lake, -leder, n. chrome leather, -leim, m. chrome gelatin chrome glue, -metall, n. chromium metal, -natron, n. (rotss) sodium dichromate (gelbes) sodium chromate, -nickel-stahl, m. chrome-nickel steel. 

Cbrom rindleder, n. chromed neat s leather, -rot, n. chrome red. -salpetersaure, /. chromonitric acid, -salz, n. chromium salt chromate. 

Potassium chromate is used in enamels rustproof metals and leather finishes. The compound also is an indicator in argentometric titrations. 

Chromate. Potassium chromate. [CAS 7789-00-6], ICj-CrO, yellow solid, soluble, formed by reaction of potassium carbonate and chromite at a high temperature in a current of air, and then extracting with water and evaporating the solution. Used (1) as a source of chromate. (2) in leather tanning, (3) in textile dyeing, (4) in inks. 

Dichromate. Sodium dichromate, [CAS 10588-01-9], Na2Cr207 2H20. red solid, soluble, powerful oxidizing agent, and consequently a fire hazard with dry car bonaceous materials. Formed by acidifying sodium chromate solution, and then evaporating. Used (1) in matches and pyrotechnics, (2) in leather tanning and in the textile industry, (3) as a source of chromate, cheaper than potassium dichromatc. 

Occupational exposure to chromium(VI) compounds in a number of industries has been associated with increased risk of respiratory system cancers, primarily bronchogenic and nasal. Among the industries investigated in retrospective mortality studies are chromate production, chromate pigment production and use, chrome plating, stainless steel welding, ferrochromium alloy production, and leather tanning. 

Studies of chromate production workers, who are exposed to a variety of chromium compounds both hexavalent and trivalent, and chromate pigment industries, where exposure is mainly to chromium(VI), have consistently demonstrated an association with respiratory system cancer. Studies in chrome platers, who are exposed to chromium(VI) and other agents, including nickel, generally support the conclusion that certain chromium(VI) compounds are carcinogenic. Studies in stainless steel welders exposed to chromium(VI) and other chemicals, and in ferrochromium alloy workers, who are exposed mainly to chromium(O) and chromium(III), but also to some chromium(VI), were inconclusive. Studies in leather tanners, who are exposed to chromium(III), were consistently negative. 

The chromates and dichromates are used in making pigments, in dying textiles, and in the tanning of leather. Chromium in the +6 oxidation state is believed to be a carcinogen so chromates and dichromates should be handled carefully. 

Oxidation states of chromium - -2, - -3, and -f-6. Oi es of chromium chronate, FeCr204, and crocoite, PbCr04. Chromium metal and its alloys ferrochrome, alloy steels, stainless steel. The aluminothermic process (Goldschrtiidt process). Electrolytic chromium. Chromium trioxide, chromic acid, dichromic acid, potassium chromate, potassium didiromate, sodium chromate, lead chromate. Equilibrium between chromate ion and dichromate ion. Chrome-tanned leather. Chromic oxide (chrome green) chromic ion, chrome alum, chromic chloride, chromic hydroxide, chromite ion. Chromous compounds. Peroxy-chromic acid. 

Estimation of Chromium.—In the analysis of chromites or of other substances containing chromium, such as leather ashes, pigments, etc., it is first necessary to obtain a solution. This is done by finely powdering the substance and heating it with a suitable flux in a crucible, preferably of nickel. Many fluxes have been employed, usually caustic alkali or alkali carbonates, but the one in most common use at present is sodium peroxide, whereby the chromium compound is rapidly converted to a chromate. - Excess of alkali is removed by boiling with ammonium carbonate, which also precipitates any iron present. The filtrate is then acidified with dilute sulphuric acid and the chromium estimated either by gravimetric or volumetric methods. 

Hazard Toxic material. TLV 0.5 mg(Cr)/m3. Use Inks, dyeing, paint pigment, leather tanning, other chromates, protection of iron against corrosion, wood preservative. 

EXPOSURE ROUTES wind transport from road dust wood treated with copper dichromate leather tanned with chromic sulfate chromate production stainless-steel production chrome plating working in tanning industries chromium waste disposal sites chromium manufacturing and processing plants consumption of food and drinking water inhalation of air... 

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