Sodium chromates

HUMAN CARCINOGEN, CONTACT WITH COMBUSTIBLE MATERIAL MAY CAUSE FIRE 

Yellow deliquescent crystals crystallizes as tetra- or decahydrate. Decahydrate loses water mp, 792°C (decahydrate mp, 20oC).  

Dust irritates the respiratory tract and eyes. Swallowing causes irritation and internal damage. Prolonged exposure causes ulceration, damage to liver and kidneys, and even cancer. Prevent inhalation of dust. Prevent contact with eyes and skin.2 TLV-TWA 0.05 mg/m3.3 

Package Lots. Place in a separate labeled container for disposal. 

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Sodium dichromate is prepared on the large scale by heating powdered chromite with sodium carbonate, with free access of air the sodium chromate first formed is treated with acid ... 

Propionaldehyde. Use 34 g. (42-6 ml.) of n propyl alcohol, and a solution containing 56 g. of sodium chromate dihydrate, 300 ml. of water and 40 ml. of concentrated sulphuric acid. The experimental details are identical with those for n-butyraldehyde, except that the addition of the dichromate solution occupies 20 minutes, the temperature at the top of the column is not allowed to rise above 70-75°, and during the subsequent heating for 15 minutes the liquid passing over below 80° is collected the receiver must be cooled in ice. The yield of propionaldehyde, b.p. 47-50°, is 12 g. 

Dissolve 15-0 g. of A.R. barium nitrate and 130 g. of A.R. cupric nitrate trihydrate in 450 ml. of water at 80°. Prepare a solution of sodium chromate by dissolving 89 g. of recrystallised sodium dichromate dihydrate in 200 ml. of water and adding 112 5 ml. of cone, ammonia solution (sp. gr. 0-90). Add the warm solution (80°) of nitrates in a thin stream, with stirring, to the sodium chromate solution (at 25°). Collect the orange precipitate by suction Bltration, wash it with two 50 ml. portions of 5fiter, drain well, and dry at 75-80° for 12 hours powder finely. 

Lead chromates are prepared by precipitation techniques from soluble salts ia aqueous media. The raw material Hst iacludes a number of different lead compounds, eg, Htharge, lead nitrate, basic lead acetate, basic lead carbonate, as well as acids, alkahes, sodium bichromate, and sodium chromate. The typical reaction can be represented by the foUowiag equation ... 

Mordant Dyes. MetaUizable azo dyes are appHed to wool by the method used for acid dyes and then treated with metal salts such as sodium chromate [7775-11-5] sodium dichromate [10588-01-9] and chromium fluoride [1488-42-5] to form the metal complex in situ. This treatment usually produces a bathochromic shift ia shade, decreases the solubUity of the coloring matter, and yields dyeiags with improved fastness properties. The chromium salts can be appHed to the substrate before dyeiag (chrome-mordant or chrome-bottom method), together with the dye ia a single bath procedure (metachrome process), or as a treatment after dyeiag (afterchrome process). 

Sihcon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between sihcon carbide and a variety of compounds at relatively high temperatures. Sodium sihcate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal sihcide. Sihcon carbide decomposes in fused alkahes such as potassium chromate or sodium chromate and in fused borax or cryohte, and reacts with carbon dioxide, hydrogen, ak, and steam. Sihcon carbide, resistant to chlorine below 700°C, reacts to form carbon and sihcon tetrachloride at high temperature. SiC dissociates in molten kon and the sihcon reacts with oxides present in the melt, a reaction of use in the metallurgy of kon and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new sihcon nitride-bonded type exhibits improved resistance to cryohte. 

Manufacture The primary iadustrial compounds of chromium made directly from chromite ore are sodium chromate, sodium dichromate, and chromic acid. Secondary chromium compounds produced ia quantity include potassium dichromate, potassium chromate, and ammonium dichromate. 

Modem manufacturing processes quench the roast by continuous discharge into the leach water held in tanks equipped with agitators. At this point the pH of the leach solution is adjusted to between 8 and 9 to precipitate aluminum and siHcon. The modem leaching operations are very rapid because no or htde lime is used. After separation of the ore residue and precipitated impurities using rotary vacuum filters, the cmde Hquid sodium chromate may need to be treated to remove vanadium, if present, in a separate operation. The ore residue and precipitants are either recycled or treated to reduce hexavalent chromium to Cr(III) before disposal. 

The neutralized, alumina-free sodium chromate solution may be marketed as a solution of 40° Bh (specific gravity = 1.38), evaporated to dryness, or crystallized to give a technical grade of sodium chromate or sodium chromate tetrahydrate [1003-82-9] Na2Cr04 4H2O. If the fuel for the kilns contains sulfur, the product contains sodium sulfate as an impurity. This compound is isomorphous with sodium chromate and hence difficult to separate. High purity sodium chromate must be made from purified sodium dichromate. 

Sodium chromate can be converted to the dichromate by a continuous process treating with sulfuric acid, carbon dioxide, or a combination of these two (Fig. 2). Evaporation of the sodium dichromate Hquor causes the precipitation of sodium sulfate and/or sodium bicarbonate, and these compounds are removed before the final sodium dichromate crystallization. The recovered sodium sulfate may be used for other purposes, and the sodium bicarbonate can replace some of the soda ash used for the roasting operation (76). The dichromate mother Hquor may be returned to the evaporators, used to adjust the pH of the leach, or marketed, usually as 69% sodium dichromate solution. 

The prices of some important chromium chemicals are given ia Table 4, and production and shipment data for sodium chromate and dichromate are given ia Table 5. Data for the productioa and shipment of chromic acid have not been available siace 1972. However, traditionally CrO has held at about 30—35% of sodium dichromate production. The estimated capacity for domestic production of sodium dichromate is 150,000 to 200,000 t/yr. 

Sodium dichromate, sodium chromate, and mixtures thereof are shipped as concentrated solutions ia tank cars and tmcks. The chloride and sulfate contents are usually somewhat higher than ia the crystalline product. Sodium dichromate is customarily shipped at a concentration of 69%... 

A dichromate or chromate solution is reduced under pressure to produce a hydrous oxide, which is filtered, washed, and calcined at 1000°C. The calcined oxide is washed to remove sodium chromate, dried, and ground. Sulfur, glucose, sulfite, and reducing gases may be used as reducing agent, and temperatures may reach 210°C and pressures 4—5 MPa (600—700 psi). 

Drilling Muds in the Petroleum and Natural Gas Industry. Since 1941, chromium chemicals have been used in the drilling of wells to combat fatigue corrosion cracking of drill strings, with about one metric ton of sodium chromate being used aimuaHy for an average West Texas well. Other early uses were in gas-condensate wells in Louisiana and East Texas. 

TABLE 2-89 Sodium Chromate (Na CrOA) TABLE 2-92 Sodium Nitrite (NaNO ) ... 

SODIUM CHLORITE SODIUM CHLOROACETATE SODIUM CHROMATE SODIUM CUPROCYANIDE SOLID SODIUM CUPROCYANIDE SOLUTION... 

Chemical Designations - Synonyms Neutral sodium chromate, anhydrous Sodium chromate (VI) Chemical Formula Na2Cr04. 

The sodium chromate produced in the isolation of chromium is itself the basis for the manufacture of all industrially important chromium chemicals. World production of chromite ores approached 12 million tonnes in 1995. 

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. 

Paraformaldehyde and sodium chromate that counteract organic contaminants left in the well from drilling operations. 

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