por What is sodium dichromate?
He sodium dichromate is an inorganic compound with the formula Na2Cr2O7. It is one of many hexavalent chromium (Cr VI) compounds. Usually, the salt is handled in its dihydrate form, whose formula would be Na2Cr2O7·H₂O.
It has two ionic bonds between the sodium molecules and the negatively charged oxygen. Chromium ore is extracted from sodium dichromate. Millions of kilograms of sodium dichromate are produced annually.
China is the largest producer of sodium dichromate, however, Chinese chemical plants have relatively low production, less than 50,000 tons per year each, compared to the Kazakhstan plant, which produces more than 100,000 tons per year.
In terms of reactivity and appearance, sodium dichromate has similar properties to potassium dichromate, but the sodium salt is more soluble in water and has a lower equivalent weight than the potassium salt.
Sodium dichromate produces toxic chrome fumes when heated. It is a strong oxidizing agent, highly corrosive.
This compound can be found in contaminated drinking water sources from different industrial processes such as galvanizing or electroplating techniques, leather tanning, and textile manufacturing.
Physical and chemical properties
Sodium dichromate is composed of crystals with a monoclinic structure, reddish-orange in color in its anhydrous and odorless form.
Its molecular weight is 261.97 g/mol in its anhydrous form and 298.00 g/mol in its dihydrate form.
It has a melting point of 356.7 °C, a boiling point of 400 °C at which it decomposes. It has a density of 2.52 g/ml.
Its solubility in water is 187 g per 100 grams at 25 °C and its solubility in ethanol is 513.2 grams per liter at 19.4 °C.
It is considered a stable compound if it is stored under the recommended conditions, and it is not flammable.
Since it is a strong oxidizing agent, it is corrosive, and in solution it is acidic, having the ability to lower the pH to 4 in a 1% w/v solution.
production methods
Sodium chromate can be converted to dichromate by a continuous process that treats with sulfuric acid, carbon dioxide, or a combination of these two.
Evaporation of the sodium dichromate liquor causes the precipitation of sodium sulfate and/or sodium bicarbonate, and these compounds are removed prior to the final crystallization of sodium dichromate.
Sodium dichromate can be made in a three-step process:
Alkaline roasting of chromite oxidation conditions.
leaching. Extraction of soluble matter from a mixture by the action of a liquid solvent.
Conversion of sodium monochromate to sodium dichromate by means of an acid.
Anhydrous sodium dichromate can be prepared by melting sodium dichromate dihydrate, crystallizing aqueous dichromate solutions above 86°C, or drying sodium dichromate solutions in spray dryers.
Sodium dichromate solutions at 69 and 70% w/v are used as a convenient and cost-effective method of shipping quantities, avoiding the need for manual handling or crystal dissolution.
Reactivity and hazards
It is a strong oxidizing agent. Incompatible with strong acids. Contact with combustible materials may cause fire. Toxic chromium oxide fumes may form in the presence of heat or fire.
The well-known “chromic acid mixture” of dichromate and sulfuric acid with organic residues gives rise to a violent exothermic reaction. This mixture, in combination with residual acetone, also leads to a violent reaction.
The combination of dichromate and sulfuric acid with alcohols, ethanol and 2-propanol, gives rise to a violent exothermic reaction. Due to the occurrence of many incidents involving the mixing of dichromate-sulfuric acid with oxidizable organic materials, it is probably best to avoid such interactions.
The combination of dichromate with hydrazine is explosive, the reaction of dichromate can be expected to be vigorous with amines in general. Addition of the dehydrated dichromate salt to acetic anhydride leads to an ultimately explosive exothermic reaction.
Boron, silicon and dichromates form pyrotechnic mixtures. A mixture of acetic acid, 2-methyl-2-pentenal and dichromate leads to a rampant reaction.
Inhalation of dust or mist causes a respiratory irritation that sometimes mimics asthma. Septal perforation may occur. It is considered poison.
Ingestion causes vomiting, diarrhea and, very rarely, stomach and kidney complications. Contact with eyes or skin causes local irritation. Repeated exposure to the skin causes dermatitis.
Sodium dichromate is carcinogenic to humans. There is evidence that hexavalent chromium or Cr(VI) compounds can cause lung cancer in humans. Sodium dichromate has been shown to cause lung cancer in animals.
Although sodium dichromate has not been identified as a teratogenic or reproductive risk compound, hexavalent chromium or Cr(VI) compounds are known to be teratogenic and cause reproductive harm such as reduced fertility and interfering with menstrual cycles. .
Sodium dichromate can cause liver and kidney damage, so it must be handled with extreme care.
In case of ingestion, the victim should drink water or milk, never induce vomiting. In case of contact with the skin or eyes, it should be treated as acid burns: the eyes are flushed with water for at least 15 minutes.
External lesions can be rubbed with a 2% sodium thiosulfate solution. In all cases a doctor should be consulted.
Uses and applications
Aside from its importance in the manufacture of other chromium chemicals, sodium dichromate also has many direct uses as an ingredient in the production of:
Metallic finish: helps resistance to corrosion and clean metal surfaces, also favors paint adhesion.
Organic products: used as oxidizing agents in the manufacture of products such as vitamin K and wax.
Pigments: used in the manufacture of inorganic chromate pigments where it produces a range of light-stable colors. Some grades of chromate are also used as corrosion inhibitors in undercoats and primers.
Ceramic: used in the preparation of colored glass and ceramic glazes.
Textile: used as a mordant for acid dyes to improve their fast coloring properties.
Chromium sulfate production.
Sodium Dichromate Dihydrate is ideal for use in various conditions, including high-temperature applications such as ceramic glazes and stained glass.
Chromic oxide, because it is harder than other metal oxides, such as titanium or iron, is ideal for environments where the temperature and process conditions are aggressive.
This substance is mainly used to produce other chromium compounds, but it is also used in bentonite sludge used in oil production, in wood preservatives, in the production of organic chemicals, and as a corrosion inhibitor.
When mixed with potassium aluminum dichromate, using the alumino-thermal process, chromic oxide produces high purity metallic chromium. This is a vital ingredient in the production of the high performance super alloys used in the aerospace industry.
In organic synthesis, sodium dichromate is used as an oxidizing agent in oxidation-reduction reactions in the presence of sulfuric acid.
For example, the oxidation of p-nitrotoluene to form p-nitrobenzoic acid, the oxidation of n-butanol to form n-butaldehyde, the formation of cyclohexanone from cyclohexanol, and the formation of adipic acid.
Biochemistry
Intratracheal instillation of sodium dichromate (CrVI) and chromium acetate hydroxide (CrIII) in male rats resulted in increased chromium concentrations in whole blood, plasma, and urine up to 72 hours after exposure. Peak concentrations were reached 6 hours after exposure.
The ratio between whole blood chromium and plasma chromium concentrations was significantly different for the Cr(VI) and Cr(III) treatments. Therefore, blood chromium and plasma chromium tests should be used for the evaluation of chromium exposure.
Chromium was also detected in peripheral lymphocytes. Cr(VI) but Cr(III) did not significantly accumulate in lymphocytes after treatment. These cells have the potential to be used as biomarkers for the assessment of exposure to chromium compounds.
References
Chemical Datasheet Sodium Dichromate. Retrieved from cameochemicals.noaa.
National Center for Biotechnology Information. CID=25408. Retrieved from pubchem.ncbi.nlm.nih.gov.
Hazardous substance fact sheet sodium dichromate. Retrieved from nj.gov: nj.gov.
Sodium dichromate. The building block for virtually all other chromium compounds. Retrieved from elementischromium.com.