Chromate and dichromate Supplier Distributor Manufacturer in chennai Taminadu india

Chromate salts contain the chromate anion, CrO2−4. Dichromate salts contain the dichromate anion, Cr2O2−7. They are oxoanions of chromium in the 6+ oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.

The primary chromium ore is the mixed metal oxide chromite, FeCr2O4, found as brittle metallic black crystals or granules. Chromite ore is heated with a mixture of calcium carbonate and sodium carbonate in the presence of air. The chromium is oxidized to the hexavalent form, while the iron forms iron(III) oxide, Fe2O3.

4 FeCr2O4 + 8 Na2CO3 + 7 O2 → 8 Na2CrO4 + 2 Fe2O3 + 8 CO2
Subsequent leaching of this material at higher temperatures dissolves the chromates, leaving a residue of insoluble iron oxide. Normally the chromate solution is further processed to make chromium metal, but a chromate salt may be obtained directly from the liquor.

Chromate containing minerals are rare. Crocoite, PbCrO4, which can occur as spectacular long red crystals, is the most commonly found chromate mineral. Rare potassium chromate minerals and related compounds are found in the Atacama desert. Among them is lópezite - the only known dichromate mineral.

Applications

Approximately 136,000 tonnes (150,000 tons) of hexavalent chromium, mainly sodium dichromate, were produced in 1985.Chromates and dichromates are used in chrome plating to protect metals from corrosion and to improve paint adhesion. Chromate and dichromate salts of heavy metals, lanthanides and alkaline earth metals are only very slightly soluble in water and are thus used as pigments. The lead containing pigment chrome yellow was used for a very long time before environmental regulations discouraged its use.[6] When used as oxidizing agents or titrants in a redox chemical reaction, chromates and dichromates convert into trivalent chromium, Cr3+, salts of which typically have a distinctively different blue-green color.