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  Potassium dichromate

Potassium dichromate (K2Cr2O7):

Preparation of potassium dichromate from chrome iron ore:

The manufacture of K2Cr2O7 from its ore includes the following steps:

1) Conversion of chrome iron ore to sodium chromate:

The powdered ore is mix with Na2CO3 and quick lime, and then roasted in a reverberatory furnace in a free exposure to air.

4FeO.Cr2O3 + 8Na2CO3 + 7O2 → 8Na2CrO4 + 2Fe2O3 + 8CO2↑

2) Conversion of Na2CrO4 to Na2Cr2O7:

Sodium chromate solution thus obtained is filtered and treated with concentrated H2SO4, whenever sodium chromate is transformed to sodium dichromate.

2Na2CrO4 + H2SO4 → Na2Cr2O7 + Na2SO4 + H2O

3) Transformation of sodium dichromate into potassium dichromate:

Hot concentrated solution of sodium dichromate is treated with KCl, whenever potassium dichromate, being too less soluble than sodium salt, crystallizes out on cooling.

Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl

922_Potassium-dichromate.jpg

 

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