Question

Which steps are involved in the manufacture of potassium dichromate from chromite ore?

Answer 1

In industrial production, finely powdered chromite ore \[\ce{(FeO_Cr2O3)}\] is heated with anhydrous sodium carbonate \[\ce{(Na2CO3)}\] and flux of lime in the air in a reverberatory furnace.

\[\ce{4(FeO*Cr2O3) + 8Na2CO3 + 7O2 ->[\Delta] 8Na2CrO4 + 2Fe2O3 + 8CO2}\].

Sodium chromate \[\ce{(Na2CrO4)}\] formed in this reaction is then extracted with water and treated with concentrated sulphuric acid to get sodium dichromate and hydrated sodium sulphate:

\[\ce{2Na2CrO4 + H2SO4 -> Na2Cr2O7 + 2NaCl + Na2Cr2O7*H2O}\]

The addition of potassium chloride to a concentrated solution of sodium dichromate precipitates less soluble orange-red coloured potassium dichromate, \[\ce{K2Cr2O7}\].

\[\ce{Na2Cr2O7 + 2KCl -> K2Cr2O7 + 2NaCl}\]