Preparation of potassium dichromate:
1. Potassium dichromate is prepared from chromite ore. The ore FeO. Cr2O3 is concentrated by gravity separation process.
2. The concentrated ore is mixed with excess sodium carbonate and lime and roasted in a reverbratory furnace.
3. The roasted mass is treated with water to separate soluble sodium chromate from insoluble iron oxide. The yellow solution of sodium chromate is treated with concentrated sulphuric acid which converts sodium chromate into sodium dichromate.
4. The above solution is concentrated to remove less soluble sodium sulphate. The resulting solution is filtered and concentrated. It is cooled to get the crystals of Na2SO2 .2H2O.
5. The saturated solution of sodium dichromate in water is mixed with KCl and then concentrated to get crystals of NaCl. It is filtered while hot and the filtrate is cooled to obtain K2Cr2O7 crystals.
