Preparation of `K_(2)Cr_(2)O_(7)` from chrome iron ore composition of chromite ore is `FeO.Cr_(2)O_(3)`.
Step I : Concentration of ore : Powdered ore is concentrated by washing with current of water in hydraulic classifier.
Step II. Roasting : Conversion of chromite ore into sodium chromate :
`{:(4FeO.Cr_(2)O_(3) +O_(2)rarr 2Fe_(2)O_(3)+4Cr_(2)O_(3)),([2Cr_(2)O_(3)+4Na_(2)CO_(3)+3O_(2)rarr4Na_(2)CrO_(4)+4CO_(4)+4CO_(2)]xx2),(barul(4FeOCr_(2)O_(3)+8Na_(2)CO_(3)+7O_(2) rarr 2Fe_(2)O_(3)+8Na_(2)CrO_(4)+8CO_(2))):}`
Step III : Conversion of `Na_(2)CrO_(4)` into `Na_(2)Cr_(2)O_(7)`
`2Na_(2)CrO_(4)+H_(2)SO_(4)" (conc.)" rarr Na_(2)Cr_(2)O_(7)+Na_(2)SO_(4)+H_(2)O`
Step IV : Conversion of `Na_(2)Cr_(2)O_(7)` to `K_(2)Cr_(2)O_(7)`
`Na_(2)Cr_(2)O_(7)+2KCl rarr K_(2)Cr_(2)O_(7)+2NaCl`
The solution is concentrated and hot solution is orange red crystals and `NaCl` remains in the solution. `K_(2)Cr_(2)O_(7)` is filtered and purified.
