Step 1:

The preparation of potassium dichromate from iron chromite ore is as follows:

Potassium dichromate is prepared from chromite ore in the following steps.

Step (1): Preparation of sodium chromate

$4FeC{r}_2{O}_4+16NaOH+{\mathrm{7O}}_2\to 8N{a}_{2}Cr{O}_4+2F{e}_2{O}_3+8H_{2}O$
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Step (2): Conversion of sodium chromate into sodium dichromate

\(2 \mathrm{Na}_{2} \mathrm{CrO}_{4}+\text { conc. } \mathrm{H}_{2} \mathrm{SO_{4}} \rightarrow \mathrm{Na}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+\mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}\)

Step(3): Conversion of sodium dichromate to potassium dichromate

$N{a}_{2}C{r}_2{O}_7+2KCl \to K_{2}C{r}_2{O}_7+2NaCl$

Potassium chloride is less soluble than sodium chloride is obtained in the form of

orange colored crystals, and can be removed by filtration.

Step 2: 

The dichromate ion$\left(C{r}_2{O}_7^{2-}\right)$ exists in equilibrium with the chromate $\left(Cr{O}_4^{2-}\right)$ion at pH 4.

However, by changing the pH, they can be interconverted.

2 CrO₄^2– + 2H⁺ → Cr₂O₇^2– + H₂O

Cr₂O₇^2– + 2 OH^- → 2 CrO₄^2– + H₂O