Chromium processing

Starting with mineral chromite, you get to sodium chromate, then sodium dichromate, then sodium chromite, then chromium (III) oxide then chromium (VI) oxide and lastly to chromium metal by aluminum thermite.

Cheat sheet

• {{#chem:FeO.Cr2O3}} chromite ore
• {{#chem:Na2CrO4}} (2-1-4) sodium chromate
• {{#chem:Na2Cr2O7}} (2-2-7) sodium dichromate
• {{#chem:Na2Cr2O4}} (2-2-4) sodium chromite

Core Reactions

1. Roast chromite ore with sodium carbonate at 1000°C in air, giving a mixture of sodium chromate and hematite

   {{#chem: 4FeO.Cr2O73 + 8Na2CO3 +&O2 {= 1000°C, air} 8Na2CrO4 + 2Fe2O3 + 8CO2(g)↑}}

2. Wash solids in water and filter giving aqueous sodium chromate

   {{#chem: Na2CrO4(s) + Fe2O3(s) + H2O = Na2CrO4(aq) + Fe2O3(s)↓}}

3. Filter
4. Discard residue (hematite).
5. Convert sodium chromate to sodium dichromate with sulfuric acid

   {{#chem: 2Na2Cr2O4 + H2SO4 = Na2Cr2O7 + Na2SO4 + H2O}}

6. Reduce sodium dichromate with carbon to give sodium chromite

   {{#chem: Na2Cr2O7 + 3C = Na2Cr2O4 + 3CO}}

7. Convert sodium chromite to chromium (III) oxide and sodium hydroxide with water

   {{#chem: Na2Cr2O4 + H2O = Cr2O3↓ + 2NaOH}}