Bauxite Bath: Purify with NaOH
Dissolve bauxite in sodium hydroxide to remove impurities.
What this lesson covers
Why it matters
Bauxite ore is messy, full of stubborn impurities like iron oxide and silica. We need a chemical bath that dissolves only the valuable aluminium component.
The idea in plain words
Match the reactants to products: Al₂O₃.2H₂O + 2NaOH → 2NaAlO₂ + 3H₂O
Predict first
What happens when bauxite meets hot, concentrated sodium hydroxide?
Aluminium oxide is amphoteric. In hot concentrated NaOH, it reacts to form soluble sodium aluminate, leaving impurities behind.
- Nothing happens; aluminium oxide is inert to bases.
- The bauxite dissolves to form soluble sodium aluminate. — correct
- It forms a precipitate of aluminium hydroxide.
- It releases oxygen gas immediately.
What you do
Add the hot concentrated NaOH to the bauxite and heat under pressure (in a digester/autoclave). Observe the alumina dissolving.
Check yourself
Why is concentrated NaOH used instead of dilute?
The reaction requires concentrated alkali and heat to proceed effectively for purification.
Identify the soluble product formed in this step.
The equation shows NaAlO₂ is the product, which is soluble in water, allowing separation from insoluble impurities.
What is the role of heat in this reaction?
The reaction conditions specify heat is required to facilitate the reaction between the oxide and the base.
- Dilute NaOH is too weak to dissolve the oxide. — correct
- Concentrated NaOH is cheaper.
- Dilute NaOH would explode.
- Aluminium hydroxide
- Sodium aluminate (NaAlO₂) — correct
- Sodium oxide
- Aluminium chloride
- To increase the rate of dissolution. — correct
- To evaporate all the water.
- Heat is not required.