reactions involved:1.leaching of bauxite ore to prepare pure alumina.
2.refining of zirconium by van-arkel method.
3.recovery of gold after gold ore has been leached with NaCN solution.
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1. Bauxite contains oxides of Si and Ti as impurities, which is leached off from its ore. NaOH is added to this powdered alumina which reacts to form the following products.
Al₂O₃ + 2NaOH + 3H₂O → 2Na[Al(OH)₄]
2Na[Al(OH)₄] + CO₂ → Al₂O₃.xH₂O + 2NaHCO₃
Al₂O₃.xH₂O → Al₂O₃ + H₂O
2. Zirconium is heated in the presence of vapours of Iodine to for ZrI₄, which is volatile. This, when heated over a filament of tungsten, gives pure Zirconium.
Impure Zr + 2I₂ → (heated) → ZrI₄
ZrI₄ → (Heated with W) → Zr + 2I₂
3. Gold can be recovered from the gold ore after it has been leached off with NaCN solution.
4Au + 8CN⁻ + 2H₂O + O₂ → 4[Au(CN)₂]⁻ + 4OH⁻
2[Au(CN)₂]⁻ + Zn → [Zn(CN)₄]²⁻ + 2Au
Al₂O₃ + 2NaOH + 3H₂O → 2Na[Al(OH)₄]
2Na[Al(OH)₄] + CO₂ → Al₂O₃.xH₂O + 2NaHCO₃
Al₂O₃.xH₂O → Al₂O₃ + H₂O
2. Zirconium is heated in the presence of vapours of Iodine to for ZrI₄, which is volatile. This, when heated over a filament of tungsten, gives pure Zirconium.
Impure Zr + 2I₂ → (heated) → ZrI₄
ZrI₄ → (Heated with W) → Zr + 2I₂
3. Gold can be recovered from the gold ore after it has been leached off with NaCN solution.
4Au + 8CN⁻ + 2H₂O + O₂ → 4[Au(CN)₂]⁻ + 4OH⁻
2[Au(CN)₂]⁻ + Zn → [Zn(CN)₄]²⁻ + 2Au
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