Leaching of alumina from bauxite (Baeyer’s process) The powered bauxite ore is diagested with a concentrated solution of NaOH at 473 – 523 K and 35 – 36 bar pressure. AI2O3 is leached out as sodium aluminate along with SiO2 as sodium silicate. Other impurities like iron oxides and TiO2 are left behind.
AI2O3(s) + 2NaOH(aq) + 3H2O(l) → 2Na[AI(OH)4](aq)
The solidum aluminate in solution is neutralised by passing CO2 gas and hydrated Al2O3 is precipitated. At this stage, the solution is seeded with freshly prepared samples of hydrated Al2O3 which induces the precipitation of hydrated Al2O3.
2Na [AI(OH)4](aq) + CO2(g) → AI2O3. XH2O(s) + 2NaHCO3(aq)
The sodium silicate remains in the solution and hy-drated alumina is filtered, dried and heated to give back pure Al2O3.
Al2O3 ⋅ xH2O(s) \(\overset{1470\,K}{\longrightarrow}\) KAl2O3( s) + xH2O
