How can you separate alumina from silica in a bauxite ore associated with silica? Give equations, If any.

How can you separate alumina from silica in a bauxite ore associated w

1.	How can you separate alumina from silica in a bauxite ore associated with silica? Give equations, If any.
Answer» Solution :Pure alumina may be separated from bauxite by Baeyer.s process as discussed below : The bauxite ore associated with silica is heated with a concentrated (45%) solution of NaOH at 473-523K and 35-36 atmosphere pressure. Under these conditions, alumina dissolves as SODIUM meta-aluminate and silica as sodium silicate leaving behind the impurities. `{:(Al_(2)O_(3)(s)+2NaOH(aq)+3H_(2)O(L)to 2Na[Al(OH)_(4)](aq)),(" AluminaSodium meta-aluminate "),(SiO_(2)(s)+2NaOH(aq)overset(473-523K)(to)Na_(2)SiO_(3)(aq)+H_(2)O(l)),(" SilicaSodium silicate "):}` The resulting solution is filtered to remove the undissolved impurities and neutralised by passing `CO_(2)` GAS. Thereafter, the solution is SEEDED with freshly prepared sample of hydrated alumina when hydrated alumina GETS precipitated leaving sodium silicate in the solution. `{:(2Na[Al(OH)_(4)](aq)+CO_(2)(g)to Al_(2)O_(3).xH_(2)O(s)+2NaHCO_(3)(aq)),("Hydrated alumina "):}` The hydrated alumina is filtered, dried and heated to give back pure `Al_(2)O_(3)`. `{:(Al_(2)O_(3).xH_(2)O(s) overset(1473K)(to) Al_(2)O_(3)(s)+H_(2)O),(" Hydrated aluminaPure alumina"):}`.