Write the equations for the reactions involved in the leaching of alumina from bauxite ore.

Explanation

Bauxite contains impurities like `SiO_(2)`, Ferric oxide `(Fe_(2)O_(3))Tio_(2)`, (Titanium oxide). Bauxite is powdered and digested (heated) with concentrated NaOH at `473 - 523 k` and 35 to 36 bar pressure. `Al_(2)O_(3)` dissolves in `NaOH` to form sodium aluminate. The insoluble `Fe_(2)O_(3) and TiO_(2)` are removed by filteration. `SiO_(2)` is converted into sodium silicate.
`Al_(2)O_(3)+2NaOH+3H_(2)Orarr 2Na[Al(OH)_(4)]`
The solution of sodium aluminate is neutralized by passing co, gas and the solution is seeded with freshly prepared hydrated `Al_(2)O_(3)` which induces the precipitation. It is filtered dried and heated to get pure `Al_(2)O_(3)` sodium silicate remains in the solutions
`2Na[Al(OH)_(4)]+CO_(2)rarrAl_(2)O_(3).3H_(2)O+NaHCO_(3)`
`Al_(2)O_(3).3H_(2)O overset(1470K)rarr Al_(2)O_(3)+3H_(2)O`