Describe the three steps involved in the leaching of bauxite to get pure alumina (equations not expected). 

Explanation

Baeyer.s process is one of the methods used.
(a) This method involves the digesting or powdered bauxite ore with concentrated NaOH at 473 - 523 K and 35 - 36 bar pressure. `Al_2O_3` is leached out as sodium aluminate (and `SiO_2` too as sodium silicate) leaving the impurities behind,
`underset("bauxite")(Al_2O_3(S)+2NaOH(aq)+3H_2O(I))tounderset("Sodium aluminate")(2Na[Al(OH)_4](aq))`
(b) Now `CO_2` gas is passed through the solution and a small amount of freshly prepared hydrated aluminium oxide is also added in order in induce the precipitation.
`2Na[Al(OH)_4](aq)+CO_2(aq)tounderset("Hydrated aluminium oxide ppt")Al_2O_3.xH_2O(s)+2NaHCO_2(aq)`
(c) The impurities of silica remain in the solution and the precipitate. formed is-filtered, washed, dried and ignited to produce pure alumina.
`Al_2O_3,xH_2O(s)tooverset(1470K)toAl_2O_3(s)+xH_2O(g)`