How can you separate alumina from silica in a bauxite are associated with silica? Give equatiions, if any.

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Solution

Baeyer's Process Bauxite ore is concentrated by the method of leaching or chemical separation,
Baeyer's process is one of the methods used.
(a) This method involves the digesting of powdered bauxite ore with concentrated NaOH at 473-523 K and 35-36 bar pressure,

$A l_{2} O_{3}$ is leached out as sodium aluminate $(a n d S i O_{2})$ too as sodium silicate) leaving the impurities behind.

(b) Now, $C O_{2}$ gas is passed through the solution and a small amount of freshly prepared hydrated aluminium oxide is also added in order to induce the precipitation.

$2 N a [(A l) (O H)_{4}] (a q) + C O_{2} (a q) ⟶ A l_{2} O_{3} . x H_{2} O (s) H y d r a t e d a l u m i n i m u m + 2 N a H C O_{3} (a q) o x i d e P P t$

(c) The impurities of silica remaining in the solution and the precipitate. formed is filtered washed, dried and ignited to produce pure aumina.
$A l_{2} O_{3} . x H_{2} O (s) 1470 K - --- \to A l_{2} O_{3} (s) + x H_{2} O (g)$

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