In aluminum extraction by the Bayer's process, alumina is extracted from bauxite by sodium hydroxide at high temperature and pressures. $$A{{l}_{2}}{{O}_{3}}(s)+2O{{H}^{-}}(aq)\to 2A{{l}^{-}}_{2}(aq)+{{H}_{2}}O(\ell )$$ Solid impurities such as $$F{{e}_{2}}{{O}_{3}}$$ and $$Si{{O}_{2}}$$ are removed and then Al$${{(OH)}^{-}}_{4}$$ is reprecipitated. $$Al{{(OH)}^{-}}_{4}\to A{{l}_{2}}{{O}_{3}}\cdot 2{{H}_{2}}O(s)+2O{{H}^{-}}(aq)$$ In the industrial world

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the water is evaporated.

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carbon dioxide is added to precipitate the alumina

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Temperature and pressure are dropped and the super- saturated solution is seeded

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both [a] and [b] are practiced

1.	In aluminum extraction by the Bayer's process, alumina is extracted from bauxite by sodium hydroxide at high temperature and pressures. \[A{{l}_{2}}{{O}_{3}}(s)+2O{{H}^{-}}(aq)\to 2A{{l}^{-}}_{2}(aq)+{{H}_{2}}O(\ell )\] Solid impurities such as \[F{{e}_{2}}{{O}_{3}}\] and \[Si{{O}_{2}}\] are removed and then Al\[{{(OH)}^{-}}_{4}\] is reprecipitated. \[Al{{(OH)}^{-}}_{4}\to A{{l}_{2}}{{O}_{3}}\cdot 2{{H}_{2}}O(s)+2O{{H}^{-}}(aq)\] In the industrial world
A.	carbon dioxide is added to precipitate the alumina
B.	Temperature and pressure are dropped and the super- saturated solution is seeded
C.	both [a] and [b] are practiced
D.	the water is evaporated.
Answer» D. the water is evaporated.

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