Question

write a balance chemical equation when caustic soda solution is heated under pressure with bauxite​

Answer 1

Answer:

Bauxite ore is a mixture of hydrated aluminium oxides and compounds of other elements such as iron. The aluminium compounds in the bauxite may be present as gibbsite 2(Al(OH)3), böhmite (γ-AlO(OH)) or diaspore (α-AlO(OH)); the different forms of the aluminium component and the impurities dictate the extraction conditions. Aluminum oxides and hydroxides are amphoteric, meaning that they are both acidic and basic. The solubility of Al(III) in water is very low but increases substantially at either high or low pH. In the Bayer process, bauxite ore is heated in a pressure vessel along with a sodium hydroxide solution (caustic soda) at a temperature of 150 to 200 °C. At these temperatures, the aluminium is dissolved as sodium aluminate (primarily [Al(OH)4]−) in an extraction process. After separation of the residue by filtering, gibbsite is precipitated when the liquid is cooled and then seeded with fine-grained aluminum hydroxide crystals from previous extractions. The precipitation may take several days without addition of seed crystals.[2]

The extraction process converts the aluminium oxide in the ore to soluble sodium aluminate, 2NaAlO2, according to the chemical equation:

Al2O3 + 2 NaOH → 2 NaAlO2 + H2O

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