Question

Name the process by which impure ore of aluminum gets purified by using a concentrated solution of an alkali.

Answer 1

Purification of Bauxite ore

1. Name of the purification process

It is the Baeyer's process that is used for the purification of impure oxides of Aluminum.

2. Chemical equations involved in Baeyer's process

• The main impurities found in the impure oxide of Aluminum$\left({\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O}\right)$ are Iron(III) oxide,${\mathrm{Fe}}_2{\mathrm{O}}_3$ and Silica$\left({\mathrm{SiO}}_2\right)$.
• It is a method of chemical purification, a fine powder of ore is treated with hot Sodium hydroxide$\left(\mathrm{NaOH}\right)$ solution.
• Impure${\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O}$ is amphoteric and gets dissolved in Sodium hydroxide solution whereas ${\mathrm{Fe}}_2{\mathrm{O}}_3$ is a basic oxide that is insoluble and removed by filtration.
• Sodium Aluminate$\left({\mathrm{NaAlO}}_2\right)$ is formed which on further acidification produces a precipitate of Aluminum hydroxide,$\mathrm{Al}{\left(\mathrm{OH}\right)}_3$ and releases sodium hydroxide in the solution.
• The formed precipitate of Aluminum hydroxide further undergoes ignition at ${1100}^{\mathrm{o}}\mathrm{C}$ and pure Alumina$\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ is extracted.
• The chemical reaction is as follows:

1. ${\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\stackrel{150-{200}^{\mathrm{o}}\mathrm{C}}{\to }2{\mathrm{NaAlO}}_2\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
2. ${\mathrm{NaAlO}}_2\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{50-{60}^{\mathrm{o}}\mathrm{C}}{\to }\mathrm{NaOH}\left(\mathrm{aq}\right)+\mathrm{Al}{\left(\mathrm{OH}\right)}_3\left(\mathrm{aq}\right)$
3. $2\mathrm{Al}\left({\mathrm{OH}}_3\right)\left(\mathrm{aq}\right)\stackrel{{1100}^{\mathrm{o}}\mathrm{C}}{\to }{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Hence, it is the Baeyer's process by which impure ore of Aluminum gets purified by using a concentrated solution of an alkali.