Question

Write the reactions involved in the following processes:
Leaching of bauxite ore to prepare pure alumina.

Answer 1

Hint: The given description is about the Bayer’s process in which pure alumina is obtained by leaching of bauxite ore. Describing the Bayer’s process and the reactions taking place to give the final product can lead us to the required answer.

Complete answer:
Let us see the Bayer’s process to answer the given illustration;
Bayer’s process- The Bayer’s process is the principal method practised in industries. Here, refining of bauxite takes place, popularly known as leaching to produce alumina. Bauxite is the most abundant and important ore of aluminium known in nature.
General description of the process- In Bayer’s process firstly, bauxite ore is heated at high temperatures in a pressure vessel along with caustic soda i.s. sodium hydroxide. At the temperature of nearly $200{}^\circ C$ aluminium from the ore gets dissolved as hydrated sodium aluminate.
This then is allowed to be passed over by carbon dioxide gas to obtain hydrated aluminium oxide which would be easier to be dehydrated and finally obtain alumina at higher temperatures.
The reactions to describe the above process can be stated as;
$\begin{align}
& A{{l}_{2}}{{O}_{3}}_{\left( s \right)}+2NaO{{H}_{\left( aq \right)}}+3{{H}_{2}}{{O}_{\left( l \right)}}\to 2Na{{\left[ Al{{\left( OH \right)}_{4}} \right]}_{\left( aq \right)}} \\
& 2Na{{\left[ Al{{\left( OH \right)}_{4}} \right]}_{\left( aq \right)}}+2C{{O}_{2\left( g \right)}}\to A{{l}_{2}}{{O}_{3}}.x{{H}_{2}}{{O}_{\left( s \right)}}+2NaHC{{O}_{3\left( aq \right)}} \\
& A{{l}_{2}}{{O}_{3}}.x{{H}_{2}}{{O}_{\left( s \right)}}\xrightarrow{1470K}A{{l}_{2}}{{O}_{3\left( s \right)}}+x{{H}_{2}}{{O}_{\left( g \right)}} \\
& \\
\end{align}$

Note: The reactions can solely describe the process of leaching of bauxite ore to produce pure alumina i.e. Bayer’s process. But it is more complex than it is described above as bauxite ore contains many other fractions of other elements too which are considered as impurities.