Question

Name the process used for the concentration of bauxite ore. Give a brief account of the process.

Answer 1

Baeyer’s process is used for the concentration of bauxite ore. When there is a greater proportion of iron oxide in bauxite, this procedure is employed. To turn any ferrous oxide into ferric oxide, the finely ground bauxite ore is first roasted at a low temperature. When aluminium oxide enters the solution while NaAlO₂ and ferric oxide do not dissolve, the roasted ore is now digested using a hot, concentrated solution of caustic soda at 423 K under pressure. Sodium silicate (Na₂SiO₃) is created when some of the silica that is present as an impurity dissolves in sodium hydroxide.

\[\ce{Al2O3 * 2H2O + 2NaOH -> 2NaAlO2 + 3H2O}\]

\[\ce{SiO2 + 2NaOH -> Na2SiO3 + H2O}\]

Sodium silicate and sodium meta aluminate are present in the filtered solution. A tiny amount of recently precipitated aluminium hydroxide from the prior process is added to this after it has been diluted with water. After stirring the combination for a few hours, sodium silicate is left in the solution as aluminium hydroxide precipitates. To obtain pure alumina, this is filtered and burned.

\[\ce{NaAlO2 + 2H2O -> NaOH + Al(OH)3}\]

\[\ce{2Al(OH)3 ->[1473 K] Al2O3 + 3H2O}\]