Separation of alumina from silica in bauxite ore associated with silica, at first the powdered ore is digested with a concentrated NaOH solution at 473 - 523 K and 35 - 36 bar pressure. This leads to the leaching out of alumina (Al₂O₃) as sodium aluminate and silica (SiO₂) as sodium silicate leaving the impurities behind.

Then, carbon dioxide gas is passed through the solution to neutralize the aluminate ion in the solution, which results in the precipitation of hydrated alumina. To induce precipitation, the solution is seeded with freshly prepared samples of hydrated alumina.

During this process, sodium silicate remains in the solution. The hydrated alumina so obtained is filtered, dried, and heated to get back pure alumina.