What is importance of leaching in extraction of al metal?
Answers
In the extraction of aluminium, the significance of leaching is to concentrate pure alumina (Al2O3)
from bauxite ore. Bauxite usually contains silica, iron oxide, and titanium oxide as impurities. In the
process of leaching, alumina is concentrated by digesting the powdered ore with a concentrated
solution of NaOH at 473-523 K and 35-36 bar. Under these conditions, alumina (Al2O3) dissolves as
sodium meta-aluminate and silica (SiO2) dissolves as sodium silicate leaving the impurities behind.
The impurities are then filtered and the solution is neutralized by passing CO2 gas. In this process,
hydrated Al2O3 gets precipitated and sodium silicate remains in the solution. Precipitation is induced
by seeding the solution with freshly prepared samples of hydrated Al2O3.
Hydrated alumina thus obtained is filtered, dried, and heated to give back pure alumina (Al2O3).