Question

What is the significance of leaching in the extraction of aluminium ?

Answer 1

Aluminium usually contains silica $\left(Si{O}_2\right)$, iron oxide $\left(F{r}_2{O}_3\right)$ and titanium oxide $\left(Ti{O}_2\right)$ as impurities. These impurities can be removed by the process of leaching During leaching, the powdered bauxite ore is heated with a concentrated (45%) solution of NaOH at 473-523 K, where alumina dissolves as sodium meta - aluminate and silica $\left(Si{O}_2\right)$ as sodium silicate leaving $F{e}_2{O}_3,Ti{O}_2$ and other impurities behind . $A{l}_2{O}_3\left(s\right)+2NaOH\left(aq\right)+3H_{2}O\left(l\right)\stackrel{473-523K}{\to }2Na\left[Al\right(OH{)}_4]aq$.