Anser the following questions? (any 1)
Explain briefly the Bayer's method for concentration of bauxite. Give related
equations.
How do we perceive different colours ?
Answers
The extraction of the metal from bauxite involves the three main steps.
Concentration of Bauxite \left( {Al}_{2}{O}_{3}.2 {H}_{2}O \right)(Al2O3.2H2O)
Concentration of ore is done by leaching which helps in removing impurities like {Fe}_{2}{O}_{3}, Si{O}_{2}Fe2O3,SiO2, etc. Bauxite is treated with NaOHNaOH to form sodium aluminate which on further reaction with C{O}_{2}CO2 gives pure Alumina.
{Al}_{2}{O}_{3} + 2 NaOH + 3 {H}_{2}O \longrightarrow 2 Na \left[ Al {\left( OH \right)}_{4} \right] \xrightarrow[-2 NaHC{O}_{3}]{2 C{O}_{2}} {Al}_{2}{O}_{3}.x{H}_{2}O \xrightarrow[1470 \; K]{\Delta} \underset{\text{Pure alumina}}{{Al}_{2}{O}_{3}} + x {H}_{2}OAl2O3+2NaOH+3H2O⟶2Na[Al(OH)4]2CO2−2NaHCO3Al2O3.xH2OΔ1470KPure aluminaAl2O3+xH2O
Electrolytic reduction of Alumina \left( {Al}_{2}{O}_{3} \right)(Al2O3)
Electrolytic reduction of pure alumina takes place in iron box (cathode) with cryolite \left( {Na}_{3}Al{F}_{6} \right)(Na3AlF6) and fluorspar \left( Ca{F}_{2} \right)(CaF