Name the chief ores of tin, iron and aluminium. What methods are employed for the concentration or purification of their ores ?

Explanation

Chied ores of
(i) Tin : cassiterite, `SnO_(2)`
(ii) Iron : haematite, `fe_(2)O_(3)`, magnetite, `Fe_(3)O_(4)`
(iii) Aluminium : bauxide, `Al_(2)O_(3).2H_(2)O`
Diaspore, `Al_(2)O_(3).H_(2)O`.
(i) Concentration of cassiterte, `SnO_(2)` : It is concentrated by gravity process.
(ii) Concentration of harmatite : The ore is crushed and washed with water to remove siliceous impurities. The washed ore is then dressed up by electromagnetic separation.
(iii) Concentration of bauxite : The ore is concentrated by Baeyer's process. The crushed ore is first heated at moderate temperature as to convert ferrous oxide into ferric oxide. It is then digested with concentrated solution of sodium hydroxide in which aluminium oxide dissolves forming soluble sodium metaluminate `(naAlO_(2))` while ferric oxide and silica remains insoluble and settle down.
`Al_(2)O_(3).2H_(2)O rarr2NaAlO_(2) + 3H_(2)O`
The filtrate containing sodium metalluminate is agitated with freshly precipitated `Al(OH)_(3)` when sodium metaluminate undergoes hydrolysis to precipitate `Al(OH)_(3)`.
`NaAlO_(2) +2H_(2)O rarr NaOH + underset("ppt") (Al(OH)_(3)darr)`
The precipitate is washed, dried, and heated to get `al_(2)O_(3)`.
`2Al(OH)_(3) overset(Delta) underset(1500^@C)rarr Al_(2)O_(3) +3H_(2)O`.