JEE Main · 2021 · 25 Jul 2021 · Shift 1 · General Principles and Processes of Isolation of Metals

In the leaching of alumina from bauxite, the ore expected to leach out in the process by reacting with NaOH is:

(A)ZnO
(B) $Fe_{2} O_{3}$
(C) $SiO_{2}$ ✓ Correct
(D) $TiO_{2}$

Answer: (C)

Solution

Bauxite is leached with hot concentrated sodium hydroxide because alumina is amphoteric and passes into solution as sodium aluminate. Whatever else in the ore is acidic or amphoteric dissolves with it, and silica is an acidic oxide:

Si O_{2} + 2 NaOH ⟶ N a_{2} Si O_{3} + H_{2} O

Iron(III) oxide is basic and titanium dioxide is inert towards alkali, so both are left behind in the red mud, and zinc oxide is not an impurity of bauxite. The oxide that leaches out along with the alumina is

Si O_{2}

JEE Main · 2021 · 25 Jul 2021 · Shift 1 · Single correct option

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JEE Main · 2021 · 25 Jul 2021 · Shift 1 · General Principles and Processes of Isolation of Metals

Solution

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