Question

How is the ore of aluminium concentrated?
(A.) Roasting
(B.) Leaching
(C.) Froth floatation
(D.) Using Wilfley table

Answer 1

Hint: Aluminium ore is called bauxite. The bauxite is purified by the Bayer Process to produce aluminium oxide, a white powder form which aluminium can be extracted. Now try to solve this question accordingly.

Complete step by step answer:

Leaching is a chemical process of concentration of aluminium ore. Here the ore dissolves in a chemical solution and the minerals will react, then dissolve leaving behind the impurities only which filter out. And finally, the metal will be obtained from the chemical solution.

Let us now take a look at how we obtain Aluminium by leaching.

Leaching of aluminium from its ore bauxite on an industrial scale is known as the Bayer process. This process will give us the end product of aluminium oxide from bauxite. The other impurities of silica, titanium oxide and various other oxides will separate.

The first step in this process is to heat the bauxite ore to temperatures of 200$^{ 0 }$C along with a sodium hydroxide solution. This will convert the aluminium oxide to a solution of sodium aluminate. The silica will dissolve itself in the process. The chemical equation is

$Al_{ 2 }O_{ 3 }+2NaOH\quad \rightarrow \quad 2NaAlO_{ 2 }+H_{ 2 }O$

We remove solid impurities by filtration from the solution obtained. Then we bubble carbon dioxide through the aqueous solution of sodium aluminate to neutralize it. Aluminium hydroxide will precipitate out as a result.

$2NaAlO_{ 2 }+CO_{ 2 }\rightarrow 2Al(OH)_{ 3 }+Na_{ 2 }CO_{ 2 }+H_{ 2 }O$

This hydrated alumina is then heated to 1470K, which gives us a pure form of aluminium hydroxide without the impurities.

$2Al(OH)_{ 3 }\rightarrow Al_{ 2 }O_{ 3 }+3H_{ 2 }O$

Therefore, we can conclude that the correct answer to this question is option B.

Note: We should know that Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium as well.