Name: Ellingham Diagram: Introduction
Uploaded: 2019-07-19
Duration: 7 min 42 s
Description: The Ellingham diagram proved to be a cornerstone for the process of reducing metal oxides to their native form. Watch this video to learn about the Ellingham...

Question

When bauxite ore contains a considerable quantity of silica as an impurity, which process is used for the purification of bauxite ore?

Accepted Answer

When bauxite $({Al}_{2} O_{3} . 2 H_{2} O)$ ore contains more than $10 %$ of silica $({SiO}_{2})$ as an impurity, Serpeck's process is used for the industrial purification of bauxite ore. In this method, powdered bauxite is mixed with carbon and heated up to $1800 ℃$ and a current of nitrogen is passed to give aluminium nitride which again reacts with water gives precipitates of $Al {(OH)}_{3}$ . It is later filtered off and calcified to get highly pure aluminium oxide (alumina). The silica impurity present will be reduced by carbon to form silicon which is volatile at high temperatures. So, it is removed easily.

$\underset{Bauxite}{{Al}_{2} O_{3} . 2 H_{2} O} + 3 C + N_{2} \to \underset{Aluminium nitride}{2 AlN} + 3 CO + 2 H_{2} O$

$\underset{Aluminium nitride}{2 AlN} + 6 H_{2} O \to 2 {NH}_{3} + \underset{Aluminium Hydroxide}{Al {(OH)}_{3}}$

$2 Al {(OH)}_{3} \overset{Calcination}{\to} {Al}_{2} O_{3} + 3 H_{2} O$

$\underset{Silica}{{SiO}_{2}} + 2 C \to \underset{Silicon}{Si} + 2 CO$

Note: Bauxite is the main ore of aluminium and when silica is present in excess it is called white bauxite.

When bauxite ore contains a considerable quantity of silica as an impurity, which process is used for the purification of bauxite ore?

Important Questions on General Principles and Processes of Isolation of Elements

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