Extraction of Crude Metal from Concentrated Ore

Table of Content

What is Crude Metal?
- Steps for Extraction of Metal
Ellingham Diagram
Calcination

What is Crude Metal?

The ore is considered as crude metal. It is a solid mass from which pure metal can be obtained.

Steps for Extraction of Metal

Extraction of metals involves three major steps:

Concentration of Ore
Isolation of metal from the concentrated Ore
Purification of the metal

Isolation of metal from the concentrated Ore involves the refining of metals from the compounds. The first step is to convert an ore into an oxide. Then the oxide is reduced using a reducing agent.

Conversion to Oxide- Metal refining is done by heating the ore in a limited supply or absence of oxygen. For example, hydrated ferric oxide is heated to form dry ferric oxide.

Fe₂O₃.xH₂O(s) → Fe₂O₃ (s) + xH₂O(g)

Fig. 1. Equation of conversion ore to oxide

Roasting- During this process, extraction is done by heating the ore in a regular supply of air. Sulphide ores of elements such as Zinc, Lead and Copper are treated and concentrated using this methodology. The sulphur in the ore, at high temperature reacts with the oxygen to form Sulphur Dioxide and escapes out.

2ZnS + 3O₂→ 2ZnO + 2SO₂

Fig. 2. Roasting

Reduction of Oxide to Metal – It is a process of removal of oxygen. Generally, reducing agents such as carbon or carbon monoxide is used in this step. Carbon is added to the metal oxide obtained from the ore and then heated.

MxOy + yC → xM + y CO

Ellingham Diagram

It is a graphical representation of Gibbs energy. These diagrams are used for finding the choice of reducing agent in the reduction of the oxides. These are used to find out the feasibility of thermal reduction of an ore.

Fig. 1. Ellingham Diagram

Limitations of Ellingham Diagram

It does not give any information regarding the kinetics of the reduction process.
These diagrams believe that reactants and products are in equilibrium, but this is not always the case.

Calcination

The process of heating in limited supply or absence of air is known as calcination.

Examples of calcination processes include the following:

decomposition of carbonate minerals, as in the calcination of limestone to drive off carbon dioxide;
decomposition of hydrated minerals, as in the calcination of bauxite and gypsum, to remove crystalline water as water vapor;
decomposition of volatile matter contained in raw petroleum coke;
removal of ammonium ions in the synthesis of zeolites.