CHEMICAL REDUCTION

Reduction reactions

Reduction is the loss of oxygen from a molecule or the gaining of one or more electrons. Reduction is a process where a substance

• Gains one or more electrons
• Loss  an oxygen atom or atoms
• Gain  a hydrogen atom or atoms 

Reduction is gain of electrons and thus gaining of negative charge. The atom that acquired electrons is said to be reduced.

Methods of reduction

In chemical reduction process, the choice of reducing agent depends upon the chemical reactivity of the metal.

Sub Topics

1.     Smelting  (Carbon reduction method)

2.     Hydrogen reduction method

3.     Carbon monoxide reduction method

4.     Magnesium reduction method

5.     Aluminium  reduction method  (Alumino Thermic Process)

6.     Self-reduction method

7.     Reduction by more electropositive metals (precipitation or hydrometallurgy)

Smelting (Carbon reduction method

This method is used for the extraction of lead, zinc, iron, copper, manganese and tin. In this method, the roasted oxide ore is mixed with carbon (charcoal, coal or coke) and a flux, and is heated to a very high temperature in a suitable furnace. Carbon reduces the oxide to metal.

Hydrogen reduction method

Hydrogen can reduce certain oxides to metals e.g.,

Carbon monoxide reduction method

In certain cases CO gas produced in the furnace itself can be used as a reducing agent. For example,

Magnesium reduction method

Oxides of certain metals are reduced by Mg e.g.,

Aluminium reduction method (Alumino Thermic Process)

Certain metal oxides cannot be reduced by carbon. Such metallic oxides can be reduced by aluminium powder. This process has been widely used to reduce TiO₂, Cr₂O₃ and Mn₃O₄ to get the corresponding metal.

Self-reduction method

When the sulphide ores of less electropositive metals like Hg, Cu, Pb, Sb etc., are heated in air, a part of the ore gets oxidized to oxide or sulphate, which then reacts with the remaining sulphide ore to give the metal and SO₂. This process is also known as self-reduction method.

Reduction by more electropositive metals (precipitation or hydrometallurgy)

This method is employed when leaching method had been used to concentrate the ore. The metals are obtained by reducing their ions in the solution as precipitates by a more electropositive metal. This method is also called as the hydrometallurgy method of reduction.

For example, when a heap of copper glance (Cu₂S) is exposed to air and water, it gets converted to copper sulphate. Copper is recovered from copper sulphate solution by adding some iron scrap to its solution.