Question

What is an auto reduction reaction?

Answer 1

For the extraction of metals, an auto reduction process is used. Metals cannot be directly extracted from its ores or minerals, therefore it requires a specialized process. Auto reduction is used for less electropositive metals.

Complete answer:
The process of extracting metals from their respective ore is called metallurgy. The process of obtaining metals in their free state from the concentrated ores is termed as extraction. Auto reduction is one of the industrial processes of metal extraction in metallurgy.
Auto reduction is a process in which ${\text{sulphide}}$ ores of less electropositive metals like $Hg,Cu,Pb$ etc. are partially heated or roasted in the air. This roasting or heating converts the ${\text{sulphide}}$ into its oxides or $sulphate$ . This then further reacts with the remaining of ${\text{sulphide}}$ ore in the absence of air to give out less electropositive metals and gas which is ${\text{sulphur dioxide}}$ as the terminating product.
An example of an auto reduction process is the $Copper$ ore extraction. In this reaction ${\text{sulphide}}$ ore of $Copper$ is heated or roasted in the presence of air which then gives it’s oxide. Then in the absence of air this reaction is further carried out by increasing the temperature to convert the leftover ${\text{sulphide}}$ ore to form metal. The principal ore of $Copper$ is $Copper{\text{ }}pyrite$ from where the metal $Copper$ is obtained. The reaction is as follow-
$2C{u_2}S + 3{O_2} \to 2CuO + 2S{O_2}$
$C{u_2}S + 2C{u_2}O \to 6Cu + 2S{O_2}$

Note:
The reason we call it an auto reduction process is because no other external agent is used for the reduction. It is not used for the metals which are more electropositive in nature. Also it is a two-step process where one is in the presence of air and then in the absence of air.