Reduction of Metal Oxide to Metal – Introduction, Methods

Reduction of Metal Oxide to Metal: The earth’s crust contains metals and is a good source of metals. Metals are most commonly found in nature in their combined state, but they can also be found in their state. A native metal is a metal that occurs naturally in its metallic state, either in pure form or as an alloy. Most metals are unable to withstand natural processes such as oxidation, corrosion, and so on. As a result, only non-reactive metals such as gold, silver, and platinum are found in their native or state. Most metals are obtained as compounds and must be filtered to remove impurities before being used in various applications. The process of extracting metals from ores is known as metallurgy, and these naturally occurring metal compounds are known as minerals. Mining is the most common method of extracting metals from the earth.

In this article, we will explore one of the steps used in extracting metals- Reducing metal oxide to metal.

What is the Reduction of Metal Oxide to Metal?

Reduction is the process of converting metal oxides into metals. Depending on the reactivity of the ore, different types of reducing agents are used for reduction. Some of the common methods which we will study are as follows-
i. Reduction by Heat (pyrometallurgy)
ii. Reduction by Coke (smelting)
iii. Reduction by Aluminium (aluminotherapy)
iv. Electrolytic Reduction

Activity Series

To reduce a metallic oxide, it must be reacted with an element higher on the reactivity series. For example, carbon is used to reduce zinc oxide because carbon is more reactive (placed higher on the reactivity scale) than zinc. Because magnesium is more reactive than carbon, it cannot be reduced with carbon.

The arrangement of metals in a vertical column in decreasing reactivity order is known as the reactivity series of metals. The most reactive metals are at the top of the reactivity series, while the least reactive metals are at the bottom.

The reactivity series is as follows:

Reduction by Heat (Pyrometallurgy)

This method is used to reduce oxides of metals in the lower part of the reactivity series, such as \({\rm{Cu}}, {\rm{Hg}},\) and \({\rm{Ag}}\). This method involves only heating, rather than any reductant, carrying out the reduction reaction.

Mercury ore, for example, can be reduced in the following ways:

Chemical Reduction

To obtain metals, various reducing agents are used for various metal – oxides. Carbon, \({\rm{AI}}, {\rm{NA}},\) and \({\rm{Ca}}\) are some of the reducing agents used. Let us see the reduction by coke/carbon and aluminium.

Reduction by Coke/Carbon

Metal oxides such as \({\rm{Zn}}, {\rm{Fe}}, {\rm{Cu}}, {\rm{Ni}}, {\rm{Sn,}}\) and \({\rm{Pb}}\) are typically reduced by using carbon as a reducing agent. Coke is mixed with roasted ore and heated to a high temperature in a furnace in this process. Coke converts metal oxides to metal.

For example-

i. \(2{\rm{F}}{{\rm{e}}_2}{{\rm{O}}_3} + 3{\rm{C}} \to 4{\rm{Fe}} + 3{\rm{C}}{{\rm{O}}_2}\)

ii. \({\rm{ZnO + C}} \to {\rm{Zn + CO}}\)

iii. \({\rm{PbO + C}} \to {\rm{Pb + CO}}\)

Reduction by Aluminium (aluminotherapy)

This is known as the thermite process, as well as aluminotherapy. \({\rm{Al}}\) has higher reactivity than carbon. \({\rm{Al}}\) is used to reduce metal-oxides that cannot be reduced by coke. \({\rm{Al}}\) attracts oxygen from the metal-oxide and converts it to aluminium oxide, releasing the metal. \({\rm{Al}}\) extracts and reduces metal oxides of \({\rm{Mn}}\) and \({\rm{Cr}}\). The following example illustrates what happens when manganese dioxide is heated with aluminium powder.

Electrolytic Reduction

The oxides of metals that are high in reactivity series like \({\rm{K, Na, Ca, Mg}}\) and \({\rm{Al}}\) can be reduced to metals by electrolytic reduction.

For example- The electrolytic reduction method is used to extract aluminium. In this method, a steel container with a graphite carbon layer is required. The container is filled with aluminium oxide and cryolite mixture, and some carbon rods are dipped in it so that they do not come into contact with the steel container. The negative charge of the battery is connected to the graphite-coated steel container, while the positive charge is connected to the carbon rods.

When the electric flow begins, so does the electrolysis. During electrolysis, \({{\rm{O}}^{{\rm{2 – }}}}\) donates an electron at the anode and produces \({{\rm{O}}_{\rm{2}}}\) gas, while \({\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}\) in the solution accepts an electron at the cathode and converts to \({\rm{Al}}\) metal.

Summary

We can conclude that metal-oxides are converted into metal using the reduction process. Metal-chloride can also be directly reduced. Reduction is the fourth process involved in the extraction of metals. The choice of reduction reaction is determined by the chemical reaction or reactivity of metals. In general, we studied the reduction of metal oxide to the respective metals by heat reduction, chemical reduction, or electrolytic reduction processes.

FAQs on Reduction of Metal Oxide to Metal

Q.1. What is the reduction of metal oxide?
Ans: Reduction is the process of converting metal oxides into metals. Depending on the reactivity of the ore, different types of reducing agents are used for reduction. Some of the common methods which we will study are as follows-
i. Reduction by Heat (pyrometallurgy)
ii. Reduction by Coke (smelting)
iii. Reduction by Aluminium (aluminotherapy)
iv. Electrolytic Reduction

Q.2. What is the self-reduction method?
Ans: This method is used for oxides of metals in the lower part of the reactivity series, such as \({\rm{Cu}}, {\rm{Hg}},\) and \({\rm{Ag}}\). This process involves only heating rather than any reductant that can carry out the reduction reaction.

Q.3. What are the methods of reduction of metal oxides?
Ans: There are three main methods of reducing metal oxides which are as follows-
i. Electrolytic reduction
ii. Chemical reduction
iii. Reduction by heat

Q.4. How many metals can be reduced by carbon reduction as well as self-reduction?
Ans: There are some metals, like copper \({\rm{(Cu)}}\) and lead \({\rm{(Pb)}}\), that can be reduced by carbon reduction and self-reduction.

Q.5. What are the two chemicals that can reduce metal oxides?
Ans: To obtain metals, various reducing agents are used for various metal – oxides. Carbon, \({\rm{Al}}, {\rm{Na}},\) and \({\rm{Ca}}\) are some of the reducing agents used.

Q.6. Which metal oxides can be reduced by carbon?
Ans: Although carbon is non-metal, it is more reactive than some metals. This means that some metals can be extracted using carbon from their metal oxides. This method is effective for zinc, iron, tin, lead, and copper.

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