Study Notes on Extraction of Low Reactive Metals

Metals are extracted from their ores. Each metal reacts differently with different substances. The extraction of any metal from its ore is dependent on the reactivity of the metal. Thus, the metals present at the bottom of the reactivity series versus those present at the top of the reactivity series follow different processes of extraction.

The following metals in the periodic table are categorised as low reactive metals as they are present at the bottom of the reactivity series. 

• Copper (Cu)
• Mercury (Hg)
• Silver (Ag)
• Platinum (Pt)
• Gold (Au)

Metals placed higher up in the reactivity series, that is, those metals above carbon, can be extracted through electrolysis. However, both low reactive metals, that is, those present at the bottom of the reactivity series, as well as those above hydrogen gas but below carbon, can be extracted by reduction with carbon.

Low Reactive Metals and their properties

• The metals present at the bottom of the reactivity series, which is below Hydrogen gas, are less reactive than Hydrogen. Therefore, they are known as low reactive Metals.
• Copper (Cu), Mercury (Hg), Silver (Ag), Platinum (Pt), and Gold (Au) are some of the low reactive metals.
• Due to the un-reactive nature of these metals, their oxides can be reduced to metals by heating alone. 
• The three least reactive metals, silver, platinum, and gold, are freely present in nature. 
• Thermal decomposition is the name for the method of extraction of low reactive metals like Hg, Ag, Pt, and Au, which can be reduced to metals by heating alone, which is a mild phenomenon.
• The lesser stable oxide or compound that a metal forms, the easier it is for it to be extracted.
• Lesser energy is required for the extraction of low reactive metals or metals present at the bottom of the reactivity series, as compared to those above hydrogen gas.

Metals and their Position in the Reactivity Series

In the following table, Hydrogen gas, a non-metal, is taken as a factor for comparison of metals that are higher in reactivity than Hydrogen gas and those that are lower in reactivity than Hydrogen gas. 

Example of extraction of low reactive metals reduced to metals by heating alone

1. Copper

Copper sulphide ore is used for the extraction of copper, a low reactive metal, by using heat alone. This involves a two-step process:

Step 1

2Cu2S + 3O2 → 2Cu2O + 2SO2

The roasting of copper glance ore in the air leads to the generation of copper (I) oxide and sulphur dioxide.

Step 2

2Cu2O + Cu2S → 6Cu + SO2

Stopping air supply for roasting and combining the copper (I) oxide with residual Cu2S, that is, copper (I) sulphide, to get copper, the metal, and sulphur dioxide.

1. Mercury

Cinnabar or HgS is an ore of mercury, which gives mercury through heating. 

This involves a two-step process:

Step 1

2HgS + 3O2 → 2HgO + 2SO2

The roasting of cinnabar ore in the air leads to the generation of mercury (II) oxide.

Step 2

2HgO → 2Hg + O2

The reduction or decomposition of mercury (II) oxide into mercury, metal and oxygen on the application of heat (300o C).

This example taking mercury as the metal shows how metals present at the bottom of the reactivity series can be reduced to metals by heating alone. In other words, mercury and copper are among the low reactive metals which have an oxide that can be reduced to metals by heating.

Conclusion

The reactivity series and the position of metals in the reactivity series are important concepts when studying the extraction of metals. It can be conclusively said and noted that the extraction of low reactive metals or those that are present at the bottom of the reactivity series is determined by their rate of reactivity, and their oxides can therefore be reduced to metals by heating. Processes for the extraction of Mercury and Copper thus become a great example of extraction of low reactive metals.