Question

Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores

Answer 1

Extraction :

• Extraction is the process of selectively removing a compound of interest from a mixture using a solvent.
• The metals can be extracted by converting the ore into metallic oxide and by reducing it into metal.
• The conversion of ore to metallic oxide can be done by calcination and roasting.
• Calcination is the process of heating to a high temperature below the melting point of metal in absence of air or a limited supply of air
• Generally, calcination is utilized to convert hydrated oxides or hydroxides and carbonates into respective oxides.
• Roasting is the process of heating to a high temperature below the melting point of metal in presence of air or oxygen.
• Generally roasting is utilized to convert sulphide ores to respective oxides.

Extraction of metals of low reactivity:

• Mercury is a metal of low reactivity.
• Cinnabar is the sulphide ore of mercury and its chemical formula is $\mathrm{HgS}$.
• Since the Cinnabar ($\mathrm{HgS}$) is a sulphide ore, first the roasting process will be carried out to convert Cinnabar($\mathrm{HgS}$) to ($\mathrm{HgO}$).

$\underset{\mathrm{Cinnabar}}{2\mathrm{HgS}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Mercuric}\mathrm{oxide}}{2\mathrm{HgO}\left(\mathrm{s}\right)}+\underset{\mathrm{Sulfur}\mathrm{dioxide}}{2{\mathrm{SO}}_2\left(\mathrm{g}\right)}$

• Now, the mercuric oxide is heated and undergoes self-reduction to obtain mercury.

$\underset{\mathrm{Mercuric}\mathrm{oxide}}{2\mathrm{HgO}\left(\mathrm{s}\right)}\to \underset{\mathrm{Mercury}}{2\mathrm{Hg}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}$

Extraction of metals of high reactivity:

• Zinc is a metal of medium reactivity.
• Zinc blende is an ore of zinc and its molecular formula can be written as $\mathrm{ZnS}$.
• Since the zinc blende ($\mathrm{ZnS}$) is a sulphide ore, first the roasting process will be carried out to convert zinc blend ($\mathrm{ZnS}$) to zinc oxide ($\mathrm{ZnO}$).

$\underset{\mathrm{Zinc}\mathrm{blende}}{2\mathrm{ZnS}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Zinc}\mathrm{oxide}}{2\mathrm{ZnO}\left(\mathrm{s}\right)}+\underset{\mathrm{Sulfur}\mathrm{dioxide}}{2{\mathrm{SO}}_2\left(\mathrm{g}\right)}$.

• Now, the reduction of the zinc oxide in the presence of carbon leads to the formation of zinc metal.

$\underset{\mathrm{Zinc}\mathrm{oxide}}{\mathrm{ZnO}\left(\mathrm{s}\right)}+\underset{\mathrm{Carbon}}{\mathrm{C}\left(\mathrm{s}\right)}\to \underset{\mathrm{Zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\mathrm{Carbon}\mathrm{monoxide}}{\mathrm{CO}\left(\mathrm{g}\right)}$