Q22.26P - Chemistry: Molecular Nature Of Matter And Change

Question

What are the distinguishing features of each extraction process:

 pyrometallurgy, electrometallurgy, and hydrometallurgy? Explain briefly how the types of metallurgy are used in the production of

(a) Fe; 

(b) Na; 

(c) Au; 

(d) Al.

Step-by-Step Solution

Answer

1. Pyrometallurgy is used to extract the metal.
2. Electrometallurgy and pyrometallurgy are used in the sodium production process.
3. Hydrometallurgy procedures are used to produce gold.
4. Pyrometallurgy, hydrometallurgy, and electrometallurgy procedures are required for aluminium extraction.

Step 1: Introduction

Aqueous solutions used to extract metals from ores in hydrometallurgy (leaching). Pyrometallurgy is concerned with chemical reactions that occur at high temperatures. Electrometallurgy is the study of metallurgical processes that occur in an electrolytic cell.

Step 2: (a) Explanation of pyrometallurgy

For metal extraction, pyrometallurgy uses heat, electrometallurgy uses an electrochemical process, and hydrometallurgy uses the metal's aqueous solution chemistry.

Iron production begins with the partial reduction of raw materials (typically hematite, coke, limestone, and mineral). The $\mathrm{hematite},{\mathrm{Fe}}_2{\mathrm{O}}_3$ is reduced to ${\mathrm{Fe}}_3{\mathrm{O}}_4$  and $\mathrm{FeO}\left(\mathrm{iron}\mathrm{oxide}\right)$ then to at temperatures between ${200}^{°}\text{C}$ and ${700}^{°}\text{C}$. Carbon monoxide $\left(\mathrm{CO}\right)$, derived by burning coke, is the reducing agent $({700}^{°}\mathrm{C}\mathrm{to}{1200}^{°}\mathrm{C})$, the iron(II) oxide is reduced to iron by ${\text{CO}}_2$.

(Fe). Acidic silica particles in the remaining impurities (text it (the gangue) combine with basic calcium oxide to generate molten debris termed slag. To summarize, the production of Fe is reliant on the heating of the ore (hematite),

Therefore, pyrometallurgy are used to extract the metal.

Step 3: (b) Production of sodium

The production of sodium, Na, involves crushing and melting the sodium mineral halide,$\text{NaCl}$, in an electrolytic apparatus known as the Downs cell. Because the process requires molten $\text{NaCl}$ and not an aqueous solution, the ore is mixed with ${\text{CaCl}}_{\text{2}}$ to lower the melting point from ${\text{801}}^{\text{°}}\text{C}$ to ${\text{580}}^{\text{°}}\text{C}$. This is because the cathode reaction in the electrolysis of an aqueous solution of would be the reduction of water to hydrogen due to reduction potentials. Sodium and chlorine are obtained via electrolysis of molten $\text{NaCl}$:

$\begin{array}{c}\left(\text{ cathode, reduction }\right):2{\mathrm{Na}}^{+}\left(\mathrm{l}\right)+2{\mathrm{e}}^{-}\to 2\mathrm{Na}\left(\mathrm{l}\right)\\ \left(\text{ anode, oxidation }\right):2{\mathrm{Cl}}^{-}\left(\mathrm{l}\right)\to {\mathrm{Cl}}_2\left(\mathrm{g}\right)+2{\mathrm{e}}^{-}\left(\text{ anode, oxidation }\right)\\ \end{array}$

Hence, electrometallurgy and pyrometallurgy are used in the sodium production process.

Step 4: (c) Procedures of Hydrometallurgy

Gold production is based on the cyanidation process. The ore is processed with a cyanide solution and zinc, and the gold is recovered as a cyanide $\mathrm{Au}{{\left(\mathrm{CN}\right)}_2}^{-}\left(\mathrm{aq}\right)$ in its water-soluble form. Because the ore only contains a small amount of gold, this procedure has harmful consequences and significant expenses.

Step 5: (d) Procedures of aluminium extraction

Aluminium production, Al comprises mining the ore (bauxite), processing it with (Bayer’s process), and removing titanium and iron impurities that create water-insoluble oxides. The residue is removed after filtration, and the filtrate is acidified, resulting in precipitation of ${\text{Al}}_2{\text{O}}_3$. The oxide is then combined with ammonium fluoride and melted in cryolite, after which it is electrolyzed in a graphite-lined furnace (Hall-Heroult process):

$2{\text{Al}}_2{\text{O}}_3+3\text{C (graphite })\to 4\text{Al}\left(\mathrm{l}\right)+3{\text{CO}}_2\left(\mathrm{g}\right)$

To summarise, pyrometallurgy, hydrometallurgy, and electrometallurgy procedures are required for aluminium extraction.