Question

The correct statement(s) related to the metal extraction processes is(are)

• A. A mixture of PbS and PbO undergoes self-reduction to produce Pb and SO₂.
• B. In the extraction process of copper from copper pyrites, silica is added to produce copper silicate.
• C. Partial oxidation of sulphide ore of copper by roasting, followed by self-reduction produces blister copper.
• D. In the cyanide process, zinc powder is utilized to precipitate gold from Na[Au(CN)₂].

Answer 1

The Correct Option is A, C, D

PbS + 2PbO → 3Pb + SO₂

The reaction involves self-reduction between PbS and PbO.

In the Bessemer converter, the raw material used is matte, consisting of Cu₂S + a small amount of FeS. Initially, air blasting is conducted to facilitate slag formation, and SiO2 is introduced from an external source.

\(\text{FeS} + \frac{3}{2}\text{O}_2 \rightarrow \text{FeO} + \text{SO}_2 \uparrow\)

\(\text{SiO}_2 + \text{FeO} \rightarrow \text{FeSiO}_3\) (slag)

During slag formation, a characteristic green flame is observed at the mouth of the Bessemer converter, indicating the presence of iron in the form of FeO. The disappearance of this green flame signifies the completion of slag formation. Subsequently, air blasting is halted, and the slag is removed.

Air blasting is then resumed for partial roasting before self-reduction, continuing until approximately two-thirds of Cu2S is converted into Cu2O. Following this stage, only heating is maintained for the self-reduction process.

\(\text{Cu}_2\text{S} + \frac{3}{2}\text{O}_2 \rightarrow \text{Cu}_2\text{O} + \text{SO}_2 \uparrow\)

\(\text{Cu}_2\text{S} + 2\text{Cu}_2\text{O} \rightarrow 6\text{Cu(l)} + \text{SO}_2 \uparrow\)(self-reduction)

Additionally,

\(\text{Cu}_2\text{S} + 2\text{O}_2 \rightarrow \text{Cu}_2\text{SO}_4\)

\(\text{Cu}_2\text{S} + \text{Cu}_2\text{SO}_4 \rightarrow 4\text{Cu} + 2\text{SO}_2 \uparrow\) (self-reduction)

The resulting molten copper is poured into a large container and allowed to cool. During cooling, dissolved SO2 rises to the surface and forms blisters, resulting in the production of blister copper.

\(2\text{Na}[Au(CN)_2] + \text{Zn} \rightarrow \text{Na}_2[Zn(CN)_4] + 2\text{Au} \downarrow\)