Extraction of Copper — Revision Notes

⚡ 30-Second Revision

Ores: — Chalcopyrite ($CuFeS_2$), Chalcocite ($Cu_2S$).
Concentration: — Froth flotation (for sulphide ores).
Roasting: — $2CuFeS_2 + O_2 \rightarrow Cu_2S + 2FeS + SO_2$; $2FeS + 3O_2 \rightarrow 2FeO + 2SO_2$.
Smelting: — $FeO + SiO_2 \rightarrow FeSiO_3$ (slag). Product: Copper Matte ($Cu_2S + FeS$).
Bessemerisation: — $2FeS + 3O_2 \rightarrow 2FeO + 2SO_2$; $FeO + SiO_2 \rightarrow FeSiO_3$; $2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$; Self-reduction: $2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$. Product: Blister Copper (98-99% pure).
Refining: — Electrolytic refining (Anode: Impure Cu, Cathode: Pure Cu, Electrolyte: $CuSO_4 + H_2SO_4$).
Anode Sludge: — Ag, Au, Pt.

2-Minute Revision

Copper is primarily extracted from its sulphide ore, chalcopyrite ($CuFeS_2$). The process begins with concentration via froth flotation, which separates hydrophobic sulphide particles from hydrophilic gangue.

Next, the concentrated ore undergoes roasting in air, converting sulphides to oxides and removing volatile impurities like sulphur dioxide. The roasted ore is then smelted in a reverberatory furnace with silica ($SiO_2$) flux.

Here, iron oxide ($FeO$) reacts with silica to form a molten slag ($FeSiO_3$), while copper and remaining iron sulphides form a molten 'copper matte' ($Cu_2S + FeS$). This matte is transferred to a Bessemer converter for Bessemerisation.

Air is blown through the matte, oxidizing remaining iron to slag and then oxidizing $Cu_2S$ to $Cu_2O$. A crucial 'self-reduction' reaction occurs: $2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$, yielding crude 'blister copper' (98-99% pure) with a characteristic surface due to escaping $SO_2$ gas.

Finally, blister copper is purified by electrolytic refining. Impure copper acts as the anode, pure copper as the cathode, and copper sulphate solution as the electrolyte. Pure copper deposits on the cathode, while noble metal impurities (Ag, Au, Pt) collect as valuable 'anode sludge'.

5-Minute Revision

The journey of copper from its ore to a pure metal is a multi-step metallurgical marvel. It typically starts with **chalcopyrite ($CuFeS_2$), the most significant sulphide ore. The first step is concentration using the froth flotation process**.

Finely powdered ore is mixed with water, collectors (e.g., pine oil to make sulphide particles hydrophobic), and frothers (e.g., cresols to stabilize froth). Air is blown, and sulphide particles attach to bubbles, forming a froth that is skimmed off, leaving gangue behind.

Next is roasting, where the concentrated ore is heated in a reverberatory furnace with excess air. This converts some sulphides to oxides and removes volatile impurities as gases. Key reactions include: $2CuFeS_2(s) + O_2(g) \rightarrow Cu_2S(s) + 2FeS(s) + SO_2(g)$ and $2FeS(s) + 3O_2(g) \rightarrow 2FeO(s) + 2SO_2(g)$.

The roasted ore then undergoes smelting in a reverberatory furnace with **silica ($SiO_2$) flux**. The acidic silica reacts with basic iron oxide ($FeO$) to form molten iron silicate ($FeSiO_3$), which is a lighter, immiscible slag that floats and is removed: $FeO(s) + SiO_2(s) \rightarrow FeSiO_3(l)$. The heavier molten layer, known as copper matte, is primarily a mixture of $Cu_2S$ and $FeS$.

This copper matte is then transferred to a Bessemer converter for Bessemerisation. Hot air is blown through the molten matte. First, remaining $FeS$ is oxidized and removed as slag. Then, $Cu_2S$ is oxidized to $Cu_2O$: $2Cu_2S(l) + 3O_2(g) \rightarrow 2Cu_2O(l) + 2SO_2(g)$.

The most critical step here is self-reduction, where $Cu_2O$ reacts with the remaining $Cu_2S$ to form crude metallic copper: $2Cu_2O(l) + Cu_2S(l) \rightarrow 6Cu(l) + SO_2(g)$. The resulting copper, containing dissolved $SO_2$ that escapes upon solidification, forms a blistered surface, hence called blister copper (98-99% pure).

Finally, electrolytic refining is employed for high-purity copper. Impure blister copper serves as the anode, thin sheets of pure copper as the cathode, and an acidified $CuSO_4$ solution as the electrolyte.

At the anode, copper and more electropositive impurities (Zn, Fe) oxidize and dissolve. Less electropositive impurities (Ag, Au, Pt) do not oxidize and fall as valuable anode sludge. At the cathode, $Cu^{2+}$ ions from the electrolyte are reduced and deposited as pure copper: $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$.

This yields copper of 99.9% to 99.99% purity.

Prelims Revision Notes

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Ores: — Primary ore is Chalcopyrite ($CuFeS_2$). Other sulphide ores: Chalcocite ($Cu_2S$). Oxide ores: Cuprite ($Cu_2O$), Malachite ($CuCO_3 \cdot Cu(OH)_2$).
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Concentration (Froth Flotation):

* Used for sulphide ores. * Principle: Differential wettability (sulphides by oil, gangue by water). * Reagents: Collectors (pine oil, xanthates), Frothers (cresols), Depressants (NaCN for ZnS).

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Roasting:

* Process: Heating concentrated ore in excess air below melting point. * Purpose: Convert sulphides to oxides, remove volatile impurities (As, Sb, S as $SO_2$). * Reactions: $2CuFeS_2 + O_2 \rightarrow Cu_2S + 2FeS + SO_2$; $2FeS + 3O_2 \rightarrow 2FeO + 2SO_2$.

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Smelting:

* Process: Heating roasted ore with silica ($SiO_2$) flux in a reverberatory furnace. * Role of $SiO_2$: Acidic flux, reacts with basic $FeO$ to form slag. * Slag: $FeO + SiO_2 \rightarrow FeSiO_3$ (iron silicate). * Product: Copper Matte (molten mixture of $Cu_2S$ and $FeS$).

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Bessemerisation:

* Process: Blowing hot air through molten copper matte in a Bessemer converter. * Reactions: * $2FeS + 3O_2 \rightarrow 2FeO + 2SO_2$; $FeO + SiO_2 \rightarrow FeSiO_3$ (slag removal). * $2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$. * Self-reduction: $2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$. * Product: Blister Copper (98-99% pure, blistered due to escaping $SO_2$).

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Refining (Electrolytic Refining):

* Purpose: To obtain high-purity copper (99.9-99.99%). * Anode: Impure copper (blister copper). * Cathode: Thin sheets of pure copper. * Electrolyte: Aqueous $CuSO_4$ solution acidified with dilute $H_2SO_4$.

* Anode reactions: $Cu \rightarrow Cu^{2+} + 2e^-$; $Zn \rightarrow Zn^{2+} + 2e^-$; $Fe \rightarrow Fe^{2+} + 2e^-$. * Cathode reaction: $Cu^{2+} + 2e^- \rightarrow Cu$. * Anode Sludge: Less electropositive metals (Ag, Au, Pt) that do not oxidize and fall to the bottom.

Valuable byproduct.

Vyyuha Quick Recall

Can Really Smell Blister Really?

Concentration (Froth Flotation)
Roasting
Smelting (Matte, Slag)
Bessemerisation (Self-reduction, Blister Copper)
Refining (Electrolytic, Anode Sludge)