Animated Solution for Chemistry - Metallurgy: Extraction of copper from copper pyrite (${\text{CuFeS}}_2$) involves

Imagine you are an alchemist tasked with extracting pure, shining copper from a dull, brassy rock. This rock is Copper Pyrite, chemically known as $CuFe{S}_2$. It is the most abundant ore of copper, but it holds a secret: the copper is tightly bound not just to sulphur, but also to iron. To liberate the copper, we must embark on a multi-stage metallurgical journey that perfectly balances thermodynamics and chemical kinetics.

Concentration via Froth Flotation

Before we can initiate any chemical reactions, we must separate the valuable ore from the useless earthy impurities (gangue). We start by crushing the massive rocks into a fine powder. Because $CuFe{S}_2$ is a sulphide ore, we employ the Froth Flotation process.

In this ingenious physical separation method, the powdered ore is mixed with water and pine oil. When air is vigorously bubbled through the mixture, the sulphide particles, which are preferentially wetted by the oil, attach themselves to the air bubbles and rise to the surface as a rich froth. The gangue, wetted by water, sinks to the bottom. This confirms that option (A) is absolutely correct.

Roasting in the Reverberatory Furnace

With our concentrated ore in hand, we move to the reverberatory furnace. Here, the ore is heated strongly in the presence of excess air—a process known as Roasting. The primary goal here is to partially oxidize the ore and drive off volatile impurities.

The complex copper pyrite breaks down into simpler sulphides:

This step sets the stage for the crucial separation of iron from copper.

Smelting and the Art of Slag Formation

Now, we face our biggest challenge: removing the iron. During the Smelting phase, the iron sulphide ($FeS$) oxidizes more readily than copper sulphide. It converts into iron oxide ($FeO$):

However, $FeO$ is a basic oxide and cannot be easily removed on its own. Here is where the magic of fluxes comes in. We add silica ($Si{O}_2$), an acidic flux, which reacts with the basic $FeO$ to form a fusible, lightweight slag called iron silicate:

This slag floats on top of the molten mixture (known as copper matte, primarily $C{u}_{2}S$ and some unreacted $FeS$) and is easily skimmed off. This confirms that option (B) is correct.

The Magic of Self-Reduction

The molten copper matte is now transferred to a Bessemer converter. This is where the most elegant chemical reaction in copper metallurgy occurs: Self-Reduction.

Instead of adding an external reducing agent like carbon, we simply blow a controlled amount of air through the molten mass. A portion of the copper sulphide oxidizes to form copper oxide:

Then, in a brilliant display of chemical self-sufficiency, this newly formed copper oxide acts as an oxidizing agent for the remaining copper sulphide. They react together to yield pure metallic copper:

This confirms that option (C) is correct.

Blister Copper and Final Refining

As the molten copper cools and solidifies, the dissolved $S{O}_2$ gas violently escapes, leaving behind a blistered, crater-like surface. This is why the product is famously called Blister Copper, which is about 98% pure.

To achieve the 99.9% purity required for electrical wiring, we must refine it. We first use a process called Poling (stirring the molten metal with green wood logs to reduce any remaining oxides) and finally Electrorefining.

Notice what we did not use: Carbon. Carbon reduction is thermodynamically unfavorable for copper at these temperatures and is typically reserved for metals like iron or zinc. Therefore, option (D) is incorrect.

By mastering this sequence, you not only solve the problem but also understand the beautiful industrial symphony that brings copper into our modern world.