Animated Solution for Chemistry - Metallurgy: Copper is purified by electrolytic refining of blister copper. The correct statement(s) about this process is (are)

When we extract copper from its ores, the initial product we get is called 'blister copper'. It's about $98\%$ to $99\%$ pure, but for electrical applications, even a tiny amount of impurity can drastically reduce its conductivity. To achieve the ultra-high purity required (around $99.95\%$), we turn to a fascinating process called electrolytic refining.

Imagine a large tank. This is our electrolytic cell, the stage where the purification magic happens. Let's break down the setup and the chemistry behind it.

In an electrolytic cell, we need two electrodes and an electrolyte. The choice of these components is crucial for the refining process.

First, we take the impure blister copper and cast it into thick blocks. These blocks are made the anode, which is connected to the positive terminal of our DC power source.

Next, we take a very thin sheet of already pure copper. This acts as the cathode, connected to the negative terminal.

For the electrolyte, we use an aqueous solution of copper sulphate (${\text{CuSO}}_4$). To make sure the solution conducts electricity efficiently, we acidify it by adding a small amount of sulphuric acid (${\text{H}}_2{\text{SO}}_4$). This perfectly aligns with the statement that an acidified aqueous ${\text{CuSO}}_4$ is used as the electrolyte.

When we switch on the power supply, a beautiful dance of ions begins.

At the anode (the impure copper block), oxidation takes place. Copper atoms lose two electrons and dissolve into the solution as copper ions:

These ${\text{Cu}}^{2+}$ ions travel through the electrolyte towards the negatively charged cathode.

At the cathode (the pure copper strip), reduction occurs. The copper ions gain two electrons and deposit themselves as solid, pure copper atoms:

As the process continues, the impure anode gradually dissolves and becomes thinner, while the pure cathode grows thicker as more and more pure copper deposits onto it. This confirms that pure copper indeed deposits at the cathode.

But what happens to the impurities that were in the blister copper? This is where the process gets even more interesting.

The impurities in blister copper generally fall into two categories: those that are more reactive than copper (like iron, zinc, and nickel) and those that are less reactive (like gold, silver, and platinum).

The more reactive impurities dissolve into the electrolyte along with the copper. However, because copper is preferentially reduced at the cathode, these impurities remain in the solution.

The less reactive, precious metal impurities do not dissolve. As the copper anode dissolves around them, they simply fall to the bottom of the tank, settling directly beneath the anode. This collection of valuable impurities is aptly named anode mud.

Therefore, the statement that impurities settle as anode-mud is also correct. In fact, the recovery of these precious metals from the anode mud often pays for the entire cost of the electrolytic refining process!