Question

Describe how electrometallurgy could be employed to. purify crude cobalt metal. Describe the compositions of the electrodes and electrolyte, and write out all electrode reactions.

Short answer

The purification of crude cobalt metal through electrometallurgy involves using a cobalt anode made from crude cobalt and a non-reactive cathode, such as graphite or stainless steel. The electrolytic cell contains an electrolyte solution of cobalt(II) sulfate (CoSO₄). Cobalt atoms from the anode are oxidized to form cobalt ions in the solution with the reaction \( Co_{(s)} \rightarrow Co^{2+}_{(aq)} + 2e^- \). Simultaneously, cobalt ions in the electrolyte solution are selectively reduced at the cathode to form pure cobalt metal with the reaction \( Co^{2+}_{(aq)} + 2e^- \rightarrow Co_{(s)} \), while impurities remain in the solution or at the anode.

Step-by-step solution

Identify the electrode materials

For the purification of crude cobalt metal using electrometallurgical methods, we will need two electrodes: a cathode where cobalt ions will be reduced and an anode where impurities, often other metals, will undergo oxidation. The cathode should be made of a non-reactive material, such as graphite or stainless steel, while a cobalt anode can be made from crude cobalt metal.

Determine the electrolyte composition

The electrolyte serves as the medium for ion transport between the two electrodes during the electrolysis process. A suitable electrolyte for the purification of cobalt should be capable of dissolving cobalt ions without forming a complex. Cobalt(II) sulfate (CoSO₄) can be used as the electrolyte because it dissolves easily in water, forming cobalt ions and sulfate ions, which is suitable for the electrolysis process.

Write the anode reaction for cobalt oxidation

During the electrolysis process, impurities, particularly other metals, will be oxidized at the anode. Cobalt atoms from the crude cobalt anode are also oxidized to form cobalt ions that will go back into the electrolyte solution. The oxidation reaction for cobalt at the anode is: \( Co_{(s)} \rightarrow Co^{2+}_{(aq)} + 2e^- \)

Write the cathode reaction for cobalt reduction

While impurities are oxidized at the anode, cobalt ions in the electrolyte are selectively reduced at the cathode to form pure cobalt metal. This reduction will occur because of the availability of electrons at the cathode. The reduction reaction for cobalt at the cathode is: \( Co^{2+}_{(aq)} + 2e^- \rightarrow Co_{(s)} \)

Describe the overall electrometallurgical process

The electrometallurgical process for purifying cobalt involves placing a crude cobalt anode and a non-reactive cathode, such as graphite or stainless steel, in an electrolytic cell containing an electrolyte solution of cobalt(II) sulfate. During the electrolysis, cobalt atoms from the crude cobalt anode are oxidized to form cobalt ions, which go back into the electrolyte solution. Simultaneously, cobalt ions in the electrolyte solution are selectively reduced at the cathode to form pure cobalt metal, while impurities present in the crude cobalt remain in the solution or at the anode. The purified cobalt metal can then be removed from the cathode and further processed or used as needed.

Key concepts

Cobalt Purification

Electrometallurgy is a powerful tool to purify cobalt, a metal commonly used in alloys and batteries. The purification process focuses on removing impurities from crude cobalt metal to improve its quality and performance in various applications. The method employed is electrorefining, where cobalt is dissolved and redeposited in a purer state.

The process begins with placing a cobalt anode, made from crude cobalt, in an electrolytic cell. As the electrolysis process unfolds, impurities such as other metals are left behind, while cobalt atoms are oxidized into ions. This separation ensures that the cobalt collected at the cathode is of higher purity. The cathode, made from non-reactive materials like stainless steel or graphite, becomes the site where pure cobalt is deposited. By the end of the electrorefining process, contaminants have been either dissolved into the electrolyte solution or retained at the anode, ensuring the cobalt retrieved from the cathode is purified.

Electrolysis Process

In the electrolysis process, an electric current passes through the electrolytic cell, facilitating a redox reaction crucial for purifying cobalt. This method separates cobalt from the impurities present in crude metal effectively.

An electrolyte with dissolved cobalt(II) ions is used, connecting two electrodes in the cell. A positive charge is applied to the anode, encouraging cobalt atoms to oxidize into cobalt cations. Simultaneously, a negative charge at the cathode attracts these cations to deposit as solid cobalt. The process meticulously carries out the transition of cobalt from its impure form at the anode to a purified state at the cathode, ensuring efficient separation and recovery of the metal.

Electrode Reactions

Electrode reactions are essential to understanding the chemistry behind electrometallurgical cobalt purification.

At the anode, the main reaction involves the oxidation of cobalt: \( Co_{(s)} \rightarrow Co^{2+}_{(aq)} + 2e^- \). The crude cobalt anode loses electrons, turning to soluble cobalt(II) ions while impurities remain as solids or form new compounds.

• The cobalt ions are then incorporated into the electrolyte, enhancing their availability for reduction.

The cathode reaction involves the reduction of these cobalt ions back to solid cobalt: \( Co^{2+}_{(aq)} + 2e^- \rightarrow Co_{(s)} \). Here, electrons are delivered to the cobalt ions at the cathode, facilitating their attachment and formation as coherent, pure metal.
The precision of these reactions ensures the effective purification of cobalt from other unwanted elements.

Electrolyte Composition

The electrolyte composition is crucial as it determines how efficiently cobalt ions move between the electrodes. For cobalt purification, cobalt(II) sulfate (CoSO₄) is an ideal choice.

The use of an aqueous solution of CoSO₄ allows cobalt ions to dissolve readily, which is necessary for their mobility in the cell. This allows effortless transit between the anode and cathode. The sulfate ions balance the solution and enable efficient conduction of electricity, facilitating seamless redox reactions at the electrodes.

• Cobalt(II) sulfate remains stable in solution, ensuring a steady supply of cobalt ions to be deposited at the cathode.
• A solution lacking additional complexing agents ensures that cobalt remains free in its ionized form, keeping the reactions straightforward.

A properly prepared electrolyte with the right composition is fundamental for maximizing the efficiency and purity of the cobalt obtained.