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

Electrometallurgy can be employed to purify crude cobalt metal through an electrolytic process using an aqueous cobalt chloride (CoCl₂) solution as the electrolyte. The impure cobalt metal serves as the anode, and a stainless steel cathode is used for cobalt deposition. The anode reaction involves oxidation of cobalt (Co(s) -> Co^{2+}(aq) + 2e^-), while the cathode reaction involves the reduction and deposition of cobalt (Co^{2+}(aq) + 2e^- -> Co(s)).

Step-by-step solution

Outline the process of electrometallurgy for cobalt purification

In electrometallurgy, metal extraction and purification are achieved through an electrolytic process. This involves using an electric current to drive the reaction, in which impure cobalt is dissolved from the anode, and pure cobalt is deposited at the cathode.

Choosing the electrolyte

First, we need to choose an electrolyte capable of dissolving cobalt ions for electrodeposition. For this purpose, a suitable option is cobalt chloride (CoCl₂) in an aqueous solution. The electrolyte should also have enough conductivity to support the required current.

Composition of the electrodes

For the anode, we can use the impure cobalt metal, which will dissolve during the process. The cathode can be made of stainless steel, where the pure cobalt will deposit on its surface.

Anode reaction - Oxidation of cobalt

At the anode, oxidation of cobalt will occur as the crude cobalt dissolves into the electrolyte. The reaction taking place at the anode is: Co(s) -> Co^{2+}(aq) + 2e^-

Cathode reaction - Reduction and deposition of cobalt

At the cathode, the cobalt ions present in the electrolyte will be reduced and deposited as pure cobalt metal. The reaction taking place at the cathode is: Co^{2+}(aq) + 2e^- -> Co(s)

Electrolyte reaction - Chloride ion migration

To maintain the overall charge balance in the electrolyte, chloride ions will migrate from the anode to the cathode. This ensures that the concentration of ions in the electrolyte remains constant. In summary, electrometallurgy can be employed to purify crude cobalt metal through an electrolytic process where impure cobalt is dissolved at the anode and pure cobalt is deposited on the stainless steel cathode. The electrolyte used for this process is an aqueous cobalt chloride (CoCl₂) solution. The anode is made of impure cobalt metal, while the cathode is made of stainless steel. The overall electrode reactions are the oxidation of cobalt at the anode (Co(s) -> Co^{2+}(aq) + 2e^-) and the reduction and deposition of cobalt at the cathode (Co^{2+}(aq) + 2e^- -> Co(s)).

Key concepts

Electrode Reactions

Electrode reactions are at the heart of the electrometallurgy process, where chemical changes occur at the electrodes due to the passage of an electric current. In the context of cobalt purification, at the anode, which is composed of the impure cobalt metal, oxidation occurs. This means that cobalt atoms lose electrons and are transformed into cobalt ions (\( Co^{2+} \)). The anodic reaction can be summarized as follows:
\[ Co(s) \rightarrow Co^{2+}(aq) + 2e^- \]
On the other side of the electrolytic cell, at the cathode made of stainless steel, a reduction reaction takes place. The cobalt ions in the electrolyte gain electrons to form pure cobalt metal that deposits on the cathode. The cathodic reaction can be written as:
\[ Co^{2+}(aq) + 2e^- \rightarrow Co(s) \]
Through these reactions, electrons are transferred between species, driving the purification process. To facilitate understanding, envision the anode as where the impure material dissolves into its constituent ions and the cathode as where the pure metal is born out of these ions.

Cobalt Purification

Cobalt purification using electrometallurgy involves separating the desirable cobalt from other impurities. The key to this process is the selective dissolution of cobalt at the anode and its subsequent deposition on the cathode. Impurities that do not dissolve or deposit under the applied electrical conditions remain in the electrolyte or form a residue.
For this process to be efficient, the electrolyte, commonly an aqueous solution of cobalt chloride (\( CoCl_2 \)), must be carefully maintained to ensure high conductivity and proper ion movement. By doing so, cobalt ions can easily travel from the anode to the cathode. In practice, this means maintaining the right temperature and electrolyte composition to optimize cobalt recovery and purity levels. Potentially, this setup could also be tailored to recover valuable by-products or remove specific impurities by adjusting the electrical parameters and electrolyte formulation.

Electrolytic Process

The electrolytic process is a method of using electric current to drive a non-spontaneous chemical reaction. In the case of cobalt purification, the impure metal serves as the anode, and the electric current causes cobalt atoms to be oxidized and dissolve into the electrolyte. These ions are then transported through the electrolyte and are reduced at the cathode, plating out as pure cobalt metal.
To maintain electrical neutrality, negatively charged ions (in this case, chloride from the cobalt chloride acid solution) migrate towards the anode. It is essential to ensure the continuity of the process by carefully controlling the electrical current and monitoring the composition of the electrolyte.
The voltage applied across the electrodes must be high enough to overcome the resistance of the electrolyte and other components in the setup but not so high as to cause undesirable side reactions. Understanding and controlling the electrolytic process parameters are crucial for the efficient and effective purification of cobalt.