Question

How is alumina melted in the electrolytic extraction process of molten alumina?

Short answer

Question: Briefly describe the steps involved in the electrolytic extraction process of molten alumina. Answer: The electrolytic extraction process of molten alumina involves preparing an electrolyte mixture of alumina and cryolite, setting up an electrolytic cell with graphite anodes and cathodes, heating the electrolyte to melt cryolite and dissolve alumina, applying electric current to initiate electrolysis, and collecting pure aluminum from the cathode while oxygen gas is released at the anode.

Step-by-step solution

Preparation of electrolyte

In the electrolytic extraction process of molten alumina, a solvent called electrolyte is needed for the melting. The electrolyte is a mixture of alumina (Al2O3) and cryolite (Na3AlF6). Cryolite is added to the mixture because it helps to decrease the melting point of alumina and increases the electrical conductivity of the solution.

Setting up the electrolytic cell

An electrolytic cell is set up consisting of a container, inert graphite anodes, and cathodes. The container is lined with graphite, which acts as the cathode, while the graphite anodes are suspended in the cell. The electrolyte mixture is added to the electrolytic cell.

Heating the electrolyte

The electrolyte mixture in the electrolytic cell is heated to a temperature between 950°C and 980°C. This temperature will melt the cryolite and allow alumina to dissolve in it, forming a homogeneous molten solution that is ready for the extraction process.

Applying electric current

An electric current is applied to the electrolytic cell. The electric current is passed through the anodes, the molten electrolyte, and the cathodes. Due to the electric current, the molten alumina undergoes electrolysis, and aluminum ions (Al^3+) and oxide ions (O^2-) are formed.

Formation of aluminum at cathodes

The aluminum ions (Al^3+) are attracted towards the cathode (graphite lining) and receive three electrons to form pure aluminum atoms. These aluminum atoms then deposit on the cathode, forming a liquid layer that can be collected. The reaction at the cathode can be described as: Al^3+ + 3e^- -> Al (s)

Formation of oxygen at anodes

The oxide ions (O^2-) move towards the anodes, where they lose their extra electrons, combine and form oxygen gas (O2) which is released at the anode. The reaction at the anode can be described as: 2O^2- -> O2 + 4e^- To summarize, alumina is melted in the electrolytic extraction process by dissolving it in molten cryolite at high temperatures in an electrolytic cell. An electric current is then applied, causing electrolysis and the formation of aluminum at the cathode and oxygen at the anode.