Which process contributes significantly to the expense of aluminium extraction?

The electrolysis of alumina is indeed a significant contributor to the expense of aluminium extraction. This process involves the use of a large amount of electrical energy to separate aluminium from its oxide, alumina (Al₂O₃). During electrolysis, alumina is dissolved in molten cryolite, a process that allows for the efficient conduction of electricity.

The high energy requirements for maintaining the temperatures needed for electrolysis and the overall electrical consumption contribute substantially to the operating costs of aluminium production. In fact, the electricity cost is often one of the largest expenses in the aluminium production process, reflecting the substantial energy needed to drive the electrolysis reaction.

Conversely, refining bauxite, though it requires energy and resources, generally involves processes such as crushing and grinding, and the Bayer process, which are less energy-intensive compared to electrolysis. Smelting iron is not related to aluminium extraction and doesn't apply to this question. Casting of aluminium products is a manufacturing process that happens after aluminium has already been extracted and doesn't relate to the extraction expenses. Thus, the electrolysis of alumina stands out as the critical process that significantly affects the cost of aluminium extraction.