Why does aluminum have a very high energy cost to produce?

Aluminum is one of the most abundant metals in Earth’s crust, but it is difficult and energy-intensive to extract from aluminum oxide. The metal is produced industrially by the Hall-Héroult process, invented in 1886, which uses electricity to reduce molten alumina dissolved in cryolite. Because the process needs very high temperatures and huge electrical input, primary aluminum production is expensive compared with recycled aluminum. This is why aluminum recycling saves a great deal of energy and has become economically important worldwide.