The way you separate aluminum from alumina is by electrolysis. Like you guessed, it is highly parallel. It is as simple as having hundreds of pots, each with huge carbon electrodes, dumping megawatts of power into the molten matrix to extract the metal. And it consumes an obscene amount of power to do so.
This is also the primary reason that aluminum recycling is so beneficial. It is dirt cheap to remelt already refined aluminum vs. smelting fresh ore, even though aluminum itself is an exceptionally common element.
https://www.youtube.com/watch?v=fa6KEwWY9HU&feature=youtu.be...
https://theconversation.com/the-trouble-with-aluminium-7245
This is also the primary reason that aluminum recycling is so beneficial. It is dirt cheap to remelt already refined aluminum vs. smelting fresh ore, even though aluminum itself is an exceptionally common element.