> Recycling involves melting the scrap, a process that requires only 5% of the energy used to produce aluminium from ore, though a significant part (up to 15% of the input material) is lost as dross (ash-like oxide).[134] An aluminium stack melter produces significantly less dross, with values reported below 1%.
That amount seems to fit with my amateur experience of melting aluminum cans. Dross pretty much floats up to the top of the molten aluminum, and you basically just scrape it off. Even bar stock aluminum from Home Depot would produce a small amount of it.
According to this page, aluminum is separated from dross in a separate process:
