Aluminum Smelting: Hall-Heroult Reduction and Alumina Feed
Hall-Heroult reduction of alumina to aluminum: cell chemistry, the dry scrubber that doubles as the alumina feed path, and why cargo quality is a smelter quality problem.
Primary aluminum is produced by the Hall-Heroult process, in which alumina is dissolved in a molten cryolite bath and reduced electrolytically in cells drawing very large direct currents. The process is the reason alumina moves by sea at all: smelters are sited where electricity is cheap rather than where bauxite is mined, so the refined oxide is shipped to them.
The full article will cover cell construction and the anode systems, the current efficiency and energy intensity that drive smelter economics, and the fume treatment plant. The last of these matters to shipping more than it appears to. A modern smelter passes cell fume through a dry scrubber in which incoming alumina is the adsorbent for hydrogen fluoride, and the alumina then goes on to feed the cells. That arrangement is why smelter-grade alumina is deliberately under-calcined to retain surface area, and why moisture and fines content in a delivered cargo are process problems rather than cosmetic ones.
It will also cover the specification a smelter buys against, and what happens upstream when a cargo fails it.