GandalfSwagOff t1_j65kctb wrote
Reply to comment by HockeyCookie in ELI5: Is aluminum common enough that it’s not a concern, or are we just really good at recycling it? by RestrictedCervical
How is that possible? There has to be some sort of loss. 100% is 100%.
snash222 t1_j65o2ct wrote
Aluminum is an element. The aluminum stays aluminum forever. You may have some “loss” by having it drip out of a melting vessel or something like that, but 100% of the aluminum still exists. Just sweep it up when it cools and put it in the next batch.
chris_p_bacon1 t1_j684ckd wrote
Surely you'd have some sort of back reaction to AlO2. I work in primary aluminium production a few certainly have issues with back reaction.
snash222 t1_j68d7q3 wrote
Yeah, I don’t know what I’m talking about. Just sounded good to me at the time.
GandalfSwagOff t1_j65ojgk wrote
I would have figured there would be vapor loss during the heating.
BoredCop t1_j65r2fq wrote
Not really vapor loss, but there typically is some loss to oxidation. Alu binds very tightly to oxygen, which is also the reason why it takes so much energy to refine from ore in the first place. Aluminium exposed to air instantly forms a thin oxide layer, which is a bit more difficult to recycle than "just melt it". Pretty sure even this oxide dross is worth recycling though, it's basically very high grade ore.
syds t1_j66920m wrote
how do u separate it? skim it out?
Skusci t1_j66sbyk wrote
Actually yeah, it's that simple. Like say you take some aluminum cans and melt them in your backyard. Some of the inks and plastics burns off from the heat. The oxides float up to the top and you can scoop them out. What you pour out after is basically clean aluminum. Big industrial process are bigger, but functionally the same. They just pay a bit more attention to not letting oxygen contact the molten aluminum to prevent unnecessary oxidation. There are still some non aluminum impurities that get in there so you can't make a lot of alloys out of it, but it's plenty fine for lots of purposes like aluminum foil and cans and stuff that aren't like making up the wing of an airplane.
The dross you skim out is mostly it's aluminum oxide, but also contains a large amount of metallic aluminum that followed along for the ride. Depending on the initial melt composition and handling it can contain anywhere from 15%-85% recoverable aluminum. That can be recovered by mixing it with molten salt fluxes. This allows the metallic aluminum to separate out while the oxides mix in with the salt in a separate layer. You get an even worse grade of aluminum out due to the large amount of flux used, but again it's still useful for lots of stuff and the whole melting process takes something like 90% less energy vs processing raw aluminum oxides. The extra contamination from the salt flux is why you don't just toss in a bunch of salt in the first place.
Afterward once the salt is loaded up so much that it isn't useful as flux anymore is allowed to cool and is pitched as trash. It's called salt cake, and is actually a decent bit hazardous. Disposing of it safely is kindof becoming a problem actually.
BurnOutBrighter6 t1_j66urgn wrote
Even if there was vapor loss, that vapor is still aluminum atoms. They'll condense somewhere and still be aluminum. So the amount of aluminum on Earth stays the same no matter how much we "use". I think that's what they're getting at with "100% recyclable".
maveric_gamer t1_j65wqqz wrote
The 100% isn't talking about getting all of the aluminum from, say, a can that you process, back from that processing, but that you can take that aluminum even with losing some of the raw material and shape it into cans that will be structurally no different from an aluminum can that was made from freshly-refined bauxite
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