I don't think you can solve that by just putting an import tax on aluminum. What about aluminum produced with cleaner energy than coal? Would you want to ask what energy source they used? Would you make it depend on the country of origin? What about for example cars? Would you also tax them for the aluminum content? Depending on the origin of that aluminum? If not it seems like you would create a disadvantage for US car manufacturers having to use the more expensive domestic or taxed imported aluminum. Or airplanes? Maybe it doesn't matter as much as I imagine because aluminum is always only part of the costs but I am convinced it would not be a trivial thing to tax dirty aluminum.
I think this is just the direction that needs to happen. The manufacturing and mining countries have a strong disincentive to carbon taxation -- the first mover gets the "prize" of losing market share to their untaxed competitors. So they will make lots of populist noises periodically, but eventually not be effective at it. Australia got rid of its carbon tax, and even when it had it it compensated many of the major polluters to shield them from its effects. China announces "targets" that are generally a little worse than what was predicted to happen already -- carbon output peaking in 2030, etc. Canada will make lots of "progressive" noises now Trudeau is in but eventually they'll do little to harm the competitiveness of their resources industry.
If you're going to get carbon taxation, it needs to happen at consumption, because that's where you're not asking turkeys to vote for Christmas. Tax materials and products at an average rate for that product by default, but at a lower carbon-dependent rate if there is an independently verified audit trail for the environmental impact of its materials and manufacture. Effectively, a VAT or GST rate that depends on environmental impact.
I would just like to add that multiple concentrates from different locations are frequently blended before being smelted into a refined product, so, even more to your point...
