[cjs_ac]

Extracting aluminium from bauxite is notoriously energy-intensive. During the nineteenth century, European aristocrats used aluminium tableware because it was more expensive than silverware. (They later switched back to silver when the novelty wore off and they realised aluminium was too light to feel right in the hand.)

[at_a_remove]

And you get all of that energy back when you powder that aluminium, mix it with rust, and manage (with difficulty) to ignite it.

[throwawaymobule]

No you don't. There are losses from inefficiency at every step.