1. Wait for thermonuke reactors. This gives you Superpowers/Abilities to vaporise everything by heating, to keep the plasma cloud in magnetic field and to sort ions with magnetic fields. 2. Build a heater/separator where you can heat and split any piece of trash into ions of pure elements and separate them into different containers. Use any stone, any piece of useless trash, sewers pulp to get thinnest metal powders (iron, alumina, calcium, magnesium, etc.). 3. Mix these powders to get the m