Energy content of metals (Ashby data)

Aluminum is 300 gigajoules per ton. That means it takes 300 gigajoules of energy to take aluminum oxide, which is what we find in nature, and turn it into aluminum metal. It's a very high energy cost. Eighty, ninety percent of the cost of aluminum is the energy cost to turn it into aluminum from its native state as the oxide, okay. Plastics have about 100 gigajoules — if you burn them, they come from oil, and if you use it as a fuel, it's about 100 gigajoules per ton. Copper is 100 gigajoules rising to 500, and the reason is, we used to have ores that were two to six percent copper in the world. We mined them out, and now we're mining ores that are less than half a percent copper. So now you're talking about getting ten pounds out of a ton. You have to mine a ton of material to get ten pounds of copper, and you refine it electrolytically usually anyway. Steel is only 50, as it turns out.