Refining metal ores is one of those things that’s really, really hard to do without emitting a huge amount of greenhouse gasses. The energy sources behind our material economies are not as easily substitutable with renewables, because what they often require is extreme heat, and sometimes the carbon itself (in the case of steelmaking and concrete). Researchers at MIT are looking at a way of directly refining molten iron oxide directly into pure iron electrolytically that results in very pure iron, and virtually no emissions, and it might work for other oxide refining processes as well.