How efficient is iron smelting ?
Thanks for the reply, but afraid it's plan B ! Actually I'm looking at starting a colony on Mars, within mass constraints given by the spaceship desgin. Probably if you wanted iron from an asteriod you'd just go to an asteroid made of iron... or stainless steel.
My exceptionally limited understanding of iron smelting is that you need carbon monoxide to reduce iron oxide to iron. This is obtained from reducing carbon dioxide (unlimited, makes up 95% of the atmosphere) by heating it with pure carbon (here, obtained from the plants the colonists are growing, hence the 300 tonne figure).
If it's possible to get iron directly from iron oxide, fantastic ! The surface is covered in the stuff. But how does this work ? Would it require greater heating than a conventional furnace ? How would impurities be removed ? About 20% of the soil is iron oxide but 60% is sand. Most could probably be filtered out but some would get through. On Earth calcium carbonate is used to absorb the silicon dioxide, but Mars doesn't have any. What I really need is some estimate of the efficiency. If the efficiency is very low, they might need a lot of their initial mass setting up iron smelting plants to get enough to do anything useful.
Heating requirments probably aren't going to be a problem, this colony would have a 10 MWe nuclear reactor (45MW thermal). An orbiting mirror could be done, but dust storms on Mars would make it unreliable. Presumably, most of the furnace could be built out of Martian rock, but if there's any really heavy stuff that you'd have to take I'd need to account for it (got 600 tonnes left to play with though). The atmosphere is about 1% of Earth's density - enough to consider as a vacuum ?