Low Earth Orbit is still fairly close to earth, cost wise. (yay SpaceX). A gram of platinum in LEO is only about 20% more expensive than a gram of platinum on Earth.
It's the stuff that's cheap but bulky like iron, water & rocket fuel ectrolyzed from water that you'll want to mine in space for use in space.
Platinum and other rare metals will simply be waste products that are profitable to ship back to Earth.
edit: my original comment used "titanium" instead of "platinum", which made it nonsensical, since titanium isn't a rare metal.
It looks like titanium costs $4/kg [1], and a SpaceX LEO launch is $2719/kg [2]. I'm not sure how much Ti is in "ferro titanium", but even if it's only 10%, the numbers aren't even close. Am I doing this wrong?
Translation: It cost 20% as much to lift titanium to orbit as it costs to refine in the first place. Which seems very wrong because it costs between $5 and $50 per kilo according to a quick search, and I'm pretty sure it costs a LOT more than that to lift a kilo into orbit.
It's the stuff that's cheap but bulky like iron, water & rocket fuel ectrolyzed from water that you'll want to mine in space for use in space.
Platinum and other rare metals will simply be waste products that are profitable to ship back to Earth.
edit: my original comment used "titanium" instead of "platinum", which made it nonsensical, since titanium isn't a rare metal.