I assume they are using renewable energy to reduce naturally-occurring iron oxide.

When the iron is burnt are they going to do with pure oxygen? Otherwise they'll get pollutants like nitrogen dioxide, possibly ozone. And the 0.5% not burnt will also become a pollutant unless carefully removed in some smokestack scrubber.

Or is this 'burning' to occur some kind of iron fuel cell? How would they liquidize the iron which is quite heavy?

Lastly, iron is heavy. Moving reduced iron could be expensive and dangerous.

Still, if sufficiently close to the renewable source this could provide much needed load leveling for intermittent sources.