It's dumb to call it a fuel - you're recovering the energy that you stored in it during refining. As a battery, a box full of iron has a lot of drawbacks - it

It's dumb to call it a fuel - you're recovering the energy that you stored in it during refining. As a battery, a box full of iron has a lot of drawbacks - it has low specific energy (you need a lot of iron to store your energy), it's heavy (it costs a lot to transport from the refinery to the place the energy is being used), and it's inneficient (burning iron to generate steam to drive a turbine might get you 40% efficiency at best, and removing the oxygen again later has its own issues). The one application that this makes sense is for generating process heat - you can slowly store energy by electrolysis and then release it as a very high temperature heat source. In most cases hydrogen would make more sense: it's simpler to electrolyze and burns hotter, but it's difficult to handle and store which might be important for the application.