Same way you sand anything, as long as the grit is harder than what your sanding it works just fine. Iron is only 4 on the Mohs Scale which is below glass, so many types of sandpaper work fine.
Check assorted youtube videos. Abrasive disks of various sorts are easy to come by, though you're likely going to want a plug-in drill or angle grinder - maybe an 18v 6AH battery would give you the oompf you'd need, but I wouldn't count on it.
The key things I'm going to highly highly highly recommend are a good filter mask, good ventilation (or excellent ventilation and a big shop fan blowing past if you have a beard) and a way to securely hold the piece you're working on. I don't have a link, but I like what one guy put together with a heavy duty board - a hook at one end through a hole, and a hook at the other through a slot that could be adjusted to fit the piece. Don't tighten down hard at all unless you want to risk breaking things, just enough to keep what you're working on from shifting around as you sand.
