I understand why you would want to get that iron off, but a coin collector will tell you to never clean a coin. It usually detracts from the value. I'd at least consult with one first, before trying anything.
Spent a couple hours at Vilano and found ~93 cents of really nasty looking modern coins, part of a lure, what looks like a throttle to a boat motor, a pull tab, and a sharks tooth. Think I'm going to program my detector for jewelry only :-) I swear one of those clad quarters was 2 ft down.