First of all, if you have an oven with a self-cleaning setting, that’s a great way to remove rust and “reset” your pans. If you don’t, Instructables user theabion points out that all you need is some white vinegar, some water, and an abrasive scrubber to make your rusted, damaged cast iron gleam like new. Mix the water and vinegar 50/50, and let the pan soak in the mixture for an hour or up to six depending on how bad the rust is. Then gently scrub the rust away from the cast iron pan with your scrubber. He used a copper pad, but you could also go with our trusty salt scrub method to remove the rust and debris as well. Whatever you do, make sure you’re complete and remove as much of the rust as possible.
http://lifehacker.com/5886819/rescue-your-cast-iron-from-rust-with-vinegar
Gardengal Bevy 