I use phosphoric acid @ 30 - 40% to remove rust. It is what is mostly used in commercial rust removers it turns the rust into iron diphosphide that is also impermeable to water and you can paint over it as well.
Ron, I two stepped the other day on a rusty tipper it got it clean but the rust is back I used 2% HF on it , maybe the HF doesn't give it the protective film like Phosporhic acid does.