We have tried everything from pressure washing, muriatic acid to 100% pure bleach to remove some rust stains from our old travel trailer safety chains. Finally got some "The Works" toilet bowl cleaner and it was removed within 10 minutes with no scrubbing. I can hardly believe it! Never have I seen imbedded rust stains removed from concrete, but this stuff really works.
We picked it up at Dollar General for $1.50
The Works® :: Toilet Bowl Cleaner
Had I had any confidence in it, I would have taken before and after pictures. Maybe someone else will do the honors.