Hey Jon, relax be glad you don’t have to deal with cigarette stains. LOL
Jon the stains he is talking about are even more difficult than rust. Some where to start anyway.
Andy,
More details next time can help will assume this is a shopping center around one of those ashtrays maybe by a garbage can. People go to put their cigarettes out before they walk into a building. The one who throws them down usually gets swept up and no stains ever arise. These ones close to garbage cans benches are the toughs ones. The reasons are these usually get wet and the tobacco gets soaked right in the surface.
The method I use in to use and acid based cleaner to try and safely lift the stains. Make your solution week and try many washes versus trying to attack it to quickly. Attacking quickly can cause you not only damage the surface but push the stain deeper into the concrete. This might result in permanent damage and never being able to remove these stains.
Andy if you need over the counter chemicals Jon have some experience here and might be able to help you. Same chemicals you would use for rust. I know Jon just went through something similar.
Thanks Andy for joining my bb I hope you find it nice and will always try to help with as much inf. as possible. Andy if you look in the links I think KO chemicals have concrete acid based cleaner. Also vendor can advise but cannot push product in this are if you go down to their section they might recommend something. Ron Strickland or mark or wiz.