[Shop-talk] Removing rust stains from concrete?

[Chris Kantarjiev]

We've been using Whink

http://www.whink.com/rust_stain_remover.htm

at our cabin for years now - it's the only thing that reliably gets out 
the rust stains caused by the iron in our well without requiring 
respiratory protection during use. It's mostly dilute hydrofluoric acid 
(if you read the label and MSDS).

They appear to have a bunch of related products; it appears that

http://www.whink.com/rust_and_iron_stain_remover.htm

might be a better choice for concrete.