Iron can leave rust marks on your concrete drive that may seem impossible to remove. Here are some methods to use for removing those unsightly red stains.
Mix 1 ounce of tri-sodium phosphate (TSP) in a gallon of hot water. This chemical can be found at hardware and paint stores. Wet the concrete and use a scrub brush to apply the solution. Scrub vigorously and let the solution soak into the concrete for 10 to 15 minutes. Rinse well.
Try a product called Iron Out, which is sold in plumbing supply stores.
Combat really bad stains with a pressure washer and muriatic acid. Apply the acid as directed by the manufacturer, leave it to soak for a few seconds, and follow with a pressure washer set at 2,500-3,000 psi. Sprinkle baking soda over the cleaned area to neutralize the acid and wash again.
Concrete is porous and should be sealed to prevent staining. Promptly rinse fertilizers containing iron off concrete surfaces.
These products can burn eyes and irritate skin. Follow the manufacturer's directions and precautions carefully. Muriatic acid is dangerous and should only be used as a last resort. Do not wash it into storm drains.