Ironite is a type of fertilizer with tiny iron granules in the mixture. This is great for plants, but terrible for concrete since the iron particles may wash onto the concrete during rainstorms, lodge there and rust. In order to remove ironite stains from concrete, you will actually need to attack the rust that has formed on these iron granules.
Clean the concrete. First, sweep off the concrete. Use the broom. Next you should pressure wash the area. Stain removal is always easier and more effective when you have a completely clear, clean area other than the stains. In some cases, the pressure washing may dislodge the iron particles and make your job even easier by getting rid of some of the ironite stains.
Mix up your oxalic acid. Oxalic acid, also called wood bleach, comes in powdered form. You just need to add water. Use the plastic bucket, and refer to the manufacturer's directions on how much water to add since each brand can be slightly different. You should wear your gloves and safety goggles from here on out.
Treat the stains with the oxalic acid solution. Apply a generous treatment of the wood bleach solution to the stains. If you like, saturate a cleaning rag with the oxalic acid and lay it over the stains. You should leave the acid on the stains for about 10 minutes.
Use the stiff brush to scrub the acid-treated stains off the driveway. In most cases, you will only need one or two applications, but you can repeat the treatment process up to 5 times. Just remember that you may be creating a lighter blotch on your driveway.
Rinse down the driveway. Use the garden hose and copious amounts of water to rinse off the concrete very thoroughly. It is important to dilute the oxalic acid very thoroughly so that it does not harm your plants or eat away at your concrete.