As long as the porcelain isn't unfired, you can use salt and lemon juice to remove the rust. To do this, you should pour salt directly onto the rust stain. Then, cut a lemon in half and squeeze the juice of the lemon onto the pile of salt. Let it sit for at least two hours. If the rust stain is old, you may have to let it soak overnight. Wipe it up with a paper towel. Finally, clean the tile with a wet towel. If the rust stain remains, repeat the process once the tile is dry.
Clean the Rust Naturally
To remove the rust stain, you can mix three tablespoons of vinegar, ¼ cup bleach and one teaspoon of dish detergent into six cups of water. Sponge this mixture onto the tile. Place the wet sponge directly onto the tile and leave it there for fifteen minutes. When this time is up, remove the sponge, wipe the tile and allow it to dry. If the stain isn't gone, it should be lighter. If this is the case, repeat the process.
Barkeeper's Friend is the only scouring powder that is mild enough to be used on porcelain without damaging it. To use this, dampen the tile with water then pour the powder onto the stain. Gently rub it in. Once you do this, let it soak for 30 minutes. Make sure to time it, as it can start to damage the tile if left on any longer. Once the time is up, wipe it up with a clean towel and rinse the tile.
This method should be a last resort, as it may scuff the surface of the tile. You should make sure that you use the finest pumice stone available. Course stones may cause deep scratches. To remove the rust, wet the tile and gently rub the stain with the stone. Make sure that the tile stays wet throughout the process.