2 -3 tablespoons salt
Wet the stain with some of the lime juice. Sprinkle liberally with salt. Add enough more lime juice to make the salt into a paste. Leave it sit for several hours or overnight. Rub and rinse. Is the stain gone?. If it's not, try repeating. You can add a bit of flour if the stain is on a vertical surface to make it stick. Works well on rust and other stains.