I tested, it works from the fire of God !!
Half a lemon squeezed in a goblet, my little rusty scrap metal immersed in it, and 4 hours later, more rust.
It seems that it also works for stains on textiles, with a little coarse salt in addition to suck the solution.
It's the same principle as coca: acids eat rust. So it should work with other citrus fruits, or vinegar.
Here it is, my green find of the moment.
PS: the second half of the lemon very advantageously accompanied my aperitif.
