I have some apple trees at my workshop, that is why it is called "Appletree works" and every year I try to make cider, and some is superb, and some goes wrong! I use the wrong stuff for derusting, and it works very well indeed, have also used it with electrolysis, and that works too. Anything with a bit of acidity will dissolve the rust, I was well impressed with some thread guages that, to look at, were really too far gone, but they cleaned to the point where the engraving is chrystal clear, and most of them are perfect bright metal again, and all done in bad cider, with no electrickery! Citric acid I suppose!
Phil