When it comes to loosening rusted bolts, some ways are more ecologically friendly than others.
Simply heating the nut will sometimes expand it before the bolt heats up, breaking the rust lock and allowing it to come off.
Adding any of the oils or penetrating or rust breaking oils can work as well, but never combine the heat and the oil, in certain cases it can give off toxic fumes, if not cause a fire.
Heat & Wax!
So Nigel from Halifax, Nova Scotia comes to the rescue with a technique that I would have never dreamed about, but it really works. He simply heats the problem nut and then melts paraffin wax, the stuff you use to can fruit, right into the joint. In every nut we tested it seriously loosened it up, with no toxic fumes problems.
Thanks Nigel -- that's one of the best tips of the year.