Anything that dissolves rust will work fine. If you use a harsh chemical, wash very well afterwards. But steel wool or green scrubby pads should do it.
Or, if you want a safe, natural method, soak them in a bucket with a 1:6 ratio of molasses and water. The diluted molasses activates a chelation process which removes the rust. It might take a few days, depending on how rusty they are, and you need to remove any grease or oil that will block the molasses.
Or, you can get a container of mixed Arm and Hammer Super Washing Soda and a battery charger and make up an electrolysis machine, which will remove rust much faster (but not as safely, as the soda wash is caustic, while molasses just smells). You'll also need to create electrodes and anodes for the electrolysis method and some wire of course.
Day after day, it reappears. Night after night my heartbeat shows the fear. Ghosts appear and fade away. Come back another day.