How do I clean a cast iron radiator humidifier with rust?

How do I get rid of the rust on my cast iron radiator humidifier? It's 2 pieces, cast iron that sits on the radiator. I fill it with water a few times a week to put moisture into the air as the radiators heat up. It's being overtaken with rust on the inside and it's now rusting out over the edges. (like a bubbling effect) Could I treat it like a cast iron frying pan to get rid of the rust? I know there is a treatment for the frying pans but I would have to look that up! Thank you to anyone that could help me with cleaning this humidifier!

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