Can you use chalk paint on a wrought iron bench that has some rust?

No, never use water based products on metal. Just wire brush off the rust and use metal spray primer. Spray with exterior spray paint.

Not at all. Kelli is correct. Instead of primer use Rustoleum Rust Reformer. No sanding needed. Then just use Rustolreum paint made for metal.

https://www.homedepot.com/p/Rust-Oleum-Automotive-10-25-oz-Rust-Reformer-Spray-Paint-248658/202623091

Thank you

I agree that you should not use water based paint on metal as the paint won’t bind or protect your piece.

An alternative would be applying a coat of oil-based primer (rust-oleum are the best) before your water-based paint, then a sealer. Still, I’d only do that for a piece that will stay indoors. Good luck!

you will want to seal it firs with an oil based product or shellac