Can I use a car jack for a broken bed leg?
Weight capacity, no problem.

Staying put, noise from motion, stubbing your toes, limited height adjustability; all probable or definite problems.

Bed frames in perfectly usable shape tend to go for a song at secondhand stores, or end up in the waste stream as they rarely get sold and too many are donated. I suggest you go buy one of them, and then see if you can find a place to take your broken frame as scrap steel rather than trash. 

Either that, or have it welded.