You need to melt it down in a big cast iron pot over a propane cooker (turkey fryer works best). You need to clean all the gunk out of it and the steel clips. Then you need to flux it several times to remove the dirt and gunk.. once that’s all done you can pour it into ingots and use it. All the crap will not come to the surface, maybe 10% of it will. You will need to read up on fluxing lead to be able to clean it completely.
Wheel weight lead is not pure lead, often times there will be tin mixed in causing it to be lighter than normal. A 1/2 oz jig might only weigh 3/8oz with wheel weight lead.