What kind of car is it? Do you have any better pictures of inside the wheel well, or know how it’s supposed to be attached? You might be able to take out some of the trim clips for the fender liner and pull the fender off and find that you can just slip it back into a groove or something. If you need to glue it, epoxy would work fine, or a silicone would work well too.

I have melted and cast ingots from thousands of dirty aluminum cans. Rinsing first is ideal of course, but all the crap floats to the top of the molten metal as slag and you can scoop it off to discard.