pool acid/Hydrocloric/Muriatic & lead/Zinc

I finally found some pool acid after looking all over and getting some pretty weird looks.

The stuff I got says Muriatic acid on the label, contains 20% Hydrocloric (41.65% by weight).

I took a sprue leftover from my last casting session and put it into a pop bottle cap full of the acid, it started to bubble some.
I left it in the acid for just a bit over 2 hours while I watched a movie.
When I checked it, it was no longer bubbling at all but had changed to a much darker color. When melted again will it turn back into shiny lead?
After a good washing in water I put it beside another sprue from the same casting session and took a picture of it, you will see it below.
The acid treated sprue is on the right.



OK, this makes me think and brings up some questions
1. Did it stop bubbling because it ate up all the zinc or because the acid was worn out? I will have to put it into a bit more acid to check.
2. Did the acid get out all the zinc or just what was on the surface?
3. Could a person melt a large batch (200+ Pounds) of contaminated lead/zinc and pour it into thin castings, just pour a bit at a time onto a concrete floor to make really thin pieces. Then soak the thin pieces in a bucket of acid to get rid of all the zinc?
4. Will the acid destroy any of the Tin/Antimony in the lead?

I think that is all my ramblings for now.

Michael Grace