|MadSci Network: Chemistry|
You could begin to answer this question by checking into an intro chemistry book and reading up on oxidation-reduction reactions. Simply stated oxidations and reductions always occur together. When one atom is reduced, something else is oxidized. Acid can be though of as a reducing agent so acid reduction occurs when acid is able to reduce (give electrons to) another substance.Whether or how fast this occurs depends on something called the redox potential, which may go beyond what you are asking. By the way, lead is more often extracted with chelating agents than with acid solutions.
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