John,
You will find jimdoc's to be very helpful in his answers, personally, I would take his advice any day even if it was not what I wished to hear.
In-fact if taken to the bank, I feel his advice was worth more than what I posted earlier.
May I suggest before experimenting with acids and metals, that a member should spend his time studying, gaining an understanding of what to expect, how metals react with acids and alkalies, what metals and acids or basic solutions become dangerous when mixed and in what situations they are dangerous or explosive...
Read Hoke's book first, then work on the getting acquainted experiments (she walks you through them, which will explain much of the chemistry where a layman can understand it), if done, your questions would have already been answered, this one and a thousand more questions you can think of to ask.
Study each metal, and chemical you intend to use and gain an understanding of reactions, dangers, precautions. Safety should be studied before using an acid or any other chemical.
There are reactions we use in recovery and refining that can easily become explosives, deadly gases, metal ions that will poison you, and contaminate the environment they come in contact with and poison others.
Recovery and refining is not something you read a little about and start experimenting with, this is a field you can spend your whole life studying and only gain a glimpse of its scope.
Experimenting with chemistry without educating yourself besides being a waste of time, it is just dangerous.
How is that for a lecture????