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Patio Process
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The earliest method of extraction was a method developed in
the Mexican mines in the mid 1500s and familiar to the miners at
Virginia City, the Patio Process. This method of processing
the rocks to extract the silver was slow, did not recover all the
silver, and did not use the added reagents as efficiently as
possible. In addition, the climate of Virginia City caused
problems with freezing.
As the metal was ground in circular open patios or
"arrastras," water, mercury, salt and roasted copper
and iron sulfides were added. (reference: Thompson, James
V., "Silver Recovery by Older Methods," Engineering and
Mining Journal, June 1991, p. 39-41). Although the
chemicals were added all at once, it is easier to think of the
reactions in sequence. The first several reactions change
the silver compounds into silver metal (step (a)), then the
silver metal is removed from the waste rock and other metals by
amalgamation (step (b)).
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Patio Process
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