Silver is produced through mining and ore refinement. The most productive silver mines are in Canada, Mexico, Peru, Australia and the United States. Bolivia is also a major silver producer. Nuggets of pure silver are exceptionally rare. Most ore must undergo purification to remove lead, arsenic, sulfur and other compounds. Silver is also produced during refinement of copper, zinc, lead and gold.
There are two major methods of silver extraction and refinement. Processes that use fire capitalize on the fact that different metals melt at different temperatures. For example, the Pattinson process separates lead and silver using fire and a series of metal pots. The final result is one pot of pure silver and one pot of pure lead.
The second major method of silver refinement is chemical purification. One of the quickest and most effective approaches is nitric acid refinement. Silver dissolves when immersed in the acid, but its impurities do not. After dissolving the ore in an acid bath, the corrosive liquid is strained into an acid-resistant container. The result is a mixture of pure nitric acid and pure silver. The silver solidifies upon the addition of silver precipitant crystals. Then the refiner lifts it out of the acid, thoroughly washes it and prepares it for smelting.