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Sources of Silver
There are silver mines all over the world. At the time of publication, the three largest producers of silver were Mexico, Peru and China. Mexico produced 128.6 million ounces, Peru 116.1 million ounces and China 99.2 million ounces. Total global production of silver in 2010 was 878 million ounces. Of this around half was used for industrial applications. A large amount of silver is produced as a byproduct of mining for lead, zinc and gold. Significant quantities of silver are produced by recycling products that contain silver, such as electronic devices and jewelry.
Mining of Silver Ore
Silver binds chemically with other elements and so is usually found in the form of silver ores of various types. Silver ore can be mined either from open pits or from underground mines. Open pits are open to the sky and are dug when the silver ore is located near to the surface. Underground mines are tunnels into the earth and are dug when the silver ore is buried deeper underground. The most common form of silver ore is called argentite, which consists of silver bonded with sulfer. Other important silver ores include copper silver glance, ruby silver and horn silver.
Smelting
Pure silver can be extracted from these ores by smelting. Smelting is a process whereby the ore is heated and mixed with a chemical reducing agent such as coal or coke. The reducing agent has the effect of changing the oxidation state of the ore so the non-silver impurities bind with the carbon in the reducing agent and are removed, leaving the pure silver behind.
The Patio Process
The Patio process is one of a variety of chemical methods of extracting pure silver from silver ore. In the Patio process, silver ore is mixed with salt, water and copper sulfide. The copper sulfide reacts with the silver in the ore to form silver chloride. The silver chloride was then mixed with the element mercury. This resulted in an amalgam, or mixture, of silver and mercury. The silver could then be extracted from the mercury by distillation. The Patio process was developed in Central America in the 18th century However, it is quite inefficient and so was superseded by the von Patera process.
The Von Patera Process
The von Patera process of extracting pure silver from silver ore was developed in the 19th century. In the von Patera process the silver ore is mixed and heated with rock salt, forming silver chloride. The silver chloride is then dissolved in sodium hyposulfite, and the solid silver appears in the sodium hyposulfite solution. This is the same chemical reaction that allows silver chloride to be used to make photographs.