Just like gold, silver too is a precious metal and it is used primarily for minting coins and creating jewelry. Historically, silver mining can be an economically lucrative endeavor and that is why when fresh deposits of silver are discovered, miners make a beeline to the area to look for their fortune.
In the last few centuries, silver mining has been instrumental in the development and growth of the US, Canada, Mexico, Bolivia, Peru, and Chile.
Looking for Silver
Silver rarely exists in nature alone as nuggets. Usually, it is found combined with arsenic, chlorine, antimony, sulfur, and sometimes with as an ore, like argentite, galena, and chlorargyrite. Galena usually contains a large amount of silver. Silver can also be found along with gold.
Silver mining companies use metallurgists and geologists to identify geographical regions that have high concentrations of silver, which can be present close to the earth’s surface or deep underground. Once the geologists find the spot that contains high concentrations of silver, the mining process begins.
Mining for Silver
Silver can be mined using open-pit mines or underground mines. As the name suggests, an open-pit mine is a gigantic hole in the ground created using heavy machinery and explosives. Silver miners open the window for open-pit mines when the silver is located close to the Earth’s surface.
When silver is present deep in the ground, miners excavate underground mines. These mines have deep shafts and several tunnels are often attached to the shafts. The tunnels lead to the silver deposits.
Silver ore is hauled from the mine to the processing plant where the silver is extracted from the main metal and then purified.
Silver Extraction and Purification
Silver usually is present with other metals, such as copper, zinc, and lead. Depending on the major metal, mining companies use the extraction method.
Extraction from Copper Concentrate: If silver is present with copper, it is necessary to smelt and convert copper concentrate into blister copper. This form of copper contains about 97 to 99 percent silver. The blister copper is put through electrolytic refining, which results in impurities collecting at the bottom of the tank. These insoluble impurities contain silver.
The impurities are smelted to oxidize all metals other than silver, platinum, and gold. This metal contains small proportions of gold and platinum, with silver being in large concentrations. The metal is then put through electrolysis in a silver copper nitrate solution. This results in the extraction of silver, which is three-nines pure.
Extraction from Lead Concentrate: If silver is present with lead, the concentrate is first roasted and then smelted to form lead bullion. The impurities present in the bullion, including silver, are then removed. The silver is removed by adding zinc to the melted lead bullion. The zinc reacts with gold and silver present in the bullion to form an insoluble compound that floats on the surface of the molten bullion.
The nuggets are removed and heated to about 800 deg C in an oxidizing condition. The lead oxidizes, leaving behind silver and gold. The silver is extracted via electrolysis and then refined using the Wohlwill process.
Extraction from Zinc Concentrate: Just like the lead concentrate, zinc concentrate containing silver is roasted and then treated with sulfuric acid. This dissolves the zinc, leaving behind silver, gold, and lead. This residue is melted and then powdered coke or coal is blown through it along with air.
The zinc turns into a metal and gets vaporized, whereas the lead is transformed into a metallic form and dissolves the gold and silver. The lead nuggets are removed and heated to around 800 deg. C in oxidizing conditions, resulting in the oxidation of lead. What remains is gold and silver. Silver is extracted using electrolysis and then refined to reach the global silver purity standard.
Silver can also be extracted from scrap. About 60 percent of the total silver produced is utilized in the photographic industry. This silver can be recycled by extracting the silver from photographic processing solutions via electrolysis, whereas photographic films are burned to ashes and the resultant ash is then subjected to leaching to extract the silver metal.
The silver present in jewelry is of high-grade. This jewelry is typically re-alloyed and the jewelry dust that forms during grinding and polishing is smelted to produce an impure form of silver, which is then put through electrolysis to refine it.