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Metal Profile: Silver

What is silver?

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Metal Profile: Silver

Silver production at KGHM Polska's facility in Poland.

© KGHM Polska Miedź S.A.

Silver is a soft, lustrous metal that has a long history as a medium of exchange in coins and currency, and as a store of wealth (silver bullion). A precious metal, silver has been used in jewellery and as a decorative metal for millennia, while, more recently, it has become an important metal for electronic, industrial and medical applications.

Properties:

  • Atomic Symbol: Ag
  • Atomic Number: 47
  • Element Category: Transition metal
  • Density: 10.5g/cm3
  • Melting Point: 1760.9 °F (960.5 °C)
  • Boiling Point: 3542 °F (1950 °C)
  • Moh's Hardness: 3.25

Characteristics:
Silver is a very malleable and ductile metal that reacts readily with sulphur, causing it to tarnish easily. It has the highest thermal and electrical conductivity of any metal, making it a valuable material for many electronic applications. Silver metal is also non-toxic and has anti-bacterial properties.

History:
Silver mining is believed to have begun as early as the 4th millennia BC. Silver, or more correctly, electrum (an alloy of gold and silver) was extracted from naturally occurring surface ores in the Anatolia region of modern day Turkey. This was used by the Mycenaeans and Minoans in decorative objects and, by about the 6th century BC, in what may have been the first coins.

By roughly 1200 BC, silver mining had shifted to the area around Laurium, outside of Athens. This remained the largest source of silver production until the first century AD. Mines eventually spread across Europe to Spain and Germany, feeding the Roman Empire's growing need for silver and its trade throughout Africa and Asia.

Centuries later, silver would also play a central role in shaping the history of the Inca and Hapsburg (Spanish) empires. The natural wealth of silver in South America attracted the Spanish due to their need to fund wars in Europe and, ultimately, led to the conquest of the Inca Empire in the 16th century.

Spanish production of silver, and its use as a means of settling debts between states, resulted in silver becoming a truly global commodity. Mines were established and expanded in Mexico, Bolivia and Peru and, according to some estimates, these three regions accounted for 85% of global silver production between 1500 and 1800.

Silver mines would later be found throughout Europe, Chile, and Japan, and discoveries continued as technological innovations spread. During the late 1800s and early 20th century, silver production boomed as a consequence of better mining techniques, the rapid discovery of new uses for silver and improved ore separation.

Production:
Silver often naturally occurs in sulphide deposits along with copper (in chalcopyrite), lead (in galena) and zinc (in sphalerite). About three quarters of virgin silver production is, consequently, extracted as a by- or co-product of these metals. The minerals most commonly mined in primary silver operations include argentite, chlorargyrite and pyragyrite.

Silver containing ore is first crushed and ground into a powder before froth flotation separates metal containing particles. During the flotation process, air is pumped through a slurry of water and ore, resulting in metal sulphides sinking to the bottom.

Depending on the type of ore, different processes are then employed to extract silver and purify the primary metal (e.g. zinc).

When silver containing copper ore is electrolytically refined silver accumulates at the bottom of the refining tank. This can be smelted, cast and itself electrolysed in a solution of silver-copper nitrate to produce 99.9-99.99% (commercial grade) silver

After flotation, zinc concentrates are roasted and leached with sulphuric acid, which results in residue that contains lead, silver and gold. This residue - or slag - can be melted and treated with powdered coal and hot air producing a lead, silver and gold bullion. Treated with zinc, during what is known as the Parker process, gold and silver in lead bullion, or lead concentrates, form compounds and float to the surface.

The gold-silver residue is then heated to about 800° C (1,450° F) oxidizing any remaining lead content in a process called cupellation. It can then be refined electrolytically and boiled with sulfuric acid to separate the gold and silver.

According to the Silver Institute, 950 million ounces of silver were produced in 2010. Just over 20% of this silver came from recycled materials. The largest producing countries were Mexico (128.6 million ounces), Peru (116.1) and China (99.2). The largest silver producing companies during the same period were BHP Billiton, Fresnillo PLC and KGHM Polska.

Applications:
Silver is used in three main areas:

  1. industrial and medical applications
  2. jewellery
  3. modes of investment

Although in decline, silver's main industrial application is traditionally in photography, which accounts for about 7% of total silver demand. Photographic film depends upon silver halide crystals, which are light sensitive, in order to produce negative images for radiography, graphic arts and consumer photography.

Electrical solders, switches, contacts and fuses depend upon silver because of its efficient electrical and thermal conductivity properties. Electrically heated auto windshields, conductive adhesives and certain types of photovoltaic cells are manufactured using silver, as well as mirror and glass coatings, cellophane and batteries.

The jewellery and silverware industry accounted for about 20% of global demand in 2010. Silver is often alloyed with copper or base metals to increase the metal's durability for its use in silverware.

Silver is used in dentistry, as well as in very small quantities to sterilize water. It is used in medical equipment because of its ability to act as a bactericide and in some medications to fight infection. It can also be used on burn victims to halt infection and aid in the healing process.

Silver is perhaps, historically, most known for is its role in coinage. Today, silver bullion coins and medals are still a common form of retail investment, accounting for almost 10% of demand in 2010. It is traded on the London Bullion Market and COMEX in New York.

Sources:
Newton, Joseph. An Introduction to Metallurgy. 1947. John Wiley & Sons, Inc. (New York).
Neely, John E. Practical Metallurgy and Materials of Industry (1989). John Wiley & Sons (New York).
The Silver Institute. World Silver Survey 2011. www.silverinstitute.org
Encyclopaedia Britannica: Silver Processing. http://www.britannica.com/EBchecked/topic/544891/silver-processing

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