Silver Metallurgy

 

Although gold is very attractive, silver is the most precious metal abundant in nature and constitutes 0.00005% of the earth’s crust. Unlike gold, silver rarely occurs natively, but is most often contained in sulphides of base metals (Cu, Pb, Zn). It is a white metal that could be kept for a long time its beauty. It is believed that during the first times, the brilliant white color of the silver was related to the moon, which was reflected in the names given to this metal. In this way, the Latin name for silver, argentums is derived from the Latin root meaning white, brilliant. Silver was one of the first metals to be employed by a human been. Since antiquity, silverware has been handed down in Southern Europe and the Near and Middle East. According to many researches, the first large-scale workings of silver were developed in Asia during the 4^th millennium B.C. Some years later, silver deposits were mined in Armenia and Bactria. Other important situation is the fact that Athens began to exploit deposits of silver-lead, which brought her over 75 thousand tons of silver and were the basis of the economy for some centuries. From the ninth to fifteenth century, silver ores were processed in Romania and Czechia.

In the modern world, Mexico and the United States produce more than half of the silver of the world. Peru, Bolivia and Canada are also important producers. According to studies developed by America universities, 85% of the silver produced in Arizona comes from copper ores and most of that produced in California is a by-product of gold quartz mining. Within the borders of Russia, the first silver mines were located Bashkiria. In the eighteenth century the exploitation of large silver deposits started in Central Asia and the Caucasus. As more silver was produced, the processing methods for recovery, extraction and refining were enhanced. One important contribution to the development of silver metallurgy was done by Ivan Mokeyev, who separated gold from silver. A French Investigator, D’Arcet developed a method of refin9ng silver with sulphuric acid. The idea was to dissolve silver in boiling cupric sulphate, so that gold precipitates to the bottom and the silver is reduced to silver metal by copper. This process was employed in the 19^th century to give was subsequently to electrolysis, whose final product was 99.9% pure silver.

Considering the fact that silver is a very soft metal, it is normally employed industrially in its pure state, but is alloyed with a hardener, usually copper. Sterling silver is the name given to a standard high grade alloy containing 925 parts in 1000 of silver. Usually, the alloy is employed for tableware, jewelry and electrical contacts. The alloy of 7.5% copper work-hardness and needs annealing between roll passes. The old alloy of silanca contained small quantities of antimony and zinc, but the name of sterling silver is applied only to the specific silver-copper alloy.

Disseminated silver mineralization is quite commonly associated with gold deposits. In this way depending on the mineral composition of the ores, the mineralization may be different both in silver content and the form of its occurrence. In gold-quartz ores, silver concentrates largely in the native gold to form alloys such as electrum or micro inclusions of silver tellurides and mixed silver-gold tellurides. In gold-sulphide ores, native silver, argentite and sulphosalts of silver commonly occur. The main minerals of silver are argentite (Ag₂S), proustite (AgAsS₃), pyrargyrite (Ag₃SbS₃), pearceite (Ag.Cu₁₆As₂S₁₁), polybasite (Ag.Cu₁₆Sb₂S₁₁), Hessite (Ag₂Te) and cerargyrite (AgCl).