What is Silver Refining?

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Silver refining is the process of chemically or electromechanically treating silver in order to purify it from any impurities found in the metal, either due to nature, or by the devise of industry. While silver can and does occur in a pure state in nature, it rarely is found as such and in order to be properly used and graded, it has to undergo a process of refining to leech out any impurities found in silver ore. Likewise, silver that has been used either for currency, jewelry, or industrial purposes has to undergo a form of refining to enable it to become pure again, to be reused for similar purposes later on. In some respects, silver has to undergo refining only so that a more precious metal – gold – can be obtained, as silver and gold are usually found naturally alloyed (known as electrum) and nearly inseparable.[1]

Since ancient times, various methods of silver refining have been developed, although this usually went hand-in-hand with the process of refining gold. One of the earliest methods to help separate silver from gold and other metallic impurities is known as cupellation. Cupellation is a method which involves heating the silver until it is liquefied, refining it with the addition of certain substances such as nitric acid (which dissolves the silver into silver chloride), which is then separated from the dross or slurry with the addition of sodium carbonate.[2] This reaction is brought about by the introduction of the metal to extremely high temperatures. In this respect, cupellation is one of the earliest and most rudimentary means to refine silver and yields an end product with the purity of 85-90%.

During the Middle Ages the refining process took on a whole new turn with the discovery of potent and powerful acids capable of dissolving impurities (i. e. other metals) found in a natural ore or in an alloyed mixture. Although this yielded silver of only a specific purity, it was one of the most commonly employed methods until late into the Renaissance period. A whole other method that is still (rarely) used by artisanal silversmiths of today takes its inspiration from salt cementation. In this method, however, had the addition of liquid mercury to act as the medium for which silver could be obtained in a pure state. Known as the Patio or amalgamation method, it involved powdering the silver and mixing it with salt, powdered copper, and liquid mercury. This was further refined by allowing tethered mules to crush the granules further, slowly incorporating the silver into the copper-salt-mercury mixture.[3] This mixture was then gathered and heated in an alembic or a blast furnace, in effect distilling the silver away from the amalgam mixture, so that the end result was silver with a purity of 90-95%.

It has only been due to the introduction of modern technology that a truly fine quality of silver that is rendered at its purest state has been made possible. Nowadays, much of the industrial silver refining methods have been accomplished with the help of modern technology. One of the most commonly employed methods of modern silver refining is similar to the process used to refine gold – the electro-refining method. In this procedure, silver is separated from the impurities that it contains through the use of electrical current that is charged through a submersion of impure silver in an acidic bath.[4] This yields a silver of the highest purity, and is responsible for much of the silver that is mass-produced for industrial, monetary, and general purposes today.

What is Silver Refining? - References:

[1] http://en.wikipedia.org/wiki/Electrum
[2] http://www.cash4gold.com/sell/recovery-and-refining-of-precious-metals/how-to-refine-silver
[3] http://www.ehow.com/how-does_5182870_process-refining-silver.html
[4] http://electrochem.cwru.edu/encycl/art-m02-metals.htm

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