Introduction to recovery and refining
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To refine is to make something fine again. In this case we are making precious metals fine by removing as much as possible of any contamination. The word refine has been used since late 16'th century and has it's roots in the English words re and fine with influences from the French raffiner.
Refining of precious metals can often bee seen as a two stage process.
- Recovery : At first we are not worried about the final purity, we only wants to raise the level of precious metal to where we can use one of our standard refining tools. Basically this is done by removing any material that doesn't contain any precious metals.
For example, removing stones and stainless steel from jewellery, panning for gold in a stream, incinerating polishing wastes to remove any carbon containing material, cutting gold plated fingers from electronic scrap. Sometimes even chemical methods as cyanide leaching of ores or cementing silver onto copper could be used for recovery.
- Refining : In this step we try to increase the purity of the metal to a level where it can be sold or used in new products again. We usually ends up dissolving the metal to be able to extract the atoms of the metal via chemical methods.
Some examples of refining techniques could be using a silver cell to electrochemically make very pure silver, dissolving carat gold in aqua regia and precipitate it as pure gold, or the Miller process where chlorine gas is blown through molten gold to remove most impurities.