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Refining (metallurgy)

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Refining (metallurgy)

Refining (as in non-metallurgical uses) consists of purifying an impure material, in this case a metal. It is to be distinguished from other processes such as smelting and calcining in that those two involve a chemical change to the raw material, whereas in refining, the final material is usually identical chemically to the original one, only it is purer. The processes used are of many types, including pyrometallurgical and hydrometallurgical techniques.

Lead(Pb)

Cupellation

One ancient process for extracting the silver from lead was cupellation. Lead was melted in a bone ash 'test' or 'cupel' and air blown across the surface. This oxidised the lead to litharge, leaving a button of silver. In ancient times, the litharge was discarded, but more usually it was re-smelted to lead. "Pigs" of Roman lead have been found marked EX ARG (argentum is Latin for Silver). This presumably indicated that the lead had already been de-silvered. This process was viable economically if the lead contained at least 8 troy ounces of silver per ton of lead (178 ppm).

In the 18th century, the process was carried on using a kind of reverberatory furnace, but differing from the usual kind in that air was blown over the surface of the molten lead from bellows or (in the 19th century) blowing cylinders.[1]

Pattinson process

The Pattinson process was patented by its inventor, Hugh Lee Pattinson, in 1833. It depended on well-known material properties; essentially that lead and silver melt at different temperatures. The equipment consisted of a row of about 8-9 iron pots, which could be heated from below. Argentiferous lead was charged to the central pot and melted. This was then allowed to cool, as the lead solidified, it was skimmed off and moved to the next pot in one direction, and the remaining metal was then transferred to the next pot in the opposite direction. The process was repeated in the pots successively, and resulted in lead accumulating in the pot at one end and silver in that at the other. The process was economic for lead containing at least 250 grams of silver per ton.[1]

Parkes process

The Parkes process, patented in 1850 uses zinc to form a material which the silver enters. This floats on the lead and can be skimmed off. The silver is then recovered by volatalising the zinc.[1]

Copper

Fire refining

The initial product of copper smelting was impure black copper, which was then repeatedly melted to purify it, alternately oxidizing and reducing it. In one of the melting stages, lead was added. Gold and silver preferentially dissolved in this, thus providing a means of recovering these precious metals. To produce purer copper suitable for making copper plates or hollow-ware, further melting processes were undertaken, using charcoal as fuel. The repeated application of such fire-refining processes was capable of producing copper that was 99.25% pure

Electrolytic refining

The purest copper is obtained by an electrolytic process, undertaken using a slab of impure copper as the anode and a thin sheet of pure copper as the cathode. The electrolyte is an acidic solution of copper sulphate. By passing electricity through the cell, copper is dissolved from the anode and deposited on the cathode. However impurities either remain in solution or collect as an insoluble sludge. This process only became possible following the invention of the dynamo; it was first used in South Wales in 1869.

Iron

Wrought iron

The product of the puddling furnace), which was in turn gradually superseded by the production of mild steel by the Bessemer process.

Refined iron

The term refining is used in a narrower context. pig iron, a preliminary refining process was necessary to remove silicon. The pig iron was melted in a running out furnace and then run out into a trough. This process oxidised the silicon to form a slag, which floated on the iron and was removed by lowering a dam at the end of the trough. The product of this process was a white metal, known as finers metal and refined iron'.

Precious metals

Precious metal refining is the separation of precious metals from noble-metalliferous materials. Examples of these materials include used catalysts, electronic assemblies, ores or metal alloys.

Process

In order to isolate noble-metalliferous materials, Nitro hydrate connection. Afterwards, they go through cleaning stages or are recrystallized. The precious metals are separated from the metal salt by calcination. The noble-metalliferous materials are hydrolyzed first and thermally prepared (pyrolysed) thereafter. The processes are better yielding when using catalysts that may sometimes contain precious metals themselves. When using catalysts, the recycling product is removed in each case and driven several times through the cycle.

Bibliography

  • J. Day and R. F. Tylecote, The Industrial Revolution in Metals (The Institute of Metals, London 1991).
  • Söderberg, A. 2011. Eyvind Skáldaspillir's silver - refining and standards in pre-monetary economies in the light of finds from Sigtuna and Gotland. Situne Dei 2011. Edberg, R. Wikström, A. (eds). Sigtuna.
  • R. F. Tylecote, A history of metallurgy (Institute of materials, London 1992).
  • Newcastle University: Hugh Lee Pattinson

References

  1. ^ a b c Tylecote, 1992. pp 157-158.
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