Refining (metallurgy)

In

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.^{[clarification needed]} The processes used are of many types, including pyrometallurgical and hydrometallurgical

techniques.

Lead

Cupellation

One ancient process for extracting the silver from

oxidised the lead to litharge, and also oxidised other base metals present, the silver (and gold if present) remaining unoxidised.^[1]

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.^[2]

Pattinson process

The Pattinson process was

eutectic and typically the process stopped around 600 to 700 ounces per ton (approx 2%), so further separation is carried out by cupellation.^[5]

The process was economic for lead containing at least 250 grams of silver per ton.[2]

Parkes process

The Parkes process, patented in 1850 uses molten zinc. Zinc is not miscible with lead and when the two molten metals are mixed the zinc separates and floats to the top carrying only some 2% lead. However silver preferentially dissolves in zinc, so the zinc that floats to the top carries a significant proportion of the silver. The melt is then cooled until the zinc solidifies and the zinc crust is skimmed off. The silver is then recovered by volatalising^[spelling?] the zinc.^[2] The Parkes process largely replaced the Pattinson process, except where the lead contained insufficient silver, in which case the Pattinson process provided a method to enrich it in silver to about 40 to 60 ounces per ton, at which concentration it could be treated using the Parkes' process.^[6]

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.^{[citation needed}

]

Refined iron

The term refining is used in a narrower context. Henry Cort's original puddling process only worked where the raw material was white cast iron, rather than the grey pig iron that was the usual raw material for finery forges. To use grey 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 or 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,

reduced directly with a salt, gas, organic, and/or 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.^{[citation needed}

]

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

^ Metallurgy - An Elementary Text Book, E.L. Rhead F.I.C F.C.S, Longmans, 1895, pp225-229
^ ^a ^b ^c Tylecote, 1992. pp 157-158.
^ Tylecote, R. F. (1992). A history of metallurgy. London: Institute of Materials. pp. 157–158.
^ Rowe, 1983. pp 189–190.
^ Metallurgy - An Elementary Text Book, E.L.Rhead F.I.C F.C.S, Longmans, 1895, pp193-195
^ Metallurgy - An elementary text-book, E.L. Rhead F.I.C. F.C.S., Longmans, 1895, p195

[1] Metallurgy - An Elementary Text Book, E.L. Rhead F.I.C F.C.S, Longmans, 1895, pp225-229

[Tyle-2] Tylecote, 1992. pp 157-158.

[Tylecote-3] Tylecote, R. F. (1992). A history of metallurgy. London: Institute of Materials. pp. 157–158.

[Rowe189-4] Rowe, 1983. pp 189–190.

[5] Metallurgy - An Elementary Text Book, E.L.Rhead F.I.C F.C.S, Longmans, 1895, pp193-195

[6] Metallurgy - An elementary text-book, E.L. Rhead F.I.C. F.C.S., Longmans, 1895, p195

[1]

[2]

[5]

[6]

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