Copper refining

Copper washer manufactured using the continuous casting process, etched, diam. approx. 83 mm, purity ≥ 99.95%.

Copper refining describes a technical process for the extraction and purification of copper .

Occurrence

Copper occurs naturally as a solid metal that can be found primarily in North America , Chile and Australia . In the bound state it occurs as ore in the form of sulphides (e.g. covelline and colored copper gravel ), oxides (e.g. cuprite ), carbonates (e.g. malachite and azurite ), chlorides and arsenides . Copper ore deposits are particularly rich in the USA , Canada , Russia , Chile (world's largest producer), the Congo region , Iran ( Kerman (province) ) and Zimbabwe .

enrichment

The copper ores have a relatively low copper content, so they have to be enriched by flotation (swimming pool processing). The ground ores are mixed with water. Metal sulfides and metal oxides repel water, while the gangue rocks ( quartz , silicates ) are slightly wetted. By adding various chemicals, called frothers and collectors , the heavy ore particles are transported to the surface of the water and can be skimmed off.

Cookware

Cooking copper, containing antimony and nickel

The cleaned ore is first oxidized to copper oxide in several steps in roasting ovens , which is then reduced with copper sulfide (from the ore) to impure “cooked copper” , which has a purity of around 98.5%.

For a whole range of production areas, e.g. B. for the electrical industry, however, the purity of cooked copper is not sufficient, so that further processing is necessary.

Electrolytic copper refining

In the electrolytic copper refining electrode plates to hang out Garkupfer as anodes in an acidified copper sulfate solution. Either sheets made of pure copper or stainless steel sheets (Mt. Isa process) serve as cathodes . The electrolysis is carried out in large electrolysis tanks, in which several hundred electrodes are connected in parallel, at voltages of 0.2-0.3 volts .

Since the reacting substance on both electrodes is copper, theoretically no decomposition voltage is necessary. However, the amount of deposited copper increases proportionally with the voltage. However, too high a voltage leads to the more noble metals being oxidized and thus the copper at the cathode being contaminated again.

In the electrolysis the following processes take place: At the anode occurs oxidation of copper and all the less noble metals, so that the copper ion (Cu ²⁺ ), and the less noble metal ions (such as Ni. ²⁺ ) in solution to go. Impurities from more noble metals, which have a significantly higher normal potential (E ₀ ) than copper, are not oxidized, but fall to the ground as so-called anode sludge because the anode dissolves. At the cathode those cations of the solution are reduced (Cu ²⁺ ), which have the greatest tendency to do so, i. that is, those who have the greatest normal potential (E ₀ ). The pure copper is deposited on the cathode, while all the less noble metal ions such. B. nickel, arsenic and antimony remain in solution.

Reaction equations:

Anodic oxidation:

{\ displaystyle \ mathrm {Cu + Zn + Ni + Fe + Te + Ag + Au \ longrightarrow}}

{\ displaystyle \ mathrm {Cu ^ {2 +} + Zn ^ {2 +} + Ni ^ {2 +} + Fe ^ {2 +} + Te \ downarrow + Ag \ downarrow + Au \ downarrow + 8e ^ {- }}}

Cathodic reduction:

{\ displaystyle \ mathrm {Cu ^ {2 +} + 2e ^ {-} \ longrightarrow Cu}}

advantages

The anode sludge is a valuable by-product. From it in the copper smelters larger amounts of pure silver , gold , palladium and platinum as well as other precious metals from recycling material are obtained through further processing . The very pure, metallic copper is very soft, but very tough, malleable and ductile.

In terms of the market price of the refined metal, the energy consumption is quite low. For the production of one ton of pure copper it is around 250 kWh ; the energy costs are around one hundredth of the total price of around 6,000 US dollars per ton of copper

literature

AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 .

Individual evidence

↑ Wolfgang Bergmann: Material Technology , 456 pages, Verlag Carl Hanser Verlag GmbH & CO. KG, ISBN 3446225765 .

↑ Copper price on the stock exchange accessed online on January 19, 2019

Web links

Commons : Copper Refining - Collection of Pictures, Videos and Audio Files

Copper Production from Ore to Finished Product , overview of the steps of copper refining at copper.org