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How is copper melted?

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Copper is located in the IB group of the fourth cycle of the periodic table, which is the earliest metal used by human beings. Copper has been widely used in industry because of its excellent properties. The content of copper in the earth's crust is about 0.01%. In nature, copper exists in the form of compound. The common copper ores are chalcopyrite (CuFeS2), chalcocite (Cu2S), malachite (Cu2 (OH) 2CO3), hematite (Cu2O) and chalcopyrite (CuSO4 · 5H2O).

In the Western Han Dynasty, Liu An's Huainan Wanbi Shu has a record that "when Zeng Qingde gets iron, it turns into copper", which means that copper can be replaced by putting iron into copper sulfate solution or other copper salt solution. This method is the pioneer of modern hydrometallurgy. Copper hydrometallurgy is also called gallstone copper process, and its production process mainly includes two steps: first, dip copper, put iron in the solution of alum, so that the copper ion in the alum is replaced by iron to deposit copper; second, the replaced copper powder is collected and smelted. The essential principle of copper hydrometallurgy is to replace the weaker metals (except K, Ca and Na) with substances with stronger metallicity than copper, such as adding metal zinc or iron into copper sulfate solution to obtain copper. The main reactions are: CuSO4 + Zn = Cu + ZnSO4; CuSO4 + Fe = Cu + FeSO4.

Zhang Qian, the first person in the world to smelt copper by hydrometallurgy, combined with previous works and personal experience, wrote the book "Essentials of copper leaching". The book describes the technology of smelting copper with copper bearing water (or gall water). The copper gall method described in this book has the advantages of "low cost and rich achievements".

In the chemical laboratory, we can also simulate copper hydrometallurgy. Take a 20cm long iron wire and polish it with sandpaper. Then take 4ml copper sulfate solution into the test tube. Add the polished iron wire. After standing, it can be observed that there are purple red metals on the surface of the iron wire, and the solution gradually changes from blue to light green. The purple red metal precipitated is copper. Finally, the iron wire is taken out to collect the copper precipitated from the surface of the iron wire.

In addition, there was a method of smelting copper in ancient China - "pyrometallurgy". According to textual research, copper smelting by fire in Shang Dynasty was mainly made of malachite and charcoal. Pyrometallurgy of copper is a process in which the oxide containing copper element reacts with reducing agent at a higher temperature to produce copper. This reduction reaction needs a certain temperature, so it can produce copper in the state of heating, so it is called "pyrometallurgy copper".

It has been discovered for a long time that Malachite can produce a bright red metal after being burned. This metal is copper. The main component of malachite is basic copper carbonate [Cu2 (OH) 2CO3]. When heated, the basic copper carbonate will decompose into copper oxide, water and carbon dioxide. Carbon or carbon monoxide can reduce copper oxide, and the reactions are: Cu2 (OH) 2CO3 2CuO + H2O + CO2 ↑; C + 2CuO 2Cu + CO2 ↑; CO + CuO Cu + CO2.

In the chemical laboratory, we can use the device shown in the figure below to simulate pyrometallurgy. Weigh 10g of new copper oxide, grind it into powder, pour it into crucible and dry it. Then weigh 1.5g of new charcoal, grind it into powder, pour it into crucible and dry it. Then mix the copper oxide powder and charcoal powder evenly, spread it on the bottom of the test tube with a medicine spoon or paper slot, assemble the instrument as shown in the figure below, put one end of the glass tube into the test tube containing clear lime water, and heat it with an alcohol lamp with wind shield. When the clarified lime water becomes turbid, and the purple or red solid gradually appears in the test tube, the heating is stopped. After the reaction was completed, the glass tube which was inserted into the test tube containing clarified lime water was withdrawn first, and then the alcohol lamp was withdrawn. Finally, the powder in the test tube is poured on a clean white paper. After the powder is spread out and observed, it will be found that there is a purple solid on the paper, which is copper.

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