Electrolysis copper purification

The copper is still not pure enough for most purposes. The most common method for copper purification relies on electrolysis. Electrolysis is the process by which an electrical current is used to cause a chemical change, usually the breakdown of some substance. The copper is dissolved in sulfuric acid again and an electric current is passed through the solution. Pure copper metal is deposited on one of the metal electrodes. By repeating this process, copper of 99.9 percent purity can be made. 

Nickel. Most nickel is also refined by electrolysis. Both copper and nickel dissolve at the potential required for anodic dissolution. To prevent plating of the dissolved copper at the cathode, a diaphragm cell is used, and the anolyte is circulated through a purification circuit before entering the cathodic compartment (see Nickel and nickel alloys). 

Analysis of zinc solutions at the purification stage before electrolysis is critical and several metals present in low concentrations are monitored carefully. Methods vary from plant to plant but are highly specific and usually capable of detecting 0.1 ppm or less. Colorimetric process-control methods are used for cobalt, antimony, and germanium, turbidimetric methods for cadmium and copper. Alternatively, cadmium, cobalt, and copper are determined polarographicaHy, arsenic and antimony by a modified Gutzeit test, and nickel with a dimethylglyoxime spot test. 

Preparation. Industrially, silver is usually a by-product of processes of extraction of other metals such as copper, lead, zinc. The so-called anode slimes from the electrolytic purification of copper contain silver and the involved process is often finished by an electrolysis of a nitrate solution containing silver. 

Polonium may be purified by various processes. Such purification methods include precipitation of polonium as sulfide and then decomposing the sulfide at elevated temperatures spontaneous decomposition of polonium onto a nickel or copper surface and electrolysis of nitric acid solutions of polonium-bismuth mixture. In electrolytic purification polonium is electrodeposited onto a platinum, gold, nickel, or carbon electrode. 

Figure 5.18 The movement of ions in the purification of copper by electrolysis.

Predict the products of electrolysis of a solution of copper(n) sulfate if carbon electrodes are used instead of those made from copper as referred to in the purification of copper section. 

The principal impurities in zinc spelter are cadmium, iron, lead, arsenic, and copper. In addition to purification by electrolysis, zinc spelter may be refined by redistillation or by suitable chemical methods chosen in relation to the desired degree of purity. 

Purification of iron and nickel fraction by anion exchange resin (Dowex) Electrolysis of Fe and Ni on polished copper discs... 

Purification of metals is another important application of electrolysis. For example, impure copper from the chemical reduction of copper ore is cast into large slabs that serve as the anodes for electrolytic cells. Aqueous copper sulfate... 

Hudgens and Cali 38) have described a determination of antimony at the parts per million level in zirconium oxide. Distillation and solvent extraction were used in the radiochemical purification and antimony was mounted, prior to counting, by electrolysis onto platinum foil. Atchison and Beamer (S) have determined arsenic, phosphorus, copper, sodium, strontium, calcium, and chromium in pure magnesium. 

Purification of ores Another application of electrolysis is in the purification of metals such as copper. Most copper is mined in the form of the ores chalcopyrite (CuFeS2), chalcocite (CU2S), and malachite (Cu2C03(0H)2). The sulfides are most abundant and yield copper metal when heated strongly in the presence of oxygen. 

Electrolysis is another important purification technique. The copper metal obtained by roasting copper sulfide usually contains impurities such as zinc, iron, silver, and gold. The more electropositive metals are removed by an electrolysis process in which the impure copper acts as the anode and pure copper acts as the cathode in a sulfuric acid solution containing Cu ions (Figure 20.6). The reactions are... 

In the electrolytic purification of copper, the anodes are blister copper bars and the cathodes are made of pure copper. As electrolysis proceeds, copper is oxidized at the anode, moves through the solution as Cu ions, and is deposited on the cathode. The voltage of the cell is regulated so that more active impurities (such as iron) are left in the solution, and less active ones are not oxidized at all. The less active impurities include gold and silver, which collect as anode slime, an insoluble residue beneath the anode. The anode slime is subsequently treated to recover the valuable metals. 

High purity dihydrogen is likewise produced by electrolysing water, it is also worth mentioning here the purification of certain metals, such as copper, zinc and aluminium, by an electrorefining process involving anodic dissolution and cathodic deposition by a selective electrolysis. 

Purification of copper is achieved by electrolysis, as illustrated in Figure 23.11 . Large slabs of crude copper serve as ihe anodes in tire cell, and thin sheets of pure copper serve as the catiiodes. The electrolyte consists of an acidic solution of CUSO4. Application of a suitable voltage to flie electrodes causes oxidation of copper metal at the anode and reduction of Cu to form copper metal at the cathode. This strategy can be used because copper is both oxidized and... 

Indium is mainly won from residues during the metallurgical treatment of indium-rich zinc and lead ores. The residues are dissolved in acid and indium chloride precipitates at the inlet of chlorine gas. The indium chloride is purified from tin, copper and lead using liquid-liquid extraction. A concentrated indium solution is obtained, from which indium is precipitated on zinc sheets. The spongy metal is scraped off, fused and cast into bars. For normal use, purification by electrolysis is satisfactory. For semiconductor purposes, repeated electrolysis and zone melting create an extreme purity. In 2001 the refined indium production was about 300 tonnes. 

---