Electrolytic copper refining

Owing to the demand for very pure copper, electrolytic refining is practised on a very large scale. The cathodes are thin sheets of copper and the anodes blocks of the impure metal, and the electrolyte consists of copper(II) sulphate and free sulphuric acid the presence of the... 

Silver is also recovered during electrolytic refining of copper. Commercial fine silver contains at least 99.9% silver. Purities of 99.999+% are available commercially. 

Tellurium is occasionally found native, but is more often found as the telluride of gold (calaverite), and combined with other metals. It is recovered commercially from the anode muds that are produced during the electrolytic refining of blister copper. The U.S., Canada, Peru, and Japan are the largest Free World producers of the element. 

Electrorefining. Electrolytic refining is a purification process in which an impure metal anode is dissolved electrochemicaHy in a solution of a salt of the metal to be refined, and then recovered as a pure cathodic deposit. Electrorefining is a more efficient purification process than other chemical methods because of its selectivity. In particular, for metals such as copper, silver, gold, and lead, which exhibit Htfle irreversibHity, the operating electrode potential is close to the reversible potential, and a sharp separation can be accompHshed, both at the anode where more noble metals do not dissolve and at the cathode where more active metals do not deposit. 

The matte can be treated in different ways, depending on the copper content and on the desired product. In some cases, the copper content of the Bessemer matte is low enough to allow the material to be cast directly into sulfide anodes for electrolytic refining. Usually it is necessary first to separate the nickel and copper sulfides. The copper—nickel matte is cooled slowly for ca 4 d to faciUtate grain growth of mineral crystals of copper sulfide, nickel—sulfide, and a nickel—copper alloy. This matte is pulverized, the nickel and copper sulfides isolated by flotation, and the alloy extracted magnetically and refined electrolyticaHy. The nickel sulfide is cast into anodes for electrolysis or, more commonly, is roasted to nickel oxide and further reduced to metal for refining by electrolysis or by the carbonyl method. Alternatively, the nickel sulfide may be roasted to provide a nickel oxide sinter that is suitable for direct use by the steel industry. 

Fig. 1. Recovery of copper from sulfide ore. The residue from electrolytic refining is processed to recover gold, silver, and selenium. Courtesy of Kennecott...

The end product is either cast as anodes for electrolytic refining or, rarely, as ingots for sale as fire-refined copper. A horizontal casting wheel with 12—32 horizontal molds is normally used for anode casing. Using continuous casting machines, the copper is cast as a continuous strip to be cut to the required anode shape (28). 

Developments. Electrolytic refining requires a large capital investment, and labor costs per kilogram of copper produced are high. Most refineries have traditionally operated at current densities of about 240 A/m. Thus, a tank house area of approximately 40 m is required per ton of copper produced daily. The use of higher current densities reduces capital requirements but may impair deposition efficiency and product quaUty. 

Potassium cyanide is primarily used for fine silver plating but is also used for dyes and specialty products (see Electroplating). Electrolytic refining of platinum is carried out in fused potassium cyanide baths, in which a separation from silver is effected. Potassium cyanide is also a component of the electrolyte for the analytical separation of gold, silver, and copper from platinum. It is used with sodium cyanide for nitriding steel and also in mixtures for metal coloring by chemical or electrolytic processes. 

In the most common hydrometallurgical process, the ore is leached with ammonia or sulfuric acid to extract the copper. These processes can operate at atmospheric pressure or as pressure leach circuits. Copper is recovered from solution by electrowinning, a process similar to electrolytic refining. The process is most commonly used for leaching low-grade deposits in situ or as heaps. 

WEB Zinc is produced by electrolytic refining. The electrolytic process, which is similar to that for copper, can be represented by the two half-reactions... 

Copper is refined electrolyticallv by using an impure form of copper metal called blister copper as the anode in an electrolytic cell (Fig. 12.14). The current supply drives the oxidation of the blister copper to copper(II) ions, Cu2+, which are then reduced to pure copper metal at the cathode ... 

Preparation. Selenium is normally extracted as a by-product from electrolytic refining of copper. 

For example, copper is about 99% pure after extraction. This copper is pure enough for some uses, such as the manufacture of copper pipes for plumbing. However, the copper is not pure enough for one of its principal uses, electrical wiring. Therefore, some of the impure copper is refined electrolytically, as shown in Figure 11.25. Nickel can be refined electrolytically in a similar way. You refined copper on a small scale in Investigation 11-C. 

Metallic copper obtained above is purified by electrolytic refining. The electrolytic cell consists of a cathode made of thin sheets of very pure copper connected to the negative terminal of a direct-current generator, and a lump of extracted impure copper from the ore serving as an anode. A solution of cop-per(II) sulfate in sulfuric acid is used as electrolyte. Electrolysis causes trans-... 

Osmium and other precious metals also may be recovered from sludges generated at the anode from electrolytic refining of nickel and copper from... 

Ruthenium is derived from platinum metal ores. Method of production depends on the type of ore. However, the extraction processes are simdar to those of other nohle metals (see Platinum, Rhodium and Iridium). Ruthenium, like Rhodium, may he obtained from accumulated anode sludges in electrolytic refining of nickel or copper from certain types of ores. Also, residues from refining nickel by Mond carbonyl process contain ruthenium and other precious metals at very low concentrations. The extraction processes are very lengthy, involving smelting with suitable fluxes and acid treatments. 

Selenium is recovered from anode muds or slimes in electrolytic refining of copper. Anode mud is treated with sulfuric acid and roasted. Selenium is converted to its dioxide, which vaporizes and is collected in a wet scrubber system. 

The unsoftened lead obtained after the softening operation contains silver in small but significant quantities. Such unsoftened lead is cast into anode and subjected to electrolytic refining. The anode mud that is formed adhering to these anodes is removed by scraping. It contains bismuth, silver, gold, and other impurity metals. Silver is obtained from this anode mud by methods similar to the extraction of anode mud from the copper refining process discussed earher. 

Copper used in electrical wires and circuits should be very pure. Crude copper is refined electrochemically by using electrolytic cells. Impure copper is given a positive charge (anode), and pure copper is given a negative charge (cathode). 166 Heat, Chemical Kinetics and Eiectrochemistry... 

Electrolytic Refining of Copper. Immerse a carbon cathode and an anode cut out from a strip of crude copper into a 300-ml beaker. Pour a 20% sulphuric acid solution into the beaker. The current... 

Tellurous acid can be prepared from the residues from the electrolytic refining of copper by treating them with a solution of ammonia. On the addition of acetic acid to the resulting solution tellurous acid is obtained as a precipitate. When this precipitation is carried out in the cold the product obtained is readily soluble in alkali hydroxide, but if the precipitation takes place in a hot solution the product tends to be insoluble in the alkali hydroxides.2... 

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