Bath copper sulfate, electrolytic

The secondary pickle reservoir is also shown in Block B. Copper sulfate accumulates in this bath and eventually crystallizes out. These crystals can be recovered and sold as a copper-rich sludge or added to the electrolytic copper recovery loop. 

The constantan wire is used as a cathode and copperplate is used as an anode. Positively charged copper ions move toward the negatively charged cathode. Therefore, it accepts electrons on the cathode surface and reduces the metallic copper. Electrolyte solution consisting of 300 g copper sulfate, 54.35 mL sulfuric acid (60 B), 900 mL demineralized water, and 0.8 mL glycerin. Deposition speed is =60 cm/h. The wire passes through the bath two times in order to increase the copper deposition. 

The final processing in tire production of high-purity metals is often carried out electrolytically and is referred to as electrorefining. In this process the metal to be refined, such as copper or silver, has a typical initid purity of 95 to 99% and the aim is to reduce the impurity level to less than 0.1%. Conventional purification processes are often either inadequate or too expensive for this purpose. In electrorefining, the impure metal, e.g., copper, is placed in an electrolytic bath as an anodic plate that is paired with a cathode on which the purified metal is deposited electrolytically. The electrolyte typically consists of an aqueous solution of a salt of the metal to be purified, for example, copper sulfate, and the electrolytic cell is composed of an array of closely spaced alternating cathodes and anodes. A sample electrode pair and the configuration of the electrolytic cell are shown in Figure 3.2a. 

The other advantages which sulfuric acid has as an inert electrolyte are (i) it increases the conductance of the bath (ii) it is inexpensive (iii) it strongly inhibits the hydrolysis of cuprous sulfate (iv) it is nonvolatile and may be used at high concentrations and temperatures and (v) it does not attack lead, so that it is possible to use this metal for plant construction. The only inconvenience of sulfuric acid is that copper dissolves in it essentially as the divalent ion this means that the current consumption is double of that which would be consumed if the electrolysis were to be carried out in an electrolyte solution containing Cu+ ions. Attempts to implement this alternative have not been very successful so that the use of sulfuric acid is yet to be challenged. 

The composition of the codeposition bath is defined not only by the concentration and type of electrolyte used for depositing the matrix metal, but also by the particle loading in suspension, the pH, the temperature, and the additives used. A variety of electrolytes have been used for the electrocodeposition process including simple metal sulfate or acidic metal sulfate baths to form a metal matrix of copper, iron, nickel, cobalt, or chromium, or their alloys. Deposition of a nickel matrix has also been conducted using a Watts bath which consists of nickel sulfate, nickel chloride and boric acid, and electrolyte baths based on nickel fluoborate or nickel sulfamate. Although many of the bath chemistries used provide high current efficiency, the effect of hydrogen evolution on electrocodeposition is not discussed in the literature. 

Cathodic reduction is also used to purify some metals, such as copper. Slabs of impure copper serve as the anode, while a pure copper sheet serves as the cathode in an undivided electrolytic cell. The electrolytic bath is copper(II) sulfate. During electrolysis, Cu2+ ions leave the anode and plate on the cathode. Impurity metals more reactive than copper are oxidized and stay in solution. Less reactive metals collect at the bottom of the cell. After about a month, the enlarged copper cathodes are removed (Ebbing and Gammon, 2005). Metals can also be oxidized electrolytically at the anode (anodized). It is even possible to further oxidize some metals in a low oxidation state to a higher oxidation state. 

Electrolysis is also used to purify some metals. For example, copper for electrical use, which must be very pure, is purified by electrolysis. Slabs of impure copper serve as anodes, and pure copper sheets serve as cathodes the electrolyte bath is copper(II) sulfate, CUSO4 (Figure 20.24). During the electrolysis, copperfll) ions leave the anode slabs and plate out on the cathode sheets. Less reactive metals, such as gold, silver, and platinum, that were present in the impure copper form a valuable mud that collects on the bottom of the electrolytic cell. Metals more reactive than copper remain as ions in the electrolytic bath. After about a month in the electrolytic cell, the pure copper cathodes are much enlarged and are removed from the cell bath. 

---