Copper selenates

The solubility of CuSe04-5H20(cr) at 298.15 K is available in [32ALP/SAY], [45K1N/BEC], [84GOS2], [95STO/OJK], which report the (recalculated) values 0.915, 0.929, 0.903, and 0.941 mol(CuSe04)-kg, respectively. The review selects the mean value  

The value of the solubility product of CuSe04-5H20(cr) CuSe04-5H20(cr) Cu + SeO + 5H20(1) 

The standard Gibbs energy of formation of CuSe04-5H20(cr) is calculated from the Gibbs energy of Reaction (V.109) and the selected values of AfG° for the ions and water to be  

Feroci, Fini, Badiello, and Breccia [97FER/FIN] studied the complex formation between Cu and SeO by classical polarography and found no evidence for an interaction, see Appendix A. The review estimates from an assumed accuracy of the polarographic measurement of + 2 mV the equilibrium constant of 

The standard enthalpies of formation of CuSe04(cr) and CuSe04-5H20(cr) have been obtained from the calorimetric measurements by Selivanova, Samplavskaya, and Maier [62SEL/SAM]. The recalculated values  

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COPPER CYANIDE COPPER CYANIDE COPPER SELENATE COPPER SELENITE... 

By passing chlorine through a suspension of basic copper carbonate in aqueous selenious acid, copper selenate and copper chloride pass into solution ... 

On crystallisation, copper selenate separates, contaminated with about 1 per cent, of cupric chloride. The latter may be removed by extraction with acetone, in which it is readily soluble, whereas the selenate is only very slightly soluble after this operation the copper selenate is finally purified by recrystallisation from water. The copper may then be removed by electrolysis,1 using low current density, when selenic acid free from selenious acid and chlorine remains in the electrolyte. The solution may be concentrated until it contains about 82 per cent, of the acid by evaporating at 95° C. under reduced pressure. 

Copper selenate, like the corresponding sulphate, is best known in the form of the pentahydrate. When the latter is dehydrated at 102° C. it is converted into the monohydrate, dehydration being complete at 230° to 235° C. Copper selenate can also be obtained in the trihydrated form.8... 

By the action of ammonia on copper selenate pentahydrate, small bluish-violet needle-like crystals of copper selenate tetrammoniate mono-hydrate, CuSe04.4NH3.H20, are obtained. On exposure to the air these crystals slowly evolve, ammonia and become dull in appearance. They are soluble in water, giving a deep blue solution, which on dilution becomes lighter in colour and deposits basic copper salts. When the crystals are exposed to the action of air for many hours, the preliminary evolution of ammonia ceases and the blue product has the composition CuSe04.3NHa.H20. When the bluish-violet crystals of the tetrammoniate monohydrate are dried over lime in a desiccator under a low... 

A blue compound, apparently analogous to sulphonitronic acid (p. 251), is formed on the addition of mercury to a solution of nitrosylselenic acid in selenic acid monohydrate,5 or by reducing a solution of sodium nitrite in concentrated selenic acid by means of mercury. The presence of copper selenate facilitates the reaction. The selenonitronie acid is very readily oxidised and appears to be stable only in the presence of concentrated selenic acid. 

Double Copper Selenates.—Tutton11 has investigated the crystallographic properties of double selenates of the series R2Se04,CuSe04,6H20, R representing potassium, rubidium, caesium, or ammonium. They are isomorphous with the monoclinic double salts formed by cupric sulphate with the sulphates of potassium, rubidium, caesium, and ammonium.12... 

SEL/SAM] Selivanova, N. M., Samplavskaya, K. K., Maier, A. I., Thermochemical properties of selenates. Heat of formation of copper selenates, 7>. Inst.-Mask. Khim.-Tekhnol. Inst. im. D. I. Mendeleeva, 38, (1962), 30-36, in Russian. Cited on pages 296, 467. 

YK/M1H] Oykova, T., Mihov, D., Pavlova, P., Phase interaction in the systems sodium selenate - copper selenate - water and sodium selenate - zinc selenate - water at 25°C, Cryst. Res. Technol, 26, (1991), 1071-1075. Cited on pages 264,295. 

In mineral technology, sulfur dioxide and sulfites are used as flotation depressants for sulfide ores. In electrowinning of copper from leach solutions from ores containing iron, sulfur dioxide prereduces ferric to ferrous ions to improve current efficiency and copper cathode quaHty. Sulfur dioxide also initiates precipitation of metallic selenium from selenous acid, a by-product of copper metallurgy (326). 

The roaster product is then charged to the Dorn furnace where it is melted and the resulting metal is fire-refined to eliminate the arsenates, selenates, antimonates, teUurates, and residual copper. 

Selenium was isolated some 35 y after tellurium and, since the new element resembled tellurium, it was named from the Greek askrivr], selene, the moon. The discovery was made in 1817 by the Swedish chemist J. J. Berzelius (discoverer of Si, Ce and Th) and J. G. Gahn (discoverer of Mn) they observed a reddish-brown deposit during the burning of sulfur obtained from Fahlun copper pyrites, and showed it to be volatile and readily reducible to the new element. 

Selen-kupfer, n. copper selenide. -kupfer-silber, n. copper silver selenide (Min.) eucairite. -metall, n. metallic selenide. 

The co-reduction of copper and selenium is considered as an exception to Kroger s theory. Current-potential curves in the literature show that deposition of copper is rather compulsory to make the deposition of selenium possible. In fact, although the standard potential for Se(IV) reduction is more positive than that of copper (0.741 and 0.340 V vs. SHE, for selenous acid and cupric ion, respectively), it turns out that Se(IV) alone is reduced at more negative potentials than Cu(II). In the presence of copper, the order is reversed. 

In searching to formulate a mechanism of CuInSc2 phase formation by one-step electrodeposition from acid (pH 1-3) aqueous solutions containing millimolar concentrations of selenous acid and indium and copper sulfates, Kois et al. [178] considered a number of consecutive reactions involving the formation of Se, CuSe, and Cu2Se phases as a pre-requisite for the formation of CIS (Table 3.2). Thermodynamic and kinetic analyses on this basis were used to calculate a potential-pH diagram (Fig. 3.10) for the aqueous Cu+In-i-Se system and construct a distribution diagram of the final products in terms of deposition potential and composition ratio of Se(lV)/Cu(ll) in solution. 

A current area of interest is the use of AB cements as devices for the controlled release of biologically active species (Allen et al, 1984). AB cements can be formulated to be degradable and to release bioactive elements when placed in appropriate environments. These elements can be incorporated into the cement matrix as either the cation or the anion cement former. Special copper/cobalt phosphates/selenates have been prepared which, when placed as boluses in the rumens of cattle and sheep, have the ability to decompose and release the essential trace elements copper, cobalt and selenium in a sustained fashion over many months (Chapter 6). Although practical examples are confined to phosphate cements, others are known which are based on a variety of anions polyacrylate (Chapter 5), oxychlorides and oxysulphates (Chapter 7) and a variety of organic chelating anions (Chapter 9). The number of cements available for this purpose is very great. 

Alternatively, raw anode slimes are aerated with hot dilute sulfuric acid to remove copper. Slimes are then mixed thoroughly with sodium carbonate and roasted in the presence of sufficient air. Sodium selenate formed is leached with water. Hydrochloric acid is added to this selenate solution. Treatment with sulfur dioxide precipitates elemental selenium. Alternatively, the selenate solution is evaporated to dryness. Sodium selenate is reduced to sodium selenide by heating with carbon at high temperatures. Sodium selenide is leached with water. Air is blown over the solution. Selenide is oxidized to elemental selenium which precipitates. 

Selenotrithionates, 2 256 Selenous acid, secondary bonding by, 15 19 Self-assembling metal complexes, 46 174-175, xee also Supramolecular copper (l)/silver (I) complexes... 

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