Copper-ammonium-salt solutions

The vapor-liquid equilibrium relationships for copper-ammonium salt solutions containing dissolved carbon monoxide have been studied by a number of investigators. Hainsworth and Titus (1921) measured the vapor pressure of carbon monoxide over copper-ammonium carbonate solutions. Experimental data on formate solutions were obtained by Larson and Teitsworth (1922). Zhavoronkov and Reshchikov (1933) studied solutions of chlorides, formates, lactates, and acetates. Zhavoronkov and Chagunava (1940) made a detailed study of formate-carbonate mixtures, including the solution from an operating plant. 

A method of estimating carbon monoxide vapor pressures over aqueous copper-ammonium salt solutions, under conditions outside the range of experimental data, was proposed by van Krevelen and Baans (1950). These authors concluded that the basic chemical reaction involved in the absorption of carbon monoxide by aminoniacal solutions is expressed in equation 16-26. By considering equilibrium relationships in this reaction, they derived an equation relating the carbon monoxide partial pressure to the solution composition as follows ... 

The molar heats of vaporization of ammonia, carbon dioxide, and water from a typical copper-ammonium-salt solution (mixed formate and carbonate) have been calculated by Zhavoronkov (1939) using the Clausius-Clapeyron equation and the slopes of the log p versus 1/T lines as plotted in Figure 16-23. For the solution illustrated in this figure, he obtained the results in Table 16-19. 

Regeneration of the copper-ammonium-salt solution is accomplished primarily by pressure reduction and the application of heat. Unfortunately, these operations have other effects, e.g., the vaporization of ammonia and the production of side reactions, which result in the requirement for a somewhat complex regenerator design. The regeneration temperature should be below 180°F in order to minimize the vaporization of ammonia and occurrence of side reactions. The pressure of regeneration should be as low as economically feasible. Operation at 1 atm is probably most common. 

The copper-ammonium-salt solutions are generally not corrosive to mild steel however, the gases evolved during regeneration can be quite corrosive due to the presence of carbon dioxide. To prevent corrosion in the vapor zones, it is good practice to use stainless steel (vessels or liners) in the exhaust-gas scrubber section and above the liquid in the evaporator section. 

The tetramethylammonium salt, ((CH3)3N)g[Sig02o], was prepared and studied by Hoebbel and Wieker (126a), who converted the polysilicate ion to the trimethylsilyl derivative [CH3)3Si]g[Si.02o] characterized by analysis and mass spectroscopy. This polysilicate ion is in effect a cube of SiOz, indicating the possibility of small compact particles existing in sodium silicate solutions of SiOjiNajO ratio between 2 1 and 4 1. The copper-ammonium salt is discussed further in this chapter. 

In addition to the carbon monoxide vapor pressure, the vapor pressures of other solution components are of interest in assisting the calculation of possible losses and heat requirements. Copper-ammonium carbonate solutions have an appreciably higher vapor pressure than solutions of the formate or salts of stronger acids because of the relatively high decomposition pressure of ammonium carbonate. The total vapor pressures of a number of solutions have been measured by Zhavoronkov and Reshchikov (1933) and Zhavoronkov and Chagunava (1940). 

The salt process employs scrubbing of the gas with cuprous ammonium salt solution. Carbon monoxide forms a complex with the solution at high pressure and low temperature in the absorption column. The absorbed pure carbon monoxide is released from the solution at low pressure and high temperature. In the Cosorb process, cuprous tetrachloroaluminate (CuAlCl ) in a toluene medium is used as the absorbing liquid instead of the copper salt solution. A low corrosion rate and low energy consumption are the advantages of the Cosorb process over the previous one. 

Aqueous solutions of ammonium haUdes, like the other ammonium salts of strong acids, are acidic on storage and exposure these solutions tend to become more acidic through ammonia loss. They also have a pronounced tendency to attack ferrous and other metal surfaces, especiaHy those of copper and copper aHoys. 

Procedure (copper in crystallised copper sulphate). Weigh out accurately about 3.1 g of copper sulphate crystals, dissolve in water, and make up to 250 mL in a graduated flask. Shake well. Pipette 50 mL of this solution into a small beaker, add an equal volume of ca AM hydrochloric acid. Pass this solution through a silver reductor at the rate of 25 mL min i, and collect the filtrate in a 500 mL conical flask charged with 20 mL 0.5M iron(III) ammonium sulphate solution (prepared by dissolving the appropriate quantity of the analytical grade iron(III) salt in 0.5M sulphuric acid). Wash the reductor column with six 25 mL portions of 2M hydrochloric acid. Add 1 drop of ferroin indicator or 0.5 mL N-phenylanthranilic acid, and titrate with 0.1 M cerium(IV) sulphate solution. The end point is sharp, and the colour imparted by the Cu2+ ions does not interfere with the detection of the equivalence point. 

Determination of copper as copper(I) thiocyanate Discussion. This is an excellent method, since most thiocyanates of other metals are soluble. Separation may thus be effected from bismuth, cadmium, arsenic, antimony, tin, iron, nickel, cobalt, manganese, and zinc. The addition of 2-3 g of tartaric acid is desirable for the prevention of hydrolysis when bismuth, antimony, or tin is present. Excessive amounts of ammonium salts or of the thiocyanate precipitant should be absent, as should also oxidising agents the solution should only be slightly acidic, since the solubility of the precipitate increases with decreasing pH. Lead, mercury, the precious metals, selenium, and tellurium interfere and contaminate the precipitate. 

The precipitate is curdy (compare silver chloride) and is readily coagulated by boiling. It is washed with dilute ammonium thiocyanate solution a little sulphurous acid or ammonium hydrogensulphite is added to the wash solution to prevent any oxidation of the copper)I) salt. 

The precipitate is soluble in free mineral acids (even as little as is liberated by reaction in neutral solution), in solutions containing more than 50 per cent of ethanol by volume, in hot water (0.6 mg per 100 mL), and in concentrated ammoniacal solutions of cobalt salts, but is insoluble in dilute ammonia solution, in solutions of ammonium salts, and in dilute acetic (ethanoic) acid-sodium acetate solutions. Large amounts of aqueous ammonia and of cobalt, zinc, or copper retard the precipitation extra reagent must be added, for these elements consume dimethylglyoxime to form various soluble compounds. Better results are obtained in the presence of cobalt, manganese, or zinc by adding sodium or ammonium acetate to precipitate the complex iron(III), aluminium, and chromium(III) must, however, be absent. 

The distillate should be collected in the 200-ml. round-bottomed flask which is used in the subsequent fractionation. The distillation takes about an hour. The cake of copper salts in the flask is best removed by digestion with concentrated ammonium hydroxide solution. 

Suppose the salt bridge of a Daniell cell contains ammonium chloride solution, NHiCliaq). As positive zinc ions are produced at the anode, negative chloride ions migrate from the salt bridge into the half-cell that contains the anode. As positive copper(II) ions are removed from solution at the cathode, positive ammonium ions migrate from the salt bridge into the half-cell that contains the cathode. 

Although S-diketones cannot compete with hydroxyoximes for the extraction of copper from acid media, they do have advantages for extraction from ammoniacal leach solutions because, unlike hydroxyoximes, they do not transfer ammonia. The extraction follows Eq. (11.6), and the extent of extraction depends on the concentration of ammonia and ammonium salts. 

The hydroxo-compound, [Pd(NH3)2(OH)2], is obtained on treating the ehloro-derivative with moist silver oxide, or by precipitation from a solution of the sulphato-compound with the calculated quantity of barium hydroxide. The solution is filtered and evaporated in vacuo or in air free from carbon dioxide, when a yellow residue of microscopic octahedra is obtained. The aqueous solution is strongly alkaline, rapidly absorbs carbon dioxide from the air, and combines with evolution of heat with acids, forming the corresponding aeido-derivatives. In the dry state it may be heated to 105° C. without decomposition. Prolonged boiling with water causes it to lose ammonia, as in the case of the dibromo-derivative, leaving a brown residue. It precipitates the hydroxides of the metals copper and silver from solutions of their salts, and liberates ammonia from ammonium salts.2... 

Tetrammino-palladous Hydroxide, [Pd(NII3)4](OH)2, may be obtained by decomposing the sulphate with barium hydroxide. It separates as a colourless crystalline substance which is soluble in water and has a strong alkaline reaction. The aqueous solution is capable of precipitating copper, iron, cobalt, and nickel from solutions of their salts, and it also decomposes ammonium salts. 

Preparation of Metal Sulphides by an Exchange Decomposition Reaction. Precipitation with Ammonium Sulphide. Pour 2 ml each of solutions of iron(ll), manganese(II), zinc, cadmium, lead, antimony, and copper salts into separate test tubes. Add 2 ml of an ammonium sulphide solution to each tube. Note the colour of the formed precipitates. Write the equations of the reactions and the values of the solubility products of the sulphides of these metals (see Appendix 1, Table 12). Using the concept of the solubility product, explain the process of precipitation of sulphides under these conditions. 

Preparation of a Complex Ammonium Salt of Copper(II). Dissolve 0.5 g of finely triturated copper(II) sulphate pentahydrate in 12.5 ml of a 15% ammonia solution. If the solution is turbid, filter it. Slowly add 7.5 ml of ethanol to the filtrate and let it stand for a few hours in the cold. Filter off the formed crystals, wash them first with a mixture of ethanol and a concentrated ammonia solution (1 1), and then with ethanol and ether. Dry them at room temperature. Into what ions does the product dissociate in the solution Consider the structure of the complex ion from the viewpoint of the valence bond theory. 

The thiocyanates are generally soluble in water, the exceptions being those of lead, silver, mercury and copper. Most of them dissolve also in alcohol and ether. Aqueous solutions of the alkali thiocyanates undergo atmospheric oxidation under the influence of sunlight with solutions of medium concentration this change takes place rapidly, with separation of a yellow, amorphous precipitate consisting of pseudocyanogen sulphide, (CNS)3 (cf. p. 236). The concentration of thiocyanate most favourable to the separation of this sulphide is about 50 per cent, in summer and 10 per cent, in winter. In addition to this substance the products of the photochemical oxidation of potassium thiocyanate include hydrocyanic acid, sulphate, carbon dioxide, ammonia and ammonium salts ... 

The solution is then heated to boiling and carefully acidified to Congo Red with concentrated hydrochloric acid (sp. g. 1.19, about 600 cc.), which is added very slowly with constant stirring and scratching of the walls of the beaker. As the mixture becomes acid, the foam disappears and the thick precipitate of copper hydroxide is replaced by a granular one of crude diphenic acid. The beaker is then placed in running water until thoroughly cold the crude diphenic acid is filtered by suction and washed with faintly acid, saturated ammonium chloride solution until free from copper salts, and then with water. If dried ... 

Peroxyxanthates. A new factor in the theory and practice of flotation was found in the Mount Isa, Australia, copper flotation solution. Secondary butyl perxanthate was formed by the reaction of the xanthate with hydrogen peroxide in dilute alkaline aqueous solution and was found to be identical to a substance from the flotation solution. The perxanthate was isolated as the ammonium salt. 

Soon after the introduction of dimethylglyoxime as a specific reagent for nickel by Tschugaeff-Kraut-Brunck (1905-1907), Baudisch discovered a compound which precipitates copper and iron quantitatively from acid solutions.82 He appropriately named this reagent as cupferron . It is the water soluble ammonium salt of nitrosophenylhydroxylamine (5). When dissolved in chloroform, the whitish-grey copper compound gives a bright yellow solution and the brown yellow iron(III) compound a deep red solution. This behaviour reveals the inner complex character of these derivatives (6). 

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