Cobalt solutions ammoniacal

When hydrogen sulfide is passed through an ammoniacal or alkahne cobalt solution, a black precipitate of cobalt(II) sulfide, CoS forms. 

For catalytic waves of hydrogen evolution in ammoniacal cobalt solutions, it has been observed (132) that ery/Aro-phenylcysteine gives a higher catalytic wave than the threo form (Fig. 28). These differences can be explained partly by differences in acid dissociation constants, and partly by variations in the stability constants of the cobalt-phenyl-cysteine complexes. 

Catalytic waves in cobalt solutions. Compounds containing sulphydryl or disulphide groups give two different types of catalytic waves in buffered ammoniacal solutions of cobalt, which are very often named Brdicka catalytic waves. The simple compounds of a low molecular weight (e.g., cystine, cysteine) produce a characteristic round maximum, whereas more complicated compounds such as proteins give a typical double-wave [3,127-131]. 

Hydrometallurgical treatment for laterites has increased due to the importance these deposits have gained as sources of nickel and cobalt [1, 2]. In recent years many researchers have studied different ways to extract nickel and cobalt by ammoniacal or acidic solution leaching. 

Fig. 14. Dependence of catalytic wave of cysteine in ammoniacal buffered cobaltous solutions. 0 002 M Cobaltous chloride, 01m ammonia, 01m ammonium chloride concentration of cystine (1) 0 (2)-(8) given on the polarogram. Curves starting at 0 8 V, Hg-pool, 200 mV/absc., = 2 4 sec, m = 3 0 mg/sec, full scale sensitivity 100 A.

Pollen allergens can be determined( > from the catalytic wave which these proteins give in ammoniacal cobaltic solutions. To express the content of pollen allergens in different preparations it is necessary to choose, as a standard, the allergen from one plant. 

The determination of cystine can be carried out by using either the catalytic wave in ammoniacal cobaltous solutions< ), or the reduction wave of cystine at —0-7 V in acidic media< ° ), or at —1"4 V in Britton-Robinson pH ll-5 buffers.The results obtained with the catalytic wave are too low,< ) probably due to the effect of other amino acids in the hydrolysate on the height of the catalytic wave.( °) Moreover the method is unable to give directly the amount of both cystine and cysteine. 

Metal Extraction. As with other carboxyhc acids, neodecanoic acid can be used in the solvent extraction of metal ions from aqueous solutions. Recent appHcations include the extraction of zinc from river water for deterrnination by atomic absorption spectrophotometry (105), the coextraction of metals such as nickel, cobalt, and copper with iron (106), and the recovery of copper from ammoniacal leaching solutions (107). 

Lateritic Ores. The process used at the Nicaro plant in Cuba requires that the dried ore be roasted in a reducing atmosphere of carbon monoxide at 760°C for 90 minutes. The reduced ore is cooled and discharged into an ammoniacal leaching solution. Nickel and cobalt are held in solution until the soflds are precipitated. The solution is then thickened, filtered, and steam heated to eliminate the ammonia. Nickel and cobalt are precipitated from solution as carbonates and sulfates. This method (8) has several disadvantages (/) a relatively high reduction temperature and a long reaction time (2) formation of nickel oxides (J) a low recovery of nickel and the contamination of nickel with cobalt and (4) low cobalt recovery. Modifications to this process have been proposed but all include the undesirable high 760°C reduction temperature (9). 

A similar process has been devised by the U.S. Bureau of Mines (8) for extraction of nickel and cobalt from United States laterites. The reduction temperature is lowered to 525°C and the hoi ding time for the reaction is 15 minutes. An ammoniacal leach is also employed, but oxidation is controlled, resulting in high extraction of nickel and cobalt into solution. Mixers and settlers are added to separate and concentrate the metals in solution. Organic strippers are used to selectively remove the metals from the solution. The metals are then removed from the strippers. In the case of cobalt, spent cobalt electrolyte is used to separate the metal-containing solution and the stripper. MetaUic cobalt is then recovered by electrolysis from the solution. Using this method, 92.7 wt % nickel and 91.4 wt % cobalt have been economically extracted from domestic laterites containing 0.73 wt % nickel and 0.2 wt % cobalt (8). 

Concentration limits of the diphosphate-ion, admissible to determination of magnesium and cobalt, manganese and cobalt, zinc and cobalt by spectrophotometric method with application of the l-(2-pyridylazo)-resorcinol (PAR) are presented. Exceeding maintenance of the diphosphate-ion higher admissible supposes a preliminary its separation on the anionite in the H+-form. The optimum conditions of cobalt determination and amount of the PAR, necessary for its full fastening are established on foundation of dependence of optical density of the cobalt complex with PAR from concentration Co + and pH (buffer solutions citrate-ammoniac and acetate-ammoniac). 

The method may also be applied to the analysis of silver halides by dissolution in excess of cyanide solution and back-titration with standard silver nitrate. It can also be utilised indirectly for the determination of several metals, notably nickel, cobalt, and zinc, which form stable stoichiometric complexes with cyanide ion. Thus if a Ni(II) salt in ammoniacal solution is heated with excess of cyanide ion, the [Ni(CN)4]2 ion is formed quantitatively since it is more stable than the [Ag(CN)2] ion, the excess of cyanide may be determined by the Liebig-Deniges method. The metal ion determinations are, however, more conveniently made by titration with EDTA see the following sections. 

Sometimes the metal may be transformed into a different oxidation state thus copper(II) may be reduced in acid solution by hydroxylamine or ascorbic acid. After rendering ammoniacal, nickel or cobalt can be titrated using, for example, murexide as indicator without interference from the copper, which is now present as Cu(I). Iron(III) can often be similarly masked by reduction with ascorbic acid. 

D. Benzoin-a-oxime (cupron) (VII). This compound yields a green predpitate, CuC14Hu02N, with copper in dilute ammoniacal solution, which may be dried to constant weight at 100 °C. Ions which are predpitated by aqueous ammonia are kept in solution by the addition of tartrate the reagent is then spedfic for copper. Copper may thus be separated from cadmium, lead, nickel, cobalt, zinc, aluminium, and small amounts of iron. 

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 reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

The hexamine cobalt (II) complex is used as a coordinative catalyst, which can coordinate NO to form a nitrosyl ammine cobalt complex, and O2 to form a u -peroxo binuclear bridge complex with an oxidability equal to hydrogen peroxide, thus catalyze oxidation of NO by O2 in ammoniac aqueous solution. Experimental results under typical coal combusted flue gas treatment conditions on a laboratory packed absorber- regenerator setup show a NO removal of more than 85% can be maitained constant. 

It is important to recognize some of the limitations of the Pourbaix diagrams. One factor which has an important bearing on the thermodynamics of metal ions in aqueous solutions is the presence of complex ions. For example, in ammoniacal solutions, nickel, cobalt, and copper are present as complex ions which are characterized by their different stabilities from hydrated ions. Thus, the potential-pH diagrams for simple metal-water systems are not directly applicable in these cases. The Pourbaix diagrams relate to 25 °C but, as is known, it is often necessary to implement operation at elevated temperatures to improve reaction rates, and at elevated temperatures used in practice the thermodynamic equilibria calculated at 25 °C are no longer valid. 

Caron A process for extracting nickel and cobalt from lateritic ores by reductive roasting, followed by leaching with ammoniacal ammonium carbonate solution in the presence of oxygen. Developed by M. H. Caron at The Hague in the 1920s and used in Cuba (where the location of the mine is named Nicaro, after the metal and the inventor) and in Australia. 

The solubility of the sodium salt of DEHPA in basic (NaOH) solution has been reported, together with the effect of temperature on the water solubility of this salt [18], (Figs. 7.12 and 7.13). It is evident that the presence of salts in the aqueous phase depresses the solubility of this extractant in water (Fig. 7.11). This has been confirmed in the extraction of cobalt with DEHPA(Na) at pH 5-6, for which a solubility of the extractant was found to be <50 ppm. Furthermore, the use of DEHPA in the extraction of cobalt from an ammoniacal (pH 11) system containing sodium sulfate showed no apparent loss of extractant after 10 contacts of a DEHPA-ker-osene solvent with fresh aqueous solution [1]. Operation of pilot plants using DEHPA(NH4) and DEHPA(Na) for the extraction of cobalt, at pH 5-6 and at 60°C, showed the loss of DEHPA to be less than 50 ppm [3]. Temperature also has a significant effect on the solubility of DEHPA(Na) (Fig. 7.13). 

Nickel may he measured quantitatively hy several microanalytical gravimetric methods that include (l)formation of a red precipitate with dimethyl-glyoxime, (2) precipitation as a hlack sulfide with ammonium sulfide, (3) precipitating as a complex cyanide hy treating with alkali cyanide and bromine, and (4) precipitation as a yellow complex hy treating an ammoniacal solution of nickel with dicyandiamide sulfate (Grossman s reagent), followed hy the addition of potassium hydroxide. All of these methods can separate nickel from cobalt in solution. 

Additive compounds of ammonia and cobalt salts were first observed by Tassaert in 1799, although at that time the reaction which takes place when an aqueous ammoniacal solution of cobalt salt is exposed to air was not recognised as one involving the addition of ammonia to the molecule. From that time onwards research has been carried out on these complexes.1... 

These salts are formed from dilute ammoniacal solutions of cobaltous salts in air, or by heating aquo-pentammino-salts with ammonia. Frequently they are obtained as decomposition products of acido-pentammino-salts. They may be obtained directly from the corresponding cobaltous salt by heating with excess of ammonia and ammonium chloride,2 or from the corresponding ammonium salt by addition of lead peroxide to the aqueous solution. 

Hexammino-cobaltic Nitrate, [Co(NH3)6](N03)3.—The salt is formed by air oxidation of an ammoniacal solution of cobaltous nitrate, 1 JBrgensen, Zeitsch. anorg, Chem., 1898, 17, 455. 

The chloride, [Co(NIi3)5OH]Cl2.H20, is formed from aquo-pentammino-cobaltic chloride by dissolving it-in aqueous ammonia, warming the solution and mixing it with alcohol. It separates as a crystalline meal, and is purified by redissolving it in ammoniacal solution and adding alcohol. It crystallises in glistening scales and has similar properties to the nitrate. 

Nitrato-pentammino-cobaltic Nitrate, [Co(NH3)5N03](N03)2. —If an aqueous ammoniacal solution of eobaltous nitrate be oxidised by means of air and then heated with excess of ammonium nitrate, the nitrato-salt is formed. It is more easily prepared by dissolving eobaltous carbonate in warm dilute nitric acid and then warming the mixture with concentrated aqueous ammonia. Iodine is thereafter added, one atom for every atom of cobalt in solution, and the whole warmed until the iodine dissolves and a precipitate of hexammino-cobaltic iodido-nitrate is formed. It is filtered and the residue washed W ith dilute aqueous ammonia. The filtrate is treated with nitric acid, and the precipitate of aquo-pentammino-nitrate is converted into the nitrato-salt by heating with more nitric acid. The change from aquo-1 JOrgensen, J. prakt. Chem., 1881, 23, 227. 

Trinitro-triammino-cobalt, [Co(NH3)3(N02)3], was the first member of the series prepared. It is best prepared by treating a solution of eobaltous chloride with an ammoniacal solution of sodium nitrite and oxidising the mixture by means of air. The liquid after oxidation is allowed to stand for some days, when crystals separate these are filtered and washed with cold water to free them from chloride, and dissolved in hot water containing a little acetic acid. On cooling the acid liquid trinitro-triammine cobalt separates out, and later, from the same solution, the double salt, [Co(NH3)4(N02)2][Cb(NH3)2(N02)4], separates.1... 

Compounds of this series are derived from the so-called melano-chloride, a substance formed by oxidising an ammoniacal solution of cobaltous chloride with air and precipitating a solid by means of concentrated hydrochloric acid. From the mixed solid obtained the sparingly soluble diaquo-hexammino-u-amino-ol-dicobaltic... 

Tin and lead are the most rapid precipitants of metallic silver from the nitrate cadmium, zinc, copper, bismuth, and antimony axe moro slow in their operation, and mercury still more tardy. Chloride of silver is rapidly reduced by most of the metals which form soluble chlorides, such as zinc, iron, cadmium, cobalt, and arsenic. Zinc, copper, and arsenic rapidly reduce the ammoniacal solution of oxide of silver. Of all the metallic precipitants, zinc and cadmium are the most effective but when zinc or antimony aro used, the separated silver contains these metals. 

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