Cobaltic Solutions, Ammoniacal

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. 

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). 

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. 

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

The reaction is not disturbed by silver or copper, or by iron(III), chromium or aluminium in the presence of ammoniacal tartrate solution if zinc is present, ammonium chloride should first be added cobalt(III) ions represss the sensitivity and should be oxidized to the tervalent state with hydrogen peroxide iron(II) interferes and should be oxidized and alkaline tartrate solution added before applying the test. 

The extraction of cobalt from arsenical concentrates consisting of autooxidation acid leaching under pressure, separation, purification, hydrogen reduction of ammoniacal leach solution, and removal of sulfur and granulation of the metal was described by Mitchell (M37). The final product contained 95.6% cobalt, 3.90% nickel, and 0.03% arsenic compared to the feed concentrate with an assay of 17.5% cobalt, 1% nickel, and 24% arsenic. 

The polynuclear complexes are generally prepared from intermediate products obtained from oxidizing aqueous ammoniacal cobalt(II) solutions in air. When air is bubbled through such solutions at a moderate rate for about eight hours, a solid originally called the Fuskosulfate, now known as Vortmann s sulfate, is obtained 27, 28, 81). This reddish-black solid contains as its principal component /i-amido-ju-sulfato-octamminedico-balt(III) sulfate (the sulfate of V) and small amounts of the binuclear... 

An aqueous ammoniacal cobalt(II) chloride solution oxidized very slowly with air yields small amounts of a solid known as the melanochloride 26, 27). Werner proposed 29) that this solid contains as its major component the ion... 

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]. 

Hexaamminecobalt(III) salts are generally prepared " by the oxidation of am-moniacal cobalt(II) solutions by either H2O2 or O2 in the presence of a catalyst. The preparation procedure most often employed involves the aerial oxidation of an ammoniacal cobalt(II) solution in the presence of a carbon catalyst. The new procedure employs the same reaction conditions but utilizes a nonaqueous solvent to simplify the synthesis and to prepare the acetate salt, which is very soluble in water. 

Cobalt is produced as a coproduct of nickel or copper refining. Copper-cobalt sulfide concentrates can be processed by the RLE process. Mixed cobalt-nickel sulfides can be precipitated from ammoniacal leach solutions and as mixed nickel-cobalt hydroxide or carbonate from acid sulfate leach processes. From chloride leach solutions, cobalt can be separated by solvent extraction. Most cobalt production is associated with nickel production from sulfide and laterite ores. Pressure leaching, solvent extraction followed by the electrowinning of... 

Bubble the gas for a minute or two through a few milliliters of (a) ferrous sulfate solution, (b) 6M hydrochloric acid saturated with cupric chloride, (c) ammoniacal cobalt chloride solution. The colored compounds formed are examples of the very numerous complexes formed by nitric oxide and metallic salts (see below). In Test (a) the complex ion (FeNO)++ is formed. This is an intermediate in the preparation of NO described here. Many of these complexes are unstable and decompose when the solutions are heated. Test this statement by boiling the solutions from the above experiments. 

A cone, solution of cobalt-free NiCls 6H3O is treated with excess cone. NH3, then cooled in running water. The separation of fine crystals of [N1(NH3) bJCIs is completed by addition of an ammoniacal NH4CI solution. The precipitate is filtered off and successively washed with cone, ammonia, alcohol and ether. 

Triamminetrinitrocobalt(III)> tCo(N02)j(NH3)3], was first prepar in 1866 by Erdmann, later by Werner and Jorgensen, who prepared the complex by the air-oxidation of ammoniacal cobalt(II) salt solutions containing sodiiun nitrite and a large amount of ammonium chloride. In 1938, Duval examined the products obtained from several different procedures by absorption and infrared spectroscopy, refractive index of aqueous solutions, conductivity, and X-ray powder diffraction. He recognized two products in the Werner s preparation and the Jorgensen s preparation. In that year, Sueda reported an isomeric complex from the reaction of the [Co(N03)j(NH3)3] complex with sodium nitrite in a cold aqueous solution, which was assumed to be cis-cis isomer on the basis of the absorption spectrum. 

The uptake, of oxygen by ammoniacal cobalt(ii) solutions has been examined. Equilibrium constants for the formation of the /x-peroxo-... 

Finally, attention has been drawn to currents of hydrogen evolution which in the presence of some substances occurs at more positive potentials than in their absence. Such substances catalyze hydrogen evolution and result in high currents which are denoted catalytic hydrogen waves. Such waves are observed in the presence either of platinum group metals (57,58), where the catalysis is attributed to clusters of metals deposited on mercury or of compounds which possess acid-base properties. Catalytic effects of the latter type in solutions of simple buffers have been observed for low molecular weight compounds (59,60), as well as for proteins (61,62). Similar catalytic effects in ammoniacal cobalt (III)-solutions (63) found utilization in Brdicka reaction (64-66), used in cancer diagnosis. 

Mackenzie, J. M. W., Virnig, M. J., Boley, B. D., and Wolfe, G. A. 1998. Extraction of nickel from ammoniacal leach solutions extractant and solution chemistry issues. In Proceedings ALTA nickel/cobalt pressure leaching and hydrometallurgy forum. Melbourne ALTA Metallurgical Services. 

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.

Substances showing catalytic waves in ammoniacal cobalt or nickel solutions< > must fulfil another condition beside the two conditions mentioned above the substance has to form a complex-compound with cobalt and other components of the solution. Moreover, the acid properties of this complex and its adsorbability also seem to be of importance. The substances showing a catalytic effect of this type usually contain at least an atom of sulphur in their molecule (e.g. cysteine, dithiopyrimidine or proteins). Whether or not the presence of sulphur in the catalytically active molecule is a sufficient condition has yet to be decided. It was shown that e.g. gelatin or casein containing little or no sulphur atoms do not produce any catalytic wave of this type. Similarly, in the series of hydantoin, thiohydantoin and dithiohydantoin as well as pyrimidine, thiopyrimidine, and dithiopyrimidine, the catalytic effect was only observed for the thioderivative and it increased with the number of sulphur atoms in the molecule. 

For this purpose the effect of the concentration of potassium chloride added to a borate buffer solution (total concentration of boric acid and potassium borate 0,10 mole/liter, pH 8,4) on polaro-gp ams for the Co (II) - cysteine system, with constant cobalt chloride (1,74 mmole/liter) and cysteine (0,08 mmole/liter) concentrations, was investigated. The borate buffer solution was used in place of the traditional ammoniacal buffer solution in order to avoid a number of complications and, primarily, decrease in the buffer capacity of the ammoniacal solution near the electrode when potassium chloride is added, since ammonium ions (being proton donors) also participate in the formation of the outer layer of the electric double layer. The pH value of the solution was selected so that the solution would contain approximately equal amounts of anions and cysteine zwitterions (pl am 8.33). 

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. 

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. 

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