Cobalt concentration

Sulfide Ores ores. In the Zairian ores, cobalt sulfide as carroUite is mixed with chalcopyrite and chalcocite [21112-20-9]. For processing, the ore is finely ground and the sulfides are separated by flotation (qv) using frothers. The resulting products are leached with dilute sulfuric acid to give a copper—cobalt concentrate that is then used as a charge in an electrolytic cell to remove the copper. Because the electrolyte becomes enriched with cobalt, solution from the copper circuit is added to maintain a desirable copper concentration level. After several more steps to remove copper, iron, and aluminum, the solution is treated with milk of lime to precipitate the cobalt as the hydroxide. 

Cobalt naphthenate is generally supplied in solution in styrene, the solution commonly having a cobalt concentration of 0.5-1.0%. The cobalt solution is normally used in quantities of 0.5-4.0% based on the polyester. The accelerator solution is rather unstable as the styrene will tend to polymerise and thus although the accelerator may be metered from burettes, the latter will block up unless frequently cleaned. Cobalt naphthenate solutions in white spirit and dimethyl phthalate have proved unsatisfactory. In the first case dispersion is difficult and laminates remain highly coloured whilst with the latter inferior end-products are obtained and the solution is unstable. Stable solutions of cobalt octoate in dimethyl phthalate are possible and these are often preferred because they impart less colour to the laminate. 

The Auger depth profile obtained from a plasma polymerized acetylene film that was reacted with the same model rubber compound referred to earlier for 65 min is shown in Fig. 39 [45]. The sulfur profile is especially interesting, demonstrating a peak very near the surface, another peak just below the surface, and a third peak near the interface between the primer film and the substrate. Interestingly, the peak at the surface seems to be related to a peak in the zinc concentration while the peak just below the surface seems to be related to a peak in the cobalt concentration. These observations probably indicate the formation of zinc and cobalt complexes that are responsible for the insertion of polysulfidic pendant groups into the model rubber compound and the plasma polymer. Since zinc is located on the surface while cobalt is somewhat below the surface, it is likely that the cobalt complexes were formed first and zinc complexes were mostly formed in the later stages of the reaction, after the cobalt had been consumed. 

Coating thickness, determination, see Film thickness, determination Cobalt, concentration by use of ion-exchange membrane, 235 determination by x-ray emission spectrography, 328... 

McLaren R.G., Lawson D.M., Swift R.S., Purves D. The effects of cobalt additions on soil and herbage cobalt concentrations in some S. E. Scotland pastures. J Agri Sci 1985 105, 347-363. 

The order of addition is important. This procedure affords a solution of high cobalt concentration (approximately 0.2 M) which promotes decomposition of the excess hydrogen peroxide at a desirable rate. Substitution of sodium for potassium hydrogen carbonate makes it impossible to obtain such a high concentration of cobalt in solution. 

The oceanic distribution of cobalt is similar to that of manganese, although cobalt concentrations are 10-100 times smaller maximum concentrations are 100-300 pM in surface waters, decreasing to 10 pM at depths below 1000 m. As concentrations of cobalt in seawater are so low, it may become biolimiting in open ocean surface waters. 

In natural waters, the geochemical behavior of nickel is similar to that of cobalt (USEPA 1980). It is therefore not surprising that nickel-cobalt mixtures in drinking water of rats were additive in toxicity (WHO 1991) and that there is a high correlation between nickel and cobalt concentrations in terrestrial plants (Memon et al. 1980). 

In the deposits where oxide cobalt is present, it is common to have oxide copper minerals. The cobalt is, therefore, recovered in a bulk copper-cobalt concentrate that is processed using a hydrometallurgical technique to produce separate copper and cobalt metals. Oxide... 

Table III. XPS Measured Surface Cobalt Concentrations After H2 Reduction at 480°C of the Catalysts ...

Figure 10. Current efficiency for zinc electrowinning vs. cobalt concentration for prepared electrolytes (4) containing 65 g/L Zn and 100 g/L H1SOi T = 45°C, current density = 40 mA/cm2 (A) 0.0 ppb Sb (B) 28 ppb Sb...

Earlier it was noted that nickel and cobalt could be extracted by carboxylic and sulfonic acids, with nickel being extracted at the lower pH. However, with alkylphosphorus acids, a selectivity reversal is observed, with cobalt being favored under acid conditions. The cobalt-nickel separation factor has been shown to depend upon metal concentration, reagent structure, diluent, temperature, and the presence of a diluent modifier. Thus, with increasing cobalt concentration the color of the extractant phase changes... 

When the sulfide ore carroUite, CuS C02S3, is the starting material, first sulfides are separated by flotation with frothers. Various flotation processes are applied. The products are then treated with dilute sulfuric acid producing a solution known as copper-cobalt concentrate. This solution is then electrolyzed to remove copper. After the removal of copper, the solution is treated with calcium hydroxide to precipitate cobalt as hydroxide. Cobalt hydroxide is filtered out and separated from other impurities. Pure cobalt hydroxide then is dissolved in sulfuric acid and the solution is again electrolyzed. Electrolysis deposits metallic cobalt on the cathode. 

Fig. 11. The EPR spectra at 77 K. of OJ on CoO-MgO samples. Spectra (a) and (b) were recorded after evacuation of oxygen at 298 K, (c) and (d) in the presence of a small amount of oxygen. Spectra (a) and (c) refer to a 0.2% CoO-MgO sample, whereas spectra (b) and (d) refer to a 5% CoO-MgO sample (the cobalt concentration is expressed as Co atoms per 100 Mg atoms) (110).

Fig. 1. Produci distribution as a function of reaction time in cobalt-catalyzed CO hydrogenation. (Reprinted from Ref. 38, by courtesy of Marcel Dekker, Inc.) Reaction conditions 26.5 atm H2, 340 atm CO, 182 C, 1,4-dioxane solvent. Y = J 0[HCo(CO)4]dt cobalt concentration changes throughout reaction because of sampling. Average HCo(CO)4 concentration is 0.051 M.

The reactions discussed were carried out in aqueous solution, a cobalt concentration of 0.15Af, a cyanide-cobalt ratio of 5.1, and 1 atm. of hydrogen pressure at room temperature, except where otherwise noted. Operating procedure... 

However, when small increments of substrate were added to CoH containing added alkali (KOH, 3X cobalt concentration), 1.4 atoms of hydrogen were absorbed per mole of quinone. This effect of alkali is similar to that noted in the reduction of ferricyanide. However, with benzoquinone, the addition of excess substrate to CoH containing added alkali still resulted in the absorption of hydrogen, the hydrogen atom to substrate ratio being reduced to 0.98. Furthermore, the presence of excess quinone during the formation of cyanocobaltate(II) with added alkali did not prevent catalytic reduction. 

Benzaldehyde. The addition of less than stoichiometric quantities of benz-aldehyde to CoH (H2 atmosphere) did not result in hydrogen absorption. However, when this procedure was carried out with CoH containing added alkali (KOH, 2x cobalt concentration), hydrogen was taken up, 1.0 atom of hydrogen being absorbed per mole of substrate. Since benzyl alcohol was isolated in 66% yield, it is assumed that a portion of the product may have been formed via a competitive Cannizzaro reaction. Reinforcing this assumption is the observation of an apparent depletion of alkali during the run. 

Substituted nitrobenzenes gave similar results on reduction of less than stoichiometric quantities in the absence of added alkali, hydrogen atom-substrate ratios of 3.0 to 4.1 being obtained while cessation of hydrogen absorption occurred at H/Co = 2.0 in all cases. Azoxy and azo compounds were isolated from o-nitrotoluene (H/substrate = 3.9) p-nitrotoluene (H/substrate = 3.2) yielded a mixture of azoxy and hydroxylamine derivatives, the latter believed to be the immediate precursor of the bimolecular product. Reduction of o-nitro-anisole in the presence of added alkali (NaOH, 3.3X cobalt concentration)... 

The basic steps in the hydroformylation mechanism do not change in the presence of ligand-modified cobalt, but the kinetics of the reaction is affected.30 First-order dependence of the rate on hydrogen partial pressure and an inverse first-order dependence on CO partial pressure were observed in the unmodified system.36 At high CO pressures the rate is first-order in both alkene and cobalt concentrations. The last, product-forming, step—the cleavage of the acylcobalt... 

As long as the hydroperoxide concentration can be neglected, simplification leads to three ranges of cobalt concentrations ... 

The intermediate range where the sensitivity to traces of hydro-peroxidic contamination is such that despite considerable care reproducible results were not possible and where the complex rate equation does not lend itself to simplification. The fact that this range usually covered less than an order of magnitude (e.g., a concentration range of M/20,000 to M/5000) is not so surprising when one takes into account a termination reaction which is second order with regard to cobalt concentration. 

The autoxidation of hydrocarbons catalyzed by cobalt salts of carboxylic acid and bromide ions was kinetically studied. The rate of hydrocarbon oxidation with secondary hydrogen is exactly first order with respect to both hydrocarbon and cobalt concentration. For toluene the rate is second order with respect to cobalt and first order with respect to hydrocarbon concentration, but it is independent of hydrocarbon concentration for a long time during the oxidation. The oxidation rate increases as the carbon number of fatty acid solvent as well as of cobalt anion salt are decreased. It was suggested that the cobalt salt not only initiates the oxidation by decomposing hydroperoxide but also is responsible for the propagation step in the presence of bromide ion. 

Cobalt Concentration. The effect of bromide ion becomes appreciable at cobalt concentrations above 0.001M and quite remarkable above O.OlAf. The ratio of pBr (oxidation rate in the presence of 0.1M NaBr) to p0 (oxidation rate in the absence of NaBr) at cobalt concentration... 

Similar first-order correlation between cobalt and the rate was obtained for n-dodecane. The oxidation rate of n-dodecane decreases as cobalt concentration is increased to more than 0.05M, probably owing to chain termination by cobalt as reported for Tetralin (8). The oxidation rate of toluene is nearly second order with respect to cobalt (Figure 3). 

Figure 2. Steady rate of hydrocarbon oxidation as a function of cobalt concentration at NaBr/Co = 2/1 at 80°C.

With cobalt as catalyst the plot of log [peracetic acid] vs. time was linear for each cobalt acetate concentration. The first-order rate constants obtained at different cobalt concentrations (k2 ) were plotted as a function of total cobalt (Cot) concentration, and the plot indicates a first-order dependence on total cobalt as shown in Figure 3. The experimental rate law for the cobalt-catalyzed decomposition is thus ... 

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