Cobalt oxide precipitates

Zhu et al. [109] proposed an environmentally innocuous method of preparation by using a single-step solvothermal route in ethanol solutions. The procedure leads to simultaneous rGO reduction and iron or cobalt oxide precipitation due to the fact that the GO/rGO layers act as heterogeneous nucleation seeds during the precipitation of the metal oxide nanocrystals. In a related approach, Han et al. [110] were able to obtain Li4Ti50i2 particles anchored to rGO by solvothermal treatment of H2O/ EtOH-based suspensions of graphite oxide and the oxide powder. The process involves reduction of GO and attachment of the mixed oxide nanoparticles within a single step. 

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). 

Cobaltous bromide and cobaltous iodide in the solid state absorb ammonia with formation of hexammino-cobaltous bromide, [Co(NH3)6]Br2, and hexammino - cobaltous iodide, [Co(NH3)6]I2, respectively. The compounds are unstable, and rapidly lose ammonia on heating and decompose on solution in water. Tetrammino-cobaltous iodide, [Co(NH3)4]I2, is also known. It may be prepared by treating a concentrated solution of cobaltous iodide with ammonia a pale red precipitate is formed, which gradually dissolves on warming, giving a violet-coloured liquid from which small rose-red crystals of the tetram-mine separate. It also is unstable, and decomposes on heating or on standing in air with loss of ammonia and formation of cobalt oxide. In aqueous solution it turns brown, ammonia is evolved, and a precipitate of cobaltous oxyiodide separates. 

Coball(lI) hydroxide exists in two allolropic forms, a blue or-Co (OH) and a pink /l-Co(OH) . The hydroxide is prepared by precipitation from u cobaltous salt solution by an alkali hydroxide. When the alkali is in excess the pink ft form is produced—the blue a-furni is produced when the cobalt salt is in excess. The salt slowly oxidizes in air at mom temperature and changes to hydrated cobaltic oxide, Co-Oi - H 0. The hydroxide is practically insoluble in H 0 and in bases, but highly soluble in mineral and organic acids. The commercial salt is used as Ihe starting material in the preparation of drying agents. 

A mixture of 25 g. (0.20 mole) of sodium sulfite and 100 ml. of water is added to 29 g. (0.10 mole) of cobalt(II) nitrate 6-hydrate dissolved in 25 ml. of water, which gives a pink, mushy precipitate of cobalt(II) sulfite. Then 6 ml. of concentrated nitric acid in 10 ml. of water is added dropwise to 12 g. (0.20 mole) of 98% ethylenediamine and mixed with the cobalt sulfite, which immediately dissolves to form a brown solution. ( Caution. Spattering occurs during the addition of the nitric acid.) Air is bubbled through the solution with a wash-bottle attachment for one hour, and the solution is filtered to remove any residue of cobalt oxide. 

A mixture of 20 g. (0.062 mole) of cw-diazidobis(ethylene-diamine)cobalt(III) nitrate3 and 40 ml. of warm water is placed in a steam bath. Sodium sulfite 7.8 g. (0.062 mole) is stirred slowly into the mixture, and stirring is continued for 2 minutes. The hot solution is filtered quickly to remove cobalt oxide. Red crystals of cw-azidobis(ethylenediamine)sulfitocobalt(III) start to precipitate immediately and, after cooling in an ice bath for one hour, they are filtered. After recrystallization from boiling water (20 ml./g. of crude product), the yield is 4-5 g. (22-27%). If it is desired to prepare sodium fr[Pg.79]

The crude oxide is dissolved in hydrochloric add. To the warm liquor finely divided calcium carbonate is added gradually, with stirring, until no further predpitate is obtained. The precipitate being removed by filtration, the solution is free from iron, arsenic, and silica. The solution is then precipitated with a solution of bleaching powder,2 added slowly with constant stirring until almost the whole of the cobalt is precipitated as black hydrated oxide. By this means practically none of the nickel is thrown down. The precipitate is washed, dried, and calcined to oxide. It is then boiled with sodium carbonate solution to convert any calcium sulphate into carbonate, and after thorough washing, is treated with very dilute hydrochloric acid to remove the calcium carbonate. Finally the oxide is washed, dried, and calcined. 

Cobaltic Chloride, CoCl3, has not as yet been isolated, although indications of its possible existence are not entirely wanting. Thus, when freshly precipitated hydrated cobaltic oxide is dissolved in alcoholic hydrogen chloride, a dark green solution is produced which rapidly turns to a rose colour.9 The first dark colour suggests the presence of trivalent cobalt. 

Cobalto-cobaltic oxide has been prepared in three states of hydration. The trihydrate, Co304.3H20, results on warming cobaltous hydroxide with potassium persulphate and heating the resulting product to 100° C. with dilute nitric acid.1 It is also produced as a brown precipitate on boiling a solution of roseo-cobaltic sulphate. 

As obtained by the foregoing methods, hydrated cobaltic oxide is a blackish brown precipitate which dissolves in aqueous hydrogen chloride evolving chlorine, eolbaltous chloride passing into solution. The oxide thus behaves like a peroxide. 

Cobalt is present in almost all nickel ores. Previously there was no use for cobalt and as its value was less than that of nickel, it was not separated. Therefore, old nickel alloys contain much more cobalt than those of the present day. Two chemical methods are based on the oxidation of cobalt to three-valent ions. Cobalt is precipitated as cobalt(III) hydroxide by treating the solution with chlorine to oxidize the cobalt(II) to cobalt(III) and adding nickel carbonate to control the pH to 4 (27)... 

It has been established from these studies that the different catalytic properties of transition metal oxides (chromium, cobalt) on zirconium dioxide are attributed to their different acidic properties determined by TPDA and IR-spectroscopy. The most active catalyst is characterized by strong acidic Bronsted centers. The cobalt oxide deposited by precipitation on the zirconium-containing pentasils has a considerable oxidative activity in the reaction N0+02 N02, and for SCR-activity the definite surface acidity is necessary for methane activation. Among the binary systems, 10% CoO/(65% H-Zeolite - 35% Z1O2)... 

Our work is a tentative to rationalize the influence of the preparation parameters over the composition, active phase and catalytic activity. Modifying the pH of precipitation between 6.0 and 8.5, the surface area, the bulk, the surface composition and the active phases of the catalysts were modified significantly. Raman spectroscopy has revealed the presence of M0O3 phase only in the catalyst prepared at pH 6.0. From the literature data, we know that the precipitation of the Ni(OH)2 and Co(OH)2 occurs at pH 7 and 7.5, respectively. At pH higher than 7.5 our calculations suggest the presence of nickel or/and cobalt oxides but these phases were not detected with any of the characterization techniques used. 

The various components of the mixed precipitates that result from these interactions may subsequently or concurrently participate in the redox alterations. Often these eflFects raise the oxidation state of the manganese in the precipitate above what would be expected in a pure manganese oxide precipitated in the absence of other metal ions. Chemical thermodynamic calculations can be used to predict or explain these processes. Some effects of lead and cobalt on manganese behavior have been evaluated theoretically and experimentally. 

Mechanisms for coprecipitation of lead and cobalt with manganese oxide can be derived based on thermodynamic calculations. They can explain the increased oxidation state of manganese reached in the mixed oxide precipitates, and they provide a potential control of the solubility of the accessory metals. The effectiveness of the control has been evaluated in a preliminary way by laboratory experiments described here, and by some fleld observations. Cobalt activity seems to be controlled by manganese coprecipitation in many natural systems. Although more testing by both laboratory experiments and fleld studies is needed, the proposed mechanisms appear to be applicable to many coupled oxidation-reduction processes. 

The interaction of the precipitated cobalt oxides with the carbon nanofiber support is influenced to a large extent by heat treatment in an inert atmosphere. Heat treatment of the carbon nanofibers at 573 K resulted in an increase in the interaction between the cobalt particles and the support. Under these conditions a small amount of cobalt carbide and cobalt metal was detected by the XRD and XPS analyses. Heat treatment at 873 K resulted in a further increase in the interaction between the metal and the support leading to increasing amounts of cobalt carbide and cobalt metal. 

In this paper, oxidation of carbon nanofibers by nitric acid in combination with a deposition precipitation method was investigated as a modus operandi for the preparation of highly dispersed carbon nanofiber supported, cobalt oxides. A variety of thermal and spectroscopic techniques such as thermogravimetric... 

Dofour et al. [17] investigated the influence of synthesis method, precursor and effect of Cu addition on the WGS activity of Fe-Cr-Co catalysts. They prepared FeCr, FeCrCu, FeCrCo and FeCrCuCo formulations by oxidation precipitation method, using chloride (Cl) and sulphate (S) metal precursors. The catalytic activity results of FeCrCo and FeCrCuCo catalysts are presented in Figure 2.2. All the materials prepared from sulphate precursor showed higher carbon monoxide conversion than those synthesized with chloride. As expected Cu-promoted catalysts show better activity than Fe-Cr-Co catalysts. For the catalysts synthesized by chloride precursor, in the case of cobalt, incorporation of this metal into the magnetite lattice could improve the covalency of Fe and... 

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