Coprecipitation Of Cobalt Research Articles

In Situ Study of Reduction of MnxCo3-xO4 Mixed Oxides: The Role of Manganese Content.

A series of Mn-Co mixed oxides with a gradual variation of the Mn/Co molar ratio were prepared by coprecipitation of cobalt and manganese nitrates. The structure, chemistry, and reducibility of the oxides were studied by X-ray diffraction (XRD), X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). It was found that at concentrations of Mn below 37 atom %, a solid solution with a cubic spinel structure is formed. At concentrations above 63 atom %, a solid solution is formed on the basis of a tetragonal spinel, while at concentrations in a range of 37-63 atom %, a two-phase system, which contains tetragonal and cubic oxides, is formed. To elucidate the reduction route of mixed oxides, two approaches were used. The first was based on a gradual change in the chemical composition of Mn-Co oxides, illustrating slow changes in the TPR profiles. The second approach consisted in a combination of in situ XRD and pseudo-in situ XPS techniques, which made it possible to directly determine the structure and chemistry of the oxides under reductive conditions. It was shown that the reduction of Mn-Co mixed oxides proceeds via two stages. During the first stage, (Mn, Co)3O4 is reduced to (Mn, Co)O. During the second stage, the solid solution (Mn, Co)O is transformed into metallic cobalt and MnO. The introduction of manganese cations into the structure of cobalt oxide leads to a decrease in the rate of both reduction stages. However, the influence of additional cations on the second reduction stage is more noticeable. This is due to crystallographic peculiarities of the compounds: the conversion from the initial oxide (Mn, Co)3O4 into the intermediate oxide (Mn, Co)O requires only a small displacement of cations, whereas the formation of metallic cobalt from (Mn, Co)O requires a rearrangement of the entire structure.

Investigation conditions of formation Co–Al double layered hydroxides

The process of formation of double layered hydroxides in the system Со2 + – Al3 + – SO4 2– – ОН- at the stoichiometric ratio of Al3 +/Сo2 + = 2 cations was studied by a complex method. The possibility of coprecipitation of cobalt and aluminum hydroxides, the optimal range of pH values for the production of precipitation, which are precursors of the synthesis of aluminocobalt spinel. X-ray diffraction analysis revealed the phase composition of the final product. Spectrophotometrically determined color characteristics of spinel.

Nanocrystalline Oxides NixCo3−xO4: Sub-ppm H2S Sensing and Humidity Effect

In this work, p-type oxide semiconductors, Co3O4 and complex oxides NixCo3−xO4 (x = 0.04, 0.07, 0.1), were studied as materials for sub-ppm H2S sensing in the temperature range of 90–300 °C in dry and humid air. Nanocrystalline Co3O4 and NixCo3−xO4 (x = 0.04, 0.07, 0.1) were prepared by coprecipitation of cobalt and nickel oxalates from nitrate solutions and further annealing at 300 °C. The surface reactivity of the obtained materials toward H2S both in dry and humid atmosphere (relative humidity at 25 °C R.H. = 60%) was investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Sensor measurements showed a decrease in sensor signal toward 1 ppm H2S with an increase in Ni content because of a decrease in chemisorbed surface oxygen species. On the other hand, sensor signal increases for all samples with increasing the relative humidity that depends on reactivity of the surface hydroxyl groups, which stimulate the decomposition of surface sulfites and provide better surface regeneration at higher temperature. This assumption was additionally confirmed by the faster saturation of the conductivity curve and a decrease in the sensor response time in humid air.

Comparative Study of Strategies for Enhancing the Performance of Co3O4/Al2O3 Catalysts for Lean Methane Combustion

Spinel-type cobalt oxide is a highly active catalyst for oxidation reactions owing to its remarkable redox properties, although it generally exhibits poor mechanical, textural and structural properties. Supporting this material on a porous alumina can significantly improve these characteristics. However, the strong cobalt–alumina interaction leads to the formation of inactive cobalt aluminate, which limits the activity of the resulting catalysts. In this work, three different strategies for enhancing the performance of alumina-supported catalysts are examined: (i) surface protection of the alumina with magnesia prior to the deposition of the cobalt precursor, with the objective of minimizing the cobalt–alumina interaction; (ii) coprecipitation of cobalt along with nickel, with the aim of improving the redox properties of the deposited cobalt and (iii) surface protection of alumina with ceria, to provide both a barrier effect, minimizing the cobalt–alumina interaction, and a redox promoting effect on the deposited cobalt. Among the examined strategies, the addition of ceria (20 wt % Ce) prior to the deposition of cobalt resulted in being highly efficient. This sample was characterized by a notable abundance of both Co3+ and oxygen lattice species, derived from the partial inhibition of cobalt aluminate formation and the insertion of Ce4+ cations into the spinel lattice.

Sustainable Hydrometallurgical Recovery of Valuable Elements from Spent Nickel–Metal Hydride HEV Batteries

In the present study, the recovery of valuable metals from a Panasonic Prismatic Module 6.5 Ah NiMH 7.2 V plastic casing hybrid electric vehicle (HEV) battery has been investigated, processing the anode and cathode electrodes separately. The study focuses on the recovery of the most valuable compounds, i.e., nickel, cobalt and rare earth elements (REE). Most of the REE (La, Ce, Nd, Pr and Y) were found in the anode active material (33% by mass), whereas only a small amount of Y was found in the cathode material. The electrodes were leached in sulfuric acid and in hydrochloric acid, respectively, under different conditions. The results indicated that the dissolution kinetics of nickel could be slow as a result of slow dissolution kinetics of nickel oxide. At leaching in sulfuric acid, light rare earths were found to reprecipitate increasingly with increasing temperature and sulfuric acid concentration. Following the leaching, the separation of REE from the sulfuric acid leach liquor by precipitation as NaREE (SO4)2·H2O and from the hydrochloric acid leach solution as REE2(C2O4)3·xH2O were investigated. By adding sodium ions, the REE could be precipitated as NaREE (SO4)2·H2O with little loss of Co and Ni. By using a stoichiometric oxalic acid excess of 300%, the REE could be precipitated as oxalates while avoiding nickel and cobalt co-precipitation. By using nanofiltration it was possible to recover hydrochloric acid after leaching the anode material.

Concentration and Separation of Scandium from Ni Laterite Ore Processing Streams

The presence of a considerable amount of scandium in lateritic nickel-cobalt ores necessitates the investigation of possible processing alternatives to recover scandium as a byproduct during nickel and cobalt production. Therefore, in this study, rather than interfering with the main nickel-cobalt production circuit, the precipitation-separation behavior of scandium during a pH-controlled precipitation process from a synthetically prepared solution was investigated to adopt the Sc recovery circuit into an already existing hydrometallurgical nickel-cobalt hydroxide processing plant. The composition of the synthetic solution was determined according to the hydrometallurgical nickel laterite ore processing streams obtained from a HPAL (high-pressure sulphuric acid leaching) process. In order to selectively precipitate and concentrate scandium with minimum nickel and cobalt co-precipitation, the pH of the solution was adjusted by CaCO3, MgO, Na2CO3, and NaOH. It was found that precipitation with MgO or Na2CO3 is more advantageous to obtain a precipitate containing higher amounts of scandium with minimum mass when compared to the CaCO3 route, which makes further processing more viable. As a result of this study, it is proposed that by a simple pH-controlled precipitation process, scandium can be separated from the nickel and cobalt containing process solutions as a byproduct without affecting the conventional nickel-cobalt hydroxide production. By further processing this scandium-enriched residue by means of leaching, SX (solvent extraction), and precipitation, an intermediate (NH4)2NaScF6 product can be obtained.

Anion Exchange Synthesis of Spinel-Type Cobalt-Containing Pigments

A method is proposed for synthesizing ultramarine blue pigment by co-precipitation of cobalt and aluminum from nitrate solutions by the anion exchanger AV-17-8 in the OH form followed by roasting a precursor at 750°C for 4 h. The product obtained was studied by thermographic and x-ray radiographic analyses as well as by spectrophotometry (IR and diffuse reflection). Electron microscopy shows the pigment particles to be 50 – 80 nm in size.

Reaction temperature variations on the crystallographic state of spinel cobalt aluminate

In this study, we report a rapid and simple technique for obtaining cobalt aluminate having a spinel structure. The products were prepared from a hydroxide precursor synthesized by coprecipitation of cobalt (Co(2+)) and aluminum (Al(3+)) nitrates with an alkaline solution. The chosen precursor enabled low temperature fabrication of cobalt aluminate with a spinel structure by sintering it for 2 hours at low temperatures (>400 °C). Crystallographic and thermal analyses suggest that the low-temperature-sintered products contain Co(3+) ions stabilized by chemisorbed water and/or hydroxide groups, which was not observed for products sintered at temperatures higher than 1000 °C. The color of the products turned from clear blue (Thenard's blue) to dark green when sintering temperatures were below 1000 °C. Magnetic quantities, Curie constants, and Weiss temperatures show a strong dependence on the sintering temperature. These findings suggest that there are mixed valent states, i.e. Co(2+) and Co(3+), and unique cation distributions at the different crystallographic sites in the spinel structure, especially in the products sintered at lower temperatures.

Solution- and air-recoverable photocatalytic nanofibers by facile and cost-effective electrospinning and co-precipitation processes

While nanostructured materials are of particular academic and practical interest, their recoverability and recyclability have been of paramount industrial and environmental concerns. In the present contribution, co-precipitation was demonstrated as a facile and cost-effective approach to incorporate magnetic sensitivity and enhance the recoverability of nanofibrous materials which were frequently utilized in catalysis, energy and medical applications, etc. In particular, reusable magnetic and photocatalytic hybrid nanofibers were generated by electrospinning and co-precipitation method. First, TiO 2 nanofibers were prepared through sol–gel reaction and electrospinning process. To improve their recoverability, CoFe 2O 4 nanoparticles were decorated onto the nanofibers' surfaces via co-precipitation of cobalt and iron ions in the presence of the nanofibers suspension. Furthermore, the resulting CoFe 2O 4-decorated TiO 2 nanofibers maintained their photocatalytic activity after the modification. When suspended in a solution or spread on a dried surfaces, these nanofibers could be recollected with a magnet. These findings suggested that incorporation of ferromagnetic into the nanofibers maintained their photocatalytic performance and reduced production cost as well as the risk of human and environmental exposure through solution and air.

Copper(II)-8-hydroxquinoline coprecipitation system for preconcentration and separation of cobalt(II) and manganese(II) in real samples

A separation–preconcentration procedure based on the coprecipitation of cobalt(II) and manganese(II) ions with copper(II)-8-hydroxquinoline system has been developed. The analytical parameters including pH, amount of copper(II) as carrier element, amount of 8-hydroxquinoline, sample volume, etc., was investigated for the quantitative recoveries of Co(II) and Mn(II). No interferic effects were observed from the concomitant ions which are present in real samples. The detection limits for analyte ions by three sigma criteria were 0.86 μg L −1 for cobalt and 0.98 μg L −1 for manganese. The validation of the presented preconcentration procedure was performed by the analysis of NIST SRM 2711 Montana soil and GBW 07605 Tea certified reference materials. The procedure presented was applied to the analyte contents of real samples including natural waters and some food samples with successfully analytical results.

Magnetoelectric Measurements by Two Different Methods of Cobalt Ferrite-Barium Titanate Composites

The magnetoelectric coefficient, α = dE/dH, of different compositions of BaTiO3-CoFe2O4 composites was measured by using the dynamic method and also a new method developed in our laboratory which is based on pulsed magnetic fields. The values obtained by both methods are congruent, with the largest magnetoelectric coefficient obtained for the composite with 25% wt. Barium titanate. The magnetoelectric composites were synthesized by the ceramic method. The magnetoestrictive cobalt ferrite powders were synthesized by coprecipitation of cobalt and iron sulfates in acetone and a heat treatment at 1100°C. Commercial piezoelectric barium titanate powders were used of reactive quality (Aldrich, size < 2 μ m). The coupling via elastic deformations of these two phases inside the composite properly polarized, produced a magnetoelectric effect. The starting powders and the composites were characterized by thermal analysis, x-ray diffraction, scanning electron microscopy and particle size distribution using light scattering. Rietveld refinements were also made at the starting powders and composites.

Enhanced performances of N 2O destruction in the presence of CO over the mixed metal oxide catalysts derived from hydrotalcite-type precursors

The catalytic destruction of N 2O in the presence of CO has been performed over a fixed bed of mixed metal oxide catalysts derived by calcination from hydrotalcite-type precursors. The hydrotalcite-type precursors were obtained by co-precipitation of cobalt, aluminum and some of the transition metal nitrates such as rhodium, palladium and cerium with the addition of the precipitants under controlled pH. The reactions were carried out under atmospheric pressure in the temperature range of 150–500 °C and space velocities were set between 15,000 and 100,000/h. The presence of CO in excess of N 2O in the feed showed a positive effect on the N 2O destruction, leading to a decrease in the operation temperature with respect to direct N 2O decomposition. The N 2O destruction rates in the presence of CO were increased hundreds to thousands times than the rates in the absence of CO. The presence of NO in a small amount in the feed did not show any inhibition effect on the N 2O conversion in the presence of CO, but do show in the absence of CO. Some mechanistic aspects of the adsorption and the relevant reaction steps concerning the N 2O decomposition in the presence of CO have been suggested by using the results of experimental and analytical investigations.

Oxidative precipitation of manganese with SO 2/O 2 and separation from cobalt and nickel

The oxidation of Mn(II) and precipitation as MnO 2/Mn 2O 3 occurs spontaneously using SO 2/O 2 gas mixtures in the pH range 1–6 and temperature range 25–80 °C. The rate of Mn(II) oxidation with SO 2/O 2 is first order with respect to SO 2 partial pressure up to 5.7% SO 2 at 80 °C and half order with respect to [H +]. The rate of oxidation of Mn(II) is slow at pH<3 and increases rapidly at pH>4. Any Fe(II) is oxidised and precipitated before Mn(II). Low concentrations of manganese (0.01 M) can be selectively oxidised and precipitated from cobalt and nickel solutions at pH 3–4 with less than 1% co-precipitation of cobalt and nickel in the laboratory batch tests. The selectivity of manganese precipitation at pH 3–4 is consistent with thermodynamic data for the Mn–Ni/Co–H 2O systems.

Conversion of 2-octanol over nickel-alumina, cobalt-alumina, and alumina catalysts

Structural characterization of CoAl and NiAl coprecipitated catalysts has been accomplished using techniques such as X-ray diffraction, DTA, TGA, TG-MS, BET surface area and pore volume. The catalyst samples were prepared by coprecipitation of cobalt (or nickel) and aluminum from their aqueous salt solutions. The interaction of Co (or Ni) with aluminum has been investigated by X-ray diffraction as a function of calcination temperature. The results indicate that the interaction between Co and Al can lead to the formation of a normal spinel of CoAl 2O 4 at a very low temperature such as 473 K. On the other hand the interaction between Ni and Al is not sufficient to form well crystallized NiAl 2O 4 species at low temperatures but nickel-aluminate formation was seen above 973 K. The activity and selectivity of these catalysts for 2-octanol conversion are dependent on the reaction temperature, liquid hour space velocity (LHSV) as well as on the calcination temperature. The dehydrogenation activity of nickel based catalysts is attributed to the presence of nickel oxide whereas the dehydration activity is due to the spinel phase. The differences in the dehydration activity between alumina and nickel-alumina is mostly because of the incomplete formation of spinel phase (i.e., low temperature calcined samples). Catalytic activity of cobalt-alumina catalysts is comparable with that of alumina catalysts towards 2-octanol conversion.

Selective oxidation of isobutene to methacrolein on multiphasic molybdate-based catalysts

Synergetic effects in the selective oxidation of isobutene to methacrolein have been studied over catalysts containing several molybdate phases. Two types of catalysts have been analysed: (1) pure bismuth molybdates with Bi/Mo ratios of 2/2 and 2/3[BiMo(2/2)and BiMo(2/3)] and cobalt molybdate [Co/Mo(1/1)]; and (2) multiphasic molybdates consisting of three or four molybdates prepared by: (a) coprecipitation of cobalt and bismuth salts and calcination at high temperatures, (b) mechanically mixing in dry conditions the separate molybdates and calcining at high temperatures and (c) dispersing the separate molybdates in n-pentane and calcining at high temperatures. Synergetic effects are observed in multiphasic Bi/Mo(2/2)CoMo and BiMo(2/3) catalysts. For BiMo (2/2)CoMO catalysts the highest synergetic effects in the conversion, yield and selectivity are observed. For the catalysts before test no new phase is formed after calcination while after test X-ray measurements indicate a practically complete transformation of α-Bi 2Mo 3O 12 into γ-Bi 2MoO 6 and MoO 2 and traces of MoO 3 and Bi 2x Mo 1−xO 3. Neither contamination between phases is observed. The synergetic effects are explained by the cooperation between separate γ-Bi 2MoO 6, MoO 3 and (α+β)-CoMoO 4 phases in contact. The cooperation between phases is more effective when MoO 3 is present in a large proportion.

The formation of layered hydrotalcite-like compounds by coprecipitation of Co(II) and Ni(II) with Al(III) in aqueous ammoniacal solutions

The coprecipitation of cobalt(II) and nickel(II) with aluminum(III) in ammoniacal solutions has been investigated at 25°C using chloride reagents. It was found that cobalt(II) was greatly coprecipitated with aluminum(III) at pH 6.3–10.5 and the mole ratio of Co(II)/Al(III) in the precipitate attained a maximum value of about 3.5. The precipitates were found to form the partially crystalline layered hydrotalcite-like compound [Co 1− x Al x (OH) 2Cl x ·nH 2O]. On the other hand, the coprecipitation of Ni(II) with Al(III) was very sensitive to the solution pH and the amount coprecipitated was lower than of Co(II). The coprecipitated amount of Ni(II) was maximized at pH 8 and decreased remarkably with the increase of the solution pH. It was also found that the precipitates at pH 6.3–8.5 formed the layered hydrotalcite-like compound [Ni 1− x Al x (OH) 2·Cl x · nH 2O], while the precipitates at pH 9.5–10.5 were bayerite [ β-Al 2O 3·3H 2O]. The coprecipitated amount of divalent species was decreased in the order: chloride > sulfate > carbonate at the same conditions.

The coprecipitation behavior of Co(II) and Ni(II) with Fe(III), Cr(III) and Al(III) from aqueous ammoniacal solutions

The coprecipitation of cobalt(II) and nickel(II) with iron(III), chromium(III) and aluminum(III) from ammoniacal solutions has been investigated. The coprecipitation behavior was found to be very sensitive to the solution pH and total ammonia concentration. Co(II) and Ni(II) can be precipitated from low ammonia concentration solutions but are readily redissolved at higher ammonia concentrations. The coprecipitate of divalent and trivalent species was found to contain very large amounts of the divalent metals (up to a mole ratio M M(II)/M(III) of 2.5) when aluminum was the trivalent species, whereas with iron(III) or chromium(III), the ratio was only 0.5.

Coprecipitation of cobalt with magnesium ammonium phosphate from homogeneous solution

Coprecipitation of cobalt with magnesium ammonium phosphate from homogeneous solution

Coprecipitation of cobalt in the presence of aminoacids and citrates

The radioactive tracer method has been applied for the investigation of the influence of citric acid and amino-acids on the coprecipitation yield of cobalt traces with aluminium hydroxide precipitates. Results indicate that the presence of citric acid decreases the coprecipitation yields when 7 > pH > 8.5. Amino-acids decrease the cobalt coprecipitation yield at pH values above their isoelectric point. However this could be valid only for amino-acid concentrations above 10−4 M. Results also indicate pH regions where certain cobalt species could be separately coprecipitated on the basis of different coprecipitation yields.

Coprecipitation of cobaltwithnickeldimethylglyoxime

The coprecipitation of cobalt with nickel precipitated as the dimethylglyoxime complex has been investigated under various conditions. Precipitations were carried out in ammonia and acetate solutions, at 25° and 85°, with slow and rapid addition of the solution of the precipitating agent, and with various digestion times. In each experiment, the amount of cobalt was 612 μg and the amount of nickel was 57.6 mg. Of the methods investigated, minimum coprecipitation was achieved by slow addition of ammonia to the acid nickel, cobalt, and dimethylglyoxime solution followed by a 30-minute digestion, all processes being carried out at 25°.