Total Concentration Of Cobalt Research Articles

Mobility and Fractionation of Cobalt in Some Calcareous Soils in Iraqi Centre

Pollution is one of the major threats with potential risks to humans, animals and plants, especially pollution with heavy metals, which are characterized by their significant ability to accumulate in environmental systems and induce toxicity to living organisms, even at low concentrations and quantities. This study was conducted on some calcareous soils selected from the province s of Babylon and Diwaniyah. Soil samples were collected from ten sites, five sites from each province , from a depth of 0-30 cm, to determine the concentration of cobalt in its chemical forms (available, bound to calcium carbonate, bound to organic matter and oxides, and residual) and total concentration, in addition to knowing the effect of different soil characteristics on these chemical forms. The results showed that there was a relatively wide range in the total cobalt concentration in the study sites (16.58 - 86.76 mg kg-1), and the percentages of the available chemical phase of the metal ranged from 0.44% - 6.88%, and in the form associated with carbonates from 19.30% - 34.54%, and in the form associated with organic matter and oxides from 28.82% - 55.94%, and in the form associated with the residual fraction from 3.46% - 51.44%. Because the metals in these fractions might dissolve depending on environmental conditions, notably pH values, higher mobility levels of accessible metal ions and those partly bonded to calcium carbonate may suggest environmental contamination and a risk of toxicity in soils.

Cobalt nanoparticles embedded in porous N-doped carbon support as a superior catalyst for the p-nitrophenol reduction

We report the synthesis of a new effective cobalt-based composite for catalytic reduction of water pollutant - p-nitrophenol. ZIF-67 and its Zn-substituted analog have been used as precursors for the catalyst preparation. Their pyrolysis has resulted in cobalt nanoparticles embedded into N-doped carbon substrates. We have used polyvinylidene fluoride (PVDF) as an additive to ZIF-substrates to produce mesoporous carbon shells on the surface of the catalysts. We have found that PVDF-additive enhanced the catalytic properties of the obtained composite material. Firstly, this additive reduces the total cobalt concentration in the composite by increasing carbon content. Secondly, a porous carbon shell improves the rate of catalytic reactions. According to the experimental data, PVDF additive has allowed us to obtain materials with lower Co-content but with high catalytic activity towards p-nitrophenol reduction.

Coastal sources, sinks and strong organic complexation of dissolved cobalt within the US North Atlantic GEOTRACES transect GA03

Abstract. Cobalt is the scarcest of metallic micronutrients and displays a complex biogeochemical cycle. This study examines the distribution, chemical speciation, and biogeochemistry of dissolved cobalt during the US North Atlantic GEOTRACES transect expeditions (GA03/3_e), which took place in the fall of 2010 and 2011. Two major subsurface sources of cobalt to the North Atlantic were identified. The more prominent of the two was a large plume of cobalt emanating from the African coast off the eastern tropical North Atlantic coincident with the oxygen minimum zone (OMZ) likely due to reductive dissolution, biouptake and remineralization, and aeolian dust deposition. The occurrence of this plume in an OMZ with oxygen above suboxic levels implies a high threshold for persistence of dissolved cobalt plumes. The other major subsurface source came from Upper Labrador Seawater, which may carry high cobalt concentrations due to the interaction of this water mass with resuspended sediment at the western margin or from transport further upstream. Minor sources of cobalt came from dust, coastal surface waters and hydrothermal systems along the Mid-Atlantic Ridge. The full depth section of cobalt chemical speciation revealed near-complete complexation in surface waters, even within regions of high dust deposition. However, labile cobalt observed below the euphotic zone demonstrated that strong cobalt-binding ligands were not present in excess of the total cobalt concentration there, implying that mesopelagic labile cobalt was sourced from the remineralization of sinking organic matter. In the upper water column, correlations were observed between total cobalt and phosphate, and between labile cobalt and phosphate, demonstrating a strong biological influence on cobalt cycling. Along the western margin off the North American coast, this correlation with phosphate was no longer observed and instead a relationship between cobalt and salinity was observed, reflecting the importance of coastal input processes on cobalt distributions. In deep waters, both total and labile cobalt concentrations were lower than in intermediate depth waters, demonstrating that scavenging may remove labile cobalt from the water column. Total and labile cobalt distributions were also compared to a previously published South Atlantic GEOTRACES-compliant zonal transect (CoFeMUG, GAc01) to discern regional biogeochemical differences. Together, these Atlantic sectional studies highlight the dynamic ecological stoichiometry of total and labile cobalt. As increasing anthropogenic use and subsequent release of cobalt poses the potential to overpower natural cobalt signals in the oceans, it is more important than ever to establish a baseline understanding of cobalt distributions in the ocean.

Catalytically active cobalt-copper-oxide layers on aluminum and titanium

Oxide coatings modified with cobalt and copper oxides are obtained on titanium and aluminum by means of combining plasma electrolytic oxidation (PEO) in silicate and zirconate electrolytes and impregnation in nitrate solutions followed by annealing. The effect of PEO coatings that were preliminarily formed on aluminum and titanium in different electrolytes on the composition and surface morphology of cobaltcopper oxide composites and their activity with respect to CO oxidation is studied. The maximum total concentration of cobalt and copper is found to be typical of composite layers based on SiO2 + Al2O3/Al, while the minimum content is observed in the case of layers based on ZrO2 + TiO2/Ti, the PEO bases being characterized by the highest and lowest water-absorbing capacity, respectively. The effect of PEO coatings on the catalytic activity of cobalt-copper oxide catalysts decreases in the series SiO2 + TiO2/Ti > SiO2 + Al2O3/Al > Ce2O3 + ZrO2 + TiO2/Ti > ZrO2 + TiO2/Ti.

Combined use of HPLC–ICP-MS and microwave-assisted extraction for the determination of cobalt compounds in nutritive supplements

Speciation analysis of cobalt in nutritive supplements has been carried out using HPLC and ICP-MS equipped with a membrane desolvation sample introduction system as detector. In this study, cobalt containing compounds, namely Co(II), cyanocobalamin (CN-Cbl) and hydroxylcobalamin (OH-Cbl), were well separated by reversed phase HPLC with a C8-HPLC column as the stationary phase and 8mmolL−1 ammonium acetate in 22%v/v methanol solution (pH 4) as the mobile phase using isocratic elution. Detection limit was in the range of 0.008–0.014μg CoL−1 for various Co species. Over 98% of the total cobalt species was extracted in nutritive supplements using a 0.5%v/v HNO3 solution in a microwave field; and the spike recovery was in the range of 92–108% for various species. The HPLC–ICP-MS results showed a satisfactory agreement with the total cobalt concentrations obtained by ICP-MS analysis of completely dissolved samples.

Analysis of Bio-Obtainable Endocrine Disrupting Metals in River Water and Sediment, Sewage Influent/Effluent, Sludge, Leachate, and Concentrated Leachate, in the Irish Midlands Shannon Catchment

The application of an acid digestion and subsequent solid-phase extraction (SPE) procedure were implemented as preliminary treatments prior to quantifying the levels of potentially endocrine disrupting metals (EDMs) in a variety of solid and liquid matrices. These included (solid) river sediment, leachate sediment and sewage sludge and also (liquid) river water, landfill leachate, concentrated leachate, sewage influent, and sewage effluent, sampled in the Irish Midlands. The total concentrations of cobalt (Co), cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), lead (Pb), zinc (Zn), and manganese (Mn), after extraction and preconcentration, were determined by atomic absorption spectroscopy (AAS). Mercury (Hg) in sediment and sludge was determined using cold-vapour atomic fluorescence spectroscopy (AFS). For sewage sludge maximum values (mg/kgdw) of 4700 Ni, 1642 Mn, 100.0 Cd, 3400 Zn, 36.70 Co, 750.0 Pb, 485.8 Cr, and 1003 Cu were determined whilst in leachate sediment, maximum values (mg/kgdw) of 32.10 Ni, 815.0 Mn, 32.78 Cd, 230.3 Zn, 26.73 Co, 3525 Pb, 124.9 Cr, and 50.13 Cu were found. Over several months, the data showed elevated levels in sewage influents, effluents, and sludges compared to a battery of adjacent river water samples and corresponding sediments. There was a definite trend for target values for sediments to be exceeded, while intervention values were only exceeded for cadmium. Overall the pattern in terms of concentration was sewage > leachate > river matrices. A nonparametric assessment of the effect of sewage treatment method on median metal levels in sludge revealed statistically significant differences at the 95% level of confidence for Co, Cr, and Hg and at the 90% level of confidence for Cd.

Bridging the Gap between Macroscopic and Spectroscopic Studies of Metal Ion Sorption at the Oxide/Water Interface:  Sr(II), Co(II), and Pb(II) Sorption to Quartz

Metal sorption mechanisms were investigated for strontium, cobalt, and lead using sodium chloride, sodium nitrate, and sodium perchlorate as background electrolytes and quartz as the adsorbent. Spectroscopic analyses of concentrated sorption samples were evaluated for their ability to provide insight into the controlling sorption process for more dilute systems. For strontium, outer-sphere complexes identified using X-ray absorption spectroscopy (XAS) of concentrated samples were consistent with macroscopic sorption data collected in more dilute systems. XAS results indicated that cobalt formed a new solid phase upon sorption to silica. Macroscopic studies of cobalt sorption supported the spectroscopic data for total cobalt concentrations of 10(-5) M, regardless of the background electrolyte composition or concentration. At a lower total cobalt concentration (10(-7) M), adsorption appeared to be the prevailing mechanism of cobalt removal. Spectroscopic results suggested that lead adsorbed as an inner-sphere complex on silica. The decrease of lead removal with increasing chloride concentration was attributed to competition with aqueous lead-chloride complexes, based on thermodynamic calculations.

Organic complexation of cobalt across the Antarctic Polar Front in the Southern Ocean

There is compelling evidence to demonstrate that phytoplankton in major regions of the world’s oceans are limited by the availability of certain trace elements, notably iron. Cobalt concentrations in open-ocean waters generally range between 10 and 120 pmol L−1 but such levels were not thought to limit phytoplankton growth. Herein, we present data for total dissolved cobalt and cobalt-complexing ligands for two stations located south (station 200) and north (station 204) of the Antarctic Polar Front (APF) along 20°E in the South Atlantic sector of the Southern Ocean. Results indicate that there was little difference between total cobalt concentrations south and north of the APF, whereas ligand concentrations were significantly higher (15–20 pmol L−1) for the upper water column south of the APF. Productivity in these waters was low at the time of this study; however, numbers of large eukaryotic algal species were higher south of the APF, while north of the APF small eukaryotic and prokaryotic species dominated. The higher ligand concentrations measured at the southern station are probably related to higher algal numbers at this site. Because ligand concentrations were higher, inorganic cobalt concentrations (Co′) south of the APF are extremely low, at femtomolar levels, whereas north of the APF calculated Co′ are much higher at picomolar levels where ligand concentrations were lower.

Formation and Release of Cobalt(II) Sorption and Precipitation Products in Aging Kaolinite–Water Slurries

The uptake and release behavior of cobalt(II) was studied over thousands of hours in CO2-free aqueous suspensions of kaolinite under three pairs of total cobalt concentration (CoT) and near-neutral pH (7.5–7.8) conditions. Dissolved cobalt, aluminum, and silicon concentrations were monitored by ICPMS, and cobalt-containing products were identified by EXAFS spectroscopy. In each uptake experiment, cobalt sorbed to kaolinite as a mixture of surface-adsorbed monomers or polymers and hydrotalcite-like precipitates of the approximate composition CoxAl(OH)2x+2(An−)1/n, where 2≤x≤4 and An− is nitrate or silicate anion. Precipitate stoichiometry varied with experimental conditions, with the highest Co:Al ratio in the high CoT/high pH experiment. Cobalt surface adsorption occurred within seconds, whereas precipitation was slower and continued for the duration of the experiments. Consequently, the proportion of precipitate in the sorbed mixture increased with time in all experiments. The most rapid precipitation occurred in the high CoT/high pH experiment, where solutions were most supersaturated with respect to cobalt hydrotalcite. Precipitates incorporated some previously adsorbed cobalt, as well as cobalt from solution. Cobalt release from the solid phase was effected by lowering solution pH to 7.0. Release experiments initiated after shorter sorption times returned a larger fraction of cobalt to solution than those initiated after longer sorption times, for a fixed duration of release. In other words, sorption product stability increased with sorption time. Specifically, under the conditions of the release experiments, the hydrotalcite-like precipitates are more stable than smaller adsorbates, and precipitates that formed over longer time periods are more stable than those that formed rapidly. The latter result suggests that precipitates ripened or modified their structure or composition to become more stable over the course of the several-thousand-hour sorption experiments. Precipitates that formed over hundreds of hours or longer did not dissolve over thousands of hours at the lower pH.

Synergistic extraction of cobalt(II) with oxine/decanoic acid solution mixtures in benzene and chloroform

Synergistic extraction of Co(II) with 8-hydroxyquinoline (Hq)/decanoic acid [(HR)2] solution mixtures in benzene and chloroform was carried out at 25°C. The aqueous ionic strength and the total concentration of cobalt(II) were 0.1 (NaCl) and 1·10−5–1·10−3M, respectively. The synergistic effect is interpreted by the formation of the mixed ligand ion-pair complexes: [(Coq(Hq)2(HR))+, R−] and [(Coq(Hq)2(HR)3)+, R−] in benzene and chloroform, respectively.

Kinetics of heterogeneous oxidation of ammonium sulphite

AbstractThe heterogeneous oxidation of ammonium sulphite was investigated with cobalt sulphate catalyst at 30°C. For a wide range of concentrations the reaction was found to be nearly first order in oxygen and zero order in sulphite. These kinetics contrast with the results of homogeneous experiments which indicate that the reaction is zero order in oxygen and three‐halves order in sulphite. The catalytic effect of cobalt ions was found to be proportional to the square root of the total concentration of cobalt. The apparent activation energy for the overall oxidation was calculated to be 13 kcal/g mol. It is concluded that the kinetics in the heterogeneous system are determined by the catalyst regeneration reaction which is diffusion controlled.

Kinetics of oxidation of ammonium sulfite by rapid-mixing method

The kinetics of the reaction of oxygen with ammonium sulfite in aqueous solution have been studied by the rapid-mixing method of Hartridge and Roughton at 30°C. The rate of oxidation of ammonium sulfite was found to be approximately twice as low as that of sodium sulfite. The experimental findings showed that the reaction rate was zero order with respect to oxygen and three-halves order with respect to sulfite, and the promoting effect of cobalt ions was proportional to the square root of the total concentration of cobalt added to the reacting solution. The apparent activation energy for the overall oxidation was calculated to be 21·5 kcal per gmole. A reaction mechanism has been proposed and a rate expression derived is in good agreement with the experimental data.

Homogeneous Catalysis of D2–H2O Isotope Exchange by Pentacyanocobaltate(II)

The rate of exchange of deuterium between hydrogen gas and water catalyzed by pentacyanocobaltate(II) has been measured as a function of pressure and temperature at a constant total cobalt concentration, 0.05 M, and ionic strength, 1 M. The rates of evolution of hydrogen from solutions of hydridopentacyanocobaltate(III) have been determined under identical conditions. These data have been employed to test the validity of a mechanism for the[Formula: see text] -catalyzed isotope exchange reaction, and to clarify the controversy over the magnitude of the specific rate for the deuterium transfer step[Formula: see text]Calculations show that kinetic isotope and ion pairing effects are significant.

The interference of cobalt, nickel and copper in the determination of iron by atomic-absorption spectrophotometry in an air-acetylene flame

An investigation of interferences in the determination of iron by atomic-absorption spectrophotometry in an air-acetylene flame is reported. It has been found that three elements, cobalt, nickel and copper, exhibit serious depressive effects, the magnitude of which is strongly dependent on the flame conditions, with respect to both fuel-to-air ratio and the height of the optical path above the burner, and is also dependent on the anion present in the sample solution. The optimisation of the flame for both pure iron solutions and those containing the interfering elements, and means of suppressing these interferences, are discussed. The use of 8-hydroxyquinoline at a concentration equal to or greater than the total concentration of cobalt, nickel and copper is recommended as an effective releasing agent.

The separation and determination of Cobalt(II) and Cobalt(III)

A method for the seperation and determination of cobalt(II) and (III) has been developed. The acetylacetonate complexes of cobalt are utilized for the seperation, and analytical measurements are made by atomic absorption or visible absorption spetrophotometry. The sample is reacted with hot acetylacetone and diluted with 20% acetic acid. The cobalt (III) complex is seperated by extraction with benzene. The benzene layer is then diluted with n-pentanol and the cobalt(III) concentration is determined by atomic absorption spectrophotometry. The cobalt(II) concentration can be determined in the 20% acetic acid layer by atomic absorption. In the absence of other metals which form colored acetylacetonate complexes, the cobalt(III) concentration can be determined by the visible absorption spectrophotometry directly on the 20% acetic acid solution. The total cobalt concentration can be determined by any acceptable method for cobalt and the cobalt(II) concentration then obtained by the difference.

The Studies on Brdicka's Catalytic Hydrogen-Wave l

It is well known that the catalytic wave of protein discovered by Brdicka' shows a double wave in the solution of ammoniacal ammonium chloride containing either divalent or trivalent cobalt, and in general, the waves found with a trivalent cobalt solution are larger than those found with a divalent cobalt solution at the same total cobalt concentra tion. Brdicka2), in the series of his studies on the catalytic hydrogen wave, described that the wave was quite different in character when the ammoniacal solution contained divalent or trivalent cobalt. In order to learn more of the nature of the catalytic wave, a series of amino acids was tested, and he found that only cystine or cysteine showed a effect similar to protein in ammoniacal cobaltous solution, and that each of these compounds gave rise to a wave which was in the same position as the second wave of protein. The appearance of catalytic wave by cystine in the cobaltic solution was not described by him, and the difference of the catalytic wave in ammoniacal solution containing divalent or trivalent cobalt has not been known up to now.In 1954, Kalous and Ji.rsa discovered that during the polarographic investigation of cystine, the catalytic wave appeared even in the presence of trivalent cobalt in a solution of relatively high concentration, i.e., about 10-3M. Recently, he reported4) a complicated electrode reaction of influence of trivalent cobalt on the reduction of cystine and presented an explanation for the mechanism of the catalytic wave by using Kalousek commutatorn.In the present study, the catalytic wave of cystine with trivalent cobalt has been in vestigated by D.C. and A.C. polarograph to learn more of the electrode reactions. The parameters studied with respect to the effect on the catalytic wave were the concentration of cystine and cobalt and pressure of the dropping mercury electrode. A.C. polarographic waves showed the reduction waves corresponding to various D.C. polarographic waves given by cystine in the solution of ammoniacal trivalent cobalt. The relation between the reduction process of prewave of cystine (at -0.58 V.) and divalent cobalt at the surface of mercury produced by the reduction of trivalent cobalt, was investigated, and an explana tion for the mechanism of the catalytic wave was presented.