Initial Cobalt Concentration Research Articles

Pulsed electrodeposition of cobalt nanoparticles on copper: influence of the operating parameters on size distribution and morphology

Cobalt nanoparticles were synthesized by pulsed electrodeposition on copper substrate. Scanning electron microscopy and image analysis were used to determine morphology and particle size distribution of nanoparticle populations obtained in different operating conditions. After preliminary tests, ton and toff were set at 50 and 300ms respectively to obtain distinct nanoparticles and avoid dendritic structures. Experimental tests were performed according to two partially superimposed factorial designs with two factors at two levels. First factorial design investigated the effect of current density (I=10 and 50mA/cm2) and discharged cobalt (Q=2.5×10−3 and 1.0×10−2C); second factorial design investigated the effect of cobalt concentration (C0=0.01 and 0.1M) for the same two levels of Q. For optimized value of ton/toff, square and hexagonal shaped nanoparticles were obtained. Statistical analysis evidenced that, for C0=0.1mol/L, current density is the most influencing factor on mean size: increasing I from 10 to 50mA/cm2 determined a diminution of mean size of 240nm. For the same cobalt concentration, increasing the deposition time (Q) determined an increase of mean size of 60nm. Diminishing the initial cobalt concentration from 0.1 to 0.01mol/L determined an increase of mean size from 10nm to 36nm. For C0=0.01mol/L nanoparticles grow reaching an optimal size (36nm) and then, increasing the time of deposition, optimal sized subunits tend to aggregate.As for polydispersity of nanoparticles, statistical tests denoted that increasing I determined significant reduction of variance, while increasing the time of deposition determined a significant increase of variance.

Kinetics, Isotherms and Equilibrium Study of Co(II) Adsorption from Single and Binary Aqueous Solutions by Acacia nilotica Leaf Carbon

The removal of cobalt ion from aqueous solution by Acacia nilotica leaf carbon (HAN), is described. Effect of pH, agitation time and initial concentration on adsorption capacities of HAN was investigated in a batch mode. The adsorption process, which is pH dependent, shows maximum removal of cobalt in the pH range 5 for an initial cobalt concentration of 50mg·L–1 The experimental data have been analyzed by using the Freundlich, Langmuir, Temkin and Dubinin–Radushkevich isotherm models. The batch sorption kinetics have been tested for a pseudo-first order, pseudo-second order and Elovich kinetic models. The rate constants of adsorption for all these kinetic models have been calculated. Results showed that the intraparticle diffusion and initial sorption of Co(II) into HAN was the main rate limiting step. The adsorption of cobalt ion was confirmed through instrumental analyses such as scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The desorption and recycling ability of HAN were also found. We conclude that HAN can be used for the efficient removal of cobalt from aqueous solution.

Investigation of cobalt sulfate precipitation by alcohol and influencing factors

This work presents a method for the precipitation of cobalt sulfate by alcohols, specifically ethanol and methanol. The effect of the initial concentration of cobalt, the volumetric ratio of alcohol to cobalt sulfate solution, the addition of sulfuric acid and ammonia, and the effects of common ions on the precipitation percentage were investigated. The performances of ethanol and methanol were compared in terms of the precipitation percentage of cobalt sulfate, and explanations for different performances are offered. In the sulfate-based solution, the alcohol was shown to displace water ligands from the first coordination sphere of the cobalt(II) cations, which led to the precipitation of the cobalt ions as cobalt sulfate heptahydrate. SEM analysis revealed that the particle sizes of the powders produced by this method are smaller than those of commercially available cobalt sulfate. The scientific literature contains no data on the solubility of cobalt sulfate in ethanol. In this study, the solubility product constant (Ksp) for cobalt sulfate was experimentally calculated to be approximately 1.15 × 10−5.

Optimisation of the batch reactor for the removal of cobalt ions from chloride media

A series of experiments were carried out to determine the best medium for the recovery of cobalt by means of an electrogenerative system. Use of the electrogenerative system with a chloride medium had shown promising performance with the highest free energy of −389.8kJmol−1 compared to that with sulphate and nitrate media. Subsequently, the influence of catholyte concentrations on cobalt recovery using the electrogenerative process was carried out by varying the initial cobalt concentration and sodium chloride concentration. The results showed that almost 100% recovery was attained within 1–4h of the recovery process. Influence of pH was investigated where the electrogenerative system performed best between pH 5.0 and 7.0. Maximum cell performance of 83% with 99% cobalt removal was obtained at 90min when 100mgL−1 of Co2+ in 0.5M NaCl was taken as catholyte solution. The values of ΔHo and ΔSo of the process were evaluated as 33.41kJmol−1 and 0.13kJmol−1, respectively.

Evaluation of transgenic tobacco plants expressing a bacterial Co–Ni transporter for acquisition of cobalt

Phytoremediation is a viable strategy for management of toxic wastes in a large area/volume with low concentrations of toxic elemental pollutants. With increased industrial use of cobalt and its alloys, it has become a major metal contaminant in soils and water bodies surrounding these industries and mining sites with adverse effects on the biota. A bacterial Co–Ni permease was cloned from Rhodopseudomonas palustris and introduced into Nicotiana tabacum to explore its potential for phytoremediation and was found to be specific for cobalt and nickel. The transgenic plants accumulated more cobalt and nickel as compared to control, whereas no significant difference in accumulation of other divalent ions was observed. The transgenic plants were evaluated for cobalt content and showed increased acquisition of cobalt (up to 5 times) as compared to control. The plants were also assessed for accumulation of nickel and found to accumulate up to 2 times more nickel than control. At the same initial concentration of cobalt and nickel, transgenic plant preferentially accumulated cobalt as compared to nickel. The present study is perhaps the first attempt to develop transgenic plants expressing heterologous Co transporter with an improved capacity to uptake cobalt.

Rapid removal of cobalt (II) from aqueous solution using cuttlefish bones; equilibrium, kinetics, and thermodynamic study

ABSTRACTThe objective of this study is to assess the adsorption potential of cobalt (II) using cuttlefish bones. The bones were treated with 0.01 N HCl to enhance the heavy metal uptake. The adsorbent was characterized using scanning electron microscope and energy dispersive X‐ray spectrometer. An adsorption study was conducted in a batch system to optimize process variables such as initial concentration of cobalt (II), pH, sorbent loading, particle size, process temperature, and contact time. The optimal pH was found to be 9. The kinetic data followed the pseudosecond‐order kinetic model, and the equilibrium time was found to be 20 min. In the first minute of the adsorption process, 50% of the cobalt (II) was adsorbed by the cuttle bones. Adsorption isotherms were expressed by the Langmuir and Freundlich adsorption models. The Langmuir adsorption model fits the experimental data reasonably well compared with the Freundlich model. The maximum adsorption capacity of this new sorbent was found to be 76.6 mg g−1 at 40 °C. Thermodynamic parameters, including the Gibbs free energy (ΔGo), enthalpy (ΔHo), and entropy (ΔSo), indicated that the adsorption of cobalt (II) by cuttlefish bones was feasible and endothermic at a temperature range of 20–40 °C. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd.

An indigenous cyanobacterium, Lyngbya putealis, as biosorbent: Optimization based on statistical model

The present investigation was aimed at analyzing the potential utility of Lyngbya putealis HH-15, an indigenous cyanobacterium isolated from a metal contaminated site as a biosorbent of cobalt from aqueous solutions. Adsorption equilibrium and kinetic behavior of cobalt in aqueous solution was studied through batch mode experiments allowing the computation of kinetic parameters and maximum metal adsorption capacity. Among the experimental parameters like pH, biosorbent dose, and initial concentration of metal the most effective influencing parameters and their interactions were identified by Box–Behnken design. High value of regression coefficient between the variables and the response (R2=0.9512) and low probability value indicate excellent evaluation of experimental data by second order polynomial regression model. The response surface method indicated that 40–50mg/L initial cobalt concentration, 6.0–6.5 pH and biosorbent dose of 0.6–0.8g/100ml were optimal for biosorption of cobalt by biosorbent prepared from L. putealis.

Adsorption of cobalt(II) from aqueous solution onto hydroxyapatite/zeolite composite

The Hydroxyapatite/Zeolite (HApZ) composite were synthesized by precipitation method and used as an adsorbent for the removal of cobalt ions from the aqueous solution. The materials were characterized by scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. It has been observed that there was slight enhancement in the % removal of cobalt ions from aqueous solution by HApZ (63%) than HAp (58%) and zeolite (47%). Batch experiments were performed to observe the effect of pH, adsorbent dose, contact time and initial cobalt (II) concentration. Kinetic study shows that the adsorption process follow pseudo-second order kinetic model. Equilibrium data were well fitted to Langmuir and Freundlich isotherm model.

Biomimetic Solid‐Solution Precursors of Metal Carbonate for Nanostructured Metal Oxides: MnO/Co and MnO‐CoO Nanostructures and Their Electrochemical Properties

AbstractBiomimetic solid solutions of manganese and cobalt carbonates (MnCO3–CoCO3) are used as the precursors for the synthesis of the corresponding metal oxides. The different structures of the metal oxides with porous morphologies, such as pure manganese monoxide (MnO), the solid solution of manganese and cobalt monoxide (MnO–CoO), and the nanocomposite of MnO and metallic cobalt (MnO/Co), are obtained by the appropriate thermal treatments under a reduction atmosphere. The contents of cobalt species can be controlled by the initial cobalt concentration in the MnCO3–CoCO3 precursors. The resultant MnO/Co nanocomposites show the enhanced charge–discharge cycle stability and rate performance as an anode material of lithium‐ion battery.

Optimization of Co2+ ions removal from water solutions via polymer enhanced ultrafiltration with application of PVA and sulfonated PVA as complexing agents

The paper presents the results of the studies of UF-complexation process applied for the removal of Co2+ ions from water solutions. As binding agents for cobalt ions, the PVA polymer (Mw=10,000) and its sulfonated form, synthesized in the laboratory, have been used. The method of experimental design and response surface methodology have been employed to find out the optimal conditions for the complexation process and to evaluate the interaction between the input variables, i.e., initial cobalt concentration, pH and amount of the polymer used, expressed as a polymer/Co2+ ratio r.The data collected by the designed experiments showed that sulfonation of polymer has improved significantly the binding ability of PVA. The optimal conditions of cobalt ions complexation established by response surface model for non-sulfonated PVA polymer have been found to be as follows: the initial concentration of Co2+=5.70mgL−1, the ratio between polymer and metal ions, r=8.58 and pH=5.93. The removal efficiency of Co2+ in these conditions was 31.81%.For sulfonated PVA polymer, the optimal conditions determined are as follows: initial concentration of [Co2+]0=10mgL−1, r=1.2 and pH=6.5. For these conditions, a removal efficiency of 99.98% has been determined. The experiments showed that Co2+ removal ability of sulfonated PVA was much higher than its non-sulfonated precursor. Although the polymer concentrations used in the tests with sulfonated PVA were approximately ten times lower than the non-sulfonated one, the removal efficiency of cobalt ions was significantly higher.

Sorption of cobalt to bone char: Kinetics, competitive sorption and mechanism

Swine bone char is the combustion residues of swine bone. Cobalt adsorption to swine bone char was studied. Batch kinetics studies showed that a rapid uptake occurred during the first 5 min and was followed with a very slow intraparticle diffusion process. The sorption kinetics was ideally conformed to pseudo-second equation, indicating several mechanisms involved in the adsorption process. Equilibrium sorption isotherm studies showed that the Freundlich isotherm model satisfactorily described the sorption data. The presence of co-ions had appreciable inhibiting effects on cobalt uptake by bone char because copper and zinc had higher affinity for the bone char surface than cobalt. Calcium concentration in solution and XRD analysis showed that ion exchange was involved in the removal of Co from solution over a certain initial cobalt concentration range.

Bioaccumulation of cobalt in silkworm ( Bombyx mori L.) in relation to mulberry, soil and wastewater metal concentrations

The present study was planned to evaluate Co(II) toxicity in silkworm population. The soil was irrigated using synthetic wastewater to determine the effects of pH and initial cobalt concentration in its bioaccumulation in silkworm ( Bombyx mori L.) food chain. The amount of cobalt in wastewater, soil, mulberry and silkworm was determined by atomic absorption spectrophotometer (AAS) analysis. The obtained results clearly indicate that silkworm can be used as template to indicate local cobalt pollution as its body length, body weight and mortality rate was found to be strongly related to cobalt concentration. Higher the cobalt amount in mulberry leaves more the toxicity to silkworm population. At 400 mg/L Co concentration and pH 4 there was maximum deposition of Co in the soil from the synthetic effluent. However, in plants and silk worm the accumulation of Co was maximum at pH 4.5 at an initial Co concentration of 400 mg/L in the synthetic effluent. The maximum cobalt found in wastewater, soil, mulberry and silkworm was 400 ± 0.01, 273.5 ± 0.04, 42.85 ± 0.01, 36.62 ± 0.22 mg/kg, respectively.

Separation and concentration of cobalt from aqueous thiocyanate solutions containing cobalt–nickel by emulsion liquid membranes using TBP as extractant

In this work, the zinc plant copper cake (CINKUR Co., Turkey) was leached with hydrochloric acid and main acidic leach solution containing Zn(II), Fe(II), Pb(II), Al(III), Cu(II), Co(II) and Ni(II) ions was obtained. Except for cadmium, cobalt and nickel, the other metals were precipitated by adding various reagents and adjusting the pH of the solution. Then, cadmium was separated by solvent extraction process. After these separation processes, ammonium thiocyanate and water were added to remaining leach solution. Thus, acidic thiocyanate leach solutions used in ELM process were obtained. ELM consists of kerosene as diluent, tributyl phosphate as extractant, sorbitan monooleate (SPAN 80) as surfactant, and 6 M ammonia solution as the stripping solution. Separation and concentration of cobalt by ELM from acidic thiocyanate leach solution containing cobalt and nickel was performed. The important parameters governing the extraction behavior of cobalt have been investigated. These parameters were mixing speed, surfactant concentration, extractant concentration, phase ratio, treatment ratio, stripping solution base concentration, initial cobalt concentration in feed solution, thiocyanate concentration in the feed solution, and the feed solution pH. The results obtained showed that by appropriate selection of the extraction and stability conditions, nearly all of the cobalt ions present in the feed solution were extracted within 10 min. The separation factors of cobalt with respect to nickel, based on initial feed concentration, have experimentally found to be of as high as 310 for non-equimolar Co–Ni feed solutions.

Removal of cobalt ions from aqueous solutions by polymer assisted ultrafiltration using experimental design approach. part 1: Optimization of complexation conditions

The polymer assisted ultrafiltration process combines the selectivity of the chelating agent with the filtration ability of the membrane acting in synergy. Such hybrid process (complexation–ultrafiltration) is influenced by several factors and therefore the application of experimental design for process optimization using a reduced number of experiments is of great importance. The present work deals with the investigation and optimization of cobalt ions removal from aqueous solutions by polymer enhanced ultrafiltration using experimental design and response surface methodological approach. Polyethyleneimine has been used as chelating agent for cobalt complexation and the ultrafiltration experiments were carried out in dead-end operating mode using a flat-sheet membrane made from regenerated cellulose. The aim of this part of experiments was to find optimal conditions for cobalt complexation, i.e. the influence of initial concentration of cobalt in feed solution, polymer/metal ratio and pH of feed solution, on the rejection efficiency and binding capacity of the polymer. In this respect, the central compositional design has been used for planning the experiments and for construction of second-order response surface models applicable for predictions. The analysis of variance has been employed for statistical validation of regression models. The optimum conditions for maximum rejection efficiency of 96.65% has been figured out experimentally by gradient method and was found to be as follows: [Co 2+] 0 = 65 mg/L, polymer/metal ratio = 5.88 and pH 6.84.

Activation of molecular oxygen and its use in stereoselective tetrahydrofuran-syntheses from δ,ε-unsaturated alcohols

Bishomoallylic alcohols (pent-4-en-1-ols) underwent efficient oxidative cyclizations, if treated with O(2) and bis{2,2,2-trifluoromethyl-1-[(1R,4S)-1,7,7-trimethyl-2-(oxo-kappaO)bicyclo[2.2.1]hept-3-yliden]ethanolato-kappaO}cobalt(ii) in solutions of 2-propanol at 60 degrees C. Ring closures occurred diastereoselectively and afforded 2,3-trans- (96% de), 2,4-cis- (approximately 60% de), and 2,5-trans-substituted (>99% de) (phenyl)tetrahydrofur-2-ylmethanols as major components. Formation of bicyclic compounds and a 2,3,4,5-substituted oxolane was feasible as exemplified by syntheses of oxabicyclo[4.3.0]nonylmethanols and a derivative of natural product magnosalicin in 61-72% (90-99% de). The effectiveness of tetrahydrofuran synthesis was critically dependent on (i) solvent, (ii) reaction temperature, (iii) initial cobalt concentration, (iv) chain length between hydroxyl and vinyl groups, and (v) substitution at reacting entities. A sequence is proposed for rationalizing observed selectivities.

Zinc and cobalt phytoextraction by different plant species

AbstractPlant species sorghum (Sorghum vulgar L.), clover (Trifolium pratense L.), panikum (Panicum antidotal), and canola (Brassica napus) were tested to determine their phytoremediation potential. After a period of about 90 days, plant samples (shoots and roots) and soil samples (before and after cultivation) were collected for zinc and cobalt analyses using atomic absorption spectrometry. The highest zinc uptake was observed in canola, while panikum grass showed a high zinc accumulation affinity compared to sorghum and clover. Calculation of the recovery percentage, based on the amount of zinc removed from the soil after cultivation, ranged between 12.8 and 36.3 percent of the total initial zinc. Canola shoots exhibited the highest cobalt uptake compared to the other plant species. Calculation of the recovery percentage based on cobalt removed from the soil after cultivation ranged between 10.1 and 40.7 percent of the total initial cobalt concentration. © 2007 Wiley Periodicals, Inc.*This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

Cobalt oxide/γ-alumina catalysts prepared by equilibrium deposition filtration: The influence of the initial cobalt concentration on the structure of the oxide phase and the activity for complete benzene oxidation

In the present work we studied the influence of the initial concentration of the impregnating solution used for mounting Co(II) species on the γ-alumina surface by equilibrium deposition filtration method (edf) on the physicochemical properties and the catalytic activity of the “cobalt oxide”/γ-alumina catalysts. The complete oxidation of benzene has been used as a model reaction. Two series of catalysts (edf-X-A and edf-X-B) of varying Co content (X: up to 21 wt.% Co) were prepared using the above-mentioned method and tested at various temperatures in the range 200–300 °C using a fixed-bed reactor. In the first series (A) various Co loadings were obtained by varying the initial Co(II) concentration of the impregnating solution. In the second series (B) the corresponding Co loadings were obtained by using the impregnating solution used for the preparation of the catalyst of A series with the maximum Co(II) content and varying the impregnation time. All catalysts were characterized using various techniques, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), X-ray powder analysis (XRD), nitrogen adsorption (BET) and temperature-programmed reduction (TPR). It was found that the initial Co(II) concentration of the impregnating solution used for depositing the corresponding species on the γ-alumina surface by edf influences the catalytic activity of the “cobalt oxide”/γ-alumina catalysts with respect to the complete oxidation of benzene. The increase of the initial Co(II) concentration of the impregnating solution brings about a change in the composition of the deposited phase formed in the impregnation step by decreasing the ratio “Co(II) surface inner-sphere complexes/surface Co(II) precipitates”. Upon calcination, the Co(II) surface inner-sphere complexes are transformed to well-dispersed “cobalt oxide” phase strongly interacting with the support surface while the surface Co(II) precipitates are transformed to Co 3O 4 crystallites loosely interacting with the support surface. The former phase is responsible for the relatively high dispersion of Co observed in the A series of catalysts but it is rather inactive, while the latter exhibits lower dispersion but higher activity. Thus, the edf catalysts prepared using high initial Co(II) concentration exhibited higher catalytic activity than the corresponding ones prepared using low initial Co(II) concentration.

Bioremediation of 60Co from simulated spent decontamination solutions

Bioremediation of 60Co from simulated spent decontamination solutions by utilizing different biomass of ( Neurospora crassa, Trichoderma viridae, Mucor recemosus, Rhizopus chinensis, Penicillium citrinum, Aspergillus niger and, Aspergillus flavus) fungi is reported. Various fungal species were screened to evaluate their potential for removing cobalt from very low concentrations (0.03–0.16 μM) in presence of a high background of iron (9.33 mM) and nickel (0.93 mM) complexed with EDTA (10.3 mM). The different fungal isolates employed in this study showed a pickup of cobalt in the range 8–500 ng/g of dry biomass. The [Fe]/[Co] and [Ni]/[Co] ratios in the solutions before and after exposure to the fungi were also determined. At micromolar level the cobalt pickup by many fungi especially the mutants of N. crassa is seen to be proportional to the initial cobalt concentration taken in the solution. However, R. chinensis exhibits a low but iron concentration dependent cobalt pickup. Prior saturating the fungi with excess of iron during their growth showed the presence of selective cobalt pickup sites. The existence of cobalt specific sorption sites is shown by a model experiment with R. chinensis wherein at a constant cobalt concentration (0.034 μM) and varying iron concentrations so as to yield [Fe/Co] initial ratios in solution of 10, 100, 1000 and 287 000 have all yielded a definite Co pickup capacity in the range 8–47 ng/g. The presence of Cr(III)EDTA (3 mM) in solution along with complexed Fe and Ni has not influenced the cobalt removal. The significant feature of this study is that even when cobalt is present in trace level (sub-micromolar) in a matrix of high concentration (millimolar levels) of iron, nickel and chromium, a situation typically encountered in spent decontamination solutions arising from stainless steel based primary systems of nuclear reactors, a number of fungi studied in this work showed a good sensitivity for cobalt pickup.

Behaviour of Co(II) in solutions obtained by dissolution of cobalto–cobaltic oxide in NH 3–SO 2–H 2O medium

In an earlier study [Hydrometallurgy 58 (2000) 193], detailed kinetic work on dissolution of Co 3O 4 in an ammoniacal system using SO 2 as the reductant was carried out. It was observed that under certain experimental conditions, Co(II) becomes unstable and precipitates as Co(NH 3) 4S 2O 6·2H 2O. With a view to study the precipitation behavior of Co in the Co 3O 4–NH 3–SO 2 system, the present systematic work was done. A 2 3 factorial design was used to study the effects of three leaching parameters, i.e., NH 3, SO 2 and temperature on the dissolution and the precipitation of Co(II). The conditions for maximum Co precipitation were then chosen to study the effect of various parameters such as time and temperature of storage and initial cobalt concentration on extent of precipitation. It was observed that an increase in storage time and initial cobalt concentration increased the precipitation of Co(II). With a decrease in storage temperature, an increase in Co(II) precipitation was observed. In order to minimize the Co precipitation, the effect of addition of ammonium sulphate was studied. The increase in ammonium sulphate concentration from nil to 280 g L −1 resulted in a decrease of cobalt precipitation from 58% to 5%.

Cobalt-extraction studies on dithiocarbamate grafted on silica gel surface

Extraction of cobalt(II) ion from aqueous solution was studied using silica gel grafted with dithiocarbamate ligand (Si–dtc), which was prepared by reacting silica gel with γ-aminopropyltriethoxysilane followed by alkaline carbon disulfide. 29Si MAS NMR, IR spectra were taken to establish the grafting of dithiocarbamate ligand on silica gel. This modified surface contains 0.37 mmol g −1 of the ligand sites available for the extraction of cobalt. The sorbent extracts cobalt only when the pH of the aqueous phase is above 7 and the extraction process does not follow ideal ion-exchange mechanism. The electronic absorption spectra of cobalt present in the sorbent phase suggested the oxidation of Co(II) to Co(III). Kinetic data were fitted to surface complexation model and the rate constant ( k s) for such model was found to vary from 1.5×10 −3 to 5.82×10 −3 l mg −1 min −1 depending on the initial concentration of cobalt. An estimate of enthalpy and entropy changes accompanying the extraction was obtained by temperature variation method. The increase in the overall entropy of the system seems to favour the extraction of cobalt by Si–dtc.