Authors:I. García-Sosa, M. Solache-Ríos, and D. Hernández-Zarate
The sorption behavior of cobalt by zeolite ZSM-5 was studied. Parameters such as temperature, hydration of the zeolite (before the sorption), as well as the presence and absence of ethylenediamine during the ion exchange at room temperature and 80 °C were considered. The highest retention of cobalt was found when the sorption experiments were done at 80 °C in the presence of ethylenediamine.
The60Co hot atom reactions were studied in tris/acetylacetonato/cobalt/III/ adsorbed on silica-gel surface.57Fe Mössbauer spectra of tris/acetylacetonato/iron/III/ in the corresponding system were also measured in order to examine the state of dispersion of complex molecules on silica-gel. The retention formation processes were discussed in terms of the dependence of60Co retention on the adsorbed amount /concentration/ of cobalt/III/ complexes.
The determination of cobalt in nickel with neutron activation analysis (NAA) is hindered by an interfering nuclear reaction
induced by fast neutrons. To overcome this obstacle cold neutron beam irradiation has been carried out. As a result, a cobalt
concentration of 0.25±0.02 µg/g in nickel foil has been determined. This nickel foil is intended to become a reference material
for neutron dosimetry.
The present investigation has been revealed that homogeneous silver-tungsten (Ag–W) composite powders doped with cobalt as
sinter aid can be produced by the two-stage reduction of co-precipitated tungstate. The sintering of the powders has been
studied using dilatometry and the results showed that the critical level for activated sintering is of the order of 0.3 mass
percent cobalt with respect to the tungsten content of the compact powder. This critical level is equivalent to approximately
six to seven atomic layer coverage of the tungsten particles by cobalt. The levels of cobalt addition above the critical amount
leads to the formation of cobalt tungsten (CoW3) intermetallic compound precipitates, which become trapped within the silver phase in the sintered composite material. Microstructural
evaluation of sintered specimens has been carried out using optical and electron microscopy. Transmission electron microscopy
results revealed the neck formation between adjacent tungsten particles along with the presence of silver around the tungsten
particles. Energy dispersive X-ray (EDX) analysis also confirmed that amounts of cobalt was 0.3 mass percent, in the region
containing the silver at the tungsten particle interface which agreed with the level of activated sintering.
Authors:Santosh R. Kote, Manoj R. Bhandarkar, and Nitin L. Chutke
Imidacloprid is a member of chloronicotinyl neonicotinoid compounds. It is the most important systemic insecticide and has a wide diversity of uses: in agriculture, on turfs, on pets, and for household pests. During the last decade, Forensic Science Laboratories of Maharashtra State, India, detected a large number of human poisoning cases with imidacloprid. Since a large number of biological samples were received for toxicological analysis, thin-layer chromatography (TLC) was the method of choice. This study reports that cobalt thiocyanate was found to be a selective and sensitive spray reagent for imidacloprid in routine analysis by TLC. Imidacloprid reacts with cobalt thiocyanate which gives intense blue-colored compound. The cobalt thiocyanate reagent does not react with the organochlorine insecticides, organophosphorus insecticides, and pyrethroids. Visceral constituents (amino acids, peptides, proteins, etc.) do not interfere.
Authors:B. Randhawa, K. Prabhjinder, and Sweety Kamaljeet
Thermal decomposition of cobalt hexa(formato)ferrate(III) decahydrate, Co3[Fe(HCOO)6]2. 10H2O, has been studied up to 973 K in static air atmosphere, employing TG, DTG, DSC, XRD, ESR, Mössbauer and infrared spectroscopic techniques. Dehydration occurs in two stages in the temperature range of 340–430 K. Immediately after the removal of the last water molecule the anhydrous complex undergoes decomposition till -Fe2O3 and cobalt carbonate are formed at 588 K. In the final stage of remixing of cations, a solid state reaction between -Fe2O3 and cobalt carbonate leads to the formation of CoFe2O4 at a temperature (953 K) much lower than for the ceramic method. A saturation magnetization value of 2310 Gauss of ferrite (CoFe2O4) shows its potential to function at high frequencies.
A simple and sensitive spectrophotometric method for the determination of cobalt, nickel and copper with desferrioxamine-B (desferal) is described. The sensitivity of the colour reactions of cobalt, nickel and copper is increased by introducing desferal. The pH range for the formation of Co II, Ni II or Cu II-desferal. Chelates is 4.5–8.5, 5.5–9, and 6.5–9.5, respectively. The molar absorptivities of the chelates are 1.2·105, 5.6·104 and 4.8·104 at 545 nm, 390 nm and 680 nm, respectively. Beer's law is obeyed up to 10 g/ml of metal ion. The effect of desferal concentration, pH, standing time and interfering ions are discussed. The method was applied to the determination of trace amounts of cobalt, nickel and copper in steel and simulated radioactive wastes.
Selective separation of Co(II) from aqueous acidic solutions containing thiocyanate ions has been achieved by using 2-benzylpyridine (BPy) dissolved in benzene. Optimum conditions of extraction by 0.1M BPy are: 0.05M (HCl, HNO3) or 0.01M H2SO4+1 M KSCN. Ascorbate and sulfate ions do not affect the extraction of cobalt(II), whereas acetate, citrate and oxalate ions lower the extraction. Separation of cobalt(II) from Mn, Cr, Hf, Fe, Y, Ce, Cd, Sr, Cs and several rare earth elements can be achieved in a single extraction. Slope analysis by log-log plot reveals that neutral cobalt-thiocyanate species is extracted with the probable formula of the extracted complex as Co(BPY)3 (SCN)2.
The sorption of cobalt from aqueous solutions was studied for two Mexican clinoptilolite rich tuffs zeolitic rocks and kaolinite
clay. The effects of pH and contact time on the sorption were examined. Cobalt was determined by neutron activation analysis
of the exchanged aluminosilicates. The sorption of cobalt by the aluminosilicates was similar in the pH range from 4 to 7.
Kinetic studies showed a rapid sorption in the first 5 hours and equilibrium in about 24 hours. Sorption kinetics was best
described by the second-order Ritchie modified model. The experimental results obtained at different concentrations and room
temperature for both zeolites were fitted to Freundlich, Langmuir and Freundlich-Langmuir isotherms. The sorption pattern
was found to follow the Freundlich model.
A rapid, non-destructive method is presented for the determination molybdenum and cobalt in hydrodesulfurization catalysts
employing a PDP-11/05 computer-base radioisotope x-ray fluorescence technique. Precision for molybdenum and cobalt better
than 2.5% and 4.0%, respectively, are achieved in 100 sec of fluorescent time. The values obtained by this method are in agreement
with values from atomic absorption and neutron activation methods. Besides being nondestructive, only about 50 mg of sample
is needed, and no time-consuming acid dissolution is required as in atomic absorption and colorimetric methods. The results
for six different commercial catalysts are compared with determinations by atomic absorption, neutron activation analysis
methods as well as an x-ray fluorescence system with manual calculations of the percentage of molybdenum and cobalt.