Alkaline earth separations on microcrystalline cellulose columns

Magnesium, calcium, strontium and barium may be separated quantitatively from each other on a column of micro-crystalline cellulose. Barium and radium are also separated from each other. The metal ions are eluted from the column by methanol-hydrochloric acid in varying proportions. The separated metal ions can be titrated with EDTA. Trace amounts of metal ions may be determined by neutron activation.     

Precipitation of barium chromate in the presence of strontium and lead by complexation followed by volatilization of ammonia

Cation-release is used to precipitate barium chromate from homogeneous solution in the presence of lead and strontium. MEDTA or DCTA is added to complex the metal ions at pH 10.3 (adjusted with ammonia). On heating, the ammonia slowly volatilizes and the consequent increases in acidity releases the metal ion bound in the least stable chelate (barium). Precipitation is about 99.3-99.7% complete at pH 6.7-6.8, with less than 0.1% co-precipitation of lead or strontium. Lower pH values can be attained by volatilizing acetic or hydrochloric acid into the solution in a closed system.     

Calculation of the kinetic parameters of dehydration of lithium peroxide monohydrate in nonisothermic regime by derivatographic method

The dehydration of lithium peroxide monohydrate was studied by derivatography under nonisothermic conditions for the calculation of main kinetic parameters in the temperature range 90–146°C. Experimental conditions (sample size and the linear heating rate) caused by thermoconductivity of the object under investigation were determined. It is shown that the process under study proceeds according to the kinetic law close to the first order one (n = 0.85±0.03). Values of the activation energy and the pre-exponential factor [E _a = 86.0±0.8 kJ mol^?1, k ₀ = (2.19±0.16)×10¹¹ min^?1] were obtained. A suggestion was formulated that the dehydration mechanism of lithium peroxide monohydrate was analogous to that of the hydrates of the alkaline earth metal (calcium, barium, and strontium) peroxides.     

Thermal Decomposition of Strontium and Barium Malonates

The thermal decomposition of strontium and barium malonates has been studied isothermally and non-isothermally employing simultaneous TG-DTG-DTA, DSC, XRD and IR spectroscopic techniques. DSC of these malonates has been recorded both in oxygen and nitrogen atmospheres. The decomposition is a single step process and the end product formed is carbonate. The energy of activation and frequency factor values for the decomposition of strontium malonate are 547 kJ mol⁻¹ and 10⁴¹ s⁻¹ respectively. The activation energy and frequency factor values for isothermal dehydration of barium malonate sester-hydrate are 57–111 kJ mol⁻¹ and 10⁷–10¹² s⁻¹ respectively and the corresponding values for decomposition from DSC are 499.5 kJ mol⁻¹ and 10⁴⁴ s⁻¹ respectively. The higher thermal stability of strontium malonate as compared to that of barium salt is ascribed to its being anhydrous so that decomposition proceeds without restructuring. Their thermal stabilities have also been compared with that of respective oxalate salts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thin-layer chromatographic separation of alkaline earth metals on microcrystalline cellulose

The thin-layer chromatographic behaviour of all the alkaline earth metals except for radium on microcrystalline cellulose in methanol-nitric acid media has been investigated. The R(f) values increase in the order beryllium > magnesium > calcium > strontium > barium. The five metals can be effectively separated from each other with methanol-14M nitric acid (3:1, v/v). The system is also suitable for the separation of mixtures of two metal ions existing in widely varying proportions.     

Separation and electrodeposition of226Ra

The chemical behavior of calcium, barium and radium in the ion exchange resins Dowex 50W-X8, AG 50W-X8 and Merk I in the presence of ammonium tartrate, EDTA, and citrate has been studied. No differences were observed in results while using any one of the three resins. Calcium, barium and radium were fixed to the exchange column at pH 4.8 EDTA solution. Calcium was eluted in an EDTA solution at pH 5.3, barium and radium between pH 8–11. Elution in citrate media for calcium was achieved at pH 6.1 and for radium at pH 10. In ammonium tartrate, calcium was eluted at pH 6, barium and radium at pH 11.5. Radium was also eluted from the ion exchange resins with a 2M nitric acid solution. The radium free of calcium was electrodeposited onto a stainless steel disc cathode using a 0.1 M potassium fluoride solution, pH 12–14, with a yield of >50%. The energies of²²⁶Ra were analyzed through high resolution -spectra. The²²⁶Ra utilized for these experiments was separated from Mexican carnotite.     

The thermal decomposition of alkaline earth formates

The thermal decomposition of alkaline earth formates has been studied. Experiments with single crystals, compacts and powders of strontium formate demonstrate that the method of sample presentation can affect the rate of decomposition.For anhydrous calcuim, strontium and barium formates, isothermal kinetic runs show that the decompositions follow the Erofeev law, In(l-α) = ktⁿ; the measured activation energies were 199.4, 228 and 270 kJ/mol respectively.     

Ion exchange of radium and barium in zeolites

The sorption of radium, barium and mixture of both elements has been studied in the zeolites 3A, 5A and Y. The ratio zeolite; solution was 100 mg: 10 cm³ and the pH was 3. Carrier-free radium was completely retained in all studied zeolites. When 0.0016 meq of barium/cm³ were added, the sorption of radium decreased in the zeolite 5A only and when 0.014 meq of barium/cm³, the radium sorption was reduced in all the studied zeolites. The sorption of barium was similar to that of radium. The amounts of sodium and calcium removed from the zeolites and the proton quantity fixed to them allowed us propose the ion exchange mechaniosm. The changes and ionic radii of the species exchanged did not play an important role. However, the location of the ions in the crystalline network of each zeolite is probably an important parameter for the exchange.     

SrFeO4: Synthesis,Fe(VI) characterization and the strontium super-iron battery

Cathodes comprised of Fe(VI) salts, and capable of three electron reduction, are useful for the formation of energetic super-iron batteries. This study presents a synthesis procedure for SrFeO₄ or strontium super-iron cathodic salts, and also introduces mixed salts containing barium and strontium cations, Sr_xBa_(1−x)FeO₄. The X-ray diffraction and first IR spectra of SrFeO₄ are presented, and compared to known spectra of K₂FeO₄ and BaFeO₄. The measured solubility of SrFeO₄ is low in concentrated KOH electrolytes (0.001 mM in 13.5 M KOH), of use for alkaline cathodic chemistry. AAA batteries were prepared and discharged with this new cathode, and exhibit high discharge energies, approaching, but lower than those previously observed for barium super-iron alkaline batteries. The discharge energy further approaches the barium cell when the mixed cathode salt is employed, particularly for x=0.25–0.5 in Sr_xBa_(1−x)FeO₄.     

Ion-selective characteristics of heavy metal myristate liquid membrane electrodes

Liquid membrane electrodes of myristate soaps of heavy metals, namely copper, cadmium, zinc, nickel, cobalt, strontium and barium in a benzene-n-butanol mixture were prepared. Each electrode showed nernstian response in common metal ion test solution. The range of concentration of the test solution for the Nernstian behaviour lies between 10^?4 and 10^?1M. With a dissimilar metal ion in test solution the metal soap liquid membrane electrode indicates deviations from Nernst's equation depending on the nature of the metal ion, suggesting different selectivities for different ions. The selectivity ratios are therefore calculated.     

Determination of calcium,strontium and barium in single crystals of alkali halides by neutron activation

The determination by neutron activation of trace quantities of calcium, strontium and barium in single crystals of alkali halides has been studied. The matrix is eliminated before the irradiation by an ion-exchange procedure. Gamma spectroscopy after radiochemical separation is used to determine strontium and barium. Calcium is determined by measuring the β-activity of ⁴⁹Sc formed by the decay of ⁴⁹Ca. Long-lived radioactive tracers are used to determine the chemical yields.     

Sorption of alkaline and alkaline-earth radionuclides on zirconium phosphate sorbent Termoxid-3A from aqueous solutions

Sorption kinetic behavior of¹³⁷Cs,⁸⁵Sr,¹³³Ba and²²³Ra has been studied in the system: inorganic sorbent on the base of zirconium phosphate, Temoxid-3A, and diluted aqeous solutions. Chemosorption mechanism with the limiting step of external diffusion of the reaction between radiostrontium and the sorbent was established (n=1.304±0.0). For barium, radium and cesium radionuclides this mechanism was found to have an ion-exchange character (n<1), with limiting step of external diffusion for barium and radium radionuclides and internal diffusion for radiocesium. Termoxid-3A possesses good sorption kinetic properties. Values of the equilibrium distribution coefficients of the radionuclides studied in the suggested conditions were n·10³. Time for attaining equilibrium does not exeed 40 minutes. Purification coefficient of Moscow potable water from radiostrontium was equal to 100 when 1000 column volumes passed through. Immobilized with strontium sorbent (1.5 mg equiv. of Sr/g sorbent) keeps all its good sorption kinetic characteristics towards radionuclides studied but the mechanism of radiostrontium interaction with the sorbent changes its character from chemosorption to ion exchange (n=0.75).     

Separation des alcalino-terreux par l'edta sur resine echangeuse d'ions

The quantitative separation of a few mg of strontium and barium from several g of calcium is described. The alkaline earth carbonates are dissolved in 0.1 M EDTA, fixed at pH 4.8 on an ammoniacal Dowex column, and eluted, also with 0.1 M EDTA, calcium at pH 5.25, strontium at pH 6.0, barium at pH 9.0. The end of the calcium elution can be followed accurately by a sudden pH increase in the eluate(from 4.8 upto 5.25).     

Some aspects of the high-temperature behavior of bismuth,strontium and barium on silicon surfaces studied by total reflection X-ray fluorescence spectrometry

Thin films of novel dielectric and ferroelectric materials, such as barium strontium titanate (BST) and strontium bismuth tantalate (SBT), which are scheduled for short-term implementation into standard microelectronic device technology, contain elements like Bi, Sr and Ba which may involve risks with regard to device yield and reliability. Therefore, the high-temperature behavior of bismuth, strontium and barium impurities on Si (100) substrates was studied. Intentionally contaminated Si substrates were annealed at 1000°C under different ambient (inert, oxidizing) by rapid thermal annealing (RTA) or in a furnace and analyzed by total reflection X-ray fluorescence spectrometry (TXRF), vapor phase decomposition/TXRF (VPD/TXRF) and electrolytic metal tracer (Elymat) technique. Ba and Sr are incorporated in the existing or growing oxide during rapid thermal annealing (RTA). Cross-contamination due to gas phase transport may occur in the case of Bi, in particular under N₂ atmosphere, but is of no concern in the case of Ba and Sr. All three contaminants do not exert an influence on the minority carrier lifetime on their own. The results illustrate that TXRF and VPD/TXRF are appropriate techniques for such studies.     

Approximation of the temperature integral in the evaluation of thermoanalytical measurements

Values of the temperature integral (i) of the Arrhenius equation have been calculated. An approximately linear relationship has been established between log i and the activation energy and between log i and the reciprocal temperature. The approximate expressions are given and the accuracy of the results obtained using these expressions is compared with the accuracies achievable using other approximations in a selected activation energy and temperature range. The applicability of various approximations is briefly discussed.     

Energy of activation for the decomposition of the alkaline-earth carbonates from thermogravimetric data

Activation energies for the vacuum thermal decomposition of calcium, strontium and barium carbonates have been determined from thermogravimetric data, using the Coats and Redfern equation. A computer program, written in 4100 Algol, was used to process the data and to obtain the order (n) of the decomposition reactions. In all three cases, a value ofn=2/3 was in closest agreement with the experimental results, suggesting that decomposition occurs at a progressively shrinking spherical interface. The energies of activation obtained were in close agreement with the corresponding values of the enthalpy of decomposition, calculated at the temperature at which half of the sample had decomposed.     

Precipitation of barium chromate from homogeneous solution using complexation and replacement A separation of barium from relatively large amounts of strontium and lead

A new procedure is presented that efficiently separates barium from relatively large amounts of strontium and lead. The barium is precipitated as the chromate from a solution in which the multivalent cations are complexed with EDTA. The barium ions are homogeneously released in solution when magnesium ions are slowly introduced into the solution. The magnesium ions gradually replace the barium ions from their EDTA complexes, bringing about a precipitation of barium chromate from homogeneous solution.

This slow formation of barium chromate crystals holds co-precipitation to a minimum and produces crystals that are easily filtered and washed. More than 99.7% of the barium can be precipitated as the chromate, with less than 0.6% of the strontium, when the two ions are in equal molar concentration.     

Co-precipitation in some binary sulphate systems

Studies have been made of the distribution behaviour of tracers with alkaline earth sulphates, using the technique of precipitation from homogeneous solution. The co-precipitation of strontium with barium sulphate and of lead, lanthanum, and yttrium, separately, with barium sulphate, and with strontium sulphate, were investigated. Although there was qualitative correlation between the observed values of the distribution coefficient and the theoretical solubility product ratios for each of the binary systems studied, the divergence between theory and observation was so great that it seems unlikely that there is any quantitative correlation.     

Generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their synthetic applications

Organomagnesium compounds, represented by the Grignard reagents, are one of the most classical yet versatile carbanion species which have widely been utilized in synthetic chemistry. These reagents are typically prepared via oxidative addition of organic halides to magnesium metals, via halogen–magnesium exchange between halo(hetero)arenes and organomagnesium reagents or via deprotonative magnesiation of prefunctionalized (hetero)arenes. On the other hand, recent studies have demonstrated that the organo-alkaline earth metal complexes including those based on heavier alkaline earth metals such as calcium, strontium and barium could be generated from readily available non-polar unsaturated molecules such as alkenes, alkynes, 1,3-enynes and arenes through unique metallation processes. Nonetheless, the resulting organo-alkaline earth metal complexes could be further functionalized with a variety of electrophiles in various reaction modes. In particular, organocalcium, strontium and barium species have shown unprecedented reactivity in the downstream functionalization, which could not be observed in the reactivity of organomagnesium complexes. This perspective will focus on the newly emerging protocols for the generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their applications in chemical synthesis and catalysis.

In this perspective, we highlight the recent development of metallation protocols of non-polar unsaturated molecules for the generation of organo-alkaline earth metal compounds and their applications in chemical synthesis and catalysis.     

Use of 2, 3, 4-trihydroxyacetophenone in the spectrophotometric determination of calcium

A critical examination of the calcium-2,3,4-trihydroxyacetophenone system in an aqueous medium is presented. This system showed a broad absorbance maximum at 540 nm (?₅₄₀ = 3.55 × 10³ liters/mole-cm). The spectrophotometric determination of calcium can be effected at pH 11.2 to 12.0 in the optimum calcium concentration range of 2.5 to 9 ppm if the concentration of 2,3,4-trihydroxyacetophenone corresponds to 4 ml of 8 × 10^?3M reagent in a final volume of 25 ml. Absorbance measurements must be made within the interval of 15 to 60 min. Beer's law is followed at 540 nm for 0.5 to 10 ppm of calcium (1-cm cell). Among the ions commonly occurring with calcium, the following were found to cause an error of +2% at a calcium concentration of 5 ppm: vanadate, chromate, manganese (II), uranyl (10 ppm) and molybdate and zirconate (60 ppm); an appreciable error from strontium, barium, and iron (III) (even at 1 ppm) and an error from magnesium due to partial co-precipitation of calcium with magnesium hydroxide.