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.     

The kinetics of the crystallization of barium chromate in presence of polyphosphate and phosphonates

Summary The inhibiting effect of polyphosphate and phosphonates on the crystallization of barium chromate for both seeded and unseeded systems has been investigated using the changes in ionic conductivity of the lattice ions in supersaturated solutions containing stoichiometric concentrations of barium and chromate at 298 K. The inhibitors studied are sodium tripolyphosphate (STP), ethylenediaminetetramethylenephosphonic acid (ENTMP), and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). The effect of these inhibitors on the growth of crystals has been studied at several inhibitor concentrations. The influence of these additives on barium chromate crystallization could be interpreted in terms of aLangmuir type adsorption isotherm. The crystallization retarding effect due to inhibitors is in the orderHEDP>STP>ENTMP. The inhibitors studied can be used as effective compounds for scale formation control.Deceased     

Precipitation separation of lead and calcium,strontium, barium from acidic solutions using crown ether and tungstosilicic acid

It was found that lead reacts with 18-crown-6 (L) and tungstosilicic acid (H₄A) in acidic solutions and a compound with low solubility is formed what was confirmed by radiometric titration methods. Coprecipitation of complexion cation of PbL²⁺ with similar complexion cations of calcium, strontium and barium was studied. Formation of low soluble salts was utilized for separation of Pb from Ca, Sr and Ba from 1 mol·dm^–3 HNO₃. The ratio of Pb/Ca, Pb/Sr and Pb/Ba in the precipitation or separation factors S_pb/M undoubted depends on the ratio of the stability constants of lead and metals with 18C6 (_Pb/_M), what can be used for determination of more precise constant stability _M.     

Kinetics of the crystallization of barium chromate

Summary The kinetics of the crystallization of barium chromate have been studied conductometrically at 298 K for both spontaneous and seeded growth systems. The rate of growth follows a quadratic dependence upon the relative supersaturation which suggests a surface-controlled growth mechanism. This rate equation holds fairly well for the various supersaturation and solid/solution ratios used. The presence of seeds in the solution appears to accelerate the growth rate. Analysis of the calculated induction times in unseeded systems corroborates the surface-controlled growth mechanism. The effect of some additives on the kinetics of growth has also been studied. The retarding effect of these inhibitors is interpreted in terms of adsorption of inhibitor ions at the active crystal growth sites.Dedicated to the memory of ProfessorE. N. Rizkalla who passed away on November 29, 1993     

Oxidation of tantalum metal by lead chromate

Differential thermal analysis and gravimetry techniques have been used in the investigation of the tantalum/lead chromate pyrotechnic composition for a range of fuel/oxidant mixtures. Studies include investigation of tantalum and lead chromate individually as well as co-precipitated mixtures, when heated up to approximately 900°C in air and in nitrogen. The kinetics of oxidation of metallic fuels by metal oxides is one of the most important parameters in determining the utility of any metal oxide system in pyrotechnic applications. Infrared spectroscopy has been utilised in an attempt to characterise the reaction products in air and in nitrogen atmosphere.     

Solvent extraction of strontium and barium into nitrobenzene by using hydrogen dicarbollylcobaltate in the presence of dicyclohexano-24-crown-8

Extraction of microamounts of strontium and barium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B^?) in the presence of dicyclohexano-24-crown-8 (DCH24C8, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺, $ {\text{HL}}_{2}^{ + }, $ ML²⁺ and $ {\text{ML}}_{ 2}^{2 + } $ (M²⁺ = Sr²⁺, Ba²⁺) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined. It was found that in water–saturated nitrobenzene, the stability constants of the complexes BaL²⁺ and $ {\text{BaL}}_{ 2}{^{2 + }}, $ where L = DCH24C8, are somewhat higher than those of the corresponding species SrL²⁺ and $ {\text{SrL}}_{ 2}{^{2 + }} $ with the same ligand L.     

Monohydrates of strontium and barium hydroxide

The monohydrates of strontium and barium hydroxide have been prepared by decomposition, under vacuum, of the corresponding octahydrates. X-ray powder data for both compounds are reported, together with that for anhydrous strontium hydroxide; the latter is included in order to clarify an apparent anomaly in the literature.

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Zusammenfassung Es wurden die Monohydrate von Strontium und Bariumhydroxid im Vakuum aus den entsprechenden Octahydraten hergestellt. Röntgenographische Daten für beide Verbindungen sowie für wasserfreies Strontiumhydroxid wurden gegeben; für Letzteres, um gewisse Anom alien in der Literatur zu klären.

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Résumé Préparation des hydroxydes de strontium et de baryum monohydratés par décomposition dans le vide des octohydrates correspondants. Etude par rayons X de ces composés ainsi que de l'hydroxyde de strontium anhydre, dans le but, pour ce dernier, d'élucider certaines anomalies de la littérature.

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The authors wish to thank Mr. A. Miller for taking the X-ray powder photographs.     

Radiochemical microdetermination of Manganese, strontium and barium by ion-exchange

A rapid radiochemical ion-exchange method has been developed for the quantitative separation of microamounts of Mn, Sr and Ba in the presence of other elements with atomic numbers below 84. The method proposed, combined with neutron-activation analysis, has been successfully applied to the simultaneous determination of Mn, Sr and Ba in plant and animal tissues. The method is simple and accurate.     

Oxidative degradation of ethers promoted by strontium and barium tetraphenylimidodiphosphinates

The novel M[(OPPh2)2N]2.nTHF (M = Sr (2), Ba (3)) complexes were prepared and characterized. Upon exposure to atmospheric oxygen, 2 and 3 were transformed to the dinuclear species Sr2-[(OPPh2)2N]4.2C3H6O3 (4) and Ba(2)[(OPPh2)2N]4.2C4H8O3 (5), respectively. Compounds 4 and 5 contain coordinated carboxylic acids obtained from the oxidative degradation of DME and THF, respectively, which were used as solvents for crystallization.     

Characterization of strontium and barium manganates by abrasive stripping voltammetry

Abrasive stripping voltammetry is applied in order to characterize barium and strontium manganates-(V) and -(VI) in solid state phases. Voltammetric reduction peak potential values of KBaMnO₄, Ba₃(MnO₄)₂, Ba₃(MnO₄)_{2− x} (BO₃) _x (x=0.031(1)), Ba₅(MnO₄)₃OH, Ba₅(MnO₄)₃Cl, Sr₅(MnO₄)₃OH and BaMnO₄ are shown to be proportional to the corresponding average Mn-O distances, which were determined from X-ray powder diffractometric data through Rietveld refinement analyses. Received: 25 November 1997 / Accepted: 28 January 1998     

Stepwise precipitation of barium sulphate,chromate and vanadate by cation release

Sulphate is precipitated at pH4.5–5.0 by adding Ba-EDTA complex. Chromate and vanadate are sequentially precipitated from the filtrate at pH 6–7 and 9, respectively, by adding magnesium to displace barium from its EDTA complex. The analyses are completed gravimetrically.     

Determination of barium and strontium in sea water

A process based on ion-exchange concentration and separation followed by flame photometry has been developed for the determination of strontium and barium at natural levels in sea water. These elements are stripped from 1-I samples of sea water by means of a cation-exchange resin in the calcium form and selectively eluted with CyDTA and EDTA respectively. Factors influencing the intensity of strontium and barium in hydrogen flames have been studied. The standard deviations of the method are 0.05 p.p.m. for strontium and 0.6 p.p.b. for barium and the accuracy of the method is more than sufficient to demonstrate clearly the variability of Sr/Cl and Ba/Cl ratios with depth and location     

The photolysis of barium and strontium azides

The effect of very high intensity UV light on powdered barium and strontium azides in vacuo in the temperature ranges −70° to 100°, and −80° to 90°, has been studied. The photolytic decompositions were characterized by a high percentage decomposition and sigmoid pressure vs time plots similar to those obtained by thermal decomposition. Kinetic analysis, the determination of activation energies, studies of the dependence of reaction rates on light intensity, and the effect of water vapour, were carried out. Mechanisms for decomposition over well defined temperature ranges are proposed.     

Extraction of microamounts of calcium,strontium and barium into nitrobenzene by using hydrogen dicarbollylcobaltate in the presence of dibenzo-18-crown-6

Extraction of microamounts of calcium, strontium and barium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B⁻) in the presence of dibenzo-18-crown-6 (DB18C6, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺, ML²⁺, ML₂²⁺ and MHL₂³⁺ (M²⁺ = Ca²⁺, Sr²⁺, Ba²⁺) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.     

Extraction of lead from water into nitrobenzene by using strontium dicarbollylcobaltate in the presence of benzo-15-crown-5

Summary From extraction experiments andg-activity measurements, the extraction constant corresponding to the equilibrium Pb²⁺(aq)+SrL(nb)?PbL(nb)+Sr²⁺(aq)taking place in the two-phase water-nitrobenzene system (L = benzo-15-crown-5; aq = aqueous phase, nb = nitrobenzene phase) was evaluated aslog K_ex(Pb²⁺,SrL)=0.1±0.1. Further, the stability constant of the benzo-15-crown-5-lead complex in nitrobenzene saturated with water was calculated for a temperature of25 °C:log b_nb(PbL)=13.2±0.1.     

EXAFS investigations of strontium complexation by a polymer-supported crown ether

Extended X-ray absorption fine-structure (EXAFS) measurements have been used to probe the coordination environment of strontium ion sorbed from aqueous nitric acid solutions on an extraction chromatographic resin comprising a macrocyclic polyether dispersed on a polymeric support. The strontium EXAFS of the metal ions sorbed onto the resin are consistent with a 1:1:2 strontium:crown ether:nitrate stoichiometry in which the strontium is enveloped in the crown ether ring and both nitrate anions are coordinated to the strontium as bidentate ligands. This is the same structure and stoichiometry observed for complexes in liquid-liquid extraction when the macrocyclic polyether is dissolved in a diluent with low water miscibility like 1-octanol.     

Raman spectroscopic studies of temperature dependent anomalies of strontium,barium, lead,and calcium nitrate

Raman studies of normal and ¹⁸O-substituted Sr(NO₃)₂ have been performed over a range of temperatures (77 to 580°K) to investigate the anomalous component previously observed in the symmetric stretching region. The results suggest that the peak may have a hot band origin. Impurity ions, N ¹⁸O ¹⁶O^?₂ and vibrationally excited 1NO^?₃ ions, give rise to local modes (deep-well impurity centers) in the ν₁ and ν₄ (N ¹⁸O ¹⁶O^?₂ only) regions but delocalized modes (shallow-well impurity centers) in the other internal and external mode regions. The host lattice was able to tolerate a large fraction of this type of impurity without interference with the dynamical coupling. Anomalous properties previously reported appear to be due to freezing out of the hot band. A less complete study of Ca(NO₃)₂, Ba(NO₃)₂ at room temperature and at temperature near 500°K suggests behavior similar to Sr(NO₃)₂.     

Spectrographic determination of barium and strontium in geological samples

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Polarographic determination of Tergitol 08