Simultaneous Preconcentration and Separation of Chromium(III) and Chromium(VI) at the Low-Temperature Directed Crystallization of Natural Water

It was shown that low-temperature directed crystallization of natural water can be used for separating chromium(III) and chromium(VI). At a moderate crystallization rate (6–10 mm/h), the final part of the ingot (concentrate) is a suspension containing chromium(III) and chromium(VI) in the solid and liquid phases, respectively. It is proposed to separately determine these chromium species by atomic absorption spectrometry after separating the phases by centrifugation and dissolving the precipitate in acids.     

Zone melting as an aid to impurity determination by thermal analysis

The determination of the impurity content of a sample by means of the meltingcurve method (calorimetric analysis) is often seriously hampered when solid soluble contaminants are present. Solid solutions often occur in substances purified by crystallization or extraction. A simple test on mixed crystals is described. When three or more impurities are present the relations obtainable from a melting curve are insufficiently accurate for computing the unknown concentrations and distribution coefficients to an acceptable extent. Only melting curves obtained from samples containing one or two impurities permit an exact, simple interpretation. A complex of impurities may be analysed when the sample is subjected to zone melting and a set of melting curves is obtained for parts of the ingot.     

A Study of Calcium Nitrate Purification

Two methods of calcium nitrate purification were studied: crystallization from aqueous solutions and joint precipitation of impurities from aqueous solutions onto inorganic collectors (calcium hydroxide or carbonate and hydrated aluminum or zirconium oxides). The efficiency of purification of calcium nitrate solutions was studied and the purification coefficients were calculated for hydrated aluminum or zirconium oxides as collectors.     

Isolation of Rare Earth Element's Radionuclides from Phosphoric Acid Solutions on Cerium (III) Phosphate

Abstract

The isolation of the lanthanide phosphates by crystallization from the solutions of phosphoric acid with the concentration of 2–5 mol·dm^?3, produced during destruction of the apatite, was investigated. The kinetic parameters of crystallization of the lanthanide phosphates and the values of their solubility in phosphoric acid with various impurities under temperatures between 60–90°C have been obtained from the data on distribution of Ce¹⁴⁴ and Eu^152–154 radio- nuclides between the solution and the solid phase. The wide region of supersaturated solution metastability has been determined. The possibility to remove supersaturation in the metastable region by introduction of the cerium (III) phosphate seeds has been proved. Separation of the lanthan-ides from calcium and other accompanying elements in the apatites by crystallization of the phosphates on the CePO₄ ·0.5H₂O seed in the region of small supersaturation of strongly acid solutions has been studied. Calcium phosphate demonstrates the “salting out” effect on the lanthanide phosphates. By thermodynamic computations the ionic compositions of the produced solutions from breaking down the apatite and the solubilities of the lanthanide phosphates were obtained, which agrees with the experimental data. The distribution coefficients for the solid phase and the liquid phase are 1.1.10⁴ for cerium and 4–10³ for europeum. The lanthanides/calcium separation coefficient is 1.3·10³.     

Application of polyamorphism in water to spontaneous crystallization of emulsified LiCl-H2O solution

Aqueous solutions are widely explained by the hydration or the bound waterfree water notion. Amorphous polymorphism (polyamorphism) in pure water, which is presently under vigorous discussion, may provide a different view over the solutions. Here, I changed pressure, P, temperature, T, and concentration, C, of emulsified LiCl-H2O solutions and studied their freezing by detecting its heat evolution. It was experimentally indicated that the homogeneous nucleation of low-density crystalline ice I (phase Ih or Ic), in pure water and in solutions, connects to the polyamorphic transition of high-density amorphous ice (HDA) to low-density amorphous ice (LDA). Thus, the polyamorphism of water relates to the phase behavior of aqueous solution. In accordance with the recent simulation result, the nucleation was thought to occur in two stages: the appearance of the LDA-like state and the crystallization. Usefulness of the polyamorphic point of view about the solutions was seen.     

Determination of bivalent cationic impurities in sodium chloride by atomic absorption, and their distribution in the recrystallized salt

Bivalent cationic impurities present in NaCl crystals were determined quantitatively by atomic absorption, 1.71M NaCl solutions (10% w v ) being used without pretreatment. The sensitivity for several cations was 50-60% of that in pure water solutions. The analyses revealed a non-homogeneous distribution of the impurities, due to differences in their activity during the process of crystallization.     

Mechanical Properties of Polymeric Emboli for Occlusion of Blood Vessels

Investigations of the formation of solid emboli in an aqueous medium of biocompatible solutions of polymers were carried out. Approaches to the production of solid samples for tensile and compression tests were developed and their mechanical properties were studied. It is shown that the ultimate compressive and tensile strength of emboli formed in an aqueous medium slightly decreases with increasing time of aging in water and increases markedly with increasing polymer concentration in the embolizing solution. All the tested compounds exhibit strength sufficient to not be destroyed by the action of blood flow.     

Trends in the behavior of dissolved organic substances under the conditions of freeze extraction

Influence of the extractant and pH on the efficiency of the preconcentration of organic compounds dissolved in water is studied in freeze extraction. The revealed trends are discussed in terms of the proposed theoretical model; some new experimental proofs to it are presented. The advantages of the method proposed over liquid extraction (concentration factor) and directed low-temperature crystallization (selectivity) are demonstrated.     

Hydration of nonelectrolytes in binary aqueous solutions

Literature data on the thermodynamic properties of binary aqueous solutions of nonelectrolytes that show negative deviations from Raoult’s law due largely to the contribution of the hydration of the solute are briefly surveyed. Attention is focused on simulating the thermodynamic properties of solutions using equations of the cluster model. It is shown that the model is based on the assumption that there exists a distribution of stoichiometric hydrates over hydration numbers. In terms of the theory of ideal associated solutions, the equations for activity coefficients, osmotic coefficients, vapor pressure, and excess thermodynamic functions (volume, Gibbs energy, enthalpy, entropy) are obtained in analytical form. Basic parameters in the equations are the hydration numbers of the nonelectrolyte (the mathematical expectation of the distribution of hydrates) and the dispersions of the distribution. It is concluded that the model equations adequately describe the thermodynamic properties of a wide range of nonelectrolytes partly or completely soluble in water.     

Dynamic light scattering study of cetyltrimethylammonium bromide aqueous solutions

Cetyltrimethylammonium bromide (CTAB) aqueous solutions are studied by dynamic light scattering method in a wide concentration range covering the first and second critical micelle concentrations (CMC₁ and CMC₂, respectively). Nonmonotonic and ambiguous behavior of diffusion coefficients D with an increase in concentrations above CMC1 is revealed. An increase in the D values in the first decade of CTAB concentration above CMC1 agrees with known published data for aqueous solutions of ionic surfactants. It is shown that an increase in the ionic strength of solution with the addition of KBr leads to a decrease in the positive slope of the dependence of diffusion coefficients on CTAB concentration up to zero at 0.05 M KBr. Two relaxation processes corresponding to large and small D values are simultaneously observed in micellar solutions, beginning with 0.03 M CTAB concentration. The data obtained are compared with published data, as well as with the results of viscosity measurements. The performed analysis indicates that the observed relaxation processes are explained by the coexistence of spherical and nonspherical micelles. It is established that micelles acquire a cylindrical shape at CTAB concentrations ranging from 0.2 to 0.25 M. Hydrodynamic radii and lengths of micelles are calculated.     

Crystallization kinetics of calcium carbonate at a stoichiometric ratio of components

The formal kinetics of calcium carbonate crystallization in aqueous solutions is studied at a stoichiometric ratio of Ca²⁺ and CO₃^2- ions. The kinetics of the process was monitored by convenient and reliable methods (complexometric analysis for calcium in an aqueous solution and energy dispersive and microscopic measurement of solid particle sizes). The effect the temperature and degree of supersaturation have on the periods of induction and mass crystallization and the equilibrium concentration of calcium ions in solution is estimated at continuously controlled pH and solution ionic strength. The kinetic parameters (n, k, τ_1/2, E_a) of calcium carbonate crystallization are calculated. It is shown that calcium carbonate with a calcite structure formed at a stoichiometric ratio of reagents, and changes in the temperature (25–45°C) and the solution’s degree of supersaturation (2–6) within the considered range had no effect on the characteristics of the solid phase.     

Thermodynamic studies of aqueous and CCl4 solutions of 15-crown-5 at 298.15 K: an application of McMillan-Mayer and Kirkwood-Buff theories of solutions

The density and osmotic coefficient data for solutions of 15-crown-5 (15C5) in water and in CCl4 solvent systems at 298.15 K have been reported using techniques of densitometry and vapor pressure osmometry in the concentration range of 0.01-2 mol kg-1. The data are used to obtain apparent molar and partial molar volumes, activity coefficients of the components as a function of 15C5 concentration. Using the literature heat of dilution data for aqueous system, it has become possible to calculate entropy of mixing (DeltaS(mix)), excess entropy of solution (DeltaS(E)), and partial molar entropies of the components at different concentrations. The results of all these are compared to those obtained for aqueous 18-crown-6 solutions reported earlier. It has been observed that the partial molar volume of 15C5 goes through a minimum and that of water goes through a maximum at approximately 1.2 mol kg(-1) in aqueous solutions whereas the opposite is true in CCl4 medium but at approximately 0.5 mol kg(-1). The osmotic and activity coefficients of 15C5 and excess free energy change for solution exhibit distinct differences in the two solvent systems studied. These results have been explained in terms of hydrophobic hydration and interactions in aqueous solution while weak solvophobic association of 15C5 molecules in CCl4 solutions is proposed. The data are further subjected to analysis by applying McMillan-Mayer and Kirkwood-Buff theories of solutions. The analysis shows that osmotic second virial coefficient value for 15C5 is marginally less than that of 18C6 indicating that reduction in ring flexibility does not affect the energetics of the interactions much in aqueous solution while the same gets influenced much in nonpolar solvent CCl4.     

X-Ray analysis of aqueous concentrates using organic glassy specimens

A simple and accessible method for the production of glassy specimens from aqueous concentrates based on saccharose is proposed. During the process of such a specimen preparation an additional concentration of impurities takes place. These saccharose specimens were used for the X-ray fluorescence determination of Se in waste water with crystallization preconcentration.     

Distribution of Pb(II) species in aqueous solutions

Turbidity and zeta potential measurements were made on solid precipitates formed after raising the pH of a 10(-3) mol/l lead nitrate aqueous solutions containing 10(-2) mol/l KCl with KOH. Distribution diagrams of Pb(II) species in aqueous solutions at a total Pb(II) concentration of 10(-3) mol/l and 10(-2) mol/l KCl was constructed to explain the results. Several solubility products for solid Pb(OH)(2) were found from the literature and used to construct the diagrams. It was observed that distribution diagrams constructed using a solubility product of 1.43x10(-20) explained the experimental results better than those with other reported solubility products.     

Wetting Films of the Aqueous Cationic Polyelectrolyte Solutions on Quartz

It was shown that the stability of the wetting films of aqueous cationic polyelectrolyte solutions on the flat quartz surface depends on solution concentration. At a low concentration, the films are stable owing to the electrostatic repulsive forces. At a high polyelectrolyte concentration, the films are unstable due to the hydrophobization of quartz and the appearance of the hydrophobic attractive forces in the films. In the intermediate concentration range, the films are metastable and their lifetime depends upon the competition between the electrostatic repulsive and hydrophobic attractive forces. Thus, the concentration of cationic polyelectrolyte substantially affects the wetting conditions of the quartz surface. This conclusion can also be extended to other solid surfaces negatively charged in aqueous solutions, which is inherent to the majority of natural materials.     

Concentration of all rare earth impurities of cerium sub-group rare earth matrices

The separability of all rare earth impurities from cerium sub-group matrices was investigated. It was found that anion exchange chromatography carried out with aqueous methanol solutions of nitrates provides a useful method for the concentration of all rare earth impurities in neodymium and gadolinium matrices. The concentrate of the impurities can be processed further as required by the method chosen for their analytical determination.     

Using gas chromatography with atomic emission detection for determining organic pollutants in water

The efficiency of gas chromatography with atomic emission detection (AED) for determining the composition of complex mixtures of organic water pollutants was studied by the example of 13 compounds of different classes. It was found that the correlation between the ratio of AED signals for single element atoms of the compound in the sample and their predetermined ratio in individual solutions additionally supports the identification of impurities in water at a trace level. The determination of a compound by the concentration of one or two elements in its molecule allows the evaluation of the effect of interfering impurities on the results of analysis.     

Effect of the Conditions the Reaction on the Formation of Iron Nanoparticles during the Reduction of Iron(III) Ions with Sodium Borohydride

Abstract—Iron nanoparticles are obtained by reducing iron(III) chloride with sodium borohydride in aqueous solutions at room temperature without using stabilizing agents. The obtained samples are characterized by X-ray diffraction analysis, low-temperature adsorption of argon, and transmission electron microscopy. The effect of the concentration of reagent solutions, the molar ratio of reagents, and exposure to ultrasound and inert atmosphere (Ar) on the size and composition of the resulting particles is found. Depending on the conditions of borohydride reduction of iron salts in an aqueous solution, both agglomerates of iron nanoparticles (5–50 nm) of 200 nm or larger and individual iron nanoparticles of 1 to 20 nm in size can be obtained. The presence and concentration of wustite and magnetite in the composition of the obtained particles mainly depend on the concentration of the reducing agent.     

Diffusion coefficients of lithium chloride and potassium chloride in hydrogel membranes derived from acrylamide

Diffusion of non-associated electrolytes (potassium chloride and lithium chloride) in concentrated aqueous solutions (0.1-1.0 mol dm⁻³) has been studied in hydrogels derived from acrylamide and methyl methacrylate to study the mechanism of electrolyte transport. The preparation of two gels with different monomer ratio compositions resulted in obtaining membranes of substantially different hydrophilic character with polymer fractions of 0.3 and 0.5.Cukier hydrodynamic model was applied to explain the dependence of the diffusion coefficients of KCl and LiCl on the electrolyte concentration in hydrogel obtained experimentally. It was shown that the increase of the diffusion coefficients is accompanied with a decrease of the mean distance of approach of the ions. This can be explained by the formation of ion-pairs, resulting in a further contribution to diffusion once there is a decrease in the hydrodynamic resistance of the medium to the diffusing particles. Parameters, which characterise such a behaviour quantitatively, are different for different electrolytes and depend on water content in the gel.     

Solubility of Itaconic Acid in Aqueous Ethanol Mixtures from 278.15 K to 333.15 K

Data on corresponding solid?Cliquid equilibrium of itaconic acid in binary aqueous ethanol solutions are essential for industrial design and further theoretical studies. Using the analytical stirred-flask method, the solubility of itaconic acid in pure water solvent and mixed solvents were measured over the temperature range from 278.15 to 333.15 K at atmospheric pressure. The effect of solvent composition and temperature on the solubility is discussed. The solubility data were correlated with the Combined Nearly Ideal Binary Solvent/Redlich (CNIBS/R-K) model. The solubility measured in this study can be used for the itaconic acid purification or optical resolution by the preferential crystallization procedure.