Separation of rare earth elements in the tributyl phosphate–Ln(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>–Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> system in the counter current process

The 40-step extraction process to separate rare earth elements (RЕEs) according to the praseodymium–cerium line with the use of mixer–settler extractors in a 100% TBP–Ln(NO₃)₃–Ca(NO₃)₂ system is implemented. A lanthanum–cerium concentrate containing less than 0.03 wt % of the remaining REEs is obtained. The flow diagram of the separation process of a rare earth (RE) concentrate isolated from phosphogypsum is considered.     

Solubility in the diagonal sections of the 2KCl + Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> ⇆ 2KNO<Subscript>3</Subscript> + CaCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system

Solubility data in the diagonal sections of the quaternary reciprocal 2KCl + Ca(NO₃)₂ → 2KNO₃ + CaCl₂–H₂O system at 25 and 15°C are presented. It has been shown that the quaternary system has no stable diagonal at the studied temperatures, but contains a stable pair of salts, namely, potassium nitrate and calcium chloride. The obtained data can be used to optimize the thermal and concentrational parameters of the synthesis of potassium nitrate from calcium nitrate and potassium chloride.     

Phase formation in the system Zn(VO<Subscript>3</Subscript>)<Subscript>2</Subscript>–HCl–VOCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O

The phase and chemical compositions of precipitates formed in the system Zn(VO₃)₂–HCl–VOCl₂–H₂O at pH 1?3, molar ratio V⁴⁺: V⁵⁺ = 0.1?9, and 80°C were studied. It was shown that, within the range 0.4 ≤ V⁴⁺: V⁵⁺ ≤ 9, zinc vanadate with vanadium in a mixed oxidation state forms with the general formula Zn_xV⁴⁺ _yV⁵⁺ _2-yO₅ ? nH₂O (0.005 ≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3, n = 0.5?1.2). Vanadate Zn_xV₂O₅ ? nH₂O with the maximum tetravalent vanadium content (y = 0.30) was produced within the ratio range V⁴⁺: V⁵⁺ = 1.5?9.0. Investigation of the kinetics of the formation of Zn_xV₂O₅ ? nH₂O at pH 3 determined that tetravalent vanadium ions VO2+ activate the formation of zinc vanadate, and its precipitation is described by a second-order reaction. It was demonstrated that, under hydrothermal conditions at pH 3 and 180°C, zinc decavanadate in the presence of VOCl₂ can be used as a precursor for producing V₃O₇ ? H₂O nanorods 50–100 nm in diameter.     

Crystal structure of [Pb<Subscript>3</Subscript>(OH)<Subscript>4</Subscript>Co(NO<Subscript>2</Subscript>)<Subscript>3</Subscript>](NO<Subscript>3</Subscript>)(NO<Subscript>2</Subscript>)·2H<Subscript>2</Subscript>O

The structure of [Pb₃(OH)₄Co(NO₂)₃](NO₃)(NO₂)·2H₂O is determined by single crystal X-ray diffraction. The crystallographic characteristics are as follows: a = 8.9414(4) Å, b = 14.5330(5) Å, c = 24.9383(9) Å, V = 3240.6(2) ų, space group Pbca, Z = 8. The Co(III) atoms have a slightly distorted octahedral coordination formed by three nitrogen atoms belonging to nitro groups (Co–N_av is 1.91 Å) and three oxygen atoms belonging to hydroxyl groups (Co–O_av is 1.93 Å). The hydroxyl groups act as μ₃-bridges between the metal atoms. The geometric characteristics are analyzed and the packing motif is determined.     

Glass Formation in the Al<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript>–(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>SO–H<Subscript>2</Subscript>O System

The glass formation in the Al₂(SO₄)₃–(CH₃)₂SO–H₂O system was found for the first time. The competitive ability of ligands, dimethyl sulfoxide and water (which are strong donors), for entering the first coordination sphere of aluminum is considered. The possibility of mixed coordination of (CH₃)₂SO (via sulfur and oxygen atoms) in the first coordination sphere of aluminum with retention of the glass-forming ability of the sample was suggested on the basis of IR spectral study.     

Formation of nanocrystals in the ZrO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system

Formation of zirconia nanocrystals in the course of thermal treatment of an X-ray amorphous zirconium oxyhydroxide was studied. It was shown that the formation of tetragonal and monoclinic polymorphs of ZrO₂ in the temperature range from 500 to 700°C occurs owing to dehydration and crystallization of amorphous hydroxide. An increase of the temperature up to 800°C and higher activates mass transfer processes and, as a result, activates the nanoparticle growth and increases the fraction of the phase based on monoclinic modification of ZrO₂ due to mass transfer from the nanoparticles with the non-equilibrium tetragonal structure. Herewith, formed ZrO₂ nanocrystals with monoclinic structure have a broad size distribution of crystallites, and the average crystallite size after thermal treatment at 1200°C for 20 min is about 42 nm.     

Thermal decomposition of praseodymium nitrate hexahydrate Pr(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>·6H<Subscript>2</Subscript>O

The hexahydrate of praseodymium nitrate hexahydrate Pr(NO₃)₃·6H₂O does not show phase transitions in the range of 233–328 K when the compound melts in its own water of crystallization. It is suggested that the thermal decomposition is a complex step-wise process, which involves the condensation of 6 mol of the initial monomer Pr(NO₃)₃·6H₂O into a cyclic cluster 6[Pr(NO₃)₃·6H₂O]. This hexamer gradually loses water and nitric acid, and a series of intermediate amorphous oxynitrates is formed. The removal of 68% HNO₃–32% H₂O azeotrope is essentially a continuous process occurring in the liquid phase. At higher temperatures, oxynitrates undergo thermal degradation and lose water, nitrogen dioxide and oxygen, leaving behind normal praseodymium oxide Pr₂O₃. The latter absorbs approximately 1 mol of atomic oxygen from N₂O₅ disproportionation, giving rise to the non-stoichiometric higher oxide Pr₂O_3.33. All mass losses are satisfactorily accounted for under the proposed scheme of thermal decomposition.     

Polytherm of the CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>–KNO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O phase diagram

The crystallization polytherm of the ternary CO(NH₂)₂–KNO₃–H₂O system is plotted for the first time via visual polythermal analysis and calculating ternary eutonics characteristics from data on the boundary elements of two-component systems. The ternary eutonics modeling error does not exceed 3.5%. In addition to the crystallization fields of individual components, the field of the redox reaction that occurs in the system between potassium nitrate and carbamide is shown in the CO(NH₂)₂–KNO₃–H₂O diagram by a dashed outline.     

Copper(II) oxalate obtained through the reaction of 1,2-ethanediol with Cu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·3H<Subscript>2</Subscript>O

The paper presents the experimental results of the structural investigations and thermal analysis of copper(II) oxalate, a polynuclear coordination compound, obtained by a new method, through the reaction of 1,2-ethanediol with Cu(NO₃)₂·3H₂O. The reaction between 1,2-ethanediol and Cu(NO₃)₂·3H₂O occurs, under some working conditions, with the oxidation of 1,2-ethanediol to the oxalate anion (L). The synthesized polynuclear coordination compound, [CuL·0.3H₂O]_n, was characterized by chemical analysis, electronic and vibrational spectra and thermal analysis. The thermal properties of the polynuclear coordination compound have been investigated by TG, DTG and DSC. The obtained decomposition product is CuO. Powder XRD (X-ray diffraction), IR spectroscopy and TEM (transmission electron microscopy) were used to characterize the composition, the crystalline structure and the surface morphology of the copper oxide obtained through thermolysis. The thermal conversion product, copper(II) oxide, has a microporous structure with a large specific area.     

Phase and extraction equilibria in H<Subscript>2</Subscript>O–sulfonol–HCl (H<Subscript>2</Subscript>SO<Subscript>4</Subscript>) and H<Subscript>2</Subscript>O–sodium dodecyl sulfate–HCl (H<Subscript>2</Subscript>SO<Subscript>4</Subscript>) systems

Solubility isotherms of water–sulfonol–hydrochloric (or sulfuric) acid and water–sodium dodecyl sulfate–hydrochloric acid systems at 75°C and a water–sodium dodecyl sulfate–sulfuric acid system at 50°C are constructed. Regions of two-phase liquid equilibrium suitable for use in extraction are found. Concentration parameters for extraction are determined. The interfacial distribution of a series of metal ions with and without such additional complexing reagents as diantipyrylmethane and diantipyrylheptane is studied.     

Crystal Structure of Neptunium(V) Acetate [(NpO<Subscript>2</Subscript>)<Subscript>2</Subscript>(OOCCH<Subscript>3</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)] ⋅ 2H<Subscript>2</Subscript>O

A new neptunium(V) complex [(NpO₂)₂(CH₃COO)₂(H₂O)] ? 2H₂O was synthesized and its crystal structure was determined. The unit cell parameters are: a = 24.007(10) Å, b = 6.779(3) Å, c = 8.076(3) Å, space group Pnma, Z = 4, V = 1314.2(9) ų, R = 0.049, wR(F²) = 0.105. The crystal structure of the compound is composed of neutral [(NpO₂)₂(CH₃COO)₂(H₂O)] layers and molecules of the water of crystallization. Each of the crystallographically independent neptunoyl ions performs a bidentate function thus forming a composite system of cation-cation bonds.     

High-temperature reactions in the Co<Subscript>3</Subscript>Cr<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>6</Subscript>–Cr(PO<Subscript>3</Subscript>)<Subscript>3</Subscript> system

A new dichromium(III) cobalt(II) diphosphate(V) of the formula CoCr₂(P₂O₇)₂ was detected in the Co₃Cr₄(PO₄)₆–Cr(PO₃)₃ system. The new compound was obtained as a result of high-temperature solid-state reactions between CoCO₃, Cr₂O₃ and (NH₄)₂HPO₄ as well as between Cr(PO₃)₃ and Co₃Cr₄(PO₄)₆. CoCr₂(P₂O₇)₂ was characterized using XRD, DTA and IR methods. Results demonstrated that CoCr₂(P₂O₇)₂ crystallizes in the triclinic system and its unit cell parameters were calculated. Its infrared spectrum was presented. CoCr₂(P₂O₇)₂ melts incongruently at 1270±10 °C with a formation of solid α-CrPO₄. The compound Co₃Cr₄(PO₄)₆, component of the system under study, was obtained for the first time as a pure phase. Its thermal stability was also investigated. Co₃Cr₄(PO₄)₆ is stable in air up to 1410 ± 20 °C.     

Formation of binary salts in the system LiCl–CsCl–H<Subscript>2</Subscript>O

In the ternary system LiCl–CsCl–H₂O the binary salt LiCl·2CsCl·4H₂O was formed. Its structure was proved by the X-ray structural analysis. The binary compound formed in the aqueous solution by the structurally-forced insertion mechanism.     

Phase equilibria in a ternary fullerenol-d(C<Subscript>60</Subscript>(OH)<Subscript>22–24</Subscript>)–SmCl<Subscript>3</Subscript>–H<Subscript>2</Subscript>O system at 25°C

The solubility in a ternary fullerenol-d (C₆₀(OH)_22–24)–SmCl₃–H₂O system at 25°C is studied via isothermal saturation in ampules. The solubility diagram is shown to be a simple eutonic one that consists of two branches corresponding to the crystallization of fullerenol-d (C₆₀(OH)_22–24 · 30H₂O) and samarium(III) chloride SmCl₃ · 6H₂O crystallohydrates and contains one nonvariant eutonic point corresponding to saturation with both crystallohydrates. The long branch of C₆₀(OH)_22–24 · 30H₂O crystallization shows the effect of fullerenol-d salting out of saturated solutions; in contrast, the short branch of SmCl₃ · 6H₂O crystallization shows the pronounced salting-in effect of samarium(III) chloride.     

Synthesis and X-ray diffraction study of Li(H<Subscript>3</Subscript>O)[UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)] · H<Subscript>2</Subscript>O

Single crystals of Li(H₃O)[UO₂(C₂O₄)₂(H₂O)] · H₂O (I) have been synthesized and studied by X-ray diffraction. Compound I crystallizes in the monoclinic crystal system with the unit cell parameters: a = 7.1682(10) Å, b = 29.639(6) Å, c = 6.6770(12) Å, β= 112.3(7)°, space group P 2₁/c, Z = 4, R = 4.36%. Structure I contains discrete mononuclear groups [UO₂(C₂O₄)₂(H₂O)]^2? ascribed to the crystal-chemical group AB ₂ ⁰¹ M¹ (A = UO₂ ²⁺, B⁰¹ =C₂O ₄ ^2? , M¹ = H₂O), which are “cross-linked” by the lithium ions into infinite layers {Li(UO₂)(C₂O₄)₂(H₂O)₂}^? perpendicular to [010]. The hydroxonium ions are located between adjacent uranium-containing layers. A hydrogen bond system involving water molecules, oxalate ions, and hydroxonium combines the anionic layers into a three-dimensional framework.     

Synthesis and study of uranyl arsenate (UO<Subscript>2</Subscript>)<Subscript>3</Subscript>(AsO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 12H<Subscript>2</Subscript>O

A method for producing synthetic troegerite of composition(UO₂)₃(AsO₄)₂ · 12H₂. Owas developed. X-ray diffraction, IR spectrometry, X-ray fluorescence analysis, and scanning calorimetry were used to study its dehydration and thermal decomposition, to solve the structgure, and to determine X-ray diffraction and IR spectroscopic characteristics.     

Solid-Liquid Equilibria in the Quaternary Systems KCl–MgCl<Subscript>2</Subscript>–SrCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O and NaCl–KCl–SrCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O at 348 K

Solid-liquid equilibria in the quaternary systems KCl–MgCl₂–SrCl₂–H₂O and NaCl–KCl–SrCl₂–H₂O at 348 K were measured by the isothermal solution saturation method. The composition of the equilibrium solid phase, solubilities of salts, and densities of saturated solution in the two systems were determined. Phase diagrams, water content diagrams and solution density diagrams of quaternary systems were plotted according to experimental data. The phase diagram of the quaternary system NaCl–KCl–SrCl₂–H₂O has one invariant point, three univariant curves as the boundary of NaCl, KCl and SrCl₂ · 2H₂O. This phase diagrams were simple co-saturation type without complex salt and solid solution. For the quaternary system KCl–MgCl₂–SrCl₂–H₂O, one complex salt KCl · MgCl₂ · 6H₂O (Car) had been found in this system, consisted of five univariant curves, two invariant points and four crystallization regions of MgCl₂ · 6H₂O (Bis), KCl, SrCl₂ · 2H₂O and KCl · MgCl₂ · 6H₂O. And the densities transformation rules were simply discussed. Simultaneously, the solubilities and densities data in invariant point of the quaternary system NaCl–KCl–SrCl₂–H₂O had been compared with the experimental data of previous researchers.     

Physicochemical Analysis of the System Zr(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>–Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>–H<Subscript>2</Subscript>SO<Subscript>4</Subscript>–H<Subscript>2</Subscript>O at 25°С

The solubility in the quaternary water–salt system Zr(SO₄)₂ · 4Н₂О–Na₂SO₄–H₂SO₄–H₂O at 25°C was studied. It was found that, in the system, there is crystallization of not only Na₂SO₄ and Zr(SO₄)₄ · 4H₂O, but also sodium sulfate zirconates Na₂Zr(SO₄)₂(OH)₂ · 0.3H₂O, Na₄Zr(SO₄)₄ · 3H₂O, and Na₂Zr(SO₄)₂ · 3H₂O and two new compounds, S₁ and S₂, which are presumably Na₂ZrO(SO₄)₂ · 2H₂O and Na₂Zr₂O₂(SO₄)₃ · 6H₂O.