Be<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>CO<Subscript>3</Subscript> solubility in carbonate and fluoride aqueous solutions

Be₂(OH)₂CO₃ solubilities at 25°C in 0.7 M NaClO₄ solutions containing variable NaHCO₃ and Na₂CO₃ concentrations has been experimentally determined. The solubilities increase with increasing carbonate alkalinity. The results of the experiments do not contradict the suggestion that the mixed hydroxocarbonate complex Be₂(OH)₂CO ₃ ^2? is the major beryllium solute species. At fluoride concentrations higher than 250 μmol/L, the Be₂(OH)₂CO₃ solubilities noticeably increase as a result of the formation of beryllium fluoride complexes.     

Studies on the Complexation Behavior of Thorium(IV). 1. Hydrolysis Equilibria

The stability constants of thorium(IV) hydrolysis species have been measured at15, 25, and 35°C (in 1.0 mol dm^–3 NaClO₄) using both potentiometry and solventextraction. The results indicate the presence of the monomeric speciesTh(OH)³⁺, Th(OH)²⁺ ₂, Th(OH)⁺ ₃, and Th(OH)₄, in addition to the polymericspecies Th₄(OH)^{8+ 8} and Th₆(OH)⁹⁺ ₁₅. The polymeric species were found to beimportant, although the total thorium concentration was limited to 0.01–0.1mmol-dm^–3. The solvent extraction measurements required the use of acetylacetone.As such, the stability constants of thorium(IV) with acetylacetone were alsomeasured using both potentiometry and solvent extraction. All logarithms of thestability constants were found to be linear functions of the reciprocal absolutetemperature indicating that H ^o and S^o of reaction are both independent oftemperature (over the temperature range examined in the study).     

Thermodynamic models for highly charged aqueous species: Solubility of Th(IV) hydrous oxide in concentrated NaHCO3 and Na2CO3 solutions

An aqueous thermodynamic model is proposed to describe the solubility ofTh(IV) hydrous oxide in the aqueous Na⁺-HCO ₃ ^- -CO ₃ ^2- -OH^--ClO ₄ ^- -H₂O system extending to high concentration at 25‡C. This model is relatively simple in that only two aqueous species are included: Th(OH)₃CO ₃ ^- and Th(CO₃) ₅ ^6- . Pitzer ion interaction parameters, Β⁽⁰⁾ and Β^(l) for Na⁺ with Th(CO₃) ₅ ^6- , are also determined (1.31 and 30, respectively). Reconciliation of all of the experimental solubility data for Th(IV) hydrous oxide in NaClO₄ media required the introduction of a large mixing parameter for the highly charged Th(CO₃) ₄ ^- . The relatively large values required for the ion interaction parameters Β⁽⁰⁾ and Β^(l), together with commensurately large mixing terms with the bulk anionic species, resulted in considerable uncertainty in determining standard state equilibrium constants for the formation of the highly charged Th(CO₃) ₅ ^6- species. This uncertainty is a result of the large contributions from Β⁽⁰⁾ and Β^(l) to the excess solution free energy at the concentrations (0.1m) where this species becomes important. The magnitude of the mixing term implies that formation of this species depends strongly upon the bulk ionic media. X-ray absorption results, confirming the presence of the thorium pentacarbonate species in concentrated bicarbonate and carbonate solutions, are also included.     

Synergistic extraction of uranium(VI) and thorium(IV) with mixtures of Cyanex272 and other organophosphorus ligands

The extraction of thorium(IV) and uranium(VI) from nitric acid solutions has been studied using mixtures of bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272 or HA), and synergistic extractants (S) such as tri-butylphosphate (TBP), tri-octylphosphine oxide (TOPO) or bis(2,4,4-trimethylpentyl)thiophosphinic acid (Cyanex301). The results showed that these metallic ions are extracted into kerosene as Th(OH)₂(NO₃)A·HA and UO₂(NO₃)A·HA with Cyanex272 alone. In the presence of neutral organophosphorus ligands TBP and TOPO, they are found to be extracted as Th(OH)₂(NO₃)A·HA·S and UO₂(NO₃)A·HA·S. On the other hand, Th(IV), U(VI) are extracted as Th(OH)₂(NO₃)A·HA·2S and UO₂(NO₃)A·HA·S in the presence of Cyanex301. The addition of neutral extractants such as TOPO and TBP to the extraction system enhanced the extraction efficiency of both elements while Cyanex301 as an acidic extractant has improved the selectivity between uranium and thorium. The effect of TOPO on the extraction was higher than other extractants. The equilibrium constants of above species have been estimated by non-linear regression method. The extraction amounts were determined and the results were compared with those of TBP. Also, it was found that the binding to the neutral ligands by the thorium–Cyanex272 complexes follows the neutral ligand basicity sequence.     

Competition between H<Subscript>2</Subscript>O and CH<Subscript>3</Subscript>OH molecules in the formation of the simplest stable proton disolvates and their solvation in aqueous methanol solutions of KOH and CH<Subscript>3</Subscript>OK

IR spectroscopic and quantum chemical methods are used to study the competition between water and methanol molecules in the formation of the simplest stable proton disolvates and their subsequent solvation in the case of solutions of KOH in CH₃OH and CH₃OK in H₂O with similar stoichiometries (~1:3-3.5). The complexes found in these solutions are analysed to determine their composition and structure: they are found to be heteroions (CH₃O?H?OH)^– solvated by two similar solvent molecules. In both cases, there are virtually no complexes of the second possible type (CH₃OH·(CH₃O?H?OCH₃)^–··H₂O or CH₃OH·(HO?H?OH)^–·H₂O), which appears to be due to the stoichiometric compositions of the solutions. It is shown that a DFT calculation (B3LYP/6-31++G(d,p)) of linear complexes with strong (~15-30 kcal/mol) H bonds reproduces, with good accuracy, the IR spectra of the solutions, which consist mainly of these complexes.     

Kinetics of the oxidation of diethyl sulfide in the B(OH)<Subscript>3</Subscript>-H<Subscript>2</Subscript>O<Subscript>2</Subscript>/H<Subscript>2</Subscript>O system

Data obtained for the kinetics of oxidation of diethyl sulfide (Et₂S) by hydrogen peroxide in aqueous solution catalyzed by boric acid indicate that monoperoxoborates B(O₂H)(OH) ₃ ⁻ and diperoxoborates B(O₂H)₂(OH) ₂ ⁻ are the active species. The rates of the reactions of Et₂S with B(O₂H)(OH) ₃ ⁻ and B(O₂H)₂(OH) ₂ ⁻ are 2.5 and 100 times greater than with H₂O₂. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 38–42, January–February, 2007.     

Effect of humic acid on the solid phase stability and solubility of UO<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>

The stability and solubility of UO₂(OH)₂ has been studied as a function of the humic acid concentration in 0.1M NaClO₄, in the pH range from 4 to 7 under normal atmospheric conditions. The solid phase under investigation has been prepared by alkaline precipitation and characterized by TGA, ATR-FTIR, XRD, SEM and solubility measurements. According to the experimental data UO₂(OH)₂ is stable and remains the solubility limiting solid phase even in the presence of increased humic acid concentration in the solution. However, humic acid affects texture and particle size of the solid phase. Increasing humic acid concentration results in decreasing crystallite size of the UO₂(OH)₂ solid phase. Based on the solubility data, the logK _sp (UO₂(OH)₂) has been evaluated to be −22.0±0.3 and the stability constant for the UO₂(OH)HA(I) species has been estimated to be logβ ₁₁₀₁ = 15.3±0.5.     

Thorium determination in water samples by liquid scintillation counting after its separation by cloud point extraction

The aim of this study is the separation and pre-concentration of thorium from aqueous solutions by cloud point extraction (CPE) and its the radiometric determination by liquid scintillation counting (LSC). For CPE, tributyl phosphate (TBP) was used as the complexing agent and (1,1,3,3-Tetramethylbutyl)phenyl-polyethylene glycol (Triton X-114) as the surfactant. The radiometric measurements were performed after phase separation by mixing of the surfactant phase with the liquid scintillation cocktail. The effect of experimental conditions such as pH, ionic strength (e.g. [NaCl]) and the presence of other chemical species (e.g. Ca²⁺ and Fe³⁺ ions, and humic acid colloids) on the CPE separation recovery have been investigated at constant reactant ratio (m(TBP)/m(Triton) = 0.1). According to the experimental results the maximum chemical recovery is (60 ± 5)% at pH 3. Regarding the other parameters, generally Ca²⁺ and Fe³⁺ ions as well as the presence of colloidal species in solution (even at low concentrations) results in significant decrease of the chemical recovery of uranium. On the other hand increasing NaCl concentration leads to enhancement of chemical recovery. Generally, the method could be applied successfully for the radiometric determination of thorium in water solutions with relatively increased thorium content.     

On the stability of Al<Subscript>13</Subscript> Keggin cation in aqueous hydrogen peroxide solutions

We report the first attempt to study the behavior of the [AlO₄Al1₂(OH)₂₅(H₂O)₁₁]⁶⁺ (Al₁₃) Keggin cation (KC) in water–peroxide solutions. Addition of hydrogen peroxide into an aqueous solution containing the Al₁₃ KC reduces pH due to the acidity of hydrogen peroxide. According to the ²⁷Al NMR studies of water–peroxide solutions prepared just before the NMR experiment, with their pH adjusted to the initial value of 5.5 with aqueous NaOH, the Al₁₃ KC concentration decreases immediately once hydrogen peroxide is added to the initial system. Addition of 18.2 wt % hydrogen peroxide to the initial 0.88 mM Al₁₃ solution gives rise to a fourfold decline in Al₁₃ polyoxo cation concentration to 0.22 mM. Then, the KC concentration in the test system remains unchanged for 1 week. Large hydrogen peroxide amounts (27.9 wt % or higher) added to the initial system almost completely degrade the KC. Sodium sulfate added to the initial water–peroxide solution of Al₁₃ chloride where the hydrogen peroxide concentration is 5.5 wt % precipitates the earlier described Al₁₃ sulfate [AlO₄Al₁₂(OH)₂₅(H₂O)₁₁](SO₄)₃ · 16H₂O, where the aluminum polyoxo cation does not contain coordinated hydrogen peroxide molecules, peroxo or hydroperoxo groups as shown by X-ray diffraction.     

Synthesis of the mixed oxide catalysts based upon the nickel-copper hydrotalcites of the type Ni<Subscript>x</Subscript>Cu<Subscript>6-x</Subscript>Cr<Subscript>2</Subscript>(OH)<Subscript>16</Subscript>(CO<Subscript>3</Subscript>)×4H<Subscript>2</Subscript>O

Summary High resolution TG coupled to a gas evolution mass spectrometer has been used to study the thermal properties of a chromium based series of Ni/Cu hydrotalcites of formulae Ni_xCu_6-xCr₂(OH)₁₆(CO₃)×4H₂O where x varied from 6 to 0. The effect of increased Cu composition results in the increase of the endotherms and mass loss steps to higher temperatures. Evolved gas mass spectrometry shows that water is lost in a number of steps and that the interlayer carbonate anion is lost simultaneously with hydroxyl units. Differential scanning calorimetry was used to determine the heat flow steps for the thermal decomposition of the synthetic hydrotalcites. Hydrotalcites in which M²⁺ consist of Cu, Ni or Co form important precursors for mixed metal-oxide catalysts. The application of these mixed metal oxides is in the wet catalytic oxidation of low concentrations of retractable organics in water. Therefore, the thermal behaviour of synthetic hydrotalcites, Ni_xCu_6-xCr₂(OH)₁₆CO₃×nH₂O was studied by thermal analysis techniques in order to determine the correct temperatures for the synthesis of the mixed metal oxides.     

Chemistry of the CARBEX process: Identification of absorption bands of the ligands in the electronic spectra of aqueous solutions of Na<Subscript>4</Subscript>[UO<Subscript>2</Subscript>(CO<Subscript>3</Subscript>)<Subscript>3</Subscript>]

On the basis of consideration of hydration, hydrolysis, dissociation, polymerization, and ligand exchange that occur in aqueous solutions of U(VI) complexes, a new approach to the assignment of absorption bands of the ligands in electronic spectra of uranium(VI) carbonate complexes in the range 190–400 nm has been suggested. For the Na₄[UO₂(CO₃)₃] complex, the following assignment of absorption bands has been made: Na₃[UO₂(CO₃)₃]^–, 258 nm; Na₂[UO₂(CO₃)₃]^2–, 300 nm; and Na₄[UO₂(CO₃)₃], 330 nm.     

Synthesis and speciation of zirconium tetrafluoride complexes with phosphoryl-containing bases Ph<Subscript>3</Subscript>PO,Bu<Subscript>3</Subscript>PO and (Me<Subscript>2</Subscript>N)<Subscript>3</Subscript>PO in solutions

Zirconium fluoro complexes with phosphoryl-containing bases (L) have been synthesized by the reaction of a suspension of ZrF₄(dmso)₂ in toluene with an excess of Ph₃PO or Bu₃PO, as well as (Me₂N)₃PO in CH₂Cl₂. The composition and structure of the complexes in CH₂Cl₂ solutions have been studied by ¹⁹F NMR in the temperature range 293–203 K. Phosphine oxides are substituted for dmso to form mainly cis-tetrafluoro species, insignificant amounts of trans-tetrafluoro species, and mer- and fac-[ZrF₃L₃]⁺ complexes. In addition to these species, the reaction with Bu3PO yields the dimeric oxo complex (µ-O)[ZrF₃(Bu₃PO)₂]₂. Hydrolysis of fluoro complexes in CH₂Cl₂ with the use of an NBu₄OH solution in iso-PrOH does not lead to oxo and hydroxo complexes: first, the [ZrF₅L]^– complex is formed, and the final hydrolysis product is ZrF₆^2-. The fine structure of ¹⁹F NMR resonance lines for the zirconium fluoride compounds [ZrF5L]^–, cis- [ZrF₄L₂], dimeric oxo complex, and mer-[ZrF₃L₃]⁺ in organic solvents has been observed for the first time, which makes it possible to reliably identify the composition and structure of the zirconium coordination polyhedron in the complexes under consideration.     

Degree of hydration in cement paste and C<Subscript>3</Subscript>A-sodium carbonate-water systems

This research provides a fundamental understanding of the early stage hydration of Portland cement paste, tricalcium aluminate (C₃A) paste at water to cement ratio of 0.5 and C₃A suspension at water to cement ratio of 5.0 modified by 2 or 4 mass% of sodium carbonate. A high conversion of unreacted clinker minerals to gel-like hydration products in the cement-Na₂CO₃ pastes takes place rapidly between 1^st to 24^th h. Contrary the Ca(OH)₂ formation within the same time interval is retarded in the excess of CO₃²⁻ ions due to intensive rise and growth of CaCO₃ crystals in hydrated cement. Later, the conversion of clinker minerals to the hydrate phase is reduced and higher contents of calcite and vaterite relative to that of Ca(OH)₂ in comparison with those found in the Portland cement paste are observed. As a consequence a decrease in strength and an increase in porosity between hardened Portland cement paste without sodium carbonate and those modified by Na₂CO₃ are observed. C₃A hydrates very quickly with sodium carbonate between 1^st and 24^th h forming hydration products rich in bound water and characterized also by complex salts of (x)C₃A·(y)CO₂·(zH₂O type, whereas C₃A-H₂O system offers C₃AH₆ as the main hydration product. Higher content of the formed calcium aluminate hydrates in C₃A-Na₂CO₃-H₂O system also contributes to early strength increase of Portland cement paste.     

Synthesis and equilibria in solutions of hafnium fluoro complexes with phosphoryl-containing bases Ph<Subscript>3</Subscript>PO,Bu<Subscript>3</Subscript>PO,and (Me<Subscript>2</Subscript>N)<Subscript>3</Subscript>PO

The composition and equilibria in solutions of the products of reaction of HfF₄(dmso)₂ with monodentate phosphoryl-containing bases L = Ph₃PO, Bu₃PO, and (Me₂N)₃PO in CH₂Cl₂ are studied by ¹⁹F NMR. Octahedral molecular complexes cis-[HfF₄L₂] and minor amounts of trans-[HfF₄L₂] and fac-[HfF₃L₃]⁺ cations were the main products for all ligands. The oxytrifluoride complex (μ-O)[HfF₃(Bu₃PO)₂]₂ and the [HfF₅(Bu₃PO)]^– anion were identified in the case of Bu₃PO. The conclusion about the formation of the hafnium oxytrifluoro complex was verified via hydrolysis of the product of reaction between HfF₄ and Ph₃PO upon exposure to air. As a result, (μ-O)[HfF₃(Ph₃PO)₂]₂ were detected; fine-structure ¹⁹F NMR resonance lines were obtained and the spin–spin coupling constant J_FF was measured for the first time. Hydrolysis via adding a Bu₄NOH solution in i-PrOH to the HfF₄L₂ solutions in CH₂Cl₂ did not yield the expected zirconium oxyfluoro complexes with the smaller number of fluorine atoms. Due to deeper hydrolysis, equilibrium in fluoride complexes shifted towards species with higher fluorine contents, [ZrF₅L]^– and [ZrF₆]^2–, resulting in the formation of Hf(O)_x(OH)_у(i-PrOH)_z complexes that were not observed in the ¹⁹F NMR spectra and the substitution of the released fluoride ions for molecular ligands in HfF₄L₂ complexes.     

Gradual transformation of Ca(OH)<Subscript>2</Subscript> into CaCO<Subscript>3</Subscript> on cement hydration

The low temperature of decomposition of some calcium carbonates and the bending of the TG curves of hydrated cement between 500 and 800°C suggested the presence of some complex compound(s), which needed complementary investigation (XRD, TG). Stepwise transformation of portlandite (and/or lime) into calcium carbonate, with intermediate steps of calcium carbonate hydroxide hydrates (CCH-1 to CCH-5), was indicated by the previous study of two OPC. This was checked here on four cements ground for t _g=15, 20, 25 and 30 min and hydrated either in water vapour, successively at RH=1.0, 0.95 and 0.5 for 2 weeks each (WR1, WR2 and WR3, respectively) or as mortars in liquid water (1m), followed by WR as above. The d[001] spacing of portlandite was confirmed to vary: here between the lowest and the highest standard values. The diffractograms of n=32 different samples were analyzed for presence of standard CCH peaks, generally slightly displaced. These were: CCH-1 [Ca₃(CO₃)₂(OH)₂]: N=11 peaks, of three different d[hkl] spacings, CCH-2 [Ca₆(CO_2.65)₂(OH₆₅₇)₇(H₂O)₂]: N=10 for two d[hkl], CCH-3 [Ca₃(CO₃)₂(OH)₂·1.5H₂O]: N=14 for five d[hkl], CCH-4, ikaite [CaCO₃(H₂O)₆]: N=13 for six d[hkl], CCH-5[CaCO₃(H₂O)]: N=15 for five d[hkl]. Thus the most probable is the presence of the last three. The stepwise transformation of Ca(OH)₂ into CaCO₃ was confirmed:     

Potentiometric and UV-Visible Spectrophotometric Studies of the Stability of Thorium(IV) Complexes with (o-Hydroxyphenyl) Mono- and Di-Methylenephosphonic Acids

Protometric studies were performed in aqueous solutions at 25^C and 0.1 ,mol.dm⁻³ ionic strength (NaClO₄) to determine the complexing abilities of eight (o-hydroxy-phenyl) mono- and di-methylenephosphonic acids (differently substituted by chromophoric or auxochromic groups) towards thorium(IV). The number, the nature of the species present in solution, their overall stability constants over a broad acidity range and their individual electronic spectra, as resolved by computation, have been determined by potentiometry and UV-visible spectrophotometry.The formation of 1:1 species, partially protonated MLH_x and totally deprotonated [ML], as well as hydroxo species -- mononuclear ML(OH)_x and dinuclear M₂L(OH) _x is reported with thorium(IV). The results show that the complexing power, which is not very different in the lanthanide series, is much higher for thorium(IV). The ratio Th⁴⁺/Eu³⁺ reaches eight log₁₀ units with some of the ligands.     

A Quantum Chemical Study of C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>, C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Molecules and Fe@C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Endocomplex

(U)PBE0/cc-pVDZ method is used to study the structure of C₆₀Cl₃₀, C₆₀(OH)₃₀ molecules and Fe@C₆₀(OH)₃₀ endocomplex. The triplet state of the endocomplex is shown to be the lowest in energy among its four states corresponding to different spin multiplicities and positions of Fe nucleus within the fullerene cavity. This state is characterized by bonding between the iron atom and one of two benzenoid cycles of the carbon cage, six internuclear Fe–C distances (208 pm), and 1s²2s²2p⁶3s²3p⁶3d^7.24s^0.14p^0.3 electron configuration of iron with spin population of 2.36.     

Concomitant Carboxylate and Oxalate Formation From the Activation of CO2 by a Thorium(III) Complex

Improving our comprehension of diverse CO₂ activation pathways is of vital importance for the widespread future utilization of this abundant greenhouse gas. CO₂ activation by uranium(III) complexes is now relatively well understood, with oxo/carbonate formation predominating as CO₂ is readily reduced to CO, but isolated thorium(III) CO₂ activation is unprecedented. We show that the thorium(III) complex, [Th(Cp′′)₃] ( 1 , Cp′′={C₅H₃(SiMe₃)₂‐1,3}), reacts with CO₂ to give the mixed oxalate‐carboxylate thorium(IV) complex [{Th(Cp′′)₂[κ²‐O₂C{C₅H₃‐3,3′‐(SiMe₃)₂}]}₂(μ‐κ²:κ²‐C₂O₄)] ( 3 ). The concomitant formation of oxalate and carboxylate is unique for CO₂ activation, as in previous examples either reduction or insertion is favored to yield a single product. Therefore, thorium(III) CO₂ activation can differ from better understood uranium(III) chemistry.     

An unusual isotopic fractionation of boron in synthetic calcium carbonate precipitated from seawater and saline water

Inorganic calcium carbonate precipitation from natural seawater and saline water at various pH values was carried out experimentally. The results show the clear positive relationships between boron concentration and δ11B of inorganic calcium carbonate with the pH of natural seawater and saline water. However, the variations of boron isotopic fractionation between inorganic calcite and seawater/saline water with pH are inconsistent with the hypothesis that B(OH)4- is the dominant spe-cies incorporated into the biogenic calcite structure. The isotopic fractionation factors α between synthetic calcium carbonate precipitate and parent solutions increase systematically as pH increases, from 0.9884 at pH 7.60 to 1.0072 at pH 8.60 for seawater and from 0.9826 at pH 7.60 to 1.0178 at pH 8.75 for saline water. An unusual boron isotopic fractionation factor of larger than 1 in synthetic calcium carbonate precipitated from seawater/saline water at higher pH is observed, which implies that a substantial amount of the isotopically heavier B(OH)3 species must be incorporated preferentially into synthetic inorganic carbonate. The results propose that the incorporation of B(OH)3 is attributed to the formation of Mg(OH)2 at higher pH of calcifying microenvironment during the synthetic calcium carbonate precipitation. The preliminary experiment of Mg(OH)2 precipitated from artificial seawater shows that heavier 11B is enriched in Mg(OH)2 precipitation, which suggests that isotopically heavier B(OH)3 species incorporated preferentially into Mg(OH)2 precipitation. This result cannot be applied to explain the boron isotopic fractionation of marine bio-carbonate because of the possibility that the unusual environment in this study appears in formation of marine bio-carbonate is infinitesimal. We, however, must pay more attention to this phenomenon observed in this study, which accidentally appears in especially natural environment.     

The synthesis and thermochemical study of (Mg,Fe)<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes

Nanotubular (Mg,Fe²⁺,Fe³⁺)₃Si₂O₅(OH)₄ hydrosilicates with a chrysotile structure were synthesized under hydrothermal conditions. The phases prepared were studied thermochemically on a high-temperature Tian-Calvet microcalorimeter by solution calorimetry. The standard enthalpies of formation of magnesium-iron nanotubular hydrosilicates were determined. The formation of iron-containing nanotubes was shown to be lass favorable energetically than the formation of magnesium nanotubes.