Hydrate numbers of scandium sulfate as deduced from solubility data

A simple method for determination of the hydrate numbers of saturating multi-hydrate salts in developed. The method demonstrated for scandium sulfate is based upon estimation of the enthalpy of solution of the hydrates from the solubility smoothing equations. It is shown that in the Sc₂(SO₄)₃–H₂O system, contrary to common opinion, the equilibrium solid phases are: Sc₂(SO₄)₃.6H₂O at 273–295 K, Sc₂(SO₄)₃.5H₂O at 295–333 K and Sc₂(SO₄)₃.4H₂O at 333–373 K. The solubility smoothing equations for the hexa-, penta- and tetrahydrate of scandium sulfate are given.     

Kinetics of thermal dehydration of Ce2(SO4)2, n(H,D)2O (n=5, 8, 9)

The thermal dehydration of Ce₂(SO₄)₃·5H₂O, Ce₂(SO₄)₃·8H₂O, Ce₂(SO₄)₃·9H₂O and their isomorphous deuterated compounds was studied by means of thermogravimetric measurements. A kinetic analysis of the TG curves obtained was carried out by computer. The thermal stability, Arrhenius parameters and mechanism of dehydration were investigated.     

New Structure Type among Octahydrated Rare‐Earth Sulfates, β‐Ce2(SO4)3·8H2O,and a new Ce2(SO4)3·4H2O Polymorph

Syntheses, crystal structures and thermal behavior of two new hydrated cerium(III) sulfates are reported, Ce₂(SO₄)₃·4H₂O ( I ) and β‐Ce₂(SO₄)₃·8H₂O ( II ), both forming three‐dimensional networks. Compound I crystallizes in the space group P2₁/n. There are two non‐equivalent cerium atoms in the structure of I , one nine‐ and one ten‐fold coordinated to oxygen atoms. The cerium polyhedra are edge sharing, forming helically propagating chains, held together by sulfate groups. The structure is compact, all the sulfate groups are edge‐sharing with cerium polyhedra and one third of the oxygen atoms, belonging to sulfate groups, are in the S–Oμ₃–Ce₂ bonding mode. Compound II constitutes a new structure type among the octahydrated rare‐earth sulfates which belongs to the space group Pn. Each cerium atom is in contact with nine oxygen atoms, these belong to four water molecules, three corner sharing and one edge sharing sulfate groups. The crystal structure is built up by layers of [Ce(H₂O)₄(SO₄)]_nⁿ⁺ held together by doubly edge sharing sulfate groups. The dehydration of II is a three step process, forming Ce₂(SO₄)₃·5H₂O, Ce₂(SO₄)₃·4H₂O and Ce₂(SO₄)₃, respectively. During the oxidative decomposition of the anhydrous form, Ce₂(SO₄)₃, into the final product CeO₂, small amount of CeO(SO₄) as an intermediate species was detected.     

Solid complexes of iron(II) and iron(III) with rutin

Solid complex compounds of Fe(II) and Fe(III) ions with rutin were obtained. On the basis of the elementary analysis and thermogravimetric investigation, the following composition of the compounds was determined: (1) FeOH(C₂₇H₂₉O₁₆)·5H₂O, (2) Fe₂OH(C₂₇H₂₇O₁₆)·9H₂O, (3) Fe(OH)₂(C₂₇H₂₉O₁₆)·8H₂O, (4) [Fe₆(OH)₂(4H₂O)(C₁₅H₇O₁₂)SO₄]·10H₂O. The coordination site in a rutin molecule was established on the basis of spectroscopic data (UV–Vis and IR). It was supposed that rutin was bound to the iron ions via 4C=O and 5C—oxygen in the case of (1) and (3). Groups 5C–OH and 4C=O as well as 3′C–OH and 4′C–OH of the ligand participate in binding metals ions in the case of (2). At an excess of iron(III) ions with regard to rutin under the synthesis conditions of (4), a side reaction of ligand oxidation occurs. In this compound, the ligands’ role plays a quinone which arose after rutin oxidation and the substitution of Fe(II) and Fe(III) ions takes place in 4C=O, 5C–OH as well as 4′C–OH, 3′C–OH ligands groups. The magnetic measurements indicated that (1) and (3) are high-spin complexes.     

Low-temperature heat capacities and standard molar enthalpy of formation of the complex

Low-temperature heat capacities of a solid complex Zn(Val)SO₄·H₂O(s) were measured by a precision automated adiabatic calorimeter over the temperature range between 78 and 373 K. The initial dehydration temperature of the coordination compound was determined to be, T _D=327.05 K, by analysis of the heat-capacity curve. The experimental values of molar heat capacities were fitted to a polynomial equation of heat capacities (C _p,m) with the reduced temperatures (x), [x=f (T)], by least square method. The polynomial fitted values of the molar heat capacities and fundamental thermodynamic functions of the complex relative to the standard reference temperature 298.15 K were given with the interval of 5 K. Enthalpies of dissolution of the [ZnSO₄·7H₂O(s)+Val(s)] (Δ_sol H _m,l ⁰) and the Zn(Val)SO₄·H₂O(s) (Δ_sol H _m,2 ⁰) in 100.00 mL of 2 mol dm^–3 HCl(aq) at T=298.15 K were determined to be, Δ_sol H _m,l ⁰=(94.588±0.025) kJ mol^–1 and Δ_sol H _m,2 ⁰=–(46.118±0.055) kJ mol^–1, by means of a homemade isoperibol solution–reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as: Δ_f H _m ⁰ (Zn(Val)SO₄·H₂O(s), 298.15 K)=–(1850.97±1.92) kJ mol^–1, from the enthalpies of dissolution and other auxiliary thermodynamic data through a Hess thermochemical cycle. Furthermore, the reliability of the Hess thermochemical cycle was verified by comparing UV/Vis spectra and the refractive indexes of solution A (from dissolution of the [ZnSO₄·7H₂O(s)+Val(s)] mixture in 2 mol dm^–3 hydrochloric acid) and solution A’ (from dissolution of the complex Zn(Val)SO₄·H₂O(s) in 2 mol dm^–3 hydrochloric acid).     

Isopiestic Measurement of the Osmotic Coefficients of Aqueous {xH 2 SO 4 + (1− x)Fe 2 (SO 4 ) 3 } Solutions at 298.15 and 323.15 K

This study measures the osmotic coefficients of {xH₂SO₄ + (1−x)Fe₂(SO₄)₃}(aq) solutions at 298.15 and 323.15 K that have ionic strengths as great as 19.3 mol,kg⁻¹, using the isopiestic method. Experiments utilized both aqueous NaCl and H₂SO₄ as reference solutions. Equilibrium values of the osmotic coefficient obtained using the two different reference solutions were in satisfactory internal agreement. The solutions follow generally the Zdanovskii empirical linear relationship and yield values of a _w for the Fe₂(SO₄)₃–H₂O binary system at 298.15 K that are in good agreement with recent work and are consistent with other M₂(SO₄)₃–H₂O binary systems.     

Studies on lanthanoid sulphites: V. thermal decomposition of cerium and neodymium sulphites

The preparation and thermal behaviour of Ce₂(SO₃)₃· 3H₂O, Nd₂(SO₃)₃·6H₂O and Nd₂(SO₃)₃ have been studied. Cerium sulphite undergoes first dehydration which is followed by decomposition to CeO₂ in the temperature range 500 – 850 °C. The decomposition involves two intermediate phases both in air and nitrogen. According to the TG curves the phases in air are Ce₂(SO₃)₂SO₄ and Ce₂SO₃(SO₄)₂. In nitrogen, Ce₂O₂SO₄ was identified and this provides a synthetic route to cerium oxysulphate.Neodymium sulphite decomposes to Nd₂O₂SO₄ when heated in air or in nitrogen up to 950°C. The intermediate levels observed do not correspond to single phases, and the reaction mechanism depends strongly on the experimental conditions.     

Development of Accurate Chemical Equilibrium Models for Oxalate Species to High Ionic Strength in the System: Na—Ba—Ca—Mn—Sr—Cl—NO<Subscript>3</Subscript>—PO<Subscript>4</Subscript>—SO<Subscript>4</Subscript>—H<Subscript>2</Subscript>O at 25 °C

The development of an accurate aqueous thermodynamic model is described for oxalate species in the Na—Ba—Ca—Mn—Sr—Cl—NO₃—PO₄—SO₄—H₂O system at 25 °C. The model is valid to high ionic strength (as high as 10 mol·kg⁻¹) and from very acid (10 mol·kg⁻¹ H₂SO₄) to neutral and basic conditions. The model is based upon the equations of Pitzer and co-workers. The necessary ion-interaction parameters are determined by comparison with experimental data taken from the literature or determined in this study. The proposed aqueous activity and solubility model is valid for a range of applications from interpretation of studies on mineral dissolution at circumneutral pH to the dissolution of high-level waste tank sludges under acidic conditions.     

Study of the crystallization fields of nickel(II) selenites in the system NiSeO3–SeO2–H2O

The solubility of NiSeO₃–SeO₂–H₂O system in the temperature region 298–573 K was studied. The compounds of the three-component system were identified by the Schreinemakers’ method. The phase diagram of nickel(II) selenites was drawn and the crystallization fields for the different phases were determined. Depending on the conditions for hydrothermal synthesis, NiSeO₃·2H₂O, α-NiSeO₃·1/3H₂O, β-NiSeO₃·1/3H₂O, NiSeO₃ and NiSe₂O₅ were obtained. The different phases were proved and characterized by chemical, powder X-ray diffraction and thermal analyses as well as IR spectroscopy.     

Physicochemical modeling of precipitating and dissolving of gypsum in chloride solutions

Physicochemical modeling is used to study the isolation of sulfate ions as α (β)-CaSO₄ · 2H₂O from aqueous solutions. The equilibrium compositions of liquid, solid, and gas phases of the NA₂SO₄-CaCl₂-CO₂-H₂O system are calculated at 25°C, CO₂ partial pressures of 10^−1.53 kPa, CaCl₂/Na₂SO₄ molar ratios of 0.2–3.0, and CaCl₂ concentrations from 0.01 to 0.15 mol/kgH₂O. The Gibbs energies of formation for α(β)-gypsum were determined from experimental solubility data on the α(β)-gypsum-air-water system by solving the inverse problem of physicochemical modeling. The data obtained are ΔG° _f298 (α-CaSO₄ · 2H₂O) = −1796.446 kJ/mol and G° _f298 (β-CaSO₄ · 2H₂)) = −1797.317 kJ/mol. Published in Russian in Zhurnal Neorganicheskoi Khimii, 2006, Vol. 51, No. 5, pp. 889–894. This article was translated by the authors.     

Coordination Reaction of Alanine with Neodymium(III) and Erbium(III) Nitrate. Thermochemical study

The solid-state coordination reaction: Nd(NO₃)₃·6H₂O(s)+4Ala(s) → Nd(Ala)₄(NO₃)₃·H₂O(s)+5H₂O(_l) and Er(NO₃)₃·6H₂O(s)+4Ala(s) → Er(Ala)₄(NO₃)₃·H₂O(s)+5H₂O(l) have been studied by classical solution calorimetry. The molar dissolution enthalpies of the reactants and the products in 2 mol L^–1 HCl solvent of these two solid-solid coordination reactions have been measured using a calorimeter. From the results and other auxiliary quantities, the standard molar formation enthalpies of [Nd(Ala)₄(NO₃)₃·H₂O, s, 298.2 K] and[Er(Ala)₄(NO₃)₃·H₂O, s,298.2 K] at 298.2 K have been determined to be Δ_f H _m ⁰ [Nd(Ala)₄(NO₃)₃·H₂O,s, 298.2 K]=–3867.2 kJ mol^–1, and Δ_f H _m ⁰ [Er(Ala)₄(NO₃)₃·H₂O, s, 298.2 K]=–3821.5 kJ mol^–1. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chemistry of the Thermal Decomposition of Lutetium Selenities

 The solubility isotherm of the system Lu₂O₃–SeO₂–H₂O was studied at 100°C. The compounds of the three-component system were identified by Schreinemakers’ method and chemical, derivatograph and X-ray phase analyses after separation in the pure state: Lu₂(SeO₃)₃·4H₂O and LuH(SeO₃)₂·2H₂O.     

Crystallization and Phase Stability of CaSO<Subscript>4</Subscript> and CaSO<Subscript>4</Subscript> – Based Salts

Summary.  Calcium sulfate occurs in nature in form of three different minerals distinguished by the degree of hydration: gypsum (CaSO₄·2H₂O), hemihydrate (CaSO₄·0.5H₂O) and anhydrite (CaSO₄). On the one hand the conversion of these phases into each other takes place in nature and on the other hand it represents the basis of gypsum-based building materials. The present paper reviews available phase diagram and crystallization kinetics information on the formation of calcium sulfate phases, including CaSO₄-based double salts and solid solutions. Uncertainties in the solubility diagram CaSO₄–H₂O due to slow crystallization kinetics particularly of anhydrite cause uncertainties in the stable branch of crystallization. Despite several attempts to fix the transition temperatures of gypsum–anhydrite and gypsum–hemihydrate by especially designed experiments or thermodynamic data analysis, they still vary within a range from 42–60°C and 80–110°C. Electrolyte solutions decrease the transition temperatures in dependence on water activity. Dry or wet dehydration of gypsum yields hemihydrates (α-, β-) with different thermal and re-hydration behaviour, the reason of which is still unclear. However, crystal morphology has a strong influence. Gypsum forms solid solutions by incorporating the ions HPO₄ ²⁻, HAsO₄ ²⁻, SeO₄ ²⁻, CrO₄ ²⁻, as well as ion combinations Na⁺(H₂PO₄)⁻ and Ln³⁺(PO₄)³⁻. The channel structure of calcium sulfate hemihydrate allows for more flexible ion substitutions. Its ion substituted phases and certain double salts of calcium sulfate seem to play an important role as intermediates in the conversion kinetics of gypsum into anhydrite or other anhydrous double salts in aqueous solutions. The same is true for the opposite process of anhydrite hydration to gypsum. Knowledge about stability ranges (temperature, composition) of double salts with alkaline and alkaline earth sulfates (esp. Na₂SO₄, K₂SO₄, MgSO₄, SrSO₄) under anhydrous and aqueous conditions is still very incomplete, despite some progress made for the systems Na₂SO₄–CaSO₄ and K₂SO₄–CaSO₄–H₂O. Corresponding author. E-mail: daniela.freyer@chemie.tu-freiberg.de Received December 17, 2002; accepted January 10, 2003 Published online April 3, 2003     

Experimental Determination of the Isotherm at 15°C of the System Mg2+/Cl?, SO42–H2O

 The diagram of the ternary system Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram, which are MgSO₄·6H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O. The solubility field of MgSO₄·7H₂O is important whereas those of MgSO₄·6H₂O and MgCl₂·6H₂O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO₄:MgCl₂=2.73:33.80 and MgSO₄: MgCl₂=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C.     

Tribochemistry and kinetics of Al2(SO4)3·xH2O decomposition

The thermal decomposition of tribochemically activated Al₂(SO₄)₃·xH₂O was studied by TG, DTA and EMF methods. For some of the intermediate solids, X-ray diffraction and IR-spectroscopy were applied to learn more about the reaction mechanism. Thermal and EMF studies confirmed that, even after mechanical activation of Al₂(SO₄)₃·xH₂O, Al₂O(SO₄)₂ is formed as an intermediate. Isothermal kinetic experiments demonstrated that the thermochemical sulphurization of inactivated Al₂(SO₄)₃·xH₂O has an activation energy of 102.2 kJ·mol^?1 in the temperature range 850–890 K. The activation energy for activated Al₂(SO₄)₃·xH₂O in the range 850–890 K is 55.0 kJ·mol^?1. The time of thermal decomposition is almost halved when Al₂(SO₄)₃·xH₂O is activated mechanically. The results permit conclusions concerning the efficiency of the tribochemical activation of Al₂(SO₄)₃·xH₂O and the chemical and kinetic mechanisms of the desulphurization process.     

Chemistry of the Thermal Decomposition of Lutetium Selenities

Summary.  The solubility isotherm of the system Lu₂O₃–SeO₂–H₂O was studied at 100°C. The compounds of the three-component system were identified by Schreinemakers’ method and chemical, derivatograph and X-ray phase analyses after separation in the pure state: Lu₂(SeO₃)₃·4H₂O and LuH(SeO₃)₂·2H₂O. Received February 27, 2002; accepted (revised) April 26, 2002     

Chemie der Seltenerdmetalle, 17. Mitt.: Ce(III)-verbindungen der Bernsteinsäure

The Compounds CeSucCl·6H₂O, CeSucCl·3H₂O, HCeSuc ₂·H₂O and Ce₂(CO₃)₂ Suc·2H₂O were isolated and characterised by thermogravimetric analysis, I. R. spectroscopy and X-ray diffraction. The solubility of the Ce(III)-succinate and the thermic stabilities are reported.     

Spectral and thermal studies of light lanthanide 4-chlorophthalates

Conditions for the preparation of light lanthanide 4-chlorophthalates were investigated and their composition, solubility in water at 295 K, IR spectra and thermal decomposition were determined. 4-Chlorophthalates of La–Nd(III) were prepared as complexes with general formula NaLn[ClC₆H₃(CO₂)₂]₂, whereas compounds of Sm and Eu have general formula Ln₂[ClC₆H₃(CO₂)₂]₃·6H₂O. During heating all complexes decompose to oxides with intermediate formation of oxochlorides. The carboxylate groups in the complexes studied are bidentate bridging (Sm, Eu) or bidentate chelating and bridging (La–Nd).     

Re-investigations of thermal decomposition of gadolinium sulfate octahydrate

The crystals of Gd₂(SO₄)₃·8H₂O were obtained by slow crystallization from a saturated solution previously received by dissolving Gd₂O₃ in an aqueous solution of sulfuric acid. The thermal behavior of this salt was studied using simultaneous DTA–TG technique under a nitrogen and air, in the temperature range of 298–1773 K. It was found that the dehydration of gadolinium sulfate octahydrate as well as thermal decomposition of anhydrous Gd₂(SO₄)₃ undergo in two steps. The existence of two polymorphic modification of anhydrous gadolinium sulfate has been confirmed. The new XRD data for high-temperature polymorph of Gd₂(SO₄)₃ were given. All intermediate products of dehydration and thermal decomposition were characterized by EPR method.     

Fe2(SO4)3·H2SO4·28H2O,a low‐temperature water‐rich iron(III) sulfate

The title compound, diiron(III) trisulfate–sulfuric acid–water (1/1/28), has been prepared at temperatures between 235 and 239 K from acid solutions of Fe₂(SO₄)₃. Studies of the compound at 100 and 200 K are reported. The analysis reveals the structural features of an alum, (H₅O₂)Fe(SO₄)₂·12H₂O. The Fe(H₂O)₆ unit is located on a centre of inversion at (, 0, ), while the H₅O₂⁺ cation is located about an inversion centre at (, , ). The compound thus represents the first oxonium alum, although the unit cell is orthorhombic.