Phase Equilibria in the Ternary Systems KBr–K2B4O7–H2O and KCl–K2B4O7–H2O at 373 K

According to the compositions of the underground gasfield brines in the west of Sichuan Basin,the phase equilibria in the ternary systems KBr-K2B4O7-H2O and KCl-K2B4O7-H2O at 373 K were studied using the isothermal dissolution equilibrium method.The solubilities of salts and the densities of saturated solutions in these ternary systems were determined.Using the experimental data,phase diagrams and density-composition diagrams were constructed.The two phase diagrams were simple co-saturation type,each having an invariant point,two univariant curves and two crystallization regions.The equilibrium solid phases in the ternary system KBr-K2B4O7-H2O are potassium bromide （KBr） and potassium tetraborate tetrahydrate （K2B4O7·4H2O）,and those in the ternary system KCl-K2B4O7-H2O are potassium chloride （KCl） and potassium tetraborate tetrahydrate （K2B4O7·4H2O）.Comparisons of the phase diagrams of the two systems at different temperatures show that there is no change in the crystallization phases,but there are changes in the size of the crystallization regions.As temperature increases,the solubility of K2B4O7·4H2O increases rapidly,so the crystallization field of K2B4O7·4H2O becomes smaller.     

Crystal structure of yegorovite Na4[Si4O8(OH)4] · 7H2O

Doklady Earth Sciences - Using X-ray analysis, the crystal structure of yegorovite Na4[Si4O8(OH)4] · 7H2O, a newly-discovered mineral from the Lovozero alkaline complex (Kola Peninsula,...     

Raman study of MgCr2O4–Fe2+Cr2O4 and MgCr2O4–MgFe2 3+O4 synthetic series: the effects of Fe2+ and Fe3+ on Raman shifts

Two synthetic series of spinels, MgCr₂O₄–Fe²⁺Cr₂O₄ and MgCr₂O₄–MgFe₂ ³⁺O₄ have been studied by Raman spectroscopy to investigate the effects of Fe²⁺ and Fe³⁺ on their structure. In the first case, where Fe²⁺ substitutes Mg within the tetrahedral site, there is a continuous and monotonic shift of the Raman modes A_1g and E_g toward lower wavenumbers with the increase of the chromite component into the spinel, while the F_2g modes remain nearly in the same position. In the second series, for low Mg-ferrite content, Fe³⁺ substitutes for Cr in the octahedral site; when the Mg-ferrite content nears 40 %, a drastic change in the Raman spectra occurs as Fe³⁺ starts entering the tetrahedral site as well, consequently pushing Mg to occupy the octahedral one. The Raman spectral region between 620 and 700 cm^?1 is associated to the octahedral site, where three peaks are present and it is possible to observe the Cr–Fe³⁺ substitution and the effects of order–disorder in the tetrahedral site. The spectral range at 500–620 cm^?1 region shows that there is a shift of modes toward lower values with the increase of the Mg-ferrite content. The peaks in the region at 200–500 cm^?1, when observed, show little or negligible Raman shift.     

Crystallization behavior of Na2SO4–MgSO4 salt mixtures in sandstone and comparison to single salt behavior

We report on the crystallization behavior and the salt weathering potential of Na₂SO₄, MgSO₄ and an equimolar mixture of these salts in natural rock and porous stone. Geochemical modeling of the phase diagram of the ternary Na₂SO₄–MgSO₄–H₂O system was used to determine the equilibrium pathways during wetting (or deliquescence) of incongruently soluble minerals and evaporation of mixed electrolyte solutions. Model calculations include stable and metastable solubilities of the various hydrated states of the single salts and the double salts Na₂Mg(SO₄)₂·4H₂O (bloedite), Na₂Mg(SO₄)₂·5H₂O (konyaite), Na₁₂Mg₇(SO₄)₁₃·15H₂O (loeweite) and Na₆Mg(SO₄)₄ (vanthoffite). In situ Raman spectroscopy was used to study the phase transformations during wetting of pure MgSO₄·H₂O (kieserite) and of the incongruently soluble salts bloedite and konyaite. Dissolution of kieserite leads to high supersaturation resulting in crystallization of higher hydrated phases, i.e. MgSO₄·7H₂O (epsomite) and MgSO₄·6H₂O (hexahydrite). This confirms the high damage potential of magnesium sulfate in salt damage of building materials. The dissolution of the incongruently soluble double salts leads to supersaturation with respect to Na₂SO₄·10H₂O (mirabilite). However, the supersaturation was insufficient for mirabilite nucleation. The damage potential of the two single salts and an equimolar salt mixture was tested in wetting–drying experiments with porous sandstone. While the high damage potential of the single salts is confirmed, it appears that the supersaturation achieved during wetting of the double salts at room temperature is not sufficient to generate high crystallization pressures. In contrast, very high damage potentials of the double salts were found in experiments at low temperature under high salt load.1     

Li2B4O7—Na2B4O70H2O三元体系25℃相关系及物化性质实验

通过实验研究了Ｌｉ２Ｂ４Ｏ７－Ｎａ２Ｂ４Ｏ７－Ｈ２Ｏ三元体系２５℃相关 溶液的物化性质，其２５℃相图由二条溶解度曲线构成，分别对应于Ｌｉ２Ｂ４Ｏ７．３Ｈ２Ｏ、Ｎａ２Ｂ４Ｏ７．１０Ｈ２Ｏ相区，属简单共饱和型。简要讨论了该体系硼酸盐在水听溶解行为，并用经验公式描述了物有浓度的变化规律。     

Na2CO3-Na2B4O7-H2O三元体系288K相平衡研究

采用等温溶解平衡法研究了三元体系 Na2 CO3- Na2 B4 O7- H2 O 2 88K时的相平衡及平衡液相的主要物化性质 (密度 ,电导率 ,p H)。研究发现 :该三元体系为简单共饱和型 ,无复盐及固溶体形成 ,根据溶解度数据绘制出相图 ,相图中单变量曲线所对应的平衡固相分别为 :Na2 CO3· 10 H2 O,Na2 B4 O7· 10 H2 O。并简要讨论了物化性质的变化规律。     

Cation substitution in synthetic meridianiite (MgSO4·11H2O) II: variation in unit-cell parameters determined from X-ray powder diffraction data

We have prepared aqueous MgSO₄ solutions doped with various divalent metal cations (Ni²⁺, Zn²⁺, Mn²⁺, Cu²⁺, Fe²⁺, and Co²⁺) in proportions up to and including the pure end-members. These liquids have been solidified into fine-grained polycrystalline blocks of metal sulfate hydrate + ice by rapid quenching in liquid nitrogen. In a companion paper (Fortes et al., in Phys Chem Min 39) we reported the identification of various phases using X-ray powder diffraction, including meridianiite-structured undecahydrates, melanterite- and epsomite-structured heptahydrates, novel enneahydrates and a new octahydrate. In this work we report the changes in unit-cell parameters of these crystalline products where they exist over sufficient dopant concentrations. We find that there is a linear relationship between the rate of change in unit-cell volume as a function of dopant concentration and the ionic radius of the dopant cation; large ions such as Mn²⁺ produce a substantial inflation of the hydrates’ unit-cell volume, whereas smaller ions such as Ni²⁺ produce a modest reduction in unit-cell volume. Indeed, when the data for all hydrates are normalised (i.e., divided by the number of formula units per unit-cell, Z, and the hydration number, n), we find a quantitatively similar relationship for different values of n. Conversely, there is no relationship between the degree of unit-cell inflation or deflation and the limit to which a given cation will substitute into a certain hydrate structure; for example, Co²⁺ and Zn²⁺ affect the unit-cell volume of MgSO₄·11H₂O to a very similar degree, yet the solubility limits inferred in our companion paper are >60 mol. % Co²⁺ and <30 mol. % Zn²⁺.     

NiFe2O4—ZnFe2O4尖晶石固溶体中的离子占位

在１＊１０＾５Ｐａ,１４００℃条件下实验合成了不同成分的Ｎｉ（１－ｘ）ＺｎｘＦｅ２Ｏ４尖晶石,并将部分尖晶石在１１００℃和１６１０℃条件下重新平衡。采用粉晶Ｘ射线衍射法测定了尖晶石的晶胞参数。将实测的尖晶石晶胞参数与理论计算值进行对比,结果发现,在温度小于１４００℃时Ｎｉ（１－ｘ）ＺｎｘＦｅ２Ｏ４尖晶石中的四面体主要由Ｚｎ＾２＋、Ｆｅ＾３＋占据,而八面体主要由Ｎｉ＾２＋、Ｆｅ＾３＋占据,但至少当温     

Mössbauer effect study of anapaite, Ca2Fe2+(PO4)2 · 4H2O, and of its oxidation products

Mössbauer spectra (MS) of anapaite (Ca₂ Fe²⁺(PO₄)₂?·?4H₂O) and of a sample after being immersed in a 4% H₂O₂ solution at room temperature (RT) over 12 days (hereafter an4ox) were collected at temperatures in the range 4.2 to 420?K and 11 to 300?K respectively. All MS consist of symmetrical doublets, hence magnetic ordering was not observed. The temperature dependencies of the Fe²⁺ centre shifts of anapaite and an4ox were analysed with the Debye model for the lattice vibrations. The characteristic Mössbauer temperatures were found as 370?K?±?25?K and 340?K?±?25?K, and the intrinsic isomer shifts as 1.427?±?0.005?mm/s and 1.418?±?0.005?mm/s respectively. From the external-field (60?kOe) MS recorded at 4.2 and 189?K for the non-treated sample, the principal component V _zz of the electric field gradient (EFG) is determined to be positive and the asymmetry parameter η?≈?0.2 and 0.4 respectively. The temperature variations of the quadrupole splittings, ΔE _Q(T), cannot be interpreted on the basis of the thermal population of the ⁵ D electronic levels resulting from the tetragonal compression of the O₆ co-ordination. The low-temperature linear behaviour of ΔE _Q(T) is attributed to a strong orbit-lattice coupling. A field of 60 kOe applied to anapaite at 4.2?K produces magnetic hyperfine splitting with effective hyperfine fields of ?136, ?254 and ?171?kOe along the principal axes Ox, Oy and Oz of the EFG tensor respectively. Additional oxidation treatments in solutions with various H₂O₂ concentrations up to 20% and subsequent Mössbauer experiments at room temperature, have revealed that the anapaite structure is not sensitive to oxidation since eventually only a small amount of Fe²⁺ (～6.5%) is converted into Fe³⁺.     

Solid-liquid Equilibria for the Quaternary NaCl–Na2SO4–Na2B4O7–H2O System at 348 K

正1 Introduction China has very abundant liquid mineral resources.Especially,the brine resources in the west of Sichuan Basin are pushed into the first place in China,whose K and B contents are unusually high.These rare liquid mineral resources have very good exploitation prospect(Lin,2001;2006).Generally speaking,phase equilibrium     

交互四元体系Li+,Mg2+//SO2-4,B4O2-7-H2O 288 K时相平衡研究

采用等温溶解平衡法研究了288K时Li+, Mg2+//SO2-4, B4O2-7- H2O四元体系的固液相平衡关系,测定了该四元体系在288K时平衡液相的溶解度和密度.依据实验测定的平衡溶解度数据及对应的平衡固相,绘制了该四元体系的平衡相图及密度组成图.研究结果表明:交互四元体系Li+, Mg2+//SO2-4, B4O2-7- H2O 288K时平衡相图中有2个共饱点,5条单变量曲线,4个结晶区对应的平衡固相分别为Li2B4O7·3H2O,Li2SO4·H2O,MgB4O7·9H2O和MgSO4·7H2O.     

298K时三元体系K^＋／CO3^2—,B4O7^2——H2O和Li^＋／CO3^2—,B4O7^2——H2O相关系

研究了二个三元体系Ｌｉ＋／ＣＯ２－３,Ｂ４Ｏ２－７Ｈ２Ｏ（１）和Ｋ＋／ＣＯ２－３,Ｂ４Ｏ２－７Ｈ２０（２）２９８Ｋ时的相平衡关系和平衡液相的物化性质（密度、折光密、粘度、电导率、ｐＨ值）。研究表明：这二个三元体系均属简单共饱型,无复盐或固溶体形成。体系（１）的两段溶解度曲线对应于无水Ｌｉ２ＣＯ３和Ｌｉ２Ｂ４Ｏ７·３Ｈ２Ｏ结晶区,体系（２）的两段溶解度曲线对应于Ｋ２ＣＯ３·３／２Ｈ２Ｏ和Ｋ２Ｂ４Ｏ７·４Ｈ２Ｏ结晶区。     

Structural changes in the FeAl2O4–FeCr2O4 solid solution series and their consequences on natural Cr-bearing spinels

The influence of Al–Cr substitution on the spinel structure was studied in synthetic single crystals belonging to the FeCr₂O₄–FeAl₂O₄ series produced by flux growth at 1,000–1,300 °C in controlled atmosphere. Samples were characterized by single-crystal X-ray diffraction, electron microprobe analyses and Mössbauer spectroscopy. Crystals of sufficient size and quality for single-crystal X-ray diffraction were obtained in the ranges Chr_0–0.45 and Chr_70–100 but not for intermediate compositions, possibly due to a reduced stability in this range. The increase in chromite component leads to an increase in the cell edge from 8.1534 (6) to 8.3672 (1) Å and a decrease in the u parameter from 0.2645 (2) to 0.2628 (1). Chemical analyses show that Fe²⁺ is very close to 1 apfu (0.994–1.007), Al is in the range 0.0793–1.981 apfu, Cr between 0 and 1.925 apfu. In some cases, Fe³⁺ is present in amounts up to 0.031 apfu. Spinels with intermediate Cr content (Chr component between 40 and 60) are strongly zoned with Cr-rich cores and Cr-poor rims. Mössbauer analyses on powdered spinels of the runs from which single crystal has been used for X-ray structural data show values of Fe³⁺/Fe_tot consistently larger than that calculated by EMPA on single crystals, presumably due to chemical variation between single crystals from the same runs. The synthesis runs ended at a temperature of 1,000 °C, but it is possible that cation ordering continued in the Cr-poor samples towards lower temperatures, possibly down to 700 °C.     

Hydrogen bonding in coquimbite, nominally Fe2(SO4)3·9H2O, and the relationship between coquimbite and paracoquimbite

Using single-crystal X-ray diffraction at 293, 200 and 100 K, and neutron diffraction at 50 K, we have refined the positions of all atoms, including hydrogen atoms (previously undetermined), in the structure of coquimbite ( $ P {\bar 3}1c $ , a?=?10.924(2)/10.882(2) Å, c?=?17.086(3) / 17.154(3) Å, V?=?1765.8(3)/1759.2(5) ų, at 293 / 50 K, respectively). The use of neutron diffraction allowed us to determine precise and accurate hydrogen positions. The O–H distances in coquimbite at 50 K vary between 0.98 and 1.01 Å. In addition to H₂O molecules coordinated to the Al³⁺ and Fe³⁺ ions, there are rings of six “free” H₂O molecules in the coquimbite structure. These rings can be visualized as flattened octahedra with the distance between oxygen and the geometric center of the polyhedron of 2.46 Å. The hydrogen-bonding scheme undergoes no changes with decreasing temperature and the unit cell shrinks linearly from 293 to 100 K. A review of the available data on coquimbite and its “dimorph” paracoquimbite indicates that paracoquimbite may form in phases closer to the nominal composition of Fe₂(SO₄)₃·9H₂O. Coquimbite, on the other hand, has a composition approximating Fe_1.5Al_0.5(SO₄)₃·9H₂O. Hence, even a “simple” sulfate Fe_2-x Al _x (SO₄)₃·9H₂O may be structurally rather complex.     

Thermodynamic properties of tooeleite,Fe63+(As3+O3)4(SO4)(OH)4·4H2O

Tooeleite, nominally Fe₆³⁺(As³⁺O₃)₄(SO₄)(OH)₄·4H₂O, is a relatively uncommon mineral of some acid-mine drainage systems. Yet, if it does occur, it does so in large quantities, indicating that some specific conditions favor the formation of this mineral in the system Fe-As-S-O-H. In this contribution, we report the thermodynamic properties of synthetic tooeleite. The sample was characterized by powder X-ray diffraction, scanning electron microscopy, extended X-ray absorption fine-structure spectroscopy, and Mössbauer spectroscopy. These methods confirmed that the sample is pure, devoid of amorphous impurities of iron oxides, and that the oxidation state of arsenic is 3+. Using acid-solution calorimetry, the enthalpy of formation of this mineral from the elements at the standard conditions was determined as −6196.6 ± 8.6 kJ mol⁻¹. The entropy of tooeleite, calculated from low-temperature heat capacity data measured by relaxation calorimetry, is 899.0 ± 10.8 J mol⁻¹ K⁻¹. The calculated standard Gibbs free energy of formation is −5396.3 ± 9.3 kJ mol⁻¹. The log K_sp value, calculated for the reaction Fe₆(AsO₃)₄(SO₄)(OH)₄·4H₂O + 16H⁺ = 6Fe³⁺ + 4H₃AsO₃ + SO₄²⁻ + 8H₂O, is −17.25 ± 1.80. Tooeleite has stability field only at very high activities of aqueous sulfate and arsenate. As such, it does not appear to be a good candidate for arsenic immobilization at polluted sites. An inspection of speciation diagrams shows that the predominance field of Fe³⁺ and As³⁺ overlap only at strongly basic conditions. The formation of tooeleite, therefore, requires strictly selective oxidation of Fe²⁺ to Fe³⁺ and, at the same time, firm conservation of the trivalent oxidation state of arsenic. Such conditions can be realized only by biological systems (microorganisms) which can selectively oxidize one redox-active element but leave the other ones untouched. Hence, tooeleite is the first example of an “obligatory” biomineral under the conditions prevailing at or near the Earth's surface because its formation under these conditions necessitates the action of microorganisms.     

四元体系K_2SO_4-K_2B_4O_7-K_2CO_3-H_2O 273K时介稳相平衡研究

采用等温蒸发法研究K2SO4-K2B4O7-K2CO3-H2O四元体系在低温273K时的介稳固液相平衡关系,测定了介稳平衡液相的溶解度和密度。研究发现,该四元体系273K时的介稳平衡相图有3个固相结晶相区分别为K2SO4,K2B4O7.4H2O和K2CO3.3/2H2O;3条单变量曲线E1E,E2E和E3E;一个共饱点E,在共饱点E处的液相中各盐的溶解度分别为K2CO3(43.46%),K2SO4(2.52%)和K2B4O7(3.10%);研究结果表明K2CO3对K2B4O7和K2SO4有强烈的盐析作用。实验证明在富含硼钾的扎布耶盐湖卤水中,低温平衡条件下硫酸钾和硼酸钾极易从溶液中结晶析出,而碳酸钾则由于溶解度大,介稳性强,即使在低温条件下也难以从溶液中析出。     

Formation and properties of hydrosilicate liquids in the systems Na2O-Al2O3-SiO2-H2O and granite-Na2O-SiO2-H2O at 600°C and 1.5 kbar

In order to determine the mechanisms of formation and properties of natural hydrosilicate liquids (HSLs), which are formed during the transition from magmatic to hydrothermal mineral formation in granitic pegmatites and rare-metal granites, the formation of HSLs was experimentally studied in the Na₂O-SiO₂-H₂O, Na₂O-Al₂O₃-SiO₂-H₂O, and Na₂O-K₂O-Li₂O-Al₂O₃-SiO₂-H₂O systems at 600°C and 1.5 kbar. It was shown that the sequential extension of composition does not suppress HSL formation in the systems and expands the stability field of this phase. However, HSLs formed in extended chemical systems have different structure and properties: the addition of alumina induces some compression of the structure of the silicate framework of HSLs, which results in a decrease in water content in this phase and probably hinders the reversibility of its dehydration. It was demonstrated that HSL can be formed by the coagulation of silica present in a silica-oversaturated alkaline aqueous fluid. It was supposed that the HSL formed during this process has a finely dispersed structure. It was argued that anomalous enrichment in some elements in natural HSLs can be due to their sorption by the extensively developed surface of HSL at the moment of its formation.