Double Carbonate Research Articles

High pressure raman spectroscopy and X-ray diffraction of K2Ca(CO3)2 bütschliite: multiple pressure-induced phase transitions in a double carbonate

The crystal structure and bonding environment of K2Ca(CO3)2 bütschliite were probed under isothermal compression via Raman spectroscopy to 95 GPa and single crystal and powder X-ray diffraction to 12 and 68 GPa, respectively. A second order Birch-Murnaghan equation of state fit to the X-ray data yields a bulk modulus, K0=46.9\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${K}_{0}=46.9$$\\end{document} GPa with an imposed value of K0′=4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${K}_{0}^{\\prime}= 4$$\\end{document} for the ambient pressure phase. Compression of bütschliite is highly anisotropic, with contraction along the c-axis accounting for most of the volume change. Bütschliite undergoes a phase transition to a monoclinic C2/m structure at around 6 GPa, mirroring polymorphism within isostructural borates. A fit to the compression data of the monoclinic phase yields V0=322.2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{0}=322.2$$\\end{document} Å3,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$,$$\\end{document}K0=24.8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${K}_{0}=24.8$$\\end{document} GPa and K0′=4.0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${K}_{0}^{\\prime}=4.0$$\\end{document} using a third order fit; the ability to access different compression mechanisms gives rise to a more compressible material than the low-pressure phase. In particular, compression of the C2/m phase involves interlayer displacement and twisting of the [CO3] units, and an increase in coordination number of the K+ ion. Three more phase transitions, at ~ 28, 34, and 37 GPa occur based on the Raman spectra and powder diffraction data: these give rise to new [CO3] bonding environments within the structure.

Investigation on the Performance of Limestone as Filler on Various Pavement Mixtures

Abstract Additives added to the flexible pavement mixture aim to increase the strength of the pavement. Limestone which is a sedimentary rock consists of the mineral calcium carbonate (calcite) or the double carbonate of calcium and magnesium (dolomite). The use of limestone in pavement mixtures is expected to increase the performance of Marshall parameters. This study aims to determine the suitability of limestone as a filler for 3 types of pavement mixtures, namely Asphalt Concrete Wearing Course, Hot Rolled Sheet and Split Mastic Asphalt. In this study, the limestone used was sourced from Jorong Durian, Nagari Kamang Mudiak, Kamang Magek District, Agam Regency, West Sumatra Province. The tests were carried out using following variations of limestone; 0%, 25%, 50%, 75%, 100% of the total amount of filler in the mixture. The results of the study using limestone as filler obtained at an optimum content of 29% for AC-WC, 22% for HRS, and 82.5% for SMA. In addition, AC-WC pavement was found to the best increase in Marshall stability performance. Therefore, it can be concluded that limestone from Kamang Mudiak is most suitable to be added to AC-WC pavement mixtures.

Growth of large norsethite crystals in aqueous ammonium nitrate solutions

Crystallization of norsethite [BaMg(CO3)2] receives considerable attention as a key for solving geological problems, and environmental and resource issues. Noresthite is poorly soluble in water, and is synthesized via witherite [BaCO3] by solution-mediated transformation. In contrast, owing to the difficulties such as tremendous growth time and consideration of multi-step reactions, the shape and size of norsethite were not satisfactory for further investigations so far. Here we tried to increase the solubility of the crystals to overcome these difficulties of the growth by adding NH4NO3. The solubilities of norsethite and witherite in the presence of NH4NO3 were ∼35 and ∼45 times higher than those in the absence of NH4NO3, respectively. At 90 °C, the growth rate of norsethite in NH4NO3 solutions was ∼17 times higher than that in NH4NO3-free solutions, and norsethite in NH4NO3 solutions nucleated immediately after mixing the raw materials. Finally, we succeeded in synthesizing bulky norsethite crystals of 170 μm size only in one month, utilizing 0.1–1 M NH4NO3 solutions of 90 °C. We could explain the appearance of large norsethite, considering that norsethite dominantly consumes the solute by adding NH4NO3 compared with witherite. The findings provide a breakthrough in the growth technique of double carbonates.

High pressure Raman study of Na4Ca(CO3)3 from the ambient pressure to 11 GPa

ABSTRACT Na-Ca double carbonates were found as the inclusions in ‘superdeep’ Juina diamonds and as the products of high pressure experiments and thus are regarded as the potential host of CO2 in the deep mantle. Recently, Na-rich carbonate (21.0% wt. of Na2O vs. 13.6% wt. of CaO) was reported as the product of experiment with carbonated eclogite treated at 21 GPa and 1200°C. Na/Ca ratio of this carbonate corresponds to Na4Ca(CO3)3 phase with cubic symmetry synthesized at 6 GPa. The stability of Na4Ca(CO3)3 at higher pressures has not been investigated yet. Herein, we report an in situ Raman study of Na4Ca(CO3)3 carbonate up to 11 GPa in order to reveal stability of its structure at mantle pressures. Obtained results strongly imply for reversible phase transition near 8 GPa associated with decrease of symmetry. The observed phase transition questions the stability of cubic Na4Ca(CO3)3 under conditions of mantle transition zone.

Synthesis of cyclic polymers containing various backbones by means of non-stoichiometric Suzuki-Miyaura polycondensation through intramolecular catalyst transfer

Cyclic polymers bearing various backbones are selectively synthesized by means of non-stoichiometric Suzuki-Miyaura polycondensation of 1.0 equivalent of diboronate monomers containing carbon–carbon double bond (C=C), ester, ether, and carbonate linkages with 1.3 equivalents of meta- or para-dibromophenylene in the presence of t-Bu3PPd G2 precatalyst and CsF/18-crown-6 as a base. The molecular weight of the cyclic polymers increases with increasing monomer concentration. The obtained polymer containing C=C is cyclic even in the high-molecular-weight region, as confirmed by end-group analysis after degradative cross-metathesis reaction of the obtained polymer with an excess of an olefinic small molecule. This non-stoichiometric A2 + B2 Suzuki-Miyaura polycondensation is expected to be a powerful tool for the synthesis of cyclic polymers containing various functional groups in the backbone.

A high-pressure structural transition of norsethite-type BaFe(CO3)2: Comparison with BaMg(CO3)2 and BaMn(CO3)2

Abstract Investigations on the phase stability of the norsethite-type family [BaMg(CO3)2, BaMn(CO3)2, BaFe(CO3)2] under high-pressure conditions are of great significance for understanding the structure and metal cationic (Mg2+, Fe2+, Mn2+) substitution mechanism in double divalent metal carbonates. The structural evolution and equation of state of BaFe(CO3)2 were studied at high pressure up to ~7.3 GPa by synchrotron X-ray diffraction (XRD) in diamond-anvil cell (DAC) in this study. BaFe(CO3)2 undergoes a reversible phase transition from R3m (α-phase) to C2/c (γ-phase) space groups at ~3.0 GPa. The fitted elastic parameters are V0 = 377.79(2) Å3 and K0 = 40.3(7) GPa for α-BaFe(CO3)2, V0 = 483.24(5) Å3 and K0 = 91.2(24) GPa for γ-BaFe(CO3)2 using second-order Birch-Murnaghan equation of state (BM2-EoS). Besides, the vibrational properties and structural stability of complete norsethite-type minerals were also investigated first by Raman spectroscopy combined with DAC up to 11.1 GPa. Similar structural phase transitions occur in BaMg(CO3)2, BaFe(CO3)2, BaMn(CO3)2 at 2.2–2.6, 2.6–3.7, and 3.7–4.1 GPa, respectively. The onset phase transition pressures of the norsethite-type family are much lower than that of dolomite-type Ca(Mg,Fe,Mn)(CO3)2 and calcite-type (Mg,Fe,Mn)CO3 carbonates. These results provide new insights into the divalent cation substitution effects on the stability and structural evolution of carbonates under high-pressure conditions.

Investigation of K2CO3-modified CaO sorbents for CO2 capture using in-situ X-ray diffraction

Alkali metal salt promoters, such as K2CO3 investigated in this work, are known to affect the cyclic performance of CaO-based sorbents – sometimes positively, sometimes negatively. Thus far, the influence of K2CO3 (and other salt-based promoters) is poorly understood, and detailed investigations on the interaction of K2CO3 with CaO are missing. We find that low amounts of K2CO3 in the sorbents improve the cyclic performance of CaO significantly (up to a factor of three), both under mild and harsh CO2 release conditions, while large amounts of K2CO3 (>1 mol.%) reduce the positive effect on the CO2 uptake performance. Aided by in-situ X-ray diffraction measurements, we observe that the gas environment has an important influence on the stability of K-containing phases in the sorbent. At typical carbonation conditions (650 °C, 15 vol% CO2/N2), CaO and K2CO3 readily form K-Ca double carbonates (K2Ca(CO3)2, which reacts further to form K2Ca2(CO3)3). When the calcination reaction is carried out in pure N2, the K-Ca double carbonates decompose above ∼730 °C, forming K2CO3 that becomes partially volatile near its melting point of ∼900 °C, and leads to a reduction of the K content in the samples with cycling. When the calcination reaction is carried out in a CO2-rich environment, the cyclic loss of K2CO3 is reduced substantially, but the sintering of the sorbent is increased. There are indications that very low quantities of K are incorporated into the CaO structure, and the formation of K-Ca double carbonates appears to influence the structural evolution of the CaCO3 phase formed during carbonation. With very low amounts of K2CO3 present in the sorbent, we observe an increase in pore volume for pore diameters between 20 and 80 nm, which ultimately may explain the improved CO2 uptake performance compared to the CaO sorbent without K2CO3.

Kinetic oxygen isotope fractionation upon acid liberation of CO2 from artificial and natural norsethite (BaMg(CO3 )2 ), a mineral analogue of dolomite.

The analytical method to determine the stable oxygen isotope (18 O/16 O) composition of carbonates via phosphoric acid digestion leads to temperature- and solid-dependent kinetic isotope fractionation. Values for the double carbonate norsethite (BaMg(CO3 )2 ) have been unknown so far. The temperature dependence of kinetic oxygen isotope fractionation during the reaction of synthetic and natural BaMg(CO3 )2 with orthophosphoric acid (H3 PO4 ) according to the overall reaction BaMg(CO3 )2 + 2H3 PO4 = Ba2+ + Mg2+ + 2HPO4 2- + 2CO2 + 2H2 O has been examined for the first time using separate carbonate decomposition via fluorination or phosphoric acid digestion, with the resulting gases analyzed by isotope ratio monitoring mass spectrometry. In the temperature range between 25 and 70°C the kinetic fractionation factor between acid-generated CO2 and artificial and natural norsethite is described by (T in K): [Formula: see text] with A= 4.15 and B= 6.47 for natural norsethite, and A= 4.77 and B= 5.94 for synthetic norsethite. The fractionation factor measured for a poorly crystallized synthetic carbonate agrees with those for the other samples at 25°C, but is slightly lower at 50 and 70°C. No carbon isotope fractionation was found during the unidirectional acid dissolution. The kinetic oxygen isotope fractionation during phosphoric acid liberation of CO2 from BaMg(CO3 )2 is quantified. Based on published results for endmember carbonates, the results at 25°C for other double carbonates are estimated.

Raman study of quench products of alkaline carbonate melt at 3 and 6 GPa: Link to the pressure of origin

AbstractInclusions of former alkaline carbonate melts occur in igneous minerals, mantle xenoliths, and diamonds from kimberlites and lamproites. However, the identification of most daughter phases remains undetermined owing to the lack of their Raman spectra. Yet, the phase compositions of the alkali carbonate melt at different pressure are interesting to know because Na‐Ca, Na‐Mg, K‐Ca, and K‐Mg double carbonates have a number of pressure‐induced phase transitions. Here, we studied the quench products of K‐Ca, K‐Mg, and Na‐Ca carbonate melts obtained at 3 and 6 GPa. Scanning electron microscopy coupled with energy‐dispersive spectroscopy with silicon drift detector (EDS‐SDD) and Raman spectroscopy were employed for phase characterization. The following carbonates were detected among the quench products: γ‐Na2CO3, Na4Ca(CO3)3 (Ia3d), Na2Ca3(CO3)3 (P1n1), K2Ca(CO3)2 ( ) bütschliite, disordered K2Ca3(CO3)4 (Pnam), K2Mg(CO3)2 ( ), aragonite, magnesite at 6 GPa; and CaCO3‐bearing K2CO3, K2Ca(CO3)2 ( ) bütschliite, K2Ca2(CO3)3 (R3), and ordered K2Ca3(CO3)4 (P212121) at 3 GPa. The results indicate that the quench products of carbonate melt consist of carbonates thermodynamically stable at the pressure of quenching. Thus, the daughter phases in carbonatitic inclusions could be identified by obtained Raman spectra and reflect the pressure conditions of their entrapment.

Quench Products of K-Ca-Mg Carbonate Melt at 3 and 6 GPa: Implications for Carbonatite Inclusions in Mantle Minerals

Alkali-rich carbonate melts are found as inclusions in magmatic minerals, mantle xenoliths, and diamonds from kimberlites and lamproites worldwide. However, the depth of their origin and bulk melt composition remains unclear. Here, we studied quench products of K-Ca-Mg carbonate melt at 3 and 6 GPa. The following carbonates were detected at 3 GPa: K2CO3, K2Ca(CO3)2 bütschliite (R3¯2/m), o-K2Ca3(CO3)4 (P212121), K2Ca2(CO3)3 (R3), K2Mg(CO3)2 (R3¯m), Mg-bearing calcite, dolomite, and magnesite. At 6 GPa, the variety of quench carbonate phases includes K2CO3, K2Ca(CO3)2 bütschliite (R3¯2/m), d-K2Ca3(CO3)4 (Pnam), K2Mg(CO3)2 (R3¯m), aragonite, Mg-bearing calcite, dolomite, and magnesite. The data obtained indicate that alkali-bearing carbonate melts quench to the alkaline earth and double carbonates that are thermodynamically stable at quenching pressure and can be used as markers reflecting the pressure of their entrapment. Further, in this study, we established the fields of melt compositions corresponding to the distinct quench assemblages of carbonate minerals, which can be used for the reconstruction of the composition of carbonatitic melts entrapped by mantle minerals.

Phase transitions and compressibility of alkali-bearing double carbonates at high pressures: a first-principles calculations study

Phase transitions and compressibility of alkali-bearing double carbonates at high pressures: a first-principles calculations study

Effect of Dolomite Addition on the Structure and Properties of Multicomponent Amphibolite Glasses.

The structure and properties of the glass can be modified by introducing appropriate additives. Dolomite is one of the primary raw materials modifying the properties of glass, in which the essential component is calcium-magnesium double carbonate CaCO3∙MgCO3. The paper presents the research results on glasses obtained by smelting pure amphibolite and amphibolite modified with 10 and 20% dolomite additives. The raw material used was mined in the Poland region of Lower Silesia. The glass melting process was carried out in an electric furnace at 1450 °C for 2 h. The structure and properties of the glasses and crystallization products were determined by Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy—Energy Dispersive Spectroscopy (SEM-EDS). Viscosity and Vickers microhardness were also measured. It was found that the modification of amphibolite glass by adding dolomite affects the glasses’ properties and structure. The research results determined the effect of dolomite addition on the properties of alumino-silicate glasses in terms of the mineral fibre products used in the construction industry.

OPTIMIZATION AND KINETICS STUDIES OF THE DISSOLUTION OF DOLOMITE IN SULPHURIC ACID (H2SO4) VIA BOX-BEHNKEN EXPERIMENTAL DESIGN

Background: The recovery of any valuable component from dolomite as a double carbonate mineral depends on its dissolution efficiency. Aim: This study aimed to optimize and provide a simplified novel approach to the kinetics of dolomite dissolution in sulphuric acid solution using the Box-Behnken experimental design. Methods: The dolomite sample was dissolved in a sulphuric acid solution at seventeen different experimental conditions. The residue containing impurities was removed via filtration, while precipitation was carried out at the optimum conditions. Results and Discussion: The relationship between the independent and dependent variables best fits into the two-factor interaction model with a coefficient of determination of 0.9492, adjusted R² of 0.9187, and predicted R² of 0.7514. The total residual sum of 3x10-13 and adequate precision of 18.769 show that the predicted dissolution efficiency is much closer to the experimental values. The analysis of variance revealed that the individual effect of acid concentration, temperature, and dissolution time all positively contribute to the dissolution. The interactive effect of acid concentration with temperature and the interactive effect of temperature with dissolution time also positively influences the dissolution efficiency. Following the dissolution of dolomite in sulphuric acid, a white precipitate was formed at room temperature, which dissolved back at a temperature of 70 oC, agitation speed of 900 revolutions per minute, and within 10 minutes. A predictive approach using a two-factor interactive model was applied to generate the kinetic data. Conclusions: The established model equation is suitable for predicting dolomite dissolution in sulphuric acid. The application of the shrinking core model to the generated data shows that the reaction between dolomite and sulphuric acid is film diffusion control with a first-order reaction (0.6587) and activation energy of 27.5 KJmol-1k-1.

Phase stability and dense polymorph of the BaCa(CO3)2 barytocalcite carbonate.

The double carbonate BaCa(CO3)2 holds potential as host compound for carbon in the Earth’s crust and mantle. Here, we report the crystal structure determination of a high-pressure BaCa(CO3)2 phase characterized by single-crystal X-ray diffraction. This phase, named post-barytocalcite, was obtained at 5.7 GPa and can be described by a monoclinic Pm space group. The barytocalcite to post-baritocalcite phase transition involves a significant discontinuous 1.4% decrease of the unit-cell volume, and the increase of the coordination number of 1/4 and 1/2 of the Ba and Ca atoms, respectively. High-pressure powder X-ray diffraction measurements at room- and high-temperatures using synchrotron radiation and DFT calculations yield the thermal expansion of barytocalcite and, together with single-crystal data, the compressibility and anisotropy of both the low- and high-pressure phases. The calculated enthalpy differences between different BaCa(CO3)2 polymorphs confirm that barytocalcite is the thermodynamically stable phase at ambient conditions and that it undergoes the phase transition to the experimentally observed post-barytocalcite phase. The double carbonate is significantly less stable than a mixture of the CaCO3 and BaCO3 end-members above 10 GPa. The experimental observation of the high-pressure phase up to 15 GPa and 300 ºC suggests that the decomposition into its single carbonate components is kinetically hindered.

First-Principle Studies of the Structural, Electronic, Mechanical, and Vibrational Properties of Double Carbonates with a Dolomite Structure

Density functional theory with a PBE gradient functional and a dispersion correction D3(BJ) in the basis of localized orbitals of the CRYSTAL17 package are used to calculate crystal structure parameters, electronic and vibrational spectra, elastic constants of rhombohedral double carbonates М1М2 (СО3)2 (М1, М2: Mg, Ca, Mn, Cd, Zn) with a dolomite-type structure. The paper demonstrates the possibility for establishing the linear dependences for lattice constants, interatomic distances, elastic constants and polycrystalline moduli, wave numbers of individual vibrational modes on the radii of cations. The same possibility is shown for the dependences of the parameters of chemical bonds and formation energies on their electronegativities. The lattice parameters increase along with the average cation radius, but the elastic constants and moduli demonstrate their decrease. The highest compressibility of carbonates is predicted in the direction of the c axis, which is consistent with the nature of the chemical bond, where stronger carbon — oxygen bonds are present in the ab plane, and weaker metal — oxygen bonds are in the direction of the c axis. The formation energy of binary carbonates CaMg(CO3)2 produced from solid oxides and gaseous CO2 is equal to -2.82 eV. It is equal to -2.71 eV for CaCd(CO3)2, and -0.054 eV, 0.023 eV for simple carbonates, respectively. The resulting formulas can be used to assess and predict the physical properties of solid solutions of carbonates of variable composition.

Isotopic responses of magnesium to two types of dissolution-reprecipitation processes for the growth of the double-carbonate mineral norsethite

Abstract An important mechanism of carbonate mineral growth is dissolution-reprecipitation, including the transformation of amorphous precursor to crystalline carbonates, and coarsening (ripening) of fine carbonate crystals. However, the mechanistic details of cation exchange associated with carbonate mineral growth via a dissolution-reprecipitation process are still not well understood. In this study, we used Mg isotopes to probe the exchange of Mg between aqueous solutions and norsethite [BaMg(CO3)2] by systematic synthesis experiments. Norsethite is a model double carbonate, with a general formula of AB(CO3)2, where A and B stand for two different divalent ions. Formation of norsethite is comprised of three stages, including: (1) precipitation of barium-magnesium (Ba-Mg) amorphous carbonate; (2) transformation of Ba-Mg amorphous carbonate to nano-crystalline norsethite by fast dissolution-reprecipitation; and (3) coarsening (ripening) of nano-norsethite by slow dissolution-reprecipitation. Magnesium isotopes displayed distinct fractionation behaviors in each of the three stages. The Mg isotope fractionation factors (∆26Mgsolid-aq) associated with precipitation of Ba-Mg amorphous carbonate were slightly negative and temperature-dependent, from –0.83‰ at 30 °C to –0.53‰ at 70 °C. During the transformation of Ba-Mg amorphous carbonate to nano-crystalline norsethite, isotopically light Mg isotopes were further enriched in the solid phase, with apparent ∆26Mgsolid-aq decreasing to –2.12‰ at 30 °C and –1.56‰ at 70 °C. In the ripening stage, norsethite became isotopically heavier, with ∆26Mgsolid-aq increasing up to –1.95‰ at 30 °C and –1.17‰ at 70 °C. The experimental results show that non-equilibrium isotope fractionation occurred during the transformation of amorphous carbonate to nano-crystalline norsethite (i.e., fast dissolution-reprecipitation). By contrast, the subsequent ripening of the norsethite led to the evolution toward isotopic equilibrium of the system by slower exchange with a longer reaction time (i.e., slow dissolution-reprecipitation). Moreover, our first-principles calculation results indicate that the equilibrium isotope fractionation was approached, but not attained, even after 276 days of recrystallization at temperatures below 70 °C. In short, this study has identified two different types of dissolution-reprecipitation process during the carbonate mineral growth and highlights the importance of understanding formation mechanism and post-depositional history of carbonate in interpreting the isotopic data of carbonate minerals.

First-principle studies of the pressure effect on metal carbonates elastic properties

Using the ab initio methods of the density functional theory, the influence of hydrostatic pressure on the elastic properties of magnesium, zinc, cadmium, calcium carbonates with the structure of calcite, double calcium-magnesium carbonates, cadmium-magnesium, calcium-zinc with the structure of dolomite and calcium, strontium, lead, barium carbonates with the structure of aragonite is studied. Derivatives with respect to pressure for elastic constants and linear moduli, polycrystalline compression and shear moduli, transverse and longitudinal velocities of acoustic waves are obtained. Dependences on the cation radius for the ratio of the elastic constant to its pressure derivative, the velocity of longitudinal waves to its pressure derivative, the pressure derivative of the bulk modulus, the pressure derivative of the shear modulus, and other parameters of a number of metal carbonates have been established.

Rehydration Driven Na-Activation of Bentonite-Evolution of the Clay Structure and Composition.

A new method of Na-activation of raw bentonite, rich in Ca-montmorillonite, consisting of combined thermal treatment at 200 °C, followed by immediate impregnation with aqueous solution of Na2CO3 of concentration corresponding to 0.5, 1.0, 1.5, or 2.0 cation exchange capacity (CEC) of clay, was investigated. Structural and compositional evolution of the activated solids after 1, 2, 3, and 4 weeks of storage was monitored by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). XRD analysis indicated that within the investigated period of ageing transformation to Na-rich montmorillonite required Na2CO3 concentration of at least 1.0 CEC. FTIR spectra showed that, depending on the Na2CO3 concentration and ageing time, formation of Na-rich montmorillonite was accompanied by precipitation of poorly crystalline calcite, amorphous calcium carbonate, gaylussite (a double calcium-sodium carbonate), and portlandite (Ca(OH)2).

Incorporation of Europium into (Ba,Ca)2[formula omitted

Synchrotron-based powder diffraction measurements in combination with inductively coupled plasma optical emission spectrometry, Raman and fluorescence spectroscopy show that (Ba,Ca)2(CO3)2 can incorporate significant amounts (up to 6 ​mol%) of europium. This solid solution is therefore of potential interest for the solidification of nuclear waste streams involving aqueous nitrate solutions of lanthanides. Europium replaces Ba/Ca on lattice sites and is not incorporated as an interstitial defect. Charge compensation is likely due to the presence of OH−-groups as we could exclude a coupled substitution involving Na+. The Eu-containing compound is stable to at least 723 ​K. We show that the one-phase-field of (Bax,Ca(1−x))CO3 solid solutions at ambient conditions is larger (0.36 <x< 0.51) than previously thought. The synthesis routes employed here lead to compounds which have similar molar volumes than those of the naturally occurring (Ba,Ca)-double carbonates, in noted contrast to another synthetic phase, “balcite”.

The mid-infrared spectrum of a new double carbonate, BaFe[CO3

BaFe[CO3]2, a new double carbonate from the norsethite-type family of carbonates, was recently discovered and synthesized at high-pressure-temperature (high-PT) conditions. Two polymorphs of the new double carbonate were identified belonging to the R3¯m and R3¯c space groups, respectively1. In the present communication we present for the first time the mid-infrared (IR) spectra (measured with transmission infrared spectroscopy and attenuated total reflectance infrared spectroscopy) and assign the observed bands to the respective fundamental and combined IR-active modes. This study, therefore, adds new spectroscopic results to the previous crystal chemical characterization of the new double carbonate. Results are compared to those of other Ba-bearing double carbonates with the norsethite-type structures. With substitution of Ba2+ in the double carbonate lattice by increasingly smaller cations a decrease in wavenumbers of absorption bands is observed. Due to similar crystal structures, and masses and radii of the cations, the IR spectra of both BaFe[CO3]2 carbonates are similar to the ones observed for BaMn[CO3]2 and BaMg[CO3]2, with some characteristic deviations. The carbon isotope shift coefficient of 0.969 for ʋ2 of the carbonate ion group agrees with previous theoretical predictions.