Solid-state nuclear magnetic resonance investigation of synthetic phlogopite and lepidolite samples.

In the present work, our aim is to decipher the cationic ordering in the octahedral and tetrahedral sheets of two Al-rich synthetic materials, namely, phlogopites of nominal composition K(Mg3-x Alx )[Al1+x Si3-x O10 ](OH)y F2-y and lepidolites in the system trilithionite-polylithionite with composition K (Lix Al3-x )[Al4-2x Si2x O10 ](OH)y F2-y , by directly probing the aluminium distribution through 27 Al and 17 O magic-angle spinning, multiple-quantum magic-angle spinning, and 27 Al-27 Al double-quantum single-quantum nuclear magnetic resonance (NMR) experiments. Notably, 27 Al-27 Al double-quantum single-quantum magic-angle spinning NMR spectra, recorded at 9.34 and/or 20.00 T, show the spatial proximity or avoidance of the Al species inside or between the sheets. In both studied minerals, the ensemble of NMR data suggests a preference for [4] Al in the tetrahedral sheet to occupy position close to the [6] Al of the octahedral sheets.

A new activity model for Mg-Al biotites determined through an integrated approach.

A new activity model for Mg-Al biotites was formulated through an integrated approach combining various experimental results (calorimetry, line-broadening in infrared (IR) spectra, analysis of existing phase-equilibrium data) with density functional theory (DFT) calculations. The resulting model has a sound physical-experimental basis. It considers the three end-members phlogopite (Phl, KMg3[(OH)2AlSi3O10]), ordered eastonite (Eas, KMg2Al[(OH)2Al2Si2O10]), and disordered eastonite (dEas) and, thus, includes Mg-Al order-disorder. The DFT-derived disordering enthalpy, ΔH dis, associated with the disordering of Mg and Al on the M sites of Eas amounts to 34.5 ± 3 kJ/mol. Various biotite compositions along the Phl-Eas join were synthesised hydrothermally at 700 °C and 4 kbar. The most Al-rich biotite synthesized had the composition X Eas = 0.77. The samples were characterised by X-ray diffraction (XRD), microprobe analysis and IR spectroscopy. The samples were studied further using relaxation calorimetry to measure their heat capacities (C p) at temperatures from 2 to 300 K and by differential scanning calorimetry between 282 and 760 K. The calorimetric (vibrational) entropy of Phl at 298.15 K, determined from the low-T C p measurements on a pure synthetic sample, is S cal = 319.4 ± 2.2 J/(mol K). The standard entropy, S o, for Phl is 330.9 ± 2.2 J/(mol K), which is obtained by adding a configurational entropy term, S cfg, of 11.53 J/(mol K) due to tetrahedral Al-Si disorder. This value is ~1% larger than those in different data bases, which rely on older calorimetrical data measured on a natural near-Phl mica. Re-analysing phase-equilibrium data on Phl + quartz (Qz) stability with this new S o, gives a standard enthalpy of formation of Phl, Δ H f o , Phl = - 6209.83 ± 1.10 kJ/mol, which is 7-8 kJ/mol less negative than published values. The superambient C p of Phl is given by the polynomial [J/(mol K)] as follows: C p = 667.37 ± 7 - 3914.50 ± 258 · T - 0.5 - 1.52396 ± 0.15 × 10 7 · T - 2 + 2.17269 ± 0.25 × 10 9 · T - 3 . Calorimetric entropies at 298.15 K vary linearly with composition along the Phl-Eas join, indicating ideal vibrational entropies of mixing in this binary. The linear extrapolation of these results to Eas composition gives S o = 294.5 ± 3.0 J/(mol K) for this end-member. This value is in excellent agreement with its DFT-derived S o, but ~ 8% smaller than values as appearing in thermodynamic data bases. The DFT-computed superambient C p of Eas is given by the polynomial [in J/(mol K)] as follows: C p = 656.91 ± 14 - 3622.01 ± 503 · T - 0.5 - 1.70983 ± 0.33 × 10 7 · T - 2 + 2.31802 ± 0.59 × 10 9 · T - 3 . A maximum excess enthalpy of mixing, ΔH ex , of ~6 kJ/mol was derived for the Phl-Eas binary using line-broadening from IR spectra (wavenumber region 400-600 cm-1), which is in accordance with ΔH ex determined from published solution-calorimetry data. The mixing behaviour can be described by a symmetric interaction parameter W Phl , Eas H = 25.4 kJ/mol. Applying this value to published phase-equilibrium data that were undertaken to experimentally determine the Al-saturation level of biotite in the assemblage (Mg-Al)-biotite-sillimanite-sanidine-Qz, gives a Δ H f , Eas o = - 6358.5 ± 1.4 kJ/mol in good agreement with the independently DFT-derived value of Δ H f , Eas o DFT = - 6360.5 kJ/mol. Application examples demonstrate the effect of the new activity model and thermodynamic standard state data, among others, on the stability of Mg-Al biotite + Qz.

Dataset on the crystallographic, vibrational, and electronic properties of 1M-phlogopite K(Mg,Fe)3(Si3Al)O10(OH)2 obtained from Density Functional Theory investigations.

The present work reports a dataset on the crystal structure, optical properties (complex dielectric function and refractive index), infrared, reflectance and Raman spectra, and electronic properties (band structure and density of states) of the 1M-polytype of phlogopite [1]. This phyllosilicate presents chemical formula K(Mg,Fe)3(Si3Al)O10(OH)2, with Mg/Fe ratio ≥ 2. The dataset was obtained from Density Functional Theory (DFT) simulations at B3LYP-D* level, i.e., with the hybrid functional B3LYP corrected with an ad hoc DFT-D2 scheme, and all-electron Gaussian-type orbitals basis sets for all atoms in the unit cell. Furthermore, experimental confocal Raman micro-spectrometry data (spectra) collected on a single crystal phlogopite specimen are reported. The quality of the dataset was assessed by comparing the results with available X-ray diffraction and IR/Raman spectroscopy data reported in literature. The reported complete dataset is a reference for future studies in fundamental georesource exploration and exploitation, applied mineralogy, geology, and material science.

Insights into sorption speciation of uranium on phlogopite: Evidence from TRLFS and DFT calculation.

Knowledge of the sorption speciation of uranium at mineral/water interface is essential to construct reliable retention and migration models. In this work, the sorption speciation of U(VI) at the phlogopite/water interface was studied at trace concentrations by combining batch sorption, time-resolved luminescence spectroscopy, and theoretical calculation. Batch experiments showed that the sorption of U(VI) on phlogopite was strongly dependent on pH but weakly affected by ionic strength, implying that the inner-sphere surface complexation was mainly responsible for U(VI) sorption on phlogopite. The diverse luminescence spectral characteristics indicated the formation of multiple inner-sphere surface species at the phlogopite/water interface, whose abundances varied as a function of pH. A portion of U(VI) precipitated as uranyl oxyhydroxides such as metaschoepite and becquerelite at high pH. Density functional theory calculation revealed that the bidentate complex at the edge of phlogopite (≡AlO-MgO-UO2(H2O)3) was the most favorable sorption configuration for U(VI) at acidic condition. The increasing temperature enhanced the sorption of U(VI) on phlogopite without altering the sorption species, and such enhancement in U(VI) sorption was withdrawn once the temperature decreased. These findings are essential for understanding the immobilization mechanism of U(VI) in mica-rich granitic terrains at a molecular scale and building a reliable retention model.

Effects of Filler Functionalization on Filler-Embedded Natural Rubber/Ethylene-Propylene-Diene Monomer Composites.

Natural rubber (NR) presents a number of advantages over other types of rubber but has poor resistance to chemicals and aging. The incorporation of ethylene propylene diene monomer (EPDM) into the NR matrix may be able to address this issue. Mineral fillers, such as carbon black (CB) and silica are routinely incorporated into various elastomers owing to their low cost, enhanced processability, good functionality, and high resistance to chemicals and aging. Other fillers have been examined as potential alternatives to CB and silica. In this study, phlogopite was surface-modified using 10 phr of compatibilizers, such as aminopropyltriethoxysilane (A1S), aminoethylaminopropyltrimethoxysilane (A2S), or 3-glycidoxypropyltrimethoxysilane (ES), and mixed with NR/EPDM blends. The effects of untreated and surface-treated phlogopite on the mechanical properties of the rubber blend were then compared with those of common fillers (CB and silica) for rubbers. The incorporation of surface-modified phlogopite into NR/EPDM considerably enhanced various properties. The functionalization of the phlogopite surface using silane-based matters (amino- and epoxide-functionalized) led to excellent compatibility between the rubber matrix and phlogopite, thereby improving diverse properties of the elastomeric composites, with effects analogous to those of CB. The tensile strength and elongation at break of the phlogopite-embedded NR/EPDM composite were lower than those of the CB-incorporated NR/EPDM composite by 30% and 10%, respectively. Among the prepared samples, the ES-functionalized phlogopite showed the best compatibility with the rubber matrix, exhibiting a tensile strength and modulus of composites that were 35% and 18% higher, respectively, compared with those of the untreated phlogopite-incorporated NR/EPDM composite. The ES-functionalized phlogopite/NR/EPDM showed similar strength and higher modulus (by 18%) to the CB/NR/EPDM rubber composite, despite slightly lower elongation at break and toughness. The results of rebound resilience and compression set tests indicated that the elasticity of the surface-modified phlogopite/NR/EPDM rubber composite was higher than that of the silica- and CB-reinforced composites. These improvements could be attributed to enhancements in the physical and chemical interactions among the rubber matrix, stearic acid, and functionalized (compatibilized) phlogopite. Therefore, the functionalized phlogopite can be utilized in a wide range of applications for rubber compounding.

Application of Finnish phlogopite to reduce radiocesium uptake by paddy rice.

Field and pot experiments were conducted to evaluate the effectiveness of coarse Finnish phlogopite application to reduce radiocesium uptake by paddy rice (Oryza sativa L.). The application of phlogopite was expected to reduce radiocesium uptake by crops through K supply and radiocesium retention. Three fields were set in Fukushima Prefecture, and coarse (mean particle size of 450 µm) phlogopite from Siilinjärvi (Finland) was applied at a rate of 5 t ha-1. Paddy rice was cultivated for 2-4 successive years. In all fields, the average 137Cs transfer factor (TF) of brown rice harvested from plots with added phlogopite was significantly lower than that of brown rice from plots without added phlogopite over the 2-4-year experiments. TF was decreased by up to 80% following phlogopite application, without an adverse effect on yield. Exchangeable K and soil solution K were higher in the soils with added phlogopite, suggesting K released from phlogopite reduced 137Cs uptake by paddy rice. Moreover, in a pot cultivation experiment, even when 55% of the total K was removed from phlogopite prior to application, the TF in pots with phlogopite application was less than half of that in pots without added phlogopite. The results from the field study and the pot cultivation experiment suggested that the application of Finnish phlogopite is effective to reduce the TF of brown rice. Exchangeable K and tetraphenylborate-extractable-K (TPB-K) at rooting stage, and soil solution K at tillering and heading stages showed significant negative correlation with TF. TPB-K was significantly positively correlated with soil solution K at tillering stage and heading stage, whereas exchangeable K at rooting stage did not exhibit significant correlation with soil solution K at heading stage. The results suggest that TPB-K is more reliable than exchangeable K, which could facilitate as a basis of K fertilizer recommendation for radiocesium-contaminated fields.

Insight into the adsorption of europium(III) on muscovite and phlogopite: Effects of pH, electrolytes, humic substances and mica structures.

Europium(III), i.e., Eu(III), is chemically analogous to the trivalent lanthanides (Ln) and actinides (An). A good understanding of the adsorption behaviour of Eu(III) on mica group minerals is critical to the safety evaluation of the radioactive contamination. Nevertheless, the structural complexity of micaceous minerals makes it difficult to draw a consistent conclusion in the study of Eu(III) migration. In this work, we contrastively studied Eu(III) adsorption on dioctahedral muscovite and trioctahedral phlogopite as functions of pH, ionic strength, background electrolytes, interaction sequence, and fulvic acid (FA). Batch experiments showed that Eu(III) adsorption on both micas was strongly dependent on pH but quite independent on ionic strength that is determined by Na+. Planar sites are available on both muscovite and phlogopite while interlayer sites only on phlogopite under Na+ and Ca2+ electrolytes (not for K+ and Cs+). An interlayer expansion of phlogopite, as indicated by a newly appeared diffraction peak at ~6° 2-theta, occurred along with Eu(III) adsorption, which was also confirmed by transmission electron microscopy. Furthermore, the initial Eu(III) concentrations, the concentration ratios between Eu(III) and Cs+, and the reaction sequences of Eu(III)-electrolytes-FA affected both the adsorption behaviour of Eu(III) and reversely the structural alteration of phlogopite. The sequential extraction showed that the adsorbed Eu(III) was mainly in the ion-exchangeable form while the addition of FA could increase the portion of coordinative species. The currently proposed Eu(III) adsorption mechanism can shed new light on predicting the migration of Ln/An(III) at the mica-rich solid-liquid interface on a molecular scale.

Phlogopite-Reinforced Natural Rubber (NR)/Ethylene-Propylene-Diene Monomer Rubber (EPDM) Composites with Aminosilane Compatibilizer.

Rubber compounding with two or more components has been extensively employed to improve various properties. In particular, natural rubber (NR)/ethylene-propylene-diene monomer rubber (EPDM) blends have found use in tire and automotive parts. Diverse fillers have been applied to NR/EPDM blends to enhance their mechanical properties. In this study, a new class of mineral filler, phlogopite, was incorporated into an NR/EPDM blend to examine the mechanical, curing, elastic, and morphological properties of the resulting material. The combination of aminoethylaminopropyltrimethoxysilane (AEAPS) and stearic acid (SA) compatibilized the NR/EPDM/phlogopite composite, further improving various properties. The enhanced properties were compared with those of NR/EPDM/fillers composed of silica or carbon black (CB). Compared with the NR/EPDM/silica composite, the incompatibilized NR/EPDM/phlogopite composite without AEAPS exhibited poorer properties, but NR/EPDM/phlogopite compatibilized by AEAPS and SA showed improved properties. Most properties of the compatibilized NR/EPDM/phlogopite composite were similar to those of the NR/EPDM/CB composite, except for the lower abrasion resistance. The NR/EPDM/phlogopite/AEAPS rubber composite may potentially be used in various applications by replacing expensive fillers, such as CB.

Potassium distribution and isotope composition in the lithospheric mantle in relation to global Earth's reservoirs.

Recent analytical advances have provided means to measure potassium (K) isotopes in various terrestrial materials, but little is known about K distribution and stable isotope composition in the lithospheric mantle because of: (a) common low K abundances, (b) potential contamination and alteration, (c) diversity of mantle rocks and minerals hosting K in different tectonic settings. We report K abundances and δ41K values for well-studied whole-rock (WR) mantle xenoliths (spinel and garnet peridotites and pyroxenites) from mobile belts, a craton, a subduction zone, as well as for K-rich phases (mica, amphibole, silicate glass) and xenolith-bearing volcanic materials (67 samples). The xenolith materials show extremely broad ranges of K content (7 µg/g to 6.6 wt.%) and δ41K (-2.77‰ to 0.62‰). They contrast with the narrow δ41K range for host volcanic materials (-0.53‰ to -0.27‰) and literature data on oceanic basalts (melting products of upwelling asthenosphere: -0.43 ± 0.17‰, 2sd). Amphibole-bearing subduction zone peridotites show the highest WR δ41K values (0.40 to 0.62‰) likely inherited from fluids released into the mantle wedge from subducted oceanic crust. All other WR samples yield negative δ41K: -0.06‰ to -2.77‰ for peridotites and -0.17‰ to -0.52‰ for pyroxenites. The δ41K in K-rich mantle phases range from positive values (0.16 to 0.57‰) for phlogopite in strongly metasomatized peridotites to negative values (-0.27 to -0.94‰) for phlogopite, amphibole and glass pockets from other samples, which cannot be explained by equilibrium inter-mineral fractionation inferred from ab initio calculations. We attribute the broad δ41K variations to (a) isotope fractionation during fluid-rock interaction in the mantle, and (b) distinct sources of K-bearing fluids. Kinetic isotope fractionation during fluid percolation and diffusion is inferred for composite xenoliths (phlogopite and pyroxenite veins in peridotites) that have lower δ41K in the hosts than in the veins due to slower migration of 41K than 39K from the veins (former fluid channels) to host mantle. Overall, the K isotope fractionation in the lithospheric mantle appears to be greater than for magmatic fractionation in the crust. The average δ41K of normal off-craton continental lithospheric mantle calculated from the least altered fertile and lightly metasomatized lherzolites is -0.57 ± 0.28‰ (2sd). This value is within error (though a little lower) of estimates for both continental crust and MORB and OIB mantle sources indicating that these major silicate Earth reservoirs have similar bulk δ41K values, apparently due to low or negligible K isotopic fractionation during their formation by magmatic differentiation and melting. By contrast, K isotopes in modern and fossil subduction zones are fractionated via fluid-related equilibrium and kinetic processes.

Mineral Layer Fillers for the Production of Functional Materials.

An original method based on the use of technogenic waste from the processing of mineral-layered materials, in particular phlogopite for obtaining highly efficient functional compositions of the "mica-TiO2", has been developed. The composition core is a nanosized mica flake coated with mesoporous titanium dioxide of an anatase or rutile structure. Energy-saving and environmentally friendly technological methods are based on the splitting of the mica followed by heterogeneous electrohydrolysis of a mixture of titanium (IV) sulfate solution and flake particles. No destruction of the mica surface, which provided the obtained uniform coatings, has been observed. Such coatings are used in photocatalysis processes and possess a self-cleaning capability. Core-shell compositions are more economically attractive compared with titanium dioxide, in particular TiO2 grade P25 (Degusse). The core of the transparent flake and the shell of the rutile titanium dioxide endows the final product with a pearlescent optical effect. This type of material is widely used in the manufacturing of paints and varnishes, printing inks, cosmetics, etc. The use of technogenic waste could significantly reduce the cost of the final product, which would ensure its widespread use in various industries.

Comparative study of strontium adsorption on muscovite, biotite and phlogopite.

Micaceous minerals are the natural materials that can block radioactive strontium (Sr) released in the environment, and their adsorption capacity and mechanism are highly divergent owing to the different properties of micas. In this work, we comparatively studied the adsorption of Sr(II) on three typical micas, muscovite, biotite and phlogopite. The effects of pH, contact time, ionic strength, and background electrolyte were evaluated. It was found that phlogopite and muscovite had the largest solid-liquid distribution coefficient (Kd) for a reaction time of 48 h under acidic and alkaline conditions, respectively. Under alkaline conditions, as the reaction time increased to 44 days, phlogopite and muscovite showed the highest and lowest Kd, respectively. The Kd for Sr(II) adsorption on biotite and phlogopite increased with increasing pH but decreased with increasing pH for muscovite. X-ray diffraction analysis revealed that the interlayer weathering of phlogopite (a new diffraction peak appeared at 2-theta of ~6.1°) occurred along with the adsorption of Sr(II) below pH 9.0 under 0.01 mol/L NaCl. Furthermore, the adsorption of Sr(II) was significantly inhibited in the presence of 10-5 and 10-2 mol/L Cs+, resulting in similar adsorption capacity for phlogopite and muscovite at pH ~4.1. Consequently, the difference in Sr(II) adsorption on muscovite, biotite and phlogopite mainly came from the synergistic process of adsorption and weathering, which induced the differences in availability of interlayer sites among micas over a certain time.

Sorption of selenium species onto phlogopite and calcite surfaces: DFT studies.

Sorption of Se(IV) and Se(VI) species onto Mg-rich biotite (phlogopite) and calcite surfaces was investigated using molecular modelling techniques. A CASTEP code implemented into Materials Studio was used to calculate the periodic systems, site densities and site types on the phlogopite and calcite surfaces. According to the results, the Se oxyanions attach to both edge and basal surfaces of phlogopite via an oxygen atom. However, calculated sorption energies indicate that surface complexation reactions via hydrogen bonding happen on the edge surfaces of phlogopite while cation exchange reactions happen on the basal surfaces of phlogopite. These reactions occur on the so-called weak sites according to the PHREEQC modelling. On the calcite surface, only cation exchange reactions are possible, and only for neutral Se species which do not occur in low saline groundwater conditions with pH 8-10. Biotite which is an abundant mineral in crystalline rock works fairly well as a sorbent but calcite which often exists on fracture surfaces of bedrock does not act as a sorbent for Se species.

Compressibility of 2M1 muscovite-phlogopite series minerals.

Muscovite (Ms) and phlogopite (Phl) belong to the 2:1 dioctahedral and trioctahedral layer silicates, respectively, and are the end members of Ms-Phl series minerals. This series was studied in the 2M1 polytype and modeled by the substitution of three Mg2+ cations in the Phl octahedral sites by two Al3+ and one vacancy, increasing the substitution up to reach the Ms. The series was computationally examined at DFT level as a function of pressure to 9 GPa. Cell parameters as a function of pressure and composition, and bulk moduli as a function of the composition agrees with the existing experimental results. The mixing Gibbs free energy was calculated as a function of composition. From these data, approximated solvi were calculated at increasing pressure. A gap of solubility is found, decreasing the gap of solubility at high pressure.