Search Results (10)

Bone density is considered one of the many factors influencing bone structure and DNA preservation. For this reason, it is of interest in fields such as anthropology, palaeontology, and genetics. This study describes a method for bone density assessment by gradient centrifugation in Sodium Poly-Tungstate (SPT) solutions (from 2.1 to 2.6 g/cm³). Fifty milligrams of bone powder (size range of 20–50 µm) were used, with an average recovery of 89.9 (IC = 3.3% at 95% of probability). In the first phase of the experiment, the protocol was applied to ten femurs: three exhumed from the WWII mass grave of Ossero, three aged (43–50 years old) femurs from a museum collection and four fresh controls. In the subsequent phase, the analysis was extended to three petrous bones, three metacarpals, and three metatarsals exhumed from the WWII mass grave. The SPT density gradient profiles revealed marked differences among the three femur sample sets: more than 80% of the powder from control femurs was recovered in fractions with a density ≤ 2.2 g/cm³, whereas approximately 45% of the femurs from the mass grave showed a density > 2.6 g/cm³. The remaining three aged femurs displayed peculiar density patterns. Among the other bone types, metatarsals showed the lowest density values, followed by petrous bones and metacarpals. To detect degradation signatures, all nineteen bone powders were also analysed by ATR-FTIR. The femurs from the mass grave exhibited spectral features consistent with mineral recrystallisation and degradation of the organic phase, whereas the other three aged femurs showed peculiar spectral profiles; metacarpals, petrous bones and metatarsals showed intermediate spectra. PCA was applied to SPT and ATR-FTIR data, revealing correlations that support the SPT method as a novel tool for bone quality assessment. Although based on a limited sample size, this preliminary work demonstrates that SPT gradient analysis is an effective, low-cost, rapid and reliable method for assessing bone density, with potential applications in different disciplines studying aged bone samples. Lastly, principal component analysis (PCA) revealed a correlation between bone density and the yield of DNA recovered from the ten femoral specimens. Full article

Industrial technologies for processing tungsten concentrates using soda roasting or autoclave leaching are based on the production of alkaline sodium tungstate solutions that contain impurities such as silicon, phosphorus, arsenic, and others. The purification of these solutions from impurities requires the neutralization of excess soda or alkali with inorganic acids, which leads to the formation of chloride and sulfate effluents that are subsequently discharged into waste repositories. An analysis was carried out on existing methods for the production and processing of sodium tungstate solutions using HNO₃ and NH₃, as well as extraction and sorption techniques involving anion exchange resins. Currently, processes such as nanofiltration, reverse osmosis, and electrodialysis are being applied for water purification and the treatment of sulfate and chloride effluents. These processes employ various types of industrially manufactured membranes. For the purpose of electrodialysis, a two-compartment electrodialyzer setup was employed using cation-exchange membranes of the MK-40 (Russia) and EDC1R (China) types. The composition and structure of sodium tungstate, used as the starting reagents, were analyzed. Based on experiments conducted on a laboratory-scale unit with continuous circulation of the catholyte and anolyte, dependencies of various parameters on current density and process duration were established. Stepwise changes in the anolyte pH were recorded, indirectly confirming changes in the composition of the Na₂WO₄ solution, including the formation of polytungstates of variable composition and the production of H₂WO₄ via electrodialysis at pH < 2. The resulting tungstic acid solutions were also analyzed. The conducted studies on the processing of sodium tungstate solutions using electrodialysis made it possible to obtain alkaline solutions and tungstic acid at a current density of 500–1500 A/m², without the use of acid for neutralization. Yellow tungstic acid was obtained from the tungstic acid solution by evaporation. Full article

Micro-scale kinetic energy harvesters are in large demand to function as sustainable power sources for wireless sensor networks and the Internet of Things. However, one of the challenges associated with them is their inability to easily tune the frequency during the manufacturing process, requiring devices to be custom-made for each application. Previous attempts have either used active tuning, which consumes power, or passive devices that increase their energy footprint, thus decreasing power density. This study involved developing a novel passive method that does not alter the device footprint or power density. It involved creating a proof mass with an array of chambers or cavities that can be individually filled with liquid to alter the overall proof mass as well as center of gravity. The resonant frequency of a rectangular cantilever can then be altered by changing the location, density, and volume of the liquid-filled mass. The resolution can be enhanced by increasing the number of chambers, whereas the frequency tuning range can be increased by increasing the amount of liquid or density of the liquids used to fill the cavities. A piezoelectric cantilever with a 340 Hz initial resonant frequency was used as the testing device. Liquids with varying density (silicone oil, liquid sodium polytungstate, and Galinstan) were investigated. The resonant frequencies were measured experimentally by filling various cavities with these liquids to determine the tuning frequency range and resolution. The tuning ranges of the first resonant frequency mode for the device were 142–217 Hz, 108–217 Hz, and 78.4–217 Hz for silicone oil, liquid sodium polytungstate, and Galinstan, respectively, with a sub Hz resolution. Full article

Powder X-ray diffraction (XRD) is a widely accepted technique for detecting trace asbestos content in solid samples. However, accurately quantifying asbestos concentrations below 0.5 wt% presents significant challenges with XRD alone. To address this limitation, we conducted a meticulous quantitative analysis using XRD on synthetic samples of talc-based powder spiked with varying amounts of natural tremolite and anthophyllite asbestos. At concentrations exceeding 0.5 wt%, both tremolite and anthophyllite displayed distinct XRD peaks. Yet, at lower concentrations (0.1 wt% and 0.05 wt%), the diffraction peaks of the contaminants became less prominent. To improve detection sensitivity, we explored different protocols of heavy liquid separation utilizing sodium polytungstate (SPT) to concentrate asbestos relative to the other mineral components. The optimized protocol, employing SPT with a density of 2.89 g/cm³, effectively separated amphibole asbestos from lighter, commonly associated minerals, like talc, clinochlore, and mica. Subsequent powder XRD analysis of the heavy fraction confirmed the successful removal of non-target materials, enhancing the diffraction peaks of tremolite and anthophyllite. Tremolite exhibited comparatively less weight loss than anthophyllite during this separation process. This study establishes the theoretical and practical viability of employing centrifugation in a heavy liquid to separate tremolite and anthophyllite from talc, providing valuable insights for asbestos detection and quantification in challenging scenarios. Full article

A comprehensive study concerning the phase formation mechanism and growth/dissolution kinetics of sodium tungsten bronze crystals during the electrolysis of a 0.8Na₂WO₄–0.2WO₃ melt was carried out. The regularities of deposit formation on a Pt(111) working electrode were investigated experimentally using cyclic voltammetry, chronoamperometry, scanning electron microscopy, and X-ray diffraction analysis. Models have been developed to calculate the current response during the formation, growth and dissolution of a two-phase deposit consisting of Na_xWO₃ and metallic tungsten or two oxide tungsten bronzes with different sodium content. These models consider mass transfer to the electrode and nuclei; chemical and electrochemical reactions with the participation of polytungstate ions, Na⁺, Na⁰, and O²⁻; as well as the ohmic drop effect. The approach was proposed to describe the dissolution of an Na_xWO₃ crystal with a nonuniform sodium distribution. The fitting of cyclic voltammograms was performed using the Levenberg–Marquardt algorithm. The Na_xWO₃ formation/growth/dissolution mechanism was determined. Concentration profiles and diffusion coefficients of [W_nO_3n]⁻, reaction rate constants, number density of nuclei, and time dependencies of crystal size were calculated. The proposed approaches and models can be used in other systems for the cyclic voltammogram analysis and study of the mechanism and kinetics of electrode processes complicated by phase formation; parallel and sequential electrochemical and chemical reactions; as well as the formation of a deposit characterized by a nonuniform phase and/or chemical composition. Full article

A novel porous polyoxometalate (POM)-based composite (Co₄PW–PDDVAC) was prepared via the solidification of water-soluble polytungstate (Co₄PW) on the polymeric ionic liquid dimethyldodecyl-4-polyethylene benzyl ammonium chloride (PDDVAC) via a cation-exchange reaction. The solidification was confirmed by EDS, SEM, FT-IR, TGA, and so on. The strong covalent coordination and hydrogen-bonding interaction between the highly active Co²⁺ of the Co₄PW and the aspartic acid residues of proteinase K endowed the obtained Co₄PW–PDDVAC composite with excellent proteinase K adsorption properties. Thermodynamic investigations indicate that the adsorption behavior of proteinase K was consistent with the linear Langmuir isothermal model, giving an adsorption capacity as high as 1428 mg g⁻¹. The Co₄PW–PDDVAC composite was applied in the selective isolation of highly active proteinase K from Tritirachium album Limber crude enzyme fluid. Full article

Polytungstate melts are used for the electrodeposition of oxide tungsten bronzes (OTBs). The scarce information on the ionic composition and properties of these electrolytes hinders effective control of the electrochemical synthesis of OTBs with desired electrical and optical properties. In this work, a comprehensive study of Na₂WO₄–WO₃ melts that contained up to 55 mol% of tungsten trioxide was performed in the temperature range from 983 to 1073 K. Melt densities were measured using the Archimedes method. DFT calculations were carried out for various tungsten-containing compounds, including ${\mathrm{W}}_{\mathrm{x}}{\mathrm{O}}_{3\mathrm{x}-1}^{2+}$, ${\mathrm{W}}_{\mathrm{x}}{\mathrm{O}}_{3\mathrm{x}+1}^{2-}$, ${\mathrm{NaW}}_{\mathrm{x}}{\mathrm{O}}_{3\mathrm{x}+1}^{-}$, and ${\mathrm{Na}}_2{\mathrm{W}}_{\mathrm{x}}{\mathrm{O}}_{3\mathrm{x}+1}$. The calculated values of the W–O bond energy indicate that the tested compounds are stable in the specified temperature range, and the ${\mathrm{WO}}_2^{2+}$ cation is the most stable. The experimental dependences of the redox potential on the mole fraction of tungsten trioxide in the Na₂WO₄–WO₃ melt were obtained using the EMF method. A model that considers the processes of interaction between tungsten-containing ions and O²⁻ ions was proposed for the quantitative interpretation of these dependences. The equilibrium constants were found through fitting according to the Levenberg–Marquardt algorithm. The effect of the WO₃ mole fraction and temperature on the concentrations of ${\mathrm{WO}}_4^{2-}$, ${\mathrm{W}}_2{\mathrm{O}}_7^{2-}$, ${\mathrm{W}}_3{\mathrm{O}}_{10}^{2-}$, ${\mathrm{W}}_4{\mathrm{O}}_{13}^{2-}$, ${\mathrm{WO}}_2^{2+}$, and O²⁻ ions was analyzed. Full article

A novel flat renewal membrane reactor (FRMR) with mixed amine extractant N1633 dissolved in kerosene and NaOH solvent was studied for the removal of polytungstate [expressed as W₇O₂₄⁶⁻ or W (VI)] from simulated mine wastewater. FRMR contains three parts: the feeding cell, reacting cell and renewal cell. A flat membrane of polyacrylonitrile (PAN) was used in the reacting cell, which used mixed solutions of kerosene and NaOH. The amine extractant (N1633) was used as the carrier, and simulated mine wastewater containing polytungstate was used as the feeding solution. The influencing factors of the pH and the other ion strengths in the feeding solutions, the volume ratio of kerosene to NaOH solution, and the N1633 concentration in the renewal solutions were investigated in order to obtain the optimum technique parameters. It was found that the removal percentage of polytungstate could reach 92.5% in 205 min, when the concentration of the carrier (N1633) was 0.18 mol/L, the volume ratio of kerosene and NaOH in the renewal cell was 3:2, the pH in the feeding cell was 4.00, and the initial concentration of polytungstate was 3.50 × 10⁻⁴ mol/L. The stability and feasibility of FRMR were tested by the investigation of polytungstate retention and the reuse of the membrane. Full article

Geothermal waters usually have elevated tungsten concentrations, making geothermal systems important sources of tungsten in the environment. To study the transport of tungsten in hot springs to hot spring sediment, which is one of the key processes for the release of geothermally derived tungsten to the surface environment, geochemical investigations of the hot springs and their corresponding sediments in Rehai (a representative hydrothermal area in southwestern China) and systematic laboratory experiments of tungstate and polytungstate adsorption onto typical iron-bearing minerals in hot spring sediments (i.e., pyrite and goethite) were conducted. The results demonstrate that considerable tungsten concentrations (i.e., not much less than 10 µg/L), formation of polytungstates under acidic conditions, and enrichment of iron oxide minerals represented by goethite are the prerequisites for extreme enrichment of tungsten in hot spring sediments (e.g., 991 µg/g in the ZZQ spring outflow channel). The absence of any of these conditions would weaken the immobilization of aqueous tungsten and result in higher mobility of tungsten in the hot springs and its further transport downstream, possibly polluting the other natural waters in and around Rehai that serve as local drinking water sources. This study provides an insight for identifying the key geochemical processes controlling the transport and fate of undesirable elements (in this case, tungsten) in geothermal systems. Full article

A new series of soda–lime glass naturally doped with Nd and doped with 0.2 wt% of Eu₂O₃ was densified in a multi-anvil press up to 21 GPa. The densities of the millimetric samples were precisely measured using a floatation method in a heavy liquid made with sodium polytungstate. The obtained densification curve is significantly different from the calibration previously reported, reaching a maximum densification saturation of 3.55 ± 0.14%. This difference could be due to better hydrostatic conditions realized in this new study. The densified samples were characterized using Raman and Brillouin spectroscopy, as well as the emission of both Eu³⁺ and Nd³⁺. The evolution of the spectra was evaluated using integration methods to reduce error bars. The relative precision of the calibration curves is discussed. The evolution of Nd³⁺ transition was found to be the most sensitive calibration. Linear dependence with the density was found for all observables, with exception for Brillouin spectroscopy showing a divergent behavior. The Brillouin shift shows an unreported minimum for a densification ~0.4%. Full article