Structural Hydroxyl Research Articles

Heterogeneous water distribution in between peridotite xenoliths from Kaapvaal Craton kimberlites: Constraints on diamond barren nature of kimberlites

Nominally anhydrous mantle minerals (olivine, pyroxenes, garnets, etc.) in 11 peridotite xenoliths from four different uneconomic and economic Kaapvaal Craton kimberlite pipes (Matsoku, Thaba Putsoa, Pipe 200 and Bultfontein) have been investigated using Fourier transform infrared spectroscopy (FTIR). All xenoliths contain accessories of garnet, diopside, chromite, and phlogopite. High orthopyroxene content (>30 mol vol.%) in most xenoliths from all kimberlites and its interconnected channel-like nature hint towards hydrous siliceous fluid metasomatism. Peridotite xenoliths from uneconomic kimberlites show development of phlogopite and clinopyroxene (± chromite) forming veins and in garnet rims suggesting metasomatism by alkaline silico-carbonatite (possibly kimberlite-related) melt. The xenoliths contain significant H2O in olivine (17–62 ppm), orthopyroxene (21–230 ppm), and clinopyroxene (87–833 ppm), whereas garnets are dry and only show IR absorbance bands at > 3,670 cm−1 for contamination of hydrous minerals. Compared to the economic kimberlites in the Kaapvaal Craton, the uneconomic kimberlite xenoliths from this study have lower orthopyroxene and olivine H2O content. In the xenoliths affected by garnet breakdown metasomatism, the H2O content of orthopyroxene and olivine is higher and lower, respectively. The structural hydroxyl distribution profile across olivine and higher inter-mineral water partition coefficient, suggest diffusion of hydrogen and possible re-equilibration. Statistical analysis of the olivine spectra suggests that hydrogen bands at 3540, 3624, 3638, and 3672 cm−1 are a good discriminant of economic and uneconomic kimberlites and in literature, they are associated with metasomatism, weathering-associated processes, high water activity, and oxygen fugacity. The lower water concentration in xenoliths from uneconomic kimberlite from the margin of the craton than the economic kimberlites from the interior of the Kaapvaal Craton and identified metasomatism hints towards dehydration of xenoliths by water-poor and CO2-rich melts in tectonized cross-lithospheric zones causing diamond resorption and may be responsible for the diamond-poor nature of uneconomic kimberlites in northern Lesotho.

Mechanism of ozone catalysis by transition metal hydroxyl oxides: From reactive oxygen species to surface structural hydroxyl

Transition metal hydroxyl oxides have been used widely as ozone catalysts for water purification. However, the fabrication methods selected and the pollutants treated vary, making it difficult to compare their performance. In this study, ZnOOH, FeOOH, CoOOH, and MnOOH were synthesized by the same method to remove multiple structurally similar targets. Results showed that the ZnOOH performed the best, removing over 90% of all targets within 40min, and presenting the highest ozone utilization rate of 0.081min-1. Multiple ROS quantification and contribution experiments jointly demonstrated that ZnOOH had an advantage over the other catalysts only in ·OH generation, but the ·OH contributed 93% of target removal in the ZnOOH/O3 process. Structure analysis of ZnOOH suggested that its ·OH generation had little connection with the contents of surface metal and adsorbed water, but was dependent on the surface structural hydroxyl that would undergo loss at 100-300℃. This concentration of ZnOOH was 10.1mM/g, which was 1.7, 5.3, and 6.3 times higher than that of FeOOH, CoOOH, and MnOOH, respectively. Heat treatment further revealed that these surface hydroxyl mainly originated from the hydroxyl ions from water dissociation and could regenerate timely during reuse. Finally, a possible catalysis pathway was proposed.

Multistep evolution of harzburgitic mantle underneath pipe 200 kimberlite, northern Lesotho: a study on xenoliths and their implication on diamond-barren nature of pipe 200 kimberlite

AbstractThe Pipe 200 kimberlite in northern Lesotho on the southeast margin of the Kaapvaal Craton is a diamond-poor deposit despite its proximity to economically viable kimberlites like the Liqhobong kimberlite. We study harzburgite xenoliths' mineral composition, geochemistry, and pressure–temperature evolution to understand factors influencing diamond destruction. The xenoliths are classified into five types based on their petrography and geochemistry. The diversity in the mineral assemblage correlates with a sampling depth of ~ 100 to 175 km (~ 2.8 to < 5.0 GPa). The signatures of metasomatism are evident in type 3 and 4 xenoliths, where garnet breaks down to form a cluster (henceforth assemblage) of phlogopite, chromite, and diopside. Fine-grained melts associated with an uplift in the mantle to shallower depths of < 90 km (< 2.3 GPa) encompass the minerals in the assemblage, which display resorption at the boundaries. Water contents (structural hydroxyl) of olivine and possibly orthopyroxene are lower in the xenoliths with metasomatism-induced breakdown of garnet. The structural hydroxyl distribution in the nominally anhydrous minerals shows flat distribution profiles of re-equilibration due to residence in the kimberlite magma. It is supported by the disruption of the inter-mineral water partition coefficient due to olivine water diffusion during residence in the kimberlite magma. The barren nature of the Pipe 200 kimberlite is attributed to the signatures of mantle metasomatism and residence in kimberlite magma, which led to the diamond destruction. Graphical abstract

The nature of structural defects in ZIF-8 revealed with 1H and 31P MAS NMR and X-ray absorption spectroscopy.

The metal-organic frameworks (MOFs) attract interest as potential catalysts whose catalytic properties are driven by defects. Several methods have been proposed for the defects-inducing synthesis of MOFs. However, the active species formed on the defective sites remain elusive and uncharacterized, as the spectroscopic fingerprints of these species are hidden by the regular structure signals. In this work, we have performed the synthesis of ZIF-8 MOF with defect-inducing procedures using fully deuterated 2-methylimidazolate ligands to enhance the defective sites' visibility. By combining 1H and 31P MAS NMR spectroscopy and X-ray absorption spectroscopy, we have found evidence for the presence of different structural hydroxyl Zn-OH groups in the ZIF-8 materials. It is demonstrated that the ZIF-8 defect sites are represented by Zn-OH hydroxyl groups with the signals at 0.3 and -0.7 ppm in 1H MAS NMR spectrum. These species are of basic nature and may be responsible for the catalytic activity of the ZIF-8 material.

The nature of structural defects in ZIF‐8 revealed with 1H and 31P MAS NMR and X‐ray absorption spectroscopy

The metal‐organic frameworks (MOFs) attract interest as potential catalysts whose catalytic properties are driven by defects. Several methods have been proposed for the defects‐inducing synthesis of MOFs. However, the active species formed on the defective sites remain elusive and uncharacterized, as the spectroscopic fingerprints of these species are hidden by the regular structure signals. In this work, we have performed the synthesis of ZIF‐8 MOF with defect‐inducing procedures using fully deuterated 2‐methylimidazolate ligands to enhance the defective sites' visibility. By combining 1H and 31P MAS NMR spectroscopy and X‐ray absorption spectroscopy, we have found evidence for the presence of different structural hydroxyl Zn–OH groups in the ZIF‐8 materials. It is demonstrated that the ZIF‐8 defect sites are represented by Zn–OH hydroxyl groups with the signals at 0.3 and –0.7 ppm in 1H MAS NMR spectrum. These species are of basic nature and may be responsible for the catalytic activity of the ZIF‐8 material.

Thermal desorption remediation effects on soil biogeochemical properties and plant performance: Global Meta-analysis

Soil contamination remains a global problem, and numerous studies have been published for investigating soil remediation. Thermal desorption remediation (TDR) can significantly reduce the contaminants in the soil within a short time and consequently has been used worldwide. However, the soil properties respond to TDR differently and are dependent on the experimental set-up. The causative mechanisms of these differences are yet to be fully elucidated. A statistical meta-analysis was thus undertaken to evaluate the TDR treatment effects on soil properties and plant performance. This review pointed out that soil clay was reduced by 54.2%, while soil sand content was enhanced by 15.2% after TDR. This might be due to the release of cementing agents from clay minerals that resulted in the formation of soil aggregates. Soil electrical conductivity enhanced by 69.5% after TDR, which might be due to the heating-induced loss of structural hydroxyl groups and the consequent liberation of ions. The treatment of TDR leads to the reduction of plant germination rate, length, and biomass by 19.4%, 44.8%, and 20.2%, respectively, compared to that of control soil. This might be due to the residue of contaminants and the loss of soil fertility during the thermal process that inhibited plant germination and growth. Soil pH and sulfate content increased with heating temperature increased, while soil enzyme activities decreased with thermal temperature increased. Overall, the results suggested that TDR treatment has inhibited plant growth as well as ecological restoration.

Diagnostic features of rutile and cassiterite from heavy mineral concentrate samples, according to the IR microscopy data

Based on the study of rutile and cassiterite grains, using Fourier transform infrared microscopy, a new method for their determination in heavy mineral concentrate samples has been developed. The natural vibrations of the crystal lattice of these minerals are predominantly inactive in the infrared spectrum, which complicates their identification. Rutile is proposed to be determined by the absorption band ~ 1062 cm-1; and cassiterite, by the lines 1059–1065, ~ 1130, 1217–1220, and 1366–1373 cm-1. The characteristic absorption bands in the region of 3200–3400 cm-1, associated with vibrations of OH defects in the crystal lattice of these minerals, have been shown to be of particular importance for the diagnosis of rutile and cassiterite. Structural hydroxyl groups in the spectra are manifested in rutile by a line at about 3279–3283 cm-1; and in cassiterite, by lines at about 3254–3259 cm-1, ~ 3343 and ~ 3377 cm-1.

Fossil metasomatized and newly-accreted fertile lithospheric mantle volumes beneath the Bakony-Balaton Highland Volcanic Field (central Carpathian-Pannonian region)

This study focuses on upper mantle xenoliths from Sabar-hill (Bakony-Balaton Highland Volcanic Field), a newly discovered locality of mantle xenoliths, situated in the central Carpathian-Pannonian region (CPR). The investigated seven peridotite and one pyroxenite xenoliths record two episodes in the geochemical evolution of the local subcontinental lithospheric mantle. The moderately deformed Group I xenoliths reveal modal contents (≥9 vol% orthopyroxene), major element characteristics (depletion in Al2O3 and CaO in orthopyroxenes) and trace element features (e.g., enrichment in U, Pb and Sr in clinopyroxenes) typical in supra-subduction zones (i.e., mantle wedge) xenoliths. All these suggest that the studied xenoliths were formed by silica-rich fluid/melt - peridotitic wall rock interactions. The tectonic background to the formation of Group I xenoliths is likely linked to the subduction of an oceanic slab during the Mesozoic-Paleogene. This may have happened far from the current position of Sabar-hill, to where the lithosphere, including the metasomatized mantle volume, was transferred via plate extrusion. The less deformed, dominantly protogranular and porphyroclastic Group II xenoliths are depleted in light rare earth elements (LREE). In contrast, they are enriched in clinopyroxene (≥11 vol%), incompatible major elements (e.g., Al and Na) and heavy rare earth elements (HREE), by a minimum of four times compared to primitive mantle. All these suggest that Group II xenoliths represent a geochemically fertile mantle partition and the degree of partial melting affected this mantle section was limited (≤7% based on trace elements). Group II xenoliths have higher equilibrium temperatures (1088–1168 °C) compared to Group I xenoliths (1018–1089 °C). The lack of petrographic and geochemical evidence pointing to metasomatism-related annealing in Group II xenoliths suggests that they are derived from a greater depth. It follows that Group II xenoliths could represent prior asthenosphere volumes which recently accreted to the lithosphere. The lithospherization of the upper part of the asthenosphere may have initiated after the tectonic inversion of the region, when compressional tectonic regime beneath the CPR gradually overtook the former extensional one in the last ∼8 Ma. The high bulk structural hydroxyl content in both Group I (22–1699 ppm) and II (55–320 ppm) xenoliths is likely linked to the subduction events that took place in the CPR from the Mesozoic onwards. These events transported significant amounts of fluid (H2O) back to the upper mantle, affecting both the mantle wedge and the asthenosphere.

Chloride molten salt derived attapulgite with ground-breaking electrochemical performance

The existence of adsorbed water and structural water in the crystal structure of attapulgite (ATP) endows it with poor capability to store lithium ions. Herein, the chloride molten salt method was developed to function ATP materials based on theoretical calculations, which exhibit ground-breaking electrochemical performance. After the modification process, the metal ions in chloride molten salt occupy the vertices of the Mg-O octahedral structure from the liberation of structural water and hydroxyl groups in ATP, forming MaMgbAlcSixOy (M = Li, Na, or K). Using LiCl molten salt-modified ATP (Li-ATP) as a proof-of-concept, the detailed phase transition, physicochemical properties, and lithium storage capacity were investigated. Compared to the original ATP, Li-ATP achieves a nearly 7-fold increase in lithium storage capacity (498 mAh/g), featuring a promising low-cost polyanionic type anode material.

Synergistic hydroxyl mechanism on halloysite-confined PtFe alloy boosting low-temperature CO-PROX performance

Both structural and adsorbed surface hydroxyl groups in solid materials are important carriers for oxygen species transport. The role of identifiable structural hydroxyl groups in catalytic reactions, however, is often underestimated. Here, we propose a synergistic hydroxyl reaction mechanism on Pt1Fe0.33/HNTs catalyst in CO-PROX reaction, which is critical to reveal the new way of oxygen transport in the oxidation reaction. Particularly, the Pt1Fe0.33 nanoparticles (NPs) have been confined in the cavity of halloysite nanotubes (HNTs) to activate structural hydroxyl groups linked to the AlVI via a two-step reduction treatment. The activated structural hydroxyl groups exhibit sensitivity to CO, as revealed by in situ DRIFTS and MS data. The experimental and DFT data demonstrate that the cooperation of Pt, Fe, and hydroxyl sites in the active units on Pt1Fe0.33/HNTs can induce a synergistic participation of structural and adsorbed hydroxyl groups in CO oxidation through the formate pathway. In such catalytic process, the oxygen mobility is dominated by oxygen-containing hydroxyl species rather than reactive oxygen species. This work contributes to a deeper understanding of the role of hydroxyl groups in catalysis and lays the foundation for establishing a comprehensive oxidation reaction mechanism in the future.

Optimizing Edge Active Sites via Intrinsic In-Plane Iridium Deficiency in Layered Iridium Oxides for Oxygen Evolution Electrocatalysis.

Improving catalytic activity of surface iridium sites without compromising catalytic stability is the core task of designing more efficient electrocatalysts for oxygen evolution reaction (OER) in acid. This work presents phase transition of a bulk layered iridate Na2IrO3 in acid solution at room temperature, and subsequent exfoliation to produce 2D iridium oxide nanosheets with around 4nm thickness. The nanosheets consist of OH-terminated, honeycomb-type layers of edge-sharing IrO6 octahedral framework with intrinsic in-plane iridium deficiency. The nanosheet material is among the most active Ir-based catalysts reported for acidic OER and gives an iridium mass activity improvement up to a factor of 16.5 over rutile IrO2 nanoparticles. The material also exhibits good catalytic and structural stability and retains the catalytic activity for more than 1300 h. The combined experimental and theoretical results demonstrate that edge Ir sites of the layer are active centers for OER, with structural hydroxyl groups participating in the catalytic cycle of OER via a non-traditional adsorbate evolution mechanism. The existence of intrinsic in-plane iridium deficiency is the key to building a unique local environment of edge active sites that have optimal surface oxygen adsorption properties and thereby high catalytic activity.

Structure and morphology of red pigments based on sepiolite.

Sepiolite is an important raw fibrous material. A method to prepare red pigments based on sepiolite through the thermal treatment of sepiolite with sulfur and sodium sulfide hydrate is reported. Sepiolite was heated until 800 °C in order to remove zeolitic water, the first coordinated water, the second coordinated water, and structural hydroxyls. Several [S/Na2S]molar ratios in the range 0.5-7 were employed. The properties of these pigments were studied by different analytical techniques, such as colorimetric analysis, thermal analysis, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction and scanning electron microscopy. The samples with [S/Na2S] = 0.5 and 1, corresponding to high contents of sodium sulfide in the synthesis procedure, exhibit high values of the colorimetric parameter CIE a* and a maximum reflectance in the visible zone belonging to red, based on the red colour of the samples. Under the reducing conditions of the synthesis, sulfur forms polysulfides of the general formula [Sx]2-. The sodium sulfide reacts with the excess S to form polysulfides as well. From the polysulfides, the radical anions of the general formula [Sx/2]˙- originate and they are identified as the chromophore groups responsible for the color in the sulfur-based pigment analogues of ultramarines. The red colour of the samples could be mainly attributed to the presence of S4 and S4˙- identified by FTIR.

Impacts of chemical pre-treatments on the hydrogen isotope composition of clay minerals: Determining potential effects in the absence of impurities

The structural hydroxyl hydrogen (H)-isotope compositions of clay minerals are frequently used as tracers of alteration or change in paleoenvironmental and material science studies. Dissolution pre-treatments are commonly used to remove cements and H-bearing impurities prior to isotopic analysis. These pre-treatments commonly include reactions respectively with: HCl or acetic-acetate buffer, H2O2 or NaClO, and a Na-dithionite-Na-citrate-bicarbonate (DCB) solution in order to remove carbonates, organic matter, and iron (oxy)hydroxides. However, there has been inconsistent data regarding to what extent the structural hydroxyl H-isotope composition of a clay mineral is altered during exposure to these chemical pre-treatments.This study examined the “most extreme” impacts of each pre-treatment on the structural H-isotope composition of reference nontronite, montmorillonite, saponite, and kaolinite samples obtained from the Clay Minerals Society Source Clay Repository. All chemical reagents were isotopically labeled to a δ2H value ≈ +200 or +570‰, to sharply contrast the average clay starting material δ2H value ≈ –120‰. H-isotope compositions were measured before and after pre-treatments by High Temperature Elemental Conversion (TCEA) coupled with an Isotope Ratio Mass Spectrometer (IRMS). TCEA-IRMS measurements were done on potassium (K)-exchanged samples pre-dried under active vacuum at 220 °C to mitigate isotopic contamination by adsorbed water vapor.The results showed that only the H-isotope composition of kaolinite was unaffected by all pre-treatments. NaClO and DCB treatments affected the H-isotope compositions of saponite and nontronite, respectively, with the remaining pre-treatments not causing measurable changes for these two clay minerals. The HCl and H2O2 pre-treatments caused massive alteration to the H-isotope compositions for montmorillonite and are considered unadvisable for use with this clay mineral, with respect to H-isotope analysis. The study confirms the possibility of altering the H-isotope composition of clays when using common selective dissolution procedures. The choice of applied pre-treatments before H-isotope measurements for clay-bearing materials should be based on the specific properties and mineralogy of the investigated samples and the amount and type of impurities they contain.

Effect of mineralogical characteristics evolution of vermiculite upon thermal and chemical expansions on its adsorption behavior for aqueous Pb(II) removal

Vermiculite undergoes significant changes in mineralogical characteristics upon chemical (with H2O2) and thermal (roasting) expansions, resulting in a marked impact on its adsorption behavior toward Pb(II) removal. Both chemical and thermal expansions exfoliated the tightly-stacked bulk structure of raw vermiculite into ultra-thin sheets and built abundantly nanoporous channels in the lamellar region, offering sufficient adsorption sites. Meanwhile, the surface properties of hydrophilicity and negative charge in raw vermiculite remain unaltered during expansions, thus enabling an enhanced adsorption capacity through electrostatic attraction. However, severe loss of cation exchange capacity and structural hydroxyl groups due to thermal expansion damaged mixed crystal phases in vermiculite and hydrophlogopite, leading to the poorer Pb(II) removal capability. The results demonstrate that the favorable influence of chemical expansion in raw vermiculite for Pb(II) removal is attributed to enhanced cation exchange within the interlayer, functional groups of structural hydroxyl and siloxane, and negative surface charge on hydrophilic surface.

Evidence of global space weathering by solar wind on asteroid 162173 Ryugu

Reflectance spectra (0.3–4 μm) of powder samples of the third largest stone C0002 returned from the asteroid Ryugu by JAXA Hayabusa2 mission were measured and compared with proximity observation data taken by the Optical Navigation Camera - Telescopic (ONC-T) and the Near-Infrared Spectrometer (NIRS3) onboard the Hayabusa2 spacecraft. Although the characteristics of the 2.7 μm absorption band due to structural hydroxyl of the Ryugu powder samples are consistent with CI1 chondrite meteorites, NIRS3 spectra of the global surface of Ryugu exhibit a wavelength shift of +6 nm in the 2.7 μm absorption band center in comparison with those of both the powder samples and an artificial crater on the asteroid formed by the Small Carry-on Impactor (SCI). This is consistent with effects of solar wind-induced space weathering being present across the global surface of asteroid Ryugu. The darkness of the Ryugu surface in comparison with the returned samples and an upturn in reflectance observed in the average ONC-T spectrum at ultraviolet wavelengths may also be due to space weathering.

High recovery of lithium from coal residue by roasting and sulfuric acid leaching

As the price and demand for lithium metal continue to rise, super-enriched lithium coal is expected to become a new resource to obtain lithium, but there are little research studies on methods for extraction process and mechanism. In this study, a lithium-rich coal residue was leached with H2SO4 after roasting activation without any additive. The properties and morphology of raw ore, calcined samples and leaching residue were characterized by proximate analyses, XRF, ICP-OES, XRD and SEM-ESD. The major chemical compositions were Al2O3 (26.46 %), SiO2 (41.35 %), C (9.43 %) and the valuable lithium content was 550 mg/kg. The main phase compositions of the raw coal residue are kaolinite, quartz, anatase, gypsum and muscovite. The highest leaching efficiency of lithium was achieved under conditions of calcination at 500 °C, leaching reaction time of 40 min, in 15 % wt/v sulfuric acid concentration at a leaching temperature at 90 °C. The occurrence at lithium was closely associated with the kaolinite. The mechanism of roasting activation is that kaolinite loses its structural hydroxyl group and transforms into metakaolinite, and the exposed lithium can undergo ion exchange and minerals dissolution reaction with sulfuric acid.

Interaction of Nitrite Ions with Hydrated Portlandite Surfaces: Atomistic Computer Simulation Study.

The nitrite admixtures in cement and concrete are used as corrosion inhibitors for steel reinforcement and also as anti-freezing agents. The characterization of the protective properties should account for the decrease in the concentration of free NO2- ions in the pores of cement concretes due to their adsorption. Here we applied the classical molecular dynamics computer simulation approach to quantitatively study the molecular scale mechanisms of nitrite adsorption from NaNO2 aqueous solution on a portlandite surface. We used a new parameterization to model the hydrated NO2- ions in combination with the recently upgraded ClayFF force field (ClayFF-MOH) for the structure of portlandite. The new NO2- parameterization makes it possible to reproduce the properties of hydrated NO2- ions in good agreement with experimental data. In addition, the ClayFF-MOH model improves the description of the portlandite structure by explicitly taking into account the bending of Ca-O-H angles in the crystal and on its surface. The simulations showed that despite the formation of a well-structured water layer on the portlandite (001) crystal surface, NO2- ions can be strongly adsorbed. The nitrite adsorption is primarily due to the formation of hydrogen bonds between the structural hydroxyls on the portlandite surface and both the nitrogen and oxygen atoms of the NO2- ions. Due to that, the ions do not form surface adsorption complexes with a single well-defined structure but can assume various local coordinations. However, in all cases, the adsorbed ions did not show significant surface diffusional mobility. Moreover, we demonstrated that the nitrite ions can be adsorbed both near the previously-adsorbed hydrated Na+ ions as surface ion pairs, but also separately from the cations.

Natural coal gangue activated persulfate for tetracycline hydrochloride degradation: Mechanisms, theoretical calculations, and comparative study

The development of catalysts with low-cost and high-efficiency for advanced oxidation process is the key issue to remove organic pollutants. In this work, natural coal gangue (CG) was used to activate potassium monopersulfate (PMS) for the removal of tetracycline hydrochloride (TC). For comparison, sodium persulfate (PS), potassium persulfate (PDS), and hydrogen peroxide (H2O2) were also activated by CG to remove TC. The active species in the TC degradation processes in PMS/CG, PS/CG, PDS/CG, and H2O2/CG systems were investigated by capture experiments and electron spin resonance (ESR) tests. DFT calculation indicated that PMS was more easily adsorbed by CG in comparison with PS, PDS, and H2O2. In addition, Fukui function was adopted to determine how electrophilic, nucleophilic and free-radical attacks occurred on sites of TC molecules in detail. Mechanism investigation showed that the surface-bonded and structural hydroxyl groups of natural CG were favorable for the adsorption of PMS molecules onto the CG surface and thus facilitated the generation of active species, which were crucial in the TC degradation process. This paper sheds new light for natural minerals or solid wastes to participate in advanced oxidation process (AOPs) for wastewater treatment.

Thermal behavior of modern and archeological enamel and dentin by in situ temperature‐dependent Raman spectroscopy

AbstractTeeth and bones are important bioarchives, which can be altered because of diagenesis or burning (cooking, funerary cremations, and fires). Though heating and diagenesis are different processes, an experimental heating of modern bioapatite reproduces in a short time effects similar to diagenetic processes occurring over geological time. The thermal behavior of modern and archeological human enamel and dentin using the in situ thermo‐Raman spectroscopy at 83–873 K was investigated to assess the structural changes in organic and mineral components of a tooth and their interrelationship. The ν1(PO4) vibrational mode in apatite is the most anharmonic and responsible for the reaction of the structure to external influences. The γiP isobaric Grüneisen parameters for archeological (0.41) and modern (0.24) enamel are different from those for fluor‐ (0.17) and chlorapatite (0.17), which indicates a stronger reaction of PO bonds in bioapatite PO4 tetrahedra to temperature changes as compared with geologic samples. The anomalies of the thermal dependences of the ν1(PO4) peak position and (T) autocorrelation function are caused by the combined effect of different factors such as breaking of hydroxyl and hydrogen bonds, the loss of adsorbed and structural water, collagen denaturation, organic phase combustion, and removal and relocation of B‐ and A‐type carbonate ions. The thermal (273, 313, 341, and 363 K) and cold (~160 K) denaturation of collagen is reflected in the ν1(PO4) and (T) dependences. The (T) differences between modern and archeological dentin and enamel are contingent on bioapatite composition (proportions of adsorbed and structural water, hydroxyl and carbonate ions, and trace elements as well as different types of organic matter — low‐molecular noncollagen compounds and high‐molecular collagen). The results obtained contribute to the knowledge about the thermal transformations of the mineral and organic phases of modern and archeological tooth tissues and allow their structural alterations to be evaluated.

Green desorption combined with peptization technology for disposing of Cr(VI)-V(V)-containing hazardous aluminum waste to prepare high-valued pseudo-boehmite

Cr(VI)-containing aluminum residues are inevitable industrial hazardous waste in the chromate industry. To reduce and utilize these residues, a combined desorption and peptization technology for disposing of Cr(VI)-V(V)-containing boehmite hazardous waste (γ-AlOOH-Cr-V) with NaOH solutions was proposed, which realized the removal of V(V) and Cr(VI) effectively and the improvement of peptization index (PI) of obtained pseudo-boehmite (PB) synergistically. The results showed that PB with high PI (98.1%) and low content of V(V) (0.0656%) and Cr(VI) (0.0018%) could be achieved by desorbing the γ-AlOOH-Cr-V, while the surface area and pore volume would be decreased during desorption with the increase of NaOH concentration. Besides the leaching toxicity of Cr(VI) of obtained PB of 0.09 mg/L was extremely lower than that of the standard of hazardous waste. It was noted that the evolution of structural hydroxyl groups governed the improvement of peptization performance. DFT results showed that proper interlayer water content was beneficial to the adsorption of hydroxyl ions on the structural hydroxyl groups of PB. This work not only reduced the emission of Cr(VI)-V(V)containing hazardous waste, but also paved the way for the high-valued utilization of co-associated aluminum and vanadium resources in chromite.