Coordination Number Research Articles

New ion radii for oxides and oxysalts, fluorides, chlorides and nitrides.

Ion radii are derived here from the characteristic (grand mean) bond lengths for (i) 135 ions bonded to oxygen in 459 configurations (on the basis of coordination number) using 177 143 bond lengths extracted from 30 805 ordered coordination polyhedra from 9210 crystal structures; and (ii) 76 ions bonded to nitrogen in 137 configurations using 4048 bond lengths extracted from 875 ordered coordination polyhedra from 434 crystal structures. There are two broad categories of use for ion radii: (1) those methods which use the relative sizes of cation and anion radii to predict local atomic arrangements; (2) those methods which compare the radii of different cations (or the radii of different anions) to predict local atomic arrangements. There is much uncertainty with regard to the relative sizes of cations and anions, giving rise to the common failure of type (1) methods, e.g. Pauling's first rule which purports to relate the coordination adopted by cations to the radius ratio of the constituent cation and anion. Conversely, type (2) methods, which involve comparing the sizes of different cations with each other (or different anions with each other), can give very accurate predictions of site occupancies, physical properties etc. Methods belonging to type (2) can equally well use the characteristic bond lengths themselves (from which the radii are derived) in place of radii to develop correlations and predict crystal properties. Extensive quantum-mechanical calculations of electron density in crystals in the literature indicate that the radii of both cations and anions are quite variable with local arrangement, suggesting significant problems with any use of ion radii. However, the dichotomy between the experimentally derived ion radii and the quantum-mechanical calculations of electron density in crystals is removed by the recognition that ion radii are proxy variables for characteristic bond lengths in type (2) relations.

Remarkable structural effects on the extraction behavior of uranium from sulfuric acid medium using di-alkylhydrogen phosphonates: Insights from EXAFS and DFT computations

The structural effects of the carbon chain on the extraction of uranium have been examined by dialkylhydrogen phosphonates (DalHPs). The extraction of uranium by 0.55 M solutions of DalHPs in n-dodecane (n-DD) was investigated as a function of aqueous phase sulfuric and phosphoric acid concentration (0.1–6 M), and the obtained results were compared with 0.55 M solution of tri-n-butyl phosphate (TBP) in n-DD system under similar experimental conditions. The batch distribution data for the extraction of uranium from sulfuric acid and phosphoric acid medium indicated that DalHPs showed dual extraction behavior, i.e., cation exchange at lower acidities and solvation at higher acidities. The extraction of uranium from the sulfuric acid medium was found to be higher than that from the phosphoric acid medium. The extracted U-DalHPs complexes were characterized by extended X-ray absorption fine structure (EXAFS) and the local atomic structure was discerned. The coordination number of uranium was derived from the EXAFS fitting data for various sulfuric acid concentrations. Density functional theory (DFT) computations were performed to understand the electronic structure and binding affinity of U-DalHPs. An acid-dependent extraction mechanism was derived computationally to understand the complexation of U-DalHPs. The trends observed in the distribution ratios of uranium, and the coordination number deduced from EXAFS fitting was found to be in good agreement with the DFT computations. These investigations have opened up new avenues for use of DalHPs for the extraction/recovery of heavy metal ions from sulfuric acid medium.

Theoretical insight into the sulfurated poisoning process of rhenium-doped nickel catalyst

Three rhenium-doped nickel catalyst surfaces including Re-Ni(111), Re-Ni(200) and Re-Ni(220) were built via Re atom substituting one atom of upper layer Ni surfaces. The sulfurated poisoning process involving H2S adsorption and subsequent splitting steps (H2S→HS+H, HS→S+H) on the three surfaces was investigated and further compared using density functional theory (DFT) to understand the crystal-plane effect. For H2S adsorption, the H2S molecule is preferentially adsorbed on the Re top and bridge ReNi1 sites. Re-Ni(200) surface possessed lower H2S adsorption energy compared to Re-Ni(111) and Re-Ni(220) surfaces, due to its smaller coordination number and higher d-orbital intensity at Fermi level. For splitting steps, transition state search showed that the two processes on the three surfaces are all calculated as exothermic while the energy barrier is basically in the range of 0.23 eV∼0.44 eV, which signifies that the poisoning process is favorable both kinetically and thermodynamically. The splitting steps can be described as a dynamic procedure that contains intimate HS fragment activation, S–H bond stretching accompanied by H atom departure and final dissociation into HS+H or S+H co-intermediates. The valence bond changes during dissociation deduced from projected density of states (PDOS) analysis also proved the above procedure.

New cobalt(II) coordination complex for adsorption of Rhodamine B dye and its mechanistic pathway

A new mixed-ligand cobalt complex with the general formula [Co(H2O)(teaH3)(4-NBA)]·(4-NBA)·H2O (1), where (teaH3 = triethanolamine and 4-NBA = 4-nitrobenzoate), has been successfully synthesized and characterized. In this complex, triethanolamine acts as a tetradentate ligand and the 4-NBA act as monodentate ligands. The cobalt metal ion in the complex has a coordination number of 6 with a slightly distorted octahedral geometry. Furthermore, some intramolecular and intermolecular interactions have been observed in 1. Moreover, the kinetic studies on the rate of adsorption confirm that the Pseudo Second Order model accurately predicted the absorption of RhB by the complex. The higher R-squared value and the close agreement between the calculated (Qe = 207.3 mg/g) and experimental (194.4 mg/g) values indicate a satisfactory match. The hydrogen bonding interactions and other weaker electrostatic interactions between the complex and the RhB molecule enhance this adsorption.

Generating highly active oxide-phosphide heterostructure through interfacial engineering to break the energy scaling relation toward urea-assisted natural seawater electrolysis

Urea-assisted natural seawater electrolysis is an emerging technology that is effective for grid-scale carbon–neutral hydrogen mass production yet challenging. Circumventing scaling relations is an effective strategy to break through the bottleneck of natural seawater splitting. Herein, by DFT calculation, we demonstrated that the interface boundaries between Ni2P and MoO2 play an essential role in the self-relaxation of the Ni–O interfacial bond, effectively modulating a coordination number of intermediates to control independently their adsorption-free energy, thus circumventing the adsorption-energy scaling relation. Following this conceptual model, a well-defined 3D F-doped Ni2P-MoO2 heterostructure microrod array was rationally designed via an interfacial engineering strategy toward urea-assisted natural seawater electrolysis. As a result, the F-Ni2P-MoO2 exhibits eminently active and durable bifunctional catalysts for both HER and OER in acid, alkaline, and alkaline seawater-based electrolytes. By in-situ analysis, we found that a thin amorphous layer of NiOOH, which is evolved from the Ni2P during anodic reaction, is real catalytic active sites for the OER and UOR processes. Remarkable, such electrode-assembled urea-assisted natural seawater electrolyzer requires low voltages of 1.29 and 1.75 V to drive 10 and 600 mA cm−2 and demonstrates superior durability by operating continuously for 100 h at 100 mA cm−2, beyond commercial Pt/C ‖ RuO2 and most previous reports.

Unveiling the Inverse Sandwich Complexes of XeO3: A Computational Exploration.

Our study introduces the design of inverse sandwich (iSw) complexes incorporating a noble gas compound: xenon trioxide (XeO3). Through comprehensive computational analyses, we have investigated the critical factors influencing their stability by employing a variety of state-of-the-art computational tools. We demonstrated that the coordination number of xenon in the iSw complex of XeO3 with 18-crown-6 is influenced by the presence of a rare, weakly stabilizing Xe···Xe interaction between the XeO3 molecules. Furthermore, we observed that the stability of iSw complexes of 1,3,5-triphenylbenzene (TPB) and its derivatives is not solely attributed to aerogen bonding, but also involves contributions from C-H···O interactions and back-donation from the lone pair of Xe to the antibonding C-C orbitals of TPB. Additionally, the significant contributions from orbital interactions and dispersion interactions in the TPB derivatives highlight the multifaceted amphoteric properties of XeO3 and reveal that the iSw complexes of TPB and derivatives are not predominantly governed by electrostatic interactions, contrary to conventional belief.

Sub-Nanometer-Range Structural Effects From Mg2+ Incorporation in Na-Based Borosilicate Glasses Revealed by Heteronuclear NMR and MD Simulations.

Magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) experiments and molecular dynamics (MD) simulations were employed to investigate Na2O-B2O3-SiO2 and MgO-Na2O-B2O3-SiO2 glass structures up to ≈0.3 nm. This encompassed the {Na[p]}, {Mg[p]}, and {B[3], B[4]} speciations and the {Si, B[p], M[p]}-BO and {Si, B[p], M[p]}-NBO interatomic distances to the bridging oxygen (BO) and nonbridging oxygen (NBO) species, where the superscript indicates the coordination number. The MD simulations revealed the dominance of Mg[5] coordinations, as mirrored in average Mg2+ coordination numbers in the 5.2-5.5 range, which are slightly lower than those of the larger Na+ cation but with a narrower coordination distribution stemming from the higher cation field strength (CFS) of the smaller divalent Mg2+ ion. We particularly aimed to elucidate such Na+/Mg2+ CFS effects, which primarily govern the short-range structure but also the borosilicate (BS) glass network order, where both MD simulations and heteronuclear double-resonance 11B/29Si NMR experiments revealed a reduction of B[4]-O-Si linkages relative to B[3]-O-Si upon Mg2+-for-Na+ substitution. These effects were quantified and discussed in relation to previous literature on BS glasses, encompassing the implications for simplified structural models and descriptions thereof.

Coordination Number Regulation of Iron Single‐Atom Nanozyme for Enhancing H2O2 Activation and Selectively Eliminating Cephalosporin Antibiotics

AbstractNanozymes present promising alternatives to natural enzymes, but controlling nanozymes' performance and employing them for selectively removing antibiotics are extremely challenging. Employing theoretical calculations to design the coordination environments of mental and coordination atoms for directing single‐atom nanozymes synthesis emerges as a promising strategy to enhance their efficiency and selectivity in antibiotic elimination. In this study, the peroxidase‐like specificity of iron single‐atom nanozymes (FeSA‐Nx, x = 2,3, and 4) with specific Fe–N coordination numbers is demonstrated based on theoretical calculations. These calculations guide the synthesis of corresponding ultra‐thin FeSA‐Nx, achieving a high degree of consistency between theoretical predictions and experimental results. FeSA‐N3 with a Fe─N3 coordination number proves to be the most effective. The efficient electron transfer from Fe─N3 site to H2O2 reduces the free energy required for •OH generation. Quantitative structure‐activity relationship (QSAR) analysis reveals a strong positive correlation between degradation efficiency of cephalosporins and their electron‐donating capabilities (R2 = 0.820–0.929), realizing selectively eliminating cephalosporins. Integration FeSA‐N3 into ceramic membrane (FeSA‐N3/CM) improves hydrophilicity, achieving continuous and stable removal of cephalosporin. This study provides valuable insights into coordination number regulating nanozyme properties for selective antibiotics removal and offers novel perspectives for FeSA‐N3 application in integrated systems.

Nonlinear composition dependence of hydrogen bond lifetime in water-DMSO binary mixtures: The role of hydrophobic interaction.

The lifetime of a hydrogen bond between water and dimethyl sulfoxide (DMSO) is found to be considerably longer than that between two water molecules in neat water. This is counter-intuitive because the charge on the oxygen in DMSO is considerably less than that in water. Additionally, the strength of the water-dimethyl sulfoxide (w-D) hydrogen bond is found to be strongly composition dependent; the lifetime of the hydrogen bond is ten times larger at 30% than at very low concentrations. Using computer simulations, we perform microscopic structural and dynamic analysis to find that these anomalies arise at least partly from an "action-at-a-distance" effect where the attraction between the hydrophobic methyl groups results in the self-aggregation of DMSO molecules that "cages" both the rotational and linear motions of the molecules involved. This is reflected in the observed strong correlation of the lifetime with the local coordination number of the associated methyl groups. The elongated w-D h-bond lifetime causes a slowdown of collective dynamics and affects the lifetime of the w-w h-bond. This nonlinear feedback mechanism explains the strong composition dependence of viscosity and is anticipated to play a dominant role in many self-assemblies. Furthermore, the w-D hydrogen bond breaking mechanism changes from low to high DMSO concentration, a phenomenon not anticipated a priori. We introduce a new order parameter-based free energy surface of the bond breaking pathway. A two-dimensional transition state rate theory calculation is performed for the lifetime of the w-D h-bond that is found to be semi-quantitatively accurate.

Understanding Europium and Terbium Speciation and Ion Pairing in Carbonate Complexes Using Advanced Spectroscopy Techniques

Lanthanide (Ln) elements are critical materials that are typically extracted/mined together. Their separation by solvent extraction from acidic media is well known; however, there are few studies in basic media with carbonate anions. We investigated the complexation of Eu(III) and Tb(III) carbonates as solids and solutions in alkaline K2CO3, wherein we sought to access a Tb(IV) carbonate complex through ozonolysis. L3‐edge XANES of Eu and Tb carbonate solids, colorless solutions, and a red‐hued Tb solution (obtained by ozonolysis) all showed Ln(III) cations. The absence of evidence for a Tb(IV) complex was confirmed through XAS and EPR analyses, despite the solution exhibiting a deep red color. For solids and solutions, EXAFS results indicate molecular Ln(III)‐carbonato anions. In terms of the Eu(III) carbonate coordination number, the coordination does not change upon dissolution of the solid sample. Furthermore, EXAFS for the solutions revealed evidence for the association of potassium cations with the Ln(III)‐carbonato anions. This direct observation of contact ion pairing by EXAFS at room temperature is rare. The insights into Ln(III) carbonate complexation and solution speciation afforded by XANES‐EXAFS, FT‐IR, and EPR provides perspectives that serve as benchmarks for future computational and experimental efforts focused on caustic‐side solvent extraction of Ln(III) ions.

Weyl semimetallic phase in high pressure CrSb2 and structural compression studies of its high pressure polymorphs

In this study, high pressure synchrotron powder X-ray diffraction is used to investigate the compression of two high pressure polymorphs of CrSb2. The first is the CuAl2-type polymorph with an eight-fold coordinated Cr, which can be quenched to ambient conditions from high-pressure high-temperature conditions. The second is the recently discovered MoP2-type polymorph, which is induced by compression at room temperature, with a seven-fold coordinated Cr. Here, the assigned structure is unambiguously confirmed by solving it from single-crystal X-ray diffraction. Furthermore, the electrical properties of the MoP2-type polymorph were investigated theoretically and the resistance calculations under pressure were accompanied by resistance measurements under high pressure on a single crystal of CrSb2. The calculated electronic band structure for the MoP2-type phase is discussed and we show that the polymorph is semimetallic and possesses type-I Weyl points. No further phase transitions were observed for the CuAl2-type structure up to 50 GPa and 40 GPa for the MoP2-type structure. Even though the CuAl2-phase has the highest coordination number of Cr, it was found to be less compressible than the MoP2-phase having a seven-fold coordinated Cr, which was attributed to the longer Cr-Sb distance in the CuAl2-type phase. The discovery of a type-I Weyl semimetallic phase in CrSb2 opens up for discovering other Weyl semimetals in the transition metal di-pnictides under high pressure.

Bridging molecular dynamics and additive manufacturing: A study of Al-12 at% Si alloy solidification dynamics

This manuscript provides a detailed analysis of the molecular dynamics of the directional solidification process in Aluminum-Silicon (Al-12 % at Si) alloys, with a particular emphasis on applications in additive manufacturing. Utilizing molecular dynamics (MD) simulations, the study examines large systems containing 5–15 million atoms to investigate various facets of the solidification process. These include the dynamics of interface motion and the formation of Silicon (Si) precipitates. The research reveals significant variations in interface velocities and orientations across different thermal gradients and growth rates, underscoring the intricate interaction between thermal and solute flows in the microstructural development of Al-Si alloys. These findings are vital for comprehending and refining the solidification process in additive manufacturing, ultimately enhancing the mechanical strength and reliability of the final products. The paper highlights the critical role of microstructure control in printed metals and proposes future research directions, aiming to apply these insights to more complex alloy compositions and manufacturing contexts. In the concluding phase, the scikit-image library was employed to analyze dendritic formations in solidifying Al-Si alloys using MD simulations. This analysis delineates trends in dendritic count, spacing, perimeter, and area over time, offering essential perspectives on the solidification process and its implications for the alloy's microstructure and mechanical characteristics. The Si content in the Al-Si alloy used can be considered eutectic in the solidified structure. Si atoms are predominantly located at grain boundaries and precipitate regions. Coordination number analysis further confirms the presence of Si in these locations. This microstructure, characterized by a primary Al/Al-Si matrix and Si-rich eutectic regions, aligns with experimental observations in rapid solidification processes in additive manufacturing.

Theoretical study of the effects of surface Cu coordination environment on CO2 hydrogenation to CH3OH

The coordination environment of Cu (the coordination number and arrangement of surface atoms) plays an important role in CO2 hydrogenation to CH3OH. Compared with the extensive studies of the effects of coordination number, the comprehensive effects of coordination number and arrangement of surface atoms were seldom explored in literature. To unravel the effects of surface Cu coordination environment on CO2 hydrogenation to CH3OH, the adsorption and reaction behaviors of H2 and CO2 on Cu(111), (100), (110) and (211) with different coordination numbers and arrangement of surface Cu were systematically calculated by density functional theory (DFT) and kinetic Monte Carlo (kMC) simulation. It was found that the adsorption energies of intermediates in CO2 hydrogenation on Cu surfaces increase with the decrease of coordination number. When the Cu coordination numbers are similar, the charge density on the open surface derived from the different atom arrangement becomes larger and leads to stronger interaction with intermediates than that on the compact one. DFT calculation and kMC simulation indicate that methanol formation pathway follows CO2*→HCOO*→HCOOH*→H2COOH*→H2CO*→CH3O*→CH3OH* on four Cu facets; CO formation is via CO2 direct dissociation on Cu(111), (100) and (110) but COOH* dissociation on (211). The low-coordinated surface Cu with more openness on Cu(211) is the highly active site for CO2 hydrogenation to CH3OH with high turnover of frequency (3.71 × 10−4 s−1) and high selectivity (87.17 %) at 600 K, PCO2 = 7.5 atm and PH2 = 22.5 atm, which is much higher than those on Cu(111), (100) and (110). This work unravels the effects of coordination environment on CO2 hydrogenation at the molecular level and provides an important insight into the design and development of catalysts with high performance in CO2 hydrogenation to CH3OH.

Optimal Oxophilicity at the Fe-Nx Interface Enhances the Generation of Singlet Oxygen for Efficient Fenton-Like Catalysis.

In the pursuit of efficient singlet oxygen generation in Fenton-like catalysis, the utilization of single-atom catalysts (SACs) emerges as a highly desired strategy. Here, a discovery is reported that the single-atom Fe coordinated with five N-atoms on N-doped porous carbon, denoted as Fe-N5/NC, outperform its counterparts, those coordinated with four (Fe-N4/NC) or six N-atoms (Fe-N6/NC), as well as state-of-the-art SACs comprising other transition metals. Thus, Fe-N5/NC exhibits exceptional efficacy in activating peroxymonosulfate for the degradation of organic pollutants. The coordination number of N-atoms can be readily adjusted by pyrolysis of pre-assembly structures consisting of Fe3+ and various isomers of phenylenediamine. Fe-N5/NC displayed outstanding tolerance to environmental disturbances and minimal iron leaching when incorporated into a membrane reactor. A mechanistic study reveals that the axial ligand N reduces the contribution of Fe-3d orbitals in LUMO and increases the LUMO energy of Fe-N5/NC. This, in turn, reduces the oxophilicity of the Fe center, promoting the reactivity of *OO intermediate-a pivotal step for yielding singlet oxygen and the rate-determining step. These findings unveil the significance of manipulating the oxophilicity of metal atoms in single-atom catalysis and highlight the potential to augment Fenton-like catalysis performance using Fe-SACs.

The Reconstruction of Pt(001) Surface and the Shell-Like Reconstruction of the Vicinal Pt(001) Surfaces Revealed by Neural Network Potential.

In this work, a highly accurate neural network potential (NNP) is presented, named PtNNP, and the exploration of the reconstruction of the Pt(001) surface and its vicinal surfaces with it. Contrary to the most accepted understanding of the Pt(001) surface reconstruction, the study reveals that the main driving force behind Pt(001) quasi-hexagonal reconstruction is not the surface stress relaxation but the increased coordination number of the surface atoms resulting in stronger intralayer binding in the reconstructed surface layer. In agreement with experimental observations, the optimized supercell size of the reconstructed Pt(001) surface contains (5×20) unit cells. Surprisingly, the reconstruction of the vicinal Pt(001) surfaces leads to a smooth shell-like surface layer covering the whole surface and diminishing sharp step edges.

Experimental investigation of the temperature-dependent dissolution process of aluminosilicate glass and low-calcium supplementary cementitious materials under alkaline conditions

High-temperature curing is commonly employed to promote the pozzolanic activity of supplementary cementitious materials (SCMs) in cementitious systems. Herein, the temperature-dependent dissolution processes of low-calcium SCMs and synthesised aluminosilicate glass were examined at pH 13 for cementitious systems. The dissolution rate and thermal activation energy (TAE) were estimated using nonlinear fitting and the Arrhenius equation. Experimental and analytical findings demonstrated that the TAEs of investigated SCMs and aluminosilicate glasses were temperature-dependent, decreasing with increasing temperature. Moreover, the TAE of aluminosilicate glasses increased with increasing Al/Si ratio, mainly due to the higher TAE of Al2O3 compared to SiO2. In addition, the TAE of fly ash was higher than that of investigated glass, largely because the Si and Al coordination numbers increased with decreasing cooling rates, according to molecular dynamics analysis. The topological TAE derived from molecular dynamics analysis is a promising parameter for estimating the TAE of aluminosilicate glass.

Influence of wind-blown sand content on the mechanical quality state of ballast bed in sandy railways

During the operation of sandy railways, the challenge posed by wind-blown sand is a persistent issue. An in-depth study on the influence of wind-blown sand content on the macroscopic and microscopic mechanical properties of the ballast bed is of great significance for understanding the potential problems of sandy railways and proposing reasonable and adequate maintenance and repair strategies. Building upon existing research, this study proposes a new assessment indicator for sand content. Utilizing the discrete element method (DEM) and fully considering the complex interactions between ballast and sand particles, three-dimensional (3D) multi-scale analysis models of sandy ballast beds with different wind-blown sand contents are established and validated through field experiments. The effects of varying wind-blown sand content on the microscopic contact distribution and macroscopic mechanical behavior (such as resistance and support stiffness) of ballast beds are carefully analyzed. The results show that with the increase in sand content, the average contact force and coordination number between ballast particles gradually decrease, and the disparity in contact forces between different layers of the ballast bed diminishes. The longitudinal and lateral resistance of the ballast bed initially decreases and then increases, with a critical point at 10% sand content. At 15% sand content, the lateral resistance is mainly shared by the ballast shoulder. The longitudinal resistance sharing ratio is always the largest on the sleeper side, followed by that at the sleeper bottom, and the smallest on the ballast shoulder. When the sand content exceeds 10%, the contribution of sand particles to stiffness significantly increases, leading to an accelerated growth rate of the overall support stiffness of the ballast bed, which is highly detrimental to the long-term service performance of the ballast bed. In conclusion, it is recommended that maintenance and repair operations should be promptly conducted when the sand content of the ballast bed reaches or exceeds 10%.

Oxidative Addition of (Hetero)aryl (Pseudo)halides at Palladium(0): Origin and Significance of Divergent Mechanisms.

Two limiting mechanisms are possible for oxidative addition of (hetero)aryl (pseudo)halides at Pd(0): a 3-centered concerted and a nucleophilic displacement mechanism. Until now, there has been little understanding about when each mechanism is relevant. Prior investigations to distinguish between these pathways were limited to a few specific combinations of the substrate and ligand. Here, we computationally evaluated over 180 transition structures for oxidative addition in order to determine mechanistic trends based on substrate, ligand(s), and coordination number. Natural abundance 13C kinetic isotope effects provide experimental results consistent with computational predictions. Key findings include that (1) differences in highest occupied molecular orbital (HOMO) symmetries dictate that, although 12e- PdL is strongly biased toward a 3-centered concerted mechanism, 14e- PdL2 often prefers a nucleophilic displacement mechanism; (2) ligand electronics and sterics, including ligand bite angle, influence the preferred mechanism of the reaction at PdL2; (3) phenyl triflate always reacts through a displacement mechanism regardless of the catalyst structure due to the stability of a triflate anion and the inability of oxygen to effectively donate electron density to Pd; and (4) the high reactivity of C-X bonds adjacent to nitrogen in pyridine substrates relates to stereoelectronic stabilization of a nucleophilic displacement transition state. This work has implications for controlling rate and selectivity in catalytic couplings, and we demonstrate application of the mechanistic insight toward chemodivergent cross-couplings of bromochloroheteroarenes.

Variations in pore structures and permeabilities of ion adsorption rare earth ores during simulated in-situ leaching: Effect of newly formed clay particles and their swelling

In-situ leaching is essential for mining rare earth elements (REEs) from ion-adsorption rare earth (RE) ores. The efficiency of RE mining is dependent on the permeabilities of ion-adsorption RE ores, and the permeabilities are controlled by their pore structures. However, the current understanding of the pore structures and permeabilities of the RE ores during leaching is limited, particularly their dynamic variations, the controlling roles of different pore structure parameters on the permeability, the roles of the influencing factors and the mechanisms causing the variations. To investigate the above-mentioned issues, we conducted an experimental study of simulated in-situ leaching on undisturbed ion-adsorption RE ore samples under different conditions via constant waterhead permeability tests. The leaching conditions included leaching time, concentration and waterhead of the (NH4)2SO4 solution. Three-dimensional (3-D) pore structures of the RE ores before, during, and after leaching were constructed via X-ray computed tomography, and their pore structure parameters were measured using 3-D image computation. It was observed that the dynamic variations in both the pore structure parameters and permeability coefficients of the RE ores occurred in three distinct stages: rapid reduction, less rapid reduction, and little reduction. The experimental results also revealed that the permeability coefficients of the RE ores were primarily dependent on the average coordination number among the seven pore structure parameters examined, and that the pore throats larger than 30 μm in diameter served as the most effective seepage channels within the RE ores. The waterhead of the leaching solution had a stronger influence on the variations in pore structures and permeabilities compared to that of the concentration. Analysis of the particle/aggregate size distribution and mineralogical compositions of the RE ores before and after leaching indicated that the decreases in the pore structure parameters and permeabilities were largely attributed to clogging of the pore throats and pores by migrated and newly formed clays, as well as swelling of the latter. The newly formed clays were the products of the decomposition of K-feldspar and mica resulting from chemical reactions with the leaching solution. The clays from the two sources occurred in disaggregated and aggregated forms. The results of this study provide an important reference for the mining of RE ores via leaching.

Study of the Structure of Zn and Na Borophosphate Glasses Using X-ray and Neutron Scattering Techniques

The atomic structures of Zn and Na borophosphate glasses were studied using X-ray and neutron scattering techniques. Peaks assigned to the B−O, P−O, and O−O distances confirm that only BO4 units co-exist with the PO4 tetrahedra. The Zn−O and Na−O coordination numbers are found to be a little larger than four. The narrowest peaks of the Zn−O first-neighbor distances exist for the glasses along a line connecting the Zn(PO3)2 and BPO4 compositions (50 mol% P2O5), which is explained by networks of ZnO4, BO4, and PO4 tetrahedra with twofold coordinated oxygens. The calculated amounts of available oxygen support this interpretation. Broadened peaks occur for glasses with lower P2O5 contents, which is consistent with the presence of threefold coordinated oxygens. The two distinct P−O peak components of the Zn and Na borophosphate glasses differ in their relative abundances. This is interpreted as follows: Na+ cations coordinate oxygens in some P−O−B bridges, which is something not seen for the Zn2+ ions.