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One of the most important hydration phases of Portland cement is ettringite, a calcium sulfo-aluminate mineral ( C a 6 A l 2 (O H) 12 (SO 4) 3 · 26 H 2 O ) showing a great capacity of adsorbing radionuclides and other contaminant cationic and anionic species, or incorporating them into its crystal structure. In this work, the X-ray diffraction pattern and infrared spectra of a synthetized ettringite sample are recorded and simulated, employing theoretical methods based on Density Functional Theory. Despite the complexity of this phase, the calculated structure, X-ray diffraction pattern and infrared spectrum are in excellent agreement with their experimental counterparts. Since the calculated and experimental spectra are consistent, the main infrared bands are assigned using a normal coordinate analysis, some of them being completely reassigned with respect to other experimental works. The good agreement found provides strong support for the computational methods employed towards their use for studying the surface adsorption properties and the incorporation of contaminations in its structure. The density of reactive groups at the surfaces of ettringite is reported, and the surface adsorption of water molecules is studied. These surfaces appear to be highly hydrophilic, in agreement with the experimental finding that the ettringite structure may include more water molecules, at least up to 27, one more than in its standard formula. [ABSTRACT FROM AUTHOR]

Cerussite is an essential lead oxide mineral with increasing economic importance as lead sulfide resources deplete. This study utilizes density functional theory (DFT) to investigate the structural and electronic properties of the sulfurized cerussite (110) surface. The results show that when the cerussite crystal cleaves along the (110) plane, only the surface layer atoms undergo relaxation to reconstruct the surface, while the atoms located deeper have almost no impact on the reconstructed surface structure. The Pb atoms on the cerussite (110) surface react with the sulfurizing agent to form a PbS deposition layer with a structure similar to galena. This PbS deposition layer is tightly adsorbed onto the lead oxide layer through Pb-S bonds formed by S and subsurface lead oxide structure Pb atoms. The chemical reactivity of Pb atoms in the PbS layer on the sulfurized cerussite (110) surface is more potent than that of Pb atoms on the galena surface; additionally, the Pb atoms closer to the lead oxide layer exhibit slightly higher chemical reactivity than those farther away. This study provides insight into sulfurized cerussite surfaces' structure and properties at an atomic level and assists in explaining the floating behavior of cerussite. [ABSTRACT FROM AUTHOR]

This study investigates the correlation between the electronic structure of the active sites on mineral surfaces and their adsorption capacity. Density functional theory (DFT) and flotation experiments are employed to examine the bonding behavior and adsorption enthalpy of ethylxanthate on pyrite (1 0 0) and arsenopyrite (0 0 1) surfaces. The results indicate that ethylxanthate adsorbs more significantly on pyrite than on arsenopyrite. The adsorption is chemical, primarily occurring through the orbitals of sulfur in the ethylxanthate and iron on the mineral surface. Compared to arsenopyrite, the d-band center of the iron atoms on the surface of pyrite is closer to the Fermi level; thus, the adsorption strength of ethylxanthate on the pyrite surface is greater than on arsenopyrite. The d-band centers of pyrite and arsenopyrite exhibit a direct relationship with their adsorption capacity. [ABSTRACT FROM AUTHOR]

The inhibiting mechanism of high pH on the molybdenite flotation was studied using an experimental and DFT method. The experimental results found that adverse effects of pH on molybdenite flotation should be attributed to the adsorption of OH− on molybdenite [100] surface (MS100). The DFT results show the adsorption energy of H2O/OH− to molybdenite [001] surface (MS001) and MS100 is −8.61/288.30 kJ·mol−1 and −226.81/−302.44 kJ·mol−1. These indicate that H2O is weakly adsorbed on MS001, while OH− is not. Both H2O and OH− can be adsorbed onto MS100. The adsorption energy of OH− to MS100 is much stronger than that of H2O. The results of state density and charge transfer of the adsorption of OH− on MS100 further show that OH− can be chemically adsorbed on MS100 through the bonding of the O atom of OH− and the Mo atom of MS100. This causes a significant reduction in the MS100 hydrophobicity and deteriorates the fine molybdenite flotation. [ABSTRACT FROM AUTHOR]

Surface wettability is determined by the attraction of a liquid phase to a solid surface. It is typically quantified by using contact angle measurements at mineral surfaces in the case of the flotation of mineral particles. Contact angle research to describe wettability has been investigated at different scales by sessile drop measurements, molecular dynamic simulation, and atomic force microscopy. In this study, the density functional theory (DFT) was employed for predicting the surface free energy and contact angles of a well-known hydrophobic phyllosilicate mineral talc and a well-known hydrophilic phyllosilicate mineral muscovite based on the calculated interfacial energy and surface charge. The results revealed that the predicted contact angle at the atomic scale was larger than the experimental value, and identified two interactions: electrostatic interaction and hydrogen bonding, between the hydrophilic muscovite surface and the water layer, while a water-exclusion zone of 3.346 Å was found between the hydrophobic talc surface and the first water layer. This investigation gives a new perspective for wettability determination at the atomic scale. [ABSTRACT FROM AUTHOR]

In China, most of the high-sulfur iron ores have not been fully developed and utilized due to the lack of breakthrough progress in the research on the sulfur migration and the desulfurization mechanism during the roasting process. This study will focus on revealing the release and fixation mechanisms of sulfur during the roasting process to achieve the transformation of desulfurization from terminal treatment to process control. Experimental results show that as the roasting temperature increases, the release rate of SO2 also increases, reaching the maximum release rate at 900 °C. Simultaneously, it is found that at the same roasting temperature, the release rate and amount of SO2 under the O2/N2 atmosphere is significantly greater than that under the pure N2 and air atmospheres. Meanwhile, X-ray diffraction (XRD) is utilized to explore the phase composition of the roasted product and the sulfur release mechanism. In addition, the adsorption energy, stability and electron transfer of SO2 on the CaO surface are calculated through density functional theory (DFT), and the optimal adsorption active site perpendicular to the O atom (O-top) is also determined. Finally, the sulfur fixing agent CaO is used to study the SO2 fixation mechanism. When the concentration reaches 10%, the sulfur fixation efficiency reaches more than 80%. Therefore, this work will present basic knowledge and systematic guidance for the sulfur migration and release of high-sulfur iron ore under the oxidizing roasting process. [ABSTRACT FROM AUTHOR]

The high reactivity of the acetylene group enables the formation of strong chemical bonds with active sites on mineral surfaces, thereby improving the flotation performance of gold minerals. This study utilized density functional theory (DFT) to analyze the quantum chemical parameters of structure, Mulliken population, and the frontier orbitals of a thioester collector containing an acetylene group, PDEC (prop-2-yn-1-yl diethylcarbamodithioate). PDEC was compared with analogous thioester collectors Z-200 and Al-DECDT. The interaction mechanism of PDEC on the Au(1 1 1) surface was simulated, followed by empirical validation through adsorption experiments. The findings indicate that the S atom of PDEC in the carbon–sulfur group exhibits shorter covalent bond lengths, and has reduced carbon–sulfur double bonds and Mulliken population, resulting in enhanced electron localization. This confers greater selectivity to PDEC during its adsorption on mineral surfaces. Frontier orbital analysis shows that the electrons of the acetylene group possess a notable electron-accepting capacity, significantly influencing the frontier orbital energy of PDEC and playing a pivotal role in the bonding interaction with mineral surfaces. Both the S atom in the carbon–sulfur group and its acetylene group establish stable adsorption structures with the A(111) surface in a single coordination mode. The adsorption energy sequence is PDEC > Al-DECDT > Z-200. Partial density of states demonstrates that the S 3p orbit of the carbon–sulfur group hybridizes with the Au 5d orbit, while the C 2p orbit of the acetylene group engages in weaker back-donation bonding with the Au 5d orbit. This is corroborated by the electron density difference and post-adsorption Mulliken population analyses, revealing that the S atom of the carbon–sulfur group in PDEC donates electrons to the Au atom, forming dominant positive coordination bonds, whereas the acetylene group accepts partial electrons from the Au atom, resulting in weaker back-donation bonds. The adsorption experiments align with the DFT adsorption energy results. [ABSTRACT FROM AUTHOR]

The work presents the latest scientific research on the far infrared spectrum of the natural mineral villiaumite (chemical formula NaF). The three samples of villiaumite examined came from the Khibiny Mountains in the Kola Peninsula (Russia) and from Mon Saint Hilaire in Quebec (Canada). The tested villiaumite samples began to change color very slowly after being heated above 300 °C in a muffle furnace. Subsequent color changes required heating at increasingly higher temperatures for approximately 48–72 h. Samples of the reddish mineral villiaumite turned orange, pink and finally colorless (at approximately at 430 °C). Because the color of villiaumite changes under the influence of temperature, far infrared spectra were measured for the samples at room temperature and for the sample heated to 100, 200, 300, 400 and 500 °C. Additionally, using density functional theory (DFT/B3LYP/6-31+g*), the spectrum of NaF (125-atom model of crystal structure) was simulated for the first time and compared with the experimental spectrum of pure sodium fluoride (a chemical reagent) and the mineral villiaumite. [ABSTRACT FROM AUTHOR]

Chalcopyrite (CuFeS2) particles, exposing anisotropic crystal planes during the grinding process, possess comprehensive surface properties that affect their leaching behaviors. In order to investigate the influence of anisotropic crystal planes on the leaching mechanisms, CuFeS2 particles with anisotropic crystal planes were produced by employing three-head laboratory grinder mill (TM), rod mill (RM), and ball mill (BM) and were then leached in a sulfuric acid solution at pH = 1. Based on the XRD, SEM, XPS, and simulation results, (112), (102), (312), (110), (116), (100), and (001) planes were mainly exposed on the CuFeS2 surface during the crushing and grinding process. In addition, fewer (112), (102), (312), and (110) planes but more (116), (100), and (001) planes were exposed on the CuFeS2 samples in the TM method than in the RM and BM methods. Since the leaching rates were in the order of (001) > (100) > (116) > (110) > (312) > (102) > (112) planes, the Cu extractions followed an order of TM > RM > BM. This study, therefore, provides an excellent theoretical basis for the effect of anisotropic crystal planes on CuFeS2 leaching, further improving the understanding of CuFeS2 leaching mechanisms. [ABSTRACT FROM AUTHOR]

Understanding the reduction of CO2 and the origin and evolution of early life on Earth is an important research endeavor. Pyrite, due to its semiconductor properties, is believed to play a pivotal role as a reactant or catalyst in converting reducing gases, such as CO2, into organic matter. In this study, we employed density functional theory (DFT) to investigate the reduction of CO2 in the presence of H2S on the surface of pyrite. Our findings reveal that the presence of sulfur vacancies enhances the adsorption of H2S and CO2 molecules onto the pyrite surface. Interestingly, we observed the generation of the HCOOH molecule on the defective pyrite surface. Additionally, the transition state analysis indicates that H2S and CO2 molecules require the overcoming of an energy barrier (Ea) of 36.93 kJ/mol to form the HCOOH molecule. This study sheds light on the role of pyrite in the early creation of life on Earth by elucidating its impact on the reduction of carbon dioxide. [ABSTRACT FROM AUTHOR]

As Bayan Obo rare-earth tailings, which are generated after the production of mineral products with the raw ore from different mining areas, are considered secondary resources rich in valuable elements such as F, Fe, REE, and Nb, an effective method is urgently needed to recover such valuable elements for resource recycling and environmental conservation. A mineralogical analysis can enable process diagnosis, design, and optimization and is the key to comprehensively utilizing valuable elements. Hence, detailed mineralogical characterization is necessary as a starting point to develop a feasible processing flowsheet. In this study, various detection methods, namely inductively coupled plasma-optical emission spectrometry (ICP), X-ray Fluorescence Spectrometer (XRF), X-ray powder diffractometer (XRD), scanning electron microscopy system with an energy dispersive spectrometer (SEM-EDS), mineral liberation analysis (MLA), and electron probe microanalysis (EPMA), were applied to conduct detailed mineralogical characterization of Bayan Obo rare-earth tailings, and the occurrence state of Sc in the main Sc-bearing minerals was studied using density functional theory (DFT). The results showed that Fe mainly occurs in hematite, riebeckite, ankerite, siderite, and pyrite, with contents of 50.15 wt%, 27.94 wt%, 8.34 wt%, 4.92 wt%, and 5.59 wt%, respectively. Nearly all F occurs in 26.8 wt% fluorite. The main rare-earth minerals are bastnasite, apatite, and monazite (La), with contents of 5.0%, 5.0%, and 1.6% in Bayan Obo rare-earth tailings, respectively. Notably, 48.47%, 21.70%, 10.34%, and 10.28% of niobium element occurs in nioboaeschynite, pyrochlore, dingdaohengite, and ilmenorutile, respectively. Scandium was detected in five minerals, namely aegirine, riebeckite, monazite, ilmenorutile, and niobite, with average contents of 0.04 wt%, 0.22 wt%, 0.06 wt%, 0.06 wt%, and 1.58 wt%, respectively. According to the DFT analysis, the state of Sc in aegirine is different from that in riebeckite. Scandium in aegirine mainly substitutes Fe or enters the interstitial lattice site, while Sc in riebeckite tends to replace Fe. Based on these results, a process for recovering valuable elements from tailings is proposed. [ABSTRACT FROM AUTHOR]

The quality of high-purity quartz (HPQ) that used in strategic industries is normally limited due to lattice impurities. In order to reveal the migration pathway of lattice impurities in quartz particles during phase transition from α-quartz to β-quartz, α-quartz and Al3+/Li+-substituted α-quartz (S-α-quartz) was investigated under 846.15 K and 101.325 kPa based on density functional theory. Results showed that β-quartz exhibited more interstitial volume, dominating the migration of lattice impurities. This further indicates that the phase transition process was beneficial for the migration of lattice impurity from a structural point of view. Moreover, Al3+ and Li+ mainly migrated from the intracell to lattice surface along the c axis. In addition, Li+ migrated more easily than Al3+ due to higher mean square displacement values. From a thermodynamic point of view, the lower energy barrier in the case of the Al3+ and Li+ lattice suggested that the presence of lattice impurities promoted phase transition. This study therefore provides an excellent theoretical basis for the removal of lattice impurities of HPQ from an atomic perspective, for the first time. [ABSTRACT FROM AUTHOR]

The galvanic interaction of gold and associated sulfide minerals in thiocyanate systems has a significant impact on gold leaching. The density functional theory was used to further reveal the galvanic interaction between gold and associated minerals. The electron transfer between gold and its associated minerals at different galvanic interaction distances was simulated. The results show that with the increase of the contact distance between pyrite and gold, the charge of pyrite increases, indicating that it is losing electrons gradually; the charge of arsenopyrite and chalcocite decreases with the rise of the contact distance between gold and pyrite, suggesting that they are gaining electrons. In addition, gold has the greatest influence on the gain and loss of electrons in pyrite and arsenopyrite and has the least influence on chalcocite. Through the calculation of the density of states, it is found that different distances of galvanic interaction have a great influence on the density of states of surface atoms under the action of pyrite and arsenopyrite with gold but have little effect on the density of states of surface atoms under the action of chalcocite with gold. [ABSTRACT FROM AUTHOR]

Despite being one of the main sources of iron, specularite is often associated with gangue minerals such as aegirine and chlorite. Flotation separation is challenging in the mineral processing industry because of the similar surface properties of specularite, aegirine, and chlorite. This study investigates the role and selective activation mechanism of Pb2+ in the flotation separation of specularite, aegirine, and chlorite using micro-flotation experiments, solution chemistry calculations, zeta potential analysis, and the density functional theory (DFT). The results of the micro-flotation experiments show that the addition of lead ions can significantly improve the floatability of specularite, but has little impact on the floatability of aegirine and chlorite. Additionally, the solution chemistry calculations results show that PbOH+ is the main component of selectively activated specularite. The zeta potential analysis shows that Pb2+ is more inclined to adsorption on the surface of specularite, and that more collectors are adsorbed on the surface of specularite after the addition of Pb2+. Finally, the DFT calculations show that different chemical bonds are formed during the interaction between CuOH+ and the mineral surface, resulting in different adsorption energies. [ABSTRACT FROM AUTHOR]

Froth flotation is a commonly utilized beneficiation technique for effectively separating apatite from other gangue minerals, such as calcite. It is difficult to achieve good separation with fatty acid collectors due to their similar interactions with apatite and calcite. In this work, sodium N-lauroyl sarcosinate (SNLS) was used as the collector for the selective separation of calcite from apatite without a depressant. The experiments revealed that SNLS had a much better selectivity and a stronger affinity with calcite compared to apatite, with little effect on the flotation of apatite observed at a pH of 10. Fourier transform infrared (FTIR) analyses were conducted to explain the selective collector process of SNLS. The mechanism experiments demonstrate that SNLS can chemically bond to apatite and calcite minerals to produce Ca-NLS chelates. The active O atoms of the amide and carboxyl groups of SNLS accomplish this. Calcite has a greater Ca-reactivity than apatite, and as a result, the adsorption quantity on the calcite surface is greater than that on the apatite surface. FTIR analyses indicate that SNLS exhibits a greater affinity for the calcite surface than for apatite, a finding that is supported by first-principle density functional theory (DFT) calculations showing a higher adsorption energy of SNLS on the calcite surface. DFT calculations showed that SNLS forms stronger O-Ca bonds on the calcite surface and is less hindered by H2O. This work shows that the surfactant sodium N-lauroylsarcosinate (SNLS) can be an ideal collector for the flotation of phosphate minerals. [ABSTRACT FROM AUTHOR]

We explore the structural properties of Mg, MgO, and MgSiO3 liquids from ab initio computer simulations at conditions that are relevant for the interiors of giant planets, stars, shock compression measurements, and inertial confinement fusion experiments. Using path-integral Monte Carlo and density functional theory molecular dynamics, we derive the equation of state of magnesium-rich liquids in the regime of condensed and warm dense matter, with densities ranging from 0.32 to 86.11 g cm−3 and temperatures from 20,000 K to 5 × 108 K. We study the electronic structure of magnesium as a function of density and temperature and the correlations of the atomic motion, finding an unexpected local maximum in the pair correlation functions that emerges at high densities which decreases the coordination number of elemental magnesium and reveals a higher packing. This phenomenon is not observed in other magnesium liquids, which maintain a rather constant coordination number. [ABSTRACT FROM AUTHOR]

Kaolinite is one of the principal rare earth element (REE) ion-adsorption clays that hosts a wide range of elements, including Dy(III) as a representative example. Ammonium sulfate is a typical salt used to leach REEs. Due to the carbon dioxide emissions which occur during ammonia production, it is urgently necessary to develop low environmental pollution leaching agents that can replace (NH4)2SO4. MgSO4 is regarded as the most promising eco-friendly leaching agent. Herein, the first-principles plane-wave pseudopotential method based on the density functional theory (DFT) was used to investigate the stable adsorption structures of Dy(III) and its hydrated ions, MgSO4 leaching agent ions and the corresponding hydrated ions on the surface of kaolinite, which revealed the adsorption mechanism of Dy(III), Mg(II), and SO42− on the silico–oxygen plane and the aluminum–hydroxyl plane of kaolinite. Based on the research results of the steric hindrance effect of Dy(III) on the silico–oxygen plane and the aluminum–hydroxyl plane of kaolinite, the adsorption of Dy(H2O)103+ was more stable on the silico–oxygen plane. It was easier to leach out Dy(III) with MgSO4, while SO42− tended to interact with the rare earth ions in an aqueous solution. The results provide theoretical guidance for efficient rare earth extraction and obtaining novel efficient leaching agents. [ABSTRACT FROM AUTHOR]

This study used a physical activation method to prepare asphalt-pitch-derived activated carbon (Pitch AC) for an electric double-layer capacitor (EDLC) electrode. X-ray diffraction analysis and Raman spectroscopy were used to estimate the change in the crystal structure of Pitch AC with activation time. In addition, the textural properties of Pitch AC were studied by Brunauer-Emmett-Teller (BET), Dubinin-Radushkevich (DR) and non-localized density functional theory (NLDFT) equations with N2/77K isotherm adsorption-desorption curves. The electrochemical performance of the Pitch AC was analyzed using a coin-type EDLC with 1 M SBPBF4/PC via galvanostatic charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The specific surface area and total pore volume were 990–2040 m2/g and 0.42–1.51 cm3/g, respectively. The pore characteristics of the Pitch AC varied according to the activation time and changed from a microporous structure to a micro-mesoporous structure as the activation time increased. The electrochemical performance analysis also found that the specific capacity was increased from 43.6 F/g to 84.5 F/g at 0.1 A/g as activation time increased. In particular, Pitch AC-9 exhibited the best electrochemical performance (rectangular CV curve, reversible GCD, lowest ion charge transfer resistance and Warburg impedance). In addition, Pitch AC-9 was confirmed to have a specific capacitance similar to commercial activated carbon for EDLC (YP-50F). Therefore, it was considered that Pitch AC could replace commercial activated carbon for EDLC because it has excellent pore characteristics and electrochemical performance despite being manufactured through a very low-cost precursor and a simple process (physical activation method). [ABSTRACT FROM AUTHOR]

The recovery of rare earth elements from ores is crucial because of their applications in modern technology. Bastnaesite (La/Ce(CO3)F) is typically found in deposits with other gangue minerals but can be purified by flotation. Accordingly, we investigated the interactions of the collector nonyl hydroxamic acid (NHA) with bastnaesite using density functional theory (DFT) calculations. In addition, we replaced Ce sites on the bastnaesite (100) surface with La and investigated the effect on NHA adsorption. Finally, we examined the effects of co-present aluminum species, which are frequently used inhibitors for associated gangue minerals during bastnaesite flotation, on NHA adsorption and, thus, the flotation efficiency. We found that doping with La increased the strength of adsorption between NHA and the bastnaesite (100) surface. In addition, we found that Al(OH)3(s) was adsorbed more strongly than NHA. Consequently, when Al(OH)3(s) is present in the flotation pulp, it is preferentially adsorbed, which reduces the number of sites for NHA adsorption and its flotation efficiency. These findings suggest that La doping can enhance the recovery of bastnaesite and indicate that the presence of Al minerals should be minimized. [ABSTRACT FROM AUTHOR]

The fate of chemical pollutants in the environment is determined by various factors including the type and strength of their interactions with reactive surfaces in soils and sediments. In the present work the interactions of hexachlorobenzene (HCB) with the surface of a common clay mineral belonging to the smectite group montmorillonite (MNT) is studied by means of the density functional theory method. The MNT net surface charge, induced by isomorphic substitutions, is systematically varied and compensated by Ca 2 + cations. Based on the calculated electron densities, conclusions are drawn revealing the nature of their mutual interactions, the related stability of such surface complexes as well as possible molecular arrangements. It becomes apparent that the dominant contribution to the stability of HCB-MNT complexes arises from the cation- π interactions between the HCB molecule and the nearest compensating Ca 2 + cation and thus besides the MNT net surface charge the type and size of the compensating cations are expected to play a crucial role in understanding the HCB adsorption on MNT. This systematic study aims to contribute to a better mechanistic understanding of the interactions between hydrophobic organic compounds and reactive mineral surfaces. [ABSTRACT FROM AUTHOR]

One of the most widely known representatives of the apatite family is hydroxyapatite, Ca10(PO4)6(OH)2. This mineral is a part of the human dental and bone tissues, and, therefore, is widely used in medicine. Less known is oxyapatite, Ca10(PO4)6O, which has the same biocompatibility as hydroxyapatite. In this work, it is shown that oxyapatite can be obtained by heating hydroxyapatite powder at 1000 °C in vacuum. IR and NMR spectroscopy proved the absence of the hydroxyl groups in the apatite obtained. In the IR spectrum, the presence of new absorption bands of phosphate groups, indicating a symmetry disorder, was observed. Density functional theory modeling confirmed lowering of symmetry for the oxyapatite structure. Modeling the IR spectrum of oxyapatite made it possible to identify the experimentally observed new absorption bands. According to the modeling, the presence of a vacancy in a hydroxyl channel of the apatite structure lowered the symmetry. Powder X-ray diffraction data confirmed that full dehydroxylation of hydroxyapatite led to a decrease in symmetry to triclinic phase. Comparison of the formation energies showed that formation of the hydroxyapatite phase was more preferable than that of oxyapatite, which explains apatite's tendency to rehydroxylation. It was shown that the solubility of oxyapatite in water was comparable to that of hydroxyapatite. [ABSTRACT FROM AUTHOR]

The paper presents research on chloride minerals of natural origin from Kłodawa (Poland), i.e., colorless, blue and purple halite as well as colorless sylvite. Selected samples of minerals were studied by chemical analysis (ICP-OES, ICP-MS, titration methods) and crystallographic measurements. Then, for the tested halides, research was carried out using far-infrared spectroscopy. Spectroscopic studies confirmed the simple way of distinguishing NaCl and KCl minerals using far-infrared spectroscopy, known in the literature. The novelty is that the article presents for the first time the experimental far infrared spectra of natural blue and purple halite. It was observed that the blue (178 cm−1) and purple (176 cm−1) halites have the strongest infrared band slightly shifted towards higher wavenumbers compared to colorless halite (174 cm−1). As part of the work, the infrared spectra of the crystal structure models of sodium and potassium chloride were calculated for the first time using the density functional theory (with the B3LYP functional and the 6-31G* basis set, 125-atom model). The proposed approach can be used not only as a powerful method differentiating NaCl and KCl minerals, but it can also help with understanding of different defects in crystal lattices for naturally occurring halides and crystals of other minerals. [ABSTRACT FROM AUTHOR]

Zircon (ZrSiO4) provides a good pressure-holding environment for ultra-high-pressure metamorphic minerals during crust exhumation due to its high incompressibility and chemical stability. At high pressure, the zircon can transform to reidite. Previous studies show much higher phase-transition pressures at room temperature than those at high temperature (>1000 K) due to kinetic hindrance. To further investigate the kinetics of the zircon–reidite phase transition at relatively low temperatures, the phase boundary at 298–800 K was determined using a diamond anvil cell combined with in situ Raman spectra. The results show that reidite becomes thermodynamically more stable compared with zircon at 8 GPa at room temperature, and the slope of the phase boundary at 298–800 K abruptly differs from that of previous studies at 1100–1900 K. Compared with the equilibrium phase boundary calculated by the density functional theory, it indicates that the kinetic effect of the zircon–reidite phase transition is obvious, and there exists a sufficiently large energy driving force provided by an overpressure to overcome the activation energy barrier below a critical temperature of approximately 880 K. The temperature dependence of overpressure is about 0.023 GPa/K. [ABSTRACT FROM AUTHOR]

Calcium silicate hydrate (C-S-H) is the main product of cement hydration and has also been shown to be the main sorbing phase of actinide ions interacting with cement. U(IV) has been chosen as an exemplary actinide ion to study actinide sorption at C-S-H as U is the main element in highly active radioactive waste and because reducing conditions are foreseen in a deep geological repository for such waste. U(IV) surface adsorption, absorption in the interlayer, and incorporation into the calcium oxide layer of C-S-H has been modeled quantum mechanically, applying a density functional approach. For each sorption mode various sites have been considered and a combined dynamic equilibration and optimization approach has been applied to generate a set of representative stable sorption complexes. At the surface and in the interlayer similar U(IV) hydroxo complexes stabilized by Ca2+ ions have been determined as sorbates. Surface adsorption tends to be preferred over absorption in the interlayer for the same type of sites. Incorporation of U(IV) in the CaO layer yields the most favorable sorption site. This result is supported by good qualitative agreement of structures with EXAFS results for other actinides in the oxidation state IV, leading to a new interpretation of the experimental results. [ABSTRACT FROM AUTHOR]

Adsorption reactions on mineral surfaces are influenced by the overall concentration of the adsorbing metal cation. Different site types (strong vs. weak ones) are often included to describe the complexation reactions in the various concentration regimes. More specifically, strong sites are presumed to retain metal ions at low sorbate concentrations, while weak sites contribute to metal ion retention when the sorbate concentration increases. The involvement of different sites in the sorption reaction may, thereby, also be influenced by competing cations, which increase the overall metal ion concentration in the system. To date, very little is known about the complex structures and metal ion speciation in these hypothetical strong- and weak-site regimes, especially in competing scenarios. In the present study, we have investigated the uptake of the actinide americium on corundum (α–Al2O3) in the absence and presence of yttrium as competing metal by combining extended X-ray absorption fine structure spectroscopy (EXAFS) with density functional theory (DFT) calculations. Isotherm studies using the radioactive 152Eu tracer were used to identify the sorption regimes where strong sites and weak sites contribute to the sorption reaction. The overall americium concentration, as well as the presence of yttrium could be seen to influence both the amount of americium uptake by corundum, but also the speciation at the surface. More specifically, increasing the Am3+ or Y3+ concentrations from the strong site to the weak site concentration regimes in the mineral suspensions resulted in a decrease in the overall Am–O coordination number from nine to eight, with a subsequent shortening of the average Am–O bond length. DFT calculations suggest a reduction of the surface coordination with increasing metal–ion loading, postulating the formation of tetradentate and tridentate Am3+ complexes at low and high surface coverages, respectively. [ABSTRACT FROM AUTHOR]

Sodalite Na8(Al6Si6O24)Cl2 (space group P 4 ¯ 3 n ) is an important mineral belonging to the zeolite group, with several and manyfold fundamental and technological applications. Despite the interest in this mineral from different disciplines, very little is known regarding its high-pressure elastic properties. The present study aims at filling this knowledge gap, reporting the equation of state and the elastic moduli of sodalite calculated in a wide pressure range, from −6 GPa to 22 GPa. The results were obtained from Density Functional Theory simulations carried out with Gaussian-type basis sets and the well-known hybrid functional B3LYP. The DFT-D3 a posteriori correction to include the van der Waals interactions in the physical treatment of the mineral was also applied. The calculated equation of state parameters at 0 GPa and absolute zero (0 K), i.e., K0 = 70.15(7) GPa, K' = 4.46(2) and V0 = 676.85(3) Å3 are in line with the properties derived from the stiffness tensor, and in agreement with the few experimental data reported in the literature. Sodalite was found mechanically unstable when compressed above 15.6 GPa. [ABSTRACT FROM AUTHOR]

In this paper, the adsorption of cyanide and its combination with zinc sulfate on the surface of sphalerite (110) was studied by density functional theory (DFT), and its configurational relationship was analyzed by coordination chemistry. The calculation results show that the adsorption configuration stability of CN− is stronger than that of Zn(CN)2; the chemical bond of Zn(OH)2 is less covalent. The three adsorption modes all make the surface of sphalerite lose more electrons, thereby weakening the reactivity of S and Zn atoms on the sphalerite surface. During the CN− adsorption process, both the 3d and 4p orbital peak energy levels of Zn decrease, indicating the strong inhibitory effect of CN−. Coordination chemistry also shows that CN− matches the Zn ion orbital in sphalerite and the π electron pair on the Zn ion can easily interact with the empty π orbital on CN− to form π-backbonding. [ABSTRACT FROM AUTHOR]

Fluidized roasting is an efficient method to promote vanadium extraction from V-bearing mica in shale. In this study, the transformation behavior of V-bearing sericite during fluidized roasting was explored by combining experimental detections and density functional theory (DFT) calculations. TG-MS, XRD, FTIR, and SEM-EDS were used to investigate the characteristics of the roasted sericite samples. The crystal parameters of V-bearing sericite were calculated with Materials Studio. The results showed that dehydroxylation was the main reaction during roasting, which occurred between 650 °C and 960 °C. After being roasted at 900 °C for 2 h, hydroxyls were completely removed. The calculation results show that −OH was removed between the metal ions in the sericite O-layer, which turned the hexa-coordinate of V3+, Al3+, and Fe3+ into pentacoordinate. Through electronic rearrangement, the bond lengths between two ions connected by −OH were shortened from 0.18~0.20 nm to 0.17 nm. However, some chemical bonds were grown, which indicates that they are weaker and easier to transform. In addition, twisted six-membered rings were formed with obvious angle changes on the (0 0 1) surface. Furthermore, Mulliken's overlap populations of some V-O, Al-O, and Fe-O were decreased. Therefore, dehydroxylation is a determining factor in the destruction of sericite crystals during fluidized roasting, which also promotes vanadium release from shale. [ABSTRACT FROM AUTHOR]

Ion-adsorbed rare earth minerals have rare earth ions adsorbed on the surfaces of clay minerals such as kaolinite and have high contents of medium and heavy rare earth elements. They are important resources supporting the development of high-tech industries. In this study, the CASTEP module in Materials Studio was used to study the adsorption of the rare earth ion Y(III) on the interface of (Al-OH)-H2O and (Si-O)-H2O with density functional theory. The monitoring and calculation of the chemical bond of the adsorption structure showed that Y(III) on the (Al-OH)-H2O interface has a bond with O32, O34, and water molecules in the interface. In the (Si-O)-H2O interface, Y(III) interacts with O3, O4, and O10 to form new chemical bonds. The Mulliken population and density of states analysis showed that Y(III) bonds with surface oxygen atoms and water molecules in the kaolinite-H2O interface, and finally adsorbs on the surface of kaolinite in the form of metal ion hydrate. [ABSTRACT FROM AUTHOR]

At the nanoscale, particle size affects the surface reactivity of anatase–water interfaces. Here, we investigate the effect of electrolyte media and particle size on the primary charging behavior of anatase nanoparticles. Macroscopic experiments, potentiometric titrations, were used to quantitatively evaluate surface charge of a suite of monodisperse nanometer sized (4, 20, and 40 nm) anatase samples in five aqueous electrolyte solutions. The electrolyte media included alkaline chloride solutions (LiCl, NaCl, KCl, and RCl) and Na-Trifluoromethanesulfonate (NaTr). Titrations were completed at 25 °C, as a function of pH (3–11) and ionic strength (from 0.005 to 0.3 m). At the molecular scale, density functional theory (DFT) simulations were used to evaluate the most stable cation surface species on the predominant (101) anatase surface. In all electrolyte media, primary charging increased with increasing particle size. At high ionic strength, the development of negative surface charge followed reverse lyotropic behavior: charge density increased in the order RbCl < KCl < NaCl < LiCl. Positive surface charge was greater in NaCl than in NaTr media. From the DFT simulations, all cations formed inner-sphere surface species, but the most stable coordination geometry varied. The specific inner-sphere adsorption geometries are dependent on the ionic radius. The experimental data were described using surface complexation modeling (SCM), constrained by the DFT results. The SCM used the charge distribution (CD) and multisite (MUSIC) models, with a two-layer (inner- and outer-Helmholtz planes) description of the electric double layer. Subtle charging differences between the smallest and larger anatase particles were the same in each electrolyte media. These results further our understanding of solid–aqueous solution interface reactivity of nanoparticles. [ABSTRACT FROM AUTHOR]

A study of boron impurities deposited on a Si(100) surface in a SiHCl3-BCl3-H2 system is reported in this paper, using periodic density functional theory with generalized gradient approximation (GGA). The results show that the discrete distances of BCl3 and SiHCl3 from the surface of the Si(100) unit cell are 1.873 Å and 2.340 Å, respectively, and the separation energies are −35.2549 kcal/mol and −10.64 kcal/mol, respectively. BCl3 and SiHCl3 are mainly adsorbed on the surface of the Si(100) unit cell in particular molecular orientations: the positive position and the hydrogen bottom-two-front position from the analysis of the bond length change and adsorption energy. The adsorption of SiHCl3 and BCl3 is accompanied by a charge transfer from the molecule to the surface of the unit cell of 0.24 and 0.29 eV, respectively. BCl3 reacts more readily than SiHCl3 with the Si(100) surface, resulting in the deposition of boron impurities on the polysilicon surface. [ABSTRACT FROM AUTHOR]

The discovery of He retentivity in magnetite has opened up the use of the magnetite (U-Th)/He method as a thermochronometer to date the exhumation of mafic and ultramafic rocks, and also as a chronometer to date magnetite crystallization during serpentinization. However, published He diffusion data reveal more complex behavior than expected. To resolve this issue and generalize the understanding of He retention in magnetite, we conducted a multiscale theoretical study. We investigated the impact of natural point-defects (i.e., vacancies unrelated to radiation damage) and defects associated with radiation damage (i.e., vacancies and recoil damage that form amorphous zones) on He diffusion in magnetite. The theoretical results show that He diffusion is purely isotropic, and that defect-free magnetite is more He diffusive than indicated by experimental data on natural specimen. Interestingly, the obtained theoretical trapping energy of vacancies and recoil damage are very similar to those obtained from experimental diffusion data. These results suggest that He diffusion in magnetite is strongly controlled by the presence of vacancies and radiation damage, even at very low damage dose. We propose that, when using magnetite (U-Th)/He thermochronometry, the impact of vacancies and radiation damage on He retention behavior should be integrated. [ABSTRACT FROM AUTHOR]

Multiphase systems are important in minerals processing, and usually include solid-solid and solid-fluid systems, such as in wet grinding, flotation, dewatering, and magnetic separation, among several other unit operations. In this paper, the current trends in the process system engineering tasks of modeling, design, and optimization in multiphase systems, are analyzed. Different scales of size and time are included, and therefore, the analysis includes modeling at the molecular level (molecular dynamic modeling) and unit operation level (e.g., computational fluid dynamic, CFD), and the application of optimization for the design of a plant. New strategies for the modeling, design, and optimization of multiphase systems are also included, with a strong focus on the application of artificial intelligence (AI) and the combination of experimentation and modeling with response surface methodology (RSM). The integration of different modeling techniques such as CFD with discrete element simulation (DEM) and response surface methodology (RSM) with artificial neural networks (ANN) is included. The paper finishes with tools to study the uncertainty, both epistemic and stochastic, based on uncertainty and global sensitivity analyses, which is present in all mineral processing operations. It is shown that all of these areas are very active and can help in the understanding, operation, design, and optimization of mineral processing that involves multiphase systems. Future needs, such as meso-scale modeling, are highlighted. [ABSTRACT FROM AUTHOR]

β-dicalcium silicate (β-Ca2SiO4 or β-C2S in cement chemistry notation) is one of the most important minerals in cement. An improvement of its hydration rate would be the key point for developing environmentally-friendly cements with lower energy consumption and CO2 emissions. However, there is a lack of fundamental understanding on the water/β -C2S surface interactions. In this work, we aim to evaluate the water adsorption on three β-C2S surfaces at the atomic scale using density functional theory (DFT) calculations. Our results indicate that thermodynamically favorable water adsorption takes place in several surface sites with a broad range of adsorption energies (-0.78 to -1.48 eV) depending on the particular mineral surface and adsorption site. To clarify the key factor governing the adsorption of the electronic properties of water at the surface were analyzed. The partial density of states (DOS), charge analysis, and electron density difference analyses suggest a dual interaction of water with a β-C2S (100) surface including a nucleophilic interaction of the water oxygen lone pair with surface calcium atoms and an electrophilic interaction (hydrogen bond) of one water hydrogen with surface oxygen atoms. Despite the elucidation of the adsorption mechanism, no correlation was found between the electronic structure and the adsorption energies. [ABSTRACT FROM AUTHOR]

Novel collector lead(II)-benzohydroxamic acid (Pb(II)-BHA) complexes in aqueous solution were characterized by using experimental approaches, including Ultraviolet-visible (UV-Vis) spectroscopy and electrospray ionization-mass spectrometry (ESI-MS), as well as first-principle density functional theory (DFT) calculations with consideration for solvation effects. The Job plot delineated that a single coordinated Pb(BHA)+ should be formed first, and that the higher coordination number complexes can be formed subsequently. Moreover, the Pb(II)-BHA species can aggregate with each other to form complicated structures, such as Pb(BHA)2 or highly complicated complexes. ESI-MS results validated the existence of Pb-(BHA)n=1,2 under different solution pH values. Further, the first-principles calculations suggested that Pb(BHA)+ should be the most stable structure, and the Pb atom in Pb(BHA)+ will act as an active site to attack nucleophiles. These findings are meaningful to further illustrate the adsorption mechanism of Pb(II)-BHA complexes, and are helpful for developing new reagents in mineral processing. [ABSTRACT FROM AUTHOR]

The adsorption of cysteine on the pyrite (1 0 0) surface was evaluated by using first-principles-based density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS) measurements. The frontier orbitals analyses indicate that the interaction of cysteine and pyrite mainly occurs between HOMO of cysteine and LUMO of pyrite. The adsorption energy calculation shows that the configuration of the -OH of -COOH adsorbed on the Fe site is the thermodynamically preferred adsorption configuration, and it is the strongest ionic bond according to the Mulliken bond populations. As for Fe site mode, the electrons are found transferred from cysteine to Fe of pyrite (1 0 0) surface, while there is little or no electron transfer for S site mode. Projected density of states (PDOS) is analyzed further in order to clarify the interaction mechanism between cysteine and the pyrite (1 0 0) surface. After that, the presence of cysteine adsorption on the pyrite (1 0 0) surface is indicated by the qualitative results of the XPS spectra. This study provides an alternative way to enhance the knowledge of microbe-mineral interactions and find a route to improve the rate of bioleaching. [ABSTRACT FROM AUTHOR]

Silicates are among the most abundant and important inorganic materials, not only in the Earth's crust, but also in the interstellar medium in the form of micro/nanoparticles or embedded in the matrices of comets, meteorites, and other asteroidal bodies. Although the crystalline phases of silicates are indeed present in nature, amorphous forms are also highly abundant. Here, we report a theoretical investigation of the structural, dielectric, and vibrational properties of the amorphous bulk for forsterite (Mg2SiO4) as a silicate test case by a combined approach of classical molecular dynamics (MD) simulations for structure evolution and periodic quantum mechanical Density Functional Theory (DFT) calculations for electronic structure analysis. Using classical MD based on an empirical partial charge rigid ionic model within a melt-quenching scheme at different temperatures performed with the GULP 4.0 code, amorphous bulk structures for Mg2SiO4 were generated using the crystalline phase as the initial guess. This has been done for bulk structures with three different unit cell sizes, adopting a super-cell approach; that is, 1 x 1 x 2, 2 x 1 x 2, and 2 x 2 x 2. The radial distribution functions indicated a good degree of amorphization of the structures. Periodic B3LYP-geometry optimizations performed with the CRYSTAL14 code on the generated amorphous systems were used to analyze their structure; to calculate their high-frequency dielectric constants ("¥); and to simulate their IR, Raman, and reflectance spectra, which were compared with the experimental and theoretical crystalline Mg2SiO4. The most significant changes of the physicochemical properties of the amorphous systems compared to the crystalline ones are presented and discussed (e.g., larger deviations in the bond distances and angles, broadening of the IR bands, etc.), which are consistent with their disordered nature. It is also shown that by increasing the unit cell size, the bulk structures present a larger degree of amorphization. [ABSTRACT FROM AUTHOR]

Atomistic modeling of mineral-water interfaces offers a way of confirming (or refuting) experimental information about structure and reactivity. Molecular-level understanding, such as orbital-based descriptions of bonding, can be developed from charge density and electronic structure analysis. First-principles calculations can be used to identify weaknesses in empirical models. This provides direction on how to propose more robust representations of systems of increasing size that accurately represent the underlying physical factors governing reactivity. In this study, inner-sphere complex geometries of arsenate on hydrated alumina surfaces are modeled at the density functional theory (DFT)-continuum solvent level. According to experimental studies, arsenate binds to alumina surfaces in a bidentate binuclear (BB) fashion. While the DFT calculations support the preference of the BB configuration, the optimized geometries show distortion from the ideal tetrahedral geometry of the arsenic atom. This finding suggests that steric factors, and not just coordination arguments, influences reactivity. The Osurf-As-Osurf angle for the more favorable arsenate configurations is closest to the ideal tetrahedral angle of 109.5°. Comparing the results of arsenate adsorption using a small cluster model with a periodic slab model, we report that the two model geometries yield results that differ qualitatively and quantitatively. This relates the steric factors and rigidity of the surface models. [ABSTRACT FROM AUTHOR]

Halloysite nanotubes are becoming interesting materials for drug delivery. The knowledge of surface interactions is important for optimizing this application. The aim of this work is to perform a computational study of the interaction between 5-aminosalicylic acid (5-ASA) drug and halloysite nanotubes for the development of modified drug delivery systems. The optimization of this nanotube and the adsorption of different conformers of the 5-ASA drug on the internal surface of halloysite in the presence and absence of water were performed using quantum mechanical calculations by using Density Functional Theory (DFT) and methods based on atomistic force fields for molecular modeling, respectively. [ABSTRACT FROM AUTHOR]

Structural and electronic properties of Si termination, O-middle termination, and O-rich terminations of a quartz (001) surface as well as water molecule adsorption on it were simulated by means of density functional theory (DFT). Calculated results show that the O-middle termination exposing a single oxygen atom on the surface is the most stable model of quartz (001) surface, with the lowest surface energy at 1.969 J•m-2, followed by the O-rich termination and Si termination at 2.892 J•m-2 and 2.896 J•m-2, respectively. The surface properties of different terminations mainly depend on the surface-exposed silicon and oxygen atoms, as almost all the contributions to the Fermi level (EF) in density of states (DOS) are offered by the surface-exposed atoms, especially the O2p state. In the molecular adsorption model, H2O prefers to adsorb on the surface Si and O atoms, mainly via O1-H1 bond at 1.259 Å and Si1--Ow at 1.970 Å by Van der Waals force and weak hydrogen bond with an adsorption energy of -57.89 kJ•mol-1. In the dissociative adsorption model, the O-middle termination is hydroxylated after adsorption, generating two new Si--OH silanol groups on the surface and forming the OwH2...O4 hydrogen bond at a length of 2.690 Å, along with a large adsorption energy of -99.37 kJ•mol-1. These variations in the presence of H2O may have a great influence on the subsequent interfacial reactions on the quartz surface. [ABSTRACT FROM AUTHOR]

Efficiently discovering the interaction of the collector oleate and siderite is of great significance for understanding the inherent function of siderite weakening hematite reverse flotation. For this purpose, investigation of the adsorption behavior of oleate on siderite surface was performed by density functional theory (DFT) calculations associating with atomic force microscopy (AFM) imaging. The siderite crystal geometry was computationally optimized via convergence tests. Calculated results of the interaction energy and the Mulliken population verified that the collector oleate adsorbed on siderite surface and the covalent bond was established as a result of electrons transferring from O1 atoms (in oleate molecule) to Fe1 atoms (in siderite lattice). Therefore, valence-electrons' configurations of Fe1 and O1 changed into 3d6.514s0.37 and 2s1.832p4.73 from 3d6.214s0.31 and 2s1.83p4.88 correspondingly. Siderite surfaces with or without oleate functioned were examined with the aid of AFM imaging in PeakForce Tapping mode, and the functioned siderite surface was found to be covered by vesicular membrane matters with the average roughness of 16.4 t nm assuring the oleate adsorption. These results contributed to comprehending the interaction of oleate and siderite. [ABSTRACT FROM AUTHOR]

In this work, tributyltetradecyl-phosphonium chloride (TTPC), has been first introduced to be a novel and efficient cationic surfactant for cationic reverse flotation separation of quartz from magnetite. The first-principles density functional theory calculations, Zeta potential measurements and adsorption isotherm measurements consistently predict that TTPC may be a promising collector that is better than dodecyl triethyl ammonium chloride (DTAC), based on the facts that TTPC and DTAC both prefer to physically adsorb on the quartz surface owing to electrostatic force, but the active part (P+(C4H9)3) of TTPC takes much more positive charges than that (N+(CH3)3) of DTAC. The micro-flotation and Bench-scale flotation results further verify that TTPC presents a stronger collecting power and much better selectivity for iron ore reverse flotation in comparison to the conventional collector DTAC. Furthermore, the corresponding adsorption mechanism of TTPC on the quartz have also been investigated in detail. This work might show a good example to discover a potential candidate collector by analogy with a known excellent collector based on reasonable prediction. [ABSTRACT FROM AUTHOR]

A new understanding of the adsorption mechanism of oleate on cassiterite surfaces is presented by density functional theory (DFT) calculations. Various convergence tests were conducted to optimize the parameter settings for the rational simulation of cassiterite bulk unit cell and surface slabs. The calculated surface energies of four low-index cassiterite cleavage planes form an increasing sequence of (110) < (100) < (101) < (001), demonstrating (110) is the most thermodynamically stable surface of cassiterite. The interaction strengths of the oleate ion (OL-), OH-, and H2O on the SnO2 (110) face are in the order of H2O < OH- < OL-, which reveals that the OL- is able to replace the adsorbed H2O and OH- on the mineral surfaces. Mulliken population calculations and electron density difference analysis show that electrons transfer from the Sn atoms on the cassiterite (110) surface to the O atoms offered by carboxyl groups of oleate during the interaction. The populations of newly formed O1-Sn1 and O2-Sn2 bonds are 0.30 and 0.29, respectively, indicating that these two bonds are of a very low covalency. Density of states analysis reveals that the formation of an O1-Sn1 bond mainly results from the 5s and 5p orbitals of the Sn1 atom and the 2p orbital of the O1 atom. [ABSTRACT FROM AUTHOR]

The flotation, adsorption and bonding mechanisms of styrene phosphonic acid (SPA) to cassiterite were studied using microflotation tests, zeta potential measurements, solution chemistry analysis and density functional theory (DFT) calculations in this paper. Flotation results demonstrated SPA was an excellent collector for cassiterite which could recover over 85% cassiterite particles with the pH range 4.3-6.06 and 40 mg/L SPA. Zeta potential measurements and solution chemistry analysis revealed the adsorption of SPA was mainly contributed by the chemisorption of the monoanions on cassiterite surfaces. Frontier molecular orbital theory analysis and adsorption energy calculation results proved the monoanion of SPA was able to replace the OH- on cassiterite surfaces. The adsorption structure optimization results confirmed the binuclear complex was the most favorable adsorption configuration of SPA on cassiterite (110) surface. Mulliken population calculations and density of states analysis indicated during the bonding process the Sn3 atom lost electrons to O3 atom, and the bonding interaction between O3 and Sn3 atoms was mainly from the contribution of the 2p orbital of O3 atom and the 5s and 5p orbitals of Sn3 atom. [ABSTRACT FROM AUTHOR]

Fluorite (CaF2), a halogen elemental mineral, always co-exists with other minerals. The Ca element in fluorite is often replaced by rare earth elements (REEs), such as cerium (Ce) and yttrium (Y). In this work, the electronic structures of fluorite crystals containing REE (Ce, Th, U, and Y) impurities were studied by density functional theory (DFT). The calculated results showed that the presence of impurities increased the lattice parameter of fluorite. The impurities caused the Fermi level to shift towards the high energy direction, making the fluorite accept electrons more easily. The impurities except Y led to the occurrence of an impurities state in the valence band. The Mullinken population values of F-REE bonds were larger than that of F-Ca and F-F bonds, and F-Y bonds had the largest population value. Analysis of the frontier molecular orbital showed that the impurities contributed greatly to the lowest unoccupied molecular orbital (LUMO). The interaction between oleic acid and impurities-bearing fluorite were discussed. The results suggested that the incorporation of impurities would enhanced the reactivity of fluorite with oleic acid. [ABSTRACT FROM AUTHOR]

The depressing properties of sodium polyacrylate (PA-Na) for scheelite and fluorite were studied by micro-flotation tests, infrared spectroscopy (IR), zeta potentials, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). The flotation results reveal that the selective depression effect of PA-Na is better than that of sodium silicate, and PA-Na can depress fluorite more effectively than scheelite. The flotation recovery of scheelite and fluorite keeps at about 75% and 10%, respectively, at the pulp pH 9.3~9.6 and PA-Na concentration from 30 to 50 mg/L. IR spectra results suggest that PA-Na has a chemical effect on the surface of scheelite and fluorite. The zeta potential of fluorite becomes more negative than that of scheelite after PA-Na addition. XPS analysis deduces the occurrence of chemisorption between PA-Na and mineral surfaces, and the chemisorption of PA-Na on fluorite is stronger than on scheelite. DFT demonstrates that the absolute value of the adsorption energy in the presence of PA-Na is larger on the fluorite {111} surface than on the scheelite {111} surface. Thus, fluorite is more readily depressed than scheelite, which remarkably matches the micro-flotation test results. [ABSTRACT FROM AUTHOR]

The edges of montmorillonite (MMT) react strongly with metals and organic matter, but the atomic structure of the edge and its surface complexes are not unambiguous since the experimental isolation of the edge is challenging. In this study, we introduce an atomistic model of a Na MMT edge that is suitable for classical molecular dynamics (MD) simulations, in particular for the B edge, a representative edge surface of 2:1 phyllosilicates. Our model possesses the surface groups identified through density functional theory (DFT) geometry optimizations performed with variation in the structural charge deficit and Mg substitution sites. The edge structure of the classical MD simulations agreed well with previous DFT-based MD simulation results. Our MD simulations revealed an extensive H-bond network stabilizing the Na-MMT edge surface, which required an extensive simulation trajectory. Some Na counter ions formed inner-sphere complexes at two edge sites. The stronger edge site coincided with the exposed vacancy in the dioctahedral sheet; a weaker site was associated with the cleaved hexagonal cavity of the tetrahedral sheet. The six-coordinate Na complexes were not directly associated with the Mg edge site. Our simulations have demonstrated the heterogeneous surface structures, the distribution of edge surface groups and the reactivity of the MMT edge. [ABSTRACT FROM AUTHOR]

Chloride ions were found to potentially increase activity of cerussite surfaces. Dissolution experiments, zeta potential measurements, X-ray photoelectron spectroscopy (XPS) studies, and density functional theory (DFT) computation were conducted in this study. Dissolution experiments showed that the lead ion concentrations in the NaCl solution system were lower than those in the deionized water system and that the lead ion concentrations in NaCl + Na2S aqueous systems decreased by approximately one order of magnitude compared with that in the Na2S system alone. Results of zeta potential measurements revealed that the pretreatment with chloride ions of cerussite caused a more positive zeta potential than that without chloride ions. XPS analysis results indicated that the number of lead ions on the mineral surface increased after cerussite was treated with chloride ions. Results of DFT computation implied that the number of lead atoms on the mineral surface increased and that the activity improved after PbCl+ was adsorbed onto the cerussite surface. The contribution of chloride ions to the activity on the mineral surface is attributed to the increase in the number of active sites and enhancement in the activity of these sites, resulting in improved sulfidization and flotation performance. [ABSTRACT FROM AUTHOR]

Hydrometallurgical processing of chalcopyrite is hindered predominantly due to the passivation layers formed on the chalcopyrite surface. However, the effects of impurity cations released from the gangue are not yet well understood. Density functional theory (DFT) calculations were carried out to investigate monovalent cations of Na+ and K+ on chalcopyrite (001)-S surface using Materials Studio. The results show that the 3d orbital of Fe and 3p orbital of S predominantly contribute to their activities during chalcopyrite oxidation and dissolution processes. In addition, SO4 2- is more likely to be adsorbed on one Fe site in the presence of Na+, while it is preferentially adsorbed on two Fe sites in the presence of K+. However, the adsorption of both Na2SO4 and K2SO4on the chalcopyrite (001)-S surface contributes to the breakage of S–S bonds, indicating that the impurity cations of Na+ and K+ are beneficial to chalcopyrite leaching in a sulfuric environment. The adsorption energy and partial density of states (PDOS) analyses further indicate that the adsorption of Na2SO4 on chalcopyrite (001)-S surface is favored in both -BB (bidentate binuclear ) and -BM (bidentate mononuclear) modes, compared to the adsorption of K2SO4. [ABSTRACT FROM AUTHOR]

Classical molecular dynamics (MD) simulations have been performed to investigate the effects of substitutions in the octahedral sheet (Mg for Al) and layer charge on an atomistic model of the montmorillonite edge. The edge models considered substitutions in both the solvent accessible and inaccessible octahedral positions of the edge bond chain for a representative edge surface. The MD simulations based on CLAYFF, a fully-flexible forcefield widely used in the MD simulations of bulk clay minerals, predicted Mg--O bond distances at the edge and in bulk that agreed with those of the density functional theory (DFT) geometry optimizations and available experimental data. The DFT results for the edge surfaces indicated that substitutions in the solvent inaccessible positions of the edge bond chain are energetically favorable and an increase in layer charge and local substitution density coincided with the occurrence of five-coordinate, square pyramidal Mg and Al edge structures. Both computational methods predicted these square pyramidal structures, which are stabilized by water bridging H-bonds between the unsaturated bridging oxygen [(Al or Mg)--O--Si] and other surface O atoms. The MD simulations predict that the presence of Mg substitutions in the edge bond chain results in increased disorder of the edge Al polyhedra relative to the unsubstituted edge. In addition to the square pyramidal Al, these disordered structures include trigonal bipyramidal and tetrahedral Al at the edge and inverted Si tetrahedra. These simulation results represent the first test of the fully-flexible CLAYFF forcefield for classical MD simulations of the Na-monmorillonite edge and demonstrate the potential of combined classical MD simulations and DFT geometry-optimizations to elucidate the edge structure of 2:1 phyllosilicate minerals. [ABSTRACT FROM AUTHOR]