Molecular Insights into the Wettability and Hydration Mechanism of Magnesite (104) Surface

Computational modeling of cetyl phosphate adsorption on magnesite (1 0 4) surface

This paper presents molecular dynamics simulations of methanoic acid and methylamine molecules interacting with various calcite and magnesite surfaces in aqueous conditions. A new set of potentials for the interaction of nitrogen atoms with mineral surfaces is fitted and tested using ab initio methods. The results show that methanoic acid adsorption is stronger than methylamine adsorption onto calcite and magnesite surfaces. The competition between the surface water structure and the adsorbing molecule is shown to be a major component of the adsorption energy and explains why adsorption is stronger at particular surface indices and onto calcite surfaces rather than magnesite surfaces.

New insights into selective-depression mechanism of novel depressant EDTMPS on magnesite and quartz surfaces: Adsorption mechanism, DFT calculations, and adsorption model

Selective flotation of magnesite from dolomite using α-chloro-oleate acid as collector

The geometries and energies of adsorption of up to five layers of water on the {111}, {110}, and {100} surfaces of stoichiometric UO2 and PuO2 are studied computationally with Hubbard U-corrected density functional theory within the periodic boundary condition framework. This work builds on their recent study of the surface-bound water monolayers [Tegner et al., J. Phys. Chem. C 121, 1675 (2017)], and the water geometries within this first layer are used as the starting point for the present calculations. Significant variations are found in the per-layer adsorption energies, as a result of differing extents of intra- and interlayer hydrogen bonding. After the adsorption of several additional layers, the effect of the surface-bound water geometries diminishes, and the average adsorption energy per water molecule is ca. 0.5–0.6 eV (similar to that in bulk water), irrespective of the surface.

Mass spectrometry is a useful technique for studying molecular cluster sizes, their distributions, compositions, and stability. Methanol and fullerenes are among the species identified in the interstellar medium and, due to their high abundance, their interactions are an interesting investigation topic. A mass spectrometric study of mixed clusters of methanol and C60 inside helium nanodroplets is presented. Anomalies in the distribution intensities or magic numbers were observed for [CH3OH]4[C60]m+,1≤m≤7. Water molecules within clusters were also detected, arising as one of the products of intermolecular methanol dehydration. Optimized and supposedly stable geometrical structures of these molecules are presented along with corresponding HOMO–LUMO gaps and adsorption energies. A linear decrease in adsorption energy and saturation at a critical cluster size was noticed.

Atomistic computer simulation methods have been employed to model the structure of the (104) surfaces of calcite (CaCO3), dolomite [CaMg(CO3)2] and magnesite (MgCO3). Our calculations show that, under anhydrous vacuum conditions, calcite undergoes the greatest degree of surface relaxation with rotation and distortion of the carbonate group accompanied by movement of the calcium ion. The magnesite surface is the least distorted of the three carbonates, with dolomite being intermediate to the two end members. When water molecules are placed on the surface to produce complete monolayer coverage, the surfaces of all three carbonate minerals are stabilized and the amount of relaxation in the surface layers substantially reduced. Of the three phases, dolomite shows the strongest and highest number of interfacial hydrogen bonds between water and the carbonate mineral surface. These calculations suggest that the equilibrium H2O + CO32−⇌HCO3− + OH− will favour the production of hydrogen carbonate ions most strongly for dolomite, less strongly for calcite, and least likely for magnesite.

Graphyne (GY) is an allotrope composed of sp and sp2 hybridized carbon atoms. In this paper, the adsorption performance of Ti‐modified GY (Ti‐GY) system on the adsorption of CH4 molecules is studied based on first principles. The study found that the most stable adsorption site for Ti atoms is the six‐membered carbon ring pore site. There is a strong ionic interaction between the two, and the Ti‐GY system structure remains stable during the adsorption of CH4 molecules. A single Ti‐modified GY can adsorb 7 CH4 molecules on one side, and the adsorption structure is stratified, with average adsorption energy of −0.298 eV, and an adsorption capacity of 0.369 g g−1; two Ti‐modified GY adsorbs 14 CH4 molecules on double‐sided, the average adsorption energy is about −0.300 eV, and the adsorption capacity reaches 0.484 g g−1. The first layer of CH4 molecules is adsorbed, which is mainly affected by the Ti atoms. There is a strong Coulomb interaction between it and Ti. With the increase of CH4 molecules, the adsorption energy decreases; While the second layer of CH4 molecules is due to the distance Ti atoms are far away, At this time, the interaction between the CH4 molecules and the substrate is mainly the electrostatic interaction between the positively charged CH4 molecules and the negatively charged GY and the van der Waals interaction between the CH4 molecules. The adsorption performance of CH4 molecules is closely related to the pore size of the two‐dimensional adsorbent. When the pore size is small, the interaction between molecules is enhanced and the average adsorption energy is larger. On the contrary, the larger the pore size, the higher the adsorption capacity.

The accumulation of magnesite tailings (MT) poses challenges such as resource wastage, land occupation, dust generation, and environmental pollution, thereby jeopardizing both physical and mental health. Urgent attention is required for the proper treatment of this solid waste material. An in‐depth investigation into enhancing the flotation processes of MT is essential. A comprehensive comprehension of the surface properties of MT and its principal gangue minerals assumes paramount importance in facilitating the desilication and decalcification of MT via flotation. In this investigation, a first‐principles study grounded in density functional theory was employed to scrutinize the surface properties, as well as the similarities and differences in flotability, of four minerals‐quartz, magnesite, dolomite, and calcite. The findings reveal that quartz's primary cleavage plane is (1 0 1), whereas that of magnesite, dolomite, and calcite is (1 0 4). The surfaces of magnesite, dolomite, and calcite exhibit chemical similarities, with Ca atoms demonstrating higher reactivity than Mg atoms. The hydrogen bonding between dodecylamine and quartz emerges as the most robust, while adsorption energies with the three carbonate minerals exhibit minimal disparity. The ongoing focus lies on the selection and optimization tests of decalcification reagents. A moderate quantity of dodecylamine manifests a certain desilication effect. However, excessive dosage compromises selectivity. The first‐principles approach offers guiding significance for elucidating the surface properties of MT and its primary vein minerals, along with investigating the adsorption mechanisms of flotation regents.

Analysis of selective modification of sodium dihydrogen phosphate on surfaces of magnesite and dolomite: Reverse flotation separation, adsorption mechanism, and density functional theory calculations

Dodecylamine is one of the most commonly used amine collectors for the reverse flotation of magnesite ore. Through a combination of experimental research and computational simulation, the effect of n-octanol on the removal of impurities by the reverse flotation of magnesite ore was studied. The test results show that when the dosage of dodecylamine was 60 mg/L, the flotation rates of magnesite and dolomite were 59.53% and 58.02%, respectively, and the flotation rate of quartz was 97.60%. In the presence of n-octanol, the flotation rate of magnesite decreased to 56.41%, and the flotation rates of dolomite and quartz increased to 61.30% and 99.59%, respectively. The test results show that the addition of n-octanol can improve the selectivity of minerals under the same amount of collector. The adsorption of dodecylamine (dodecylamine and n-octanol) on the surface of magnesite, dolomite and quartz was simulated using quantum chemical calculations based on density functional theory (DFT) and implemented in the CASTEP module of Materials Studio. The results show that dodecylamine can adsorb to magnesite, dolomite and quartz, and the adsorption effect was strongest on quartz. After adding n-octanol, the population value of the bond between the agent and magnesite decreased from 0.19 to 0.17, indicating that the adsorption effect of the agent on magnesite was weakened. The population value of the bond between the drug and dolomite increased from 0.19 to 0.23, indicating that the adsorption effect of the drug on dolomite was enhanced. H28, H29, and H2 in the drug form bonds with O12, O20, and O20 on the surface of quartz (101), respectively, and the population values were 0.43, 0.25, and 0.09, respectively. The adsorption sites of the drug and the quartz were increased, and the adsorption effect of the quartz was markedly improved. The test and simulation results show that the dosage of the agent can be reduced in the presence of n-octanol. N-octanol is not only beneficial to the removal of silicon by amine reverse flotation but also has a certain beneficial effect on the removal of calcium by reverse flotation.

Feldspar minerals constitute an abundant group of tectosilicates in the Earth's crust. Consequently, feldspars play a significant role in a plethora of geochemical processes, including weathering, which results in carbon dioxide removal from the atmosphere by the formation of carbonates. Moreover, feldspar dusts are known as highly efficient ice nucleating particles, having a significant impact on the physical properties of mixed-phase clouds. For these processes, the interaction of water with the feldspar surface is decisive. However, little is known about the interaction of water with feldspar surfaces. More specifically, experimental data addressing the binding and in particular the desorption of the first water layer are sparse. Here, we present temperature-programmed desorption (TPD) experiments of water desorbing from the thermodynamically most stable cleavage plane of potassium-rich feldspar, microcline (001). From the interplay of these experimental data with density-functional theory (DFT) results we shed light onto the binding of the first water layer on microcline (001). The coverage-dependent TPD spectra reveal a gradual shift of the peak position from initially 235 K for low coverages towards lower temperatures until a coverage of four water molecules per primitive unit cell is reached. Above this coverage, the peak position remains fixed at about 180 K, even for high coverages. These results are in perfect agreement with DFT simulations, revealing a decrease in the adsorption energy with increasing coverage. When four water molecules per primitive unit cell are reached, the first layer is saturated and further water starts occupying the second layer. Our work confirms previous theory results from the literature and provides molecular-scale insights into the binding of water onto microcline (001).

Dissociative adsorption of water molecules on Si(001) clean surface becomes a common understanding now. The mechanism, however, has not been clarified yet. This is because it is always tacitly assumed that a water molecule is adsorbed to a surface and dissociates as a monomer. Therefore, we investigated the adsorption of water molecules on Si(001) clean surface based on the first-principles density-functional-theory (DFT) calculations and found that the adsorption energy as a water cluster dramatically increases at a silicon down-dimer site. This adsorption state accompanies a change in quality of hydrogen bond, and the water molecule can be easily dissociated via a proton-relay mechanism. Since this mechanism allows the dissociation between adjacent silicon dimers, the previous experimental results can be explained in more natural ways. We also obtained the result that implies the generality of this mechanism by analyzing of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the water monomer, dimer and Si(001) clean surface based on molecular orbital theory. These theoretical results propose the necessity of taking account of the multi-molecular process as well as the single molecular process.

Stability and reactivity study of bio-molecules brucine and colchicine towards electrophile and nucleophile attacks: Insight from DFT and MD simulations

Crystalline coordination complexes of actinides, especially in atypical oxidation states, are not only fundamentally important for expanding the notably limited knowledge on the bonding nature of a...