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The galvanic interaction between pyrite and galena surface has been investigated using density functional theory (DFT) method. The calculated results show that galvanic interactions between pyrite and galena surface are decreased with the increase of contact distance. The galvanic interactions still occurs even the distance larger than the sum of two atoms radius (≈2.8 Å), and the limit distance of galvanic interaction between galena and pyrite surface is about 10 Å, which is consistent with the quantum tunneling effect. Through Mulliken charge population calculation, it is found that electrons transfer from galena to pyrite. For galena surface, Pb 6s and 6p states lose electrons and S 3p state loses a small amount of electrons, which causes the electron loss of galena. For pyrite surface, Fe 4p state obtains large numbers of electrons, resulting in the decrease of positive charge of Fe atom. However, the 3p state of S atom loses a small numbers of electrons. The reactivity of mineral surface has also been studied by calculating the frontier orbitals of minerals. Results suggest that the highest occupied molecular orbital (HOMO) coefficients of galena are increased whereas those of pyrite are decreased with the enhancing galvanic interaction, indicating that the oxidation of galena surface would be enhanced due to the galvanic interaction. The Fukui indices and dual descriptor values of surface atoms suggest that the nucleophilicity of the galena surface increases, meanwhile, the electrophilicity of pyrite surface increases with the decrease of the contact distance. In addition, the density of states (DOS) of atoms results show that the activity of electrons in Pb 6s and 6p orbitals enhances while the activity of electrons in Fe 3d orbitals weaken due to the galvanic contact between minerals. [ABSTRACT FROM AUTHOR]

The influences of Ag, Bi, Sb and Zn impurities on the electrochemical adsorption of butyl xanthate on a galena surface were investigated. The impurity-doped and pure galena samples were synthesised by chemical precipitation and tested by X-ray diffraction (XRD) analyses. The flotation results suggest that the Ag and Bi impurities can promote the flotation of galena, while the Zn and Sb inhibit it. Both the lead- and impurity-xanthate are observed on the galena surface by infrared spectra, which suggests that the impurities on galena surface also interact with xanthate. However, Ag-xanthate and Bi-xanthate at the galena surface doped Ag or Bi may need to be further verified. The cyclic voltammetric measurements on galena microelectrodes reveal two oxidation peaks for both the pure and impurity-doped PbS, while no obvious reduction peaks are observed. It is found that the presence of Ag and Bi enhances the oxidation of xanthate on the galena surface, while the Zn and Sb impurities inhibit the oxidation of xanthate on the galena surface. The amount of electrochemically adsorbed xanthate on the galena surface varies based on the type of impurity and has a positive correlation with the flotation recovery of galena. [ABSTRACT FROM AUTHOR]

[Display omitted] • Galvanic interaction between chalcopyrite and galena has been studied by DFT method. • Galvanic interaction weakens the bonding DOS of O-Fe bonds, S-Cu bonds and S-Fe bonds. • Oxidation peak of electrode with a mix of chalcopyrite and galena is weaker than pure. Chalcopyrite is often associated with galena in nature, which brings great difficulties to the flotation recovery of chalcopyrite. One of the main reasons for these difficulties is that galvanic interaction between chalcopyrite and galena has a significant effect on the oxidation and flotation behavior of chalcopyrite. In this paper, density functional theory and cyclic voltammetry measurement were used to study galvanic interaction between chalcopyrite and galena and its effect on the adsorption of oxygen and xanthate molecules on chalcopyrite (0 0 1) surface. The results show that the galvanic interaction inhibits the dissociation of oxygen molecules on the surface of chalcopyrite (0 0 1), and it also weakens the bonding DOS of O-Fe bonds, S-Cu bonds and S-Fe bonds, which may be detrimental to the adsorption of xanthate and oxygen molecules on the surface of chalcopyrite (0 0 1). The cyclic voltammetry measurements results show that compared with pure chalcopyrite and pure galena electrode, the oxidation peak intensity of the electrode with a mass ratio of chalcopyrite and galena of 1:1 near 0.4 V is weaker at pH 9.18 and a butyl xanthate concentration of 0.001 mol/L, which is consistent with the results of DFT studies. [ABSTRACT FROM AUTHOR]

We investigate the galvanic interaction between galena and eight different grinding media including low carbon steel (carbon content 0.1 wt%), medium carbon steel (carbon content 0.3 wt%), high carbon steel (carbon content 0.9 wt%), and grinding medium containing 0.1 wt% Ce, 0.1 wt% La, 0.1 wt% Y, 4.6 wt% Cr, or 1.5 wt% Mn, and the effects of those galvanic interactions on the surface structure, surface activity and adsorption of oxygen and xanthate molecules on galena surface have also been investigated. [Display omitted] • The galvanic effect between galena and grinding media was studied using DFT method. • Medium carbon steel can enhance the oxidation of galena surface by galvanic effect. • Grinding medium containing La enhance the adsorption of xanthate on galena surface. Galena has different electrostatic potentials from grinding medium. Collision and friction occur between them in the grinding process, which lead to electron transfer and charge redistribution on galena surface, affecting surface oxidation and galena recovery. In this paper, the galvanic interaction between galena and eight different grinding media including low carbon steel (carbon content 0.1 wt%), medium carbon steel (carbon content 0.3 wt%), high carbon steel (carbon content 0.9 wt%), and grinding medium containing 0.1 wt% Ce, 0.1 wt% La, 0.1 wt% Y, 4.6 wt% Cr, or 1.5 wt% Mn has been studied using DFT method. The effects of those galvanic interactions on the surface structure, surface activity and adsorption of oxygen and xanthate molecules on galena surface have been investigated. The results show that the adsorption of oxygen and xanthate molecules on the surface of galena is the strongest with medium carbon steel (carbon content is 0.3 wt%), followed by low carbon steel and high carbon steel. In addition, compared with the grinding media containing chromium, cerium, yttrium and manganese, the grinding medium containing lanthanum (lanthanum content is 0.1 wt%) is more conducive to the adsorption of oxygen and xanthate molecules on the surface of galena. [ABSTRACT FROM AUTHOR]

The control of crystal morphology is crucial to preparation of α-hemihydrate gypsum (α-HH). α-HH was prepared from phosphogypsum (PG) in Na 2 SO 4 solution at different temperatures. The effect of maleic acid (C 4 H 4 O 4 ) on the dehydration rate and growth behavior of α-HH was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the interactions of C 4 H 4 O 4 molecule with the α-HH surface were studied using density functional theory (DFT) calculations. The results show that the increase in Na 2 SO 4 concentration and solution temperature can shorten the dehydration time of PG. Maleic acid inhibits the conversion of PG to α-HH by prolonging the crystal growth period. α-HH crystals prefer to grow along the c-axis and present a long columnar crystal. With an increase in the maleic acid concentration from 0.00 to 5.76 mM, the morphology of α-HH evolves from a needle-like whisker to a short equiaxial crystal, and the corresponding aspect ratio decreases from 14.19 to 0.91. The calculation results indicate that the strong interactions between the C 4 H 4 O 4 molecule and the (1 1 1) crystal plane of α-HH are largely attributable to the bonding of both the single-bond oxygen (O 1 ) and double-bond oxygen (O 2 ) in C 4 H 4 O 4 with the Ca atoms of the (1 1 1) crystal plane and that the chemisorption of C 4 H 4 O 4 can occur on the (1 1 1) crystal plane with the lowest adsorption energy of −201.65 kJ/mol. C 4 H 4 O 4 adsorption on the (1 1 0) crystal plane is through a single O 2 Ca bond with an adsorption energy of −95.32 kJ/mol. The interaction between the (0 1 0) crystal plane and C 4 H 4 O 4 is weak. It can be concluded that maleic acid can preferentially adsorb on the (1 1 1) crystal plane and retard crystal growth along the c-axis during the preparation of α-HH from PG. [ABSTRACT FROM AUTHOR]

Pyrite is a mineral often associated with coal in coal seams and is a major source of sulfur in coal. Coal–pyrite is widely distributed, easily available, low-cost, and non-toxic, and has high light absorption coefficient. So, it shows potential for various applications. In this paper, the density-functional theory (DFT + U) is used to construct coal–pyrite with carbon doped in the sulfur and iron vacancies of pyrite. The effects of different carbon defects, different carbon doping concentrations, and different doping distributions in the same concentration on the electronic structure and optical properties of coal–pyrite were studied. The results show that the absorption coefficient and reflectivity of coal–pyrite, when its carbon atom substitutes the iron and sulfur atoms in the sulfur and iron vacancies, are significantly higher than those of the perfect pyrite, indicating that coal–pyrite has potential for application in the field of photovoltaic materials. When carbon is doped in the sulfur vacancy, this impurity state reduces the width of the forbidden band; with the increase in the doping concentration, the width of the forbidden band decreases and the visible-light absorption coefficient increases. The distribution of carbon impurities impacts the band gap but has almost no effect on the light absorption coefficient, complex dielectric function, and reflectivity, indicating that the application of coal–pyrite to photovoltaic materials should mainly consider the carbon doping concentration instead of the distribution of carbon impurities. The research results provide a theoretical reference for the application of coal–pyrite in the field of photoelectric materials. [ABSTRACT FROM AUTHOR]

Using phosphogypsum (mainly composed of dihydrate gypsum) as raw material to prepare α-hemihydrate gypsum (α-HH) is an effective way for high-value utilization of phosphogypsum solid waste. Sodium ions can effectively promote the transformation of dihydrate gypsum to α-HH and enhance the driving force of crystal transformation. However, during this process, sodium impurities may be doped into the α-HH crystals, resulting in an efflorescence phenomenon when α-HH products are used, which affects the use of the products. In this paper, the formation of sodium impurities in the process of preparing α-HH in NaCl solution was studied by the laboratory test, XRD, XPS, SEM and XRF. Possible forms and diffusion paths of sodium impurities in hemihydrate gypsum crystals are studied by density functional based tight binding methods. The results show that sodium impurities tend to exist in hemihydrate gypsum crystals by doping at interstitial sites. Moreover, there are a large number of interstitial sites in hemihydrate gypsum, which are critical for the diffusion of sodium impurities. [Display omitted] • Possible forms and diffusion paths of Na impurities in hemihydrate gypsum crystals are studied. • The interstitial site in hemihydrate gypsum crystals is critical for Na impurity doping and diffusion. • The crystal transformation of DH to α-HH in solution is the key condition for the formation of Na impurity. [ABSTRACT FROM AUTHOR]

Effects of carbon chain length, carbon chain isomerism, C C double bonds number on fatty acid adsorption on FAP (0 0 1) surface have been investigated based on DFT. The results revealed that fatty acid collector can form stable adsorption configuration at Ca1 (surf) site. Chemical adsorption was formed between O (mole) of fatty acid collector and the Ca1 (surf) of fluorapatite (0 0 1) surface; hydrogen bond adsorption was formed between the H (mole) of fatty acid and the O (surf) of-[PO 4 ]- of FAP (0 0 1) surface. Fatty acid collectors and FAP (0 0 1) surface are bonding by means of the hybridization of O (mole) 2p and Ca (surf) 4d orbitals, H (mole) 1s and O (surf) 2p orbital. The analysis of adsorption energy, DOS, electron density, Mulliken charge population and Mulliken bond population revealed that with the carbon chain growing within certain limits, the absolute value of the adsorption energy and the overlapping area between the DOS curve of O (mole) and Ca (surf) was greater, while that of H (mole) 1s and O (surf) 2p basically remained unchanged. As C C double bonds of fatty acids increased within certain limits, the adsorption energy and the overlapping area between the state density curve of O (mole) and Ca (surf), H (mole) and O (surf) basically remained unchanged. The substituent groups of fatty acid changed, the absolute value of the adsorption energy and the overlapping area between the state density curve had a major change. The influence of fatty acids adsorption on FAP (0 0 1) surface depends mainly on the interaction between O (mole) and Ca (surf). [ABSTRACT FROM AUTHOR]

The adsorption of surfactants on a solid surface could alter its wettability, which offers a wide range of relevant applications such as mineral flotation, hydrophobic material preparation and nanomaterial dispersion. The morphology of adsorbed oleate on a collophane surface was visualized using the peakforce tapping mode of atomic force microscopy (AFM), and its effect on the wettability of collophane was analysed by contact angle measurements, adsorption measurements and molecular dynamics (MD) simulations. The AFM images demonstrated that the adsorbed structure varied with different oleate concentrations. First, the small cylindrical micelles with concomitant monolayer and bilayer structures were observed above the hemimicelle concentration ( hmc ) of 1 × 10 −5  mol/L, which enhanced the hydrophobicity of the collophane surface, and the collophane surface was not completely covered with the oleate monolayer due to surface heterogeneity. Then, large cylindrical micelles with a major bilayer were formed as the critical micelle concentration ( cmc ) of 1 × 10 −3  mol/L was approached, which decreased its hydrophobicity, and finally the formation of large cylindrical micelles with multilayer at the cmc caused the hydrophilicity of the collophane surface. Therefore, there was a suitable equilibrium concentration between the hmc and cmc for oleate as a collector during mineral flotation, and oleate could also be used as a dispersant for colloidal stability when its equilibrium concentration reached the cmc. The effect of the adsorbed structure on the wettability of collophane was also confirmed by MD simulations. This study provides a good understanding of the surface modification of particles by surfactants for flotation and dispersion applications. [ABSTRACT FROM AUTHOR]