Yongjun Xian

Dynamic Simulation of the Thermal Decomposition of Pyrite Under Vacuum

The ultrasoft pseudopotential plane wave method is applied to dynamic simulation of the thermal decomposition mechanism of FeS2 under vacuum. The FeS2 (100), (111), and (210) surface relaxation and the geometric and electronic structure of the reactants and products are calculated. The results indicate that FeS2 (100) is the most preferred surface to dissociate and also the most common cleavage surface. The thermal decomposition mechanism of FeS2 is explained by dynamic simulation on a micro stratum: in general, the S-Fe bond gradually elongated until it fractured, the S-S bond strengthened gradually, the S-Fe bond was cleaved to form S, the force is relatively weaker between different layers, and thermal decomposition occurred easily between the layers. Simultaneously, the intermediate products, such as FexSy, were formed. Evidence of Fe pyrolysis into Fe metal was not found, and the intermediate products decomposed further. The contributions of the p and d orbitals of Fe increased, whereas that of the s orbital decreased. The contributions of the s and p orbitals of S decreased. The results obtained from FeS2 thermal decomposition experiments under vacuum and differential thermal analysis—thermogravimetry are consistent with the results of calculation and simulation.

New influence factor inducing difficulty in selective flotation separation of Cu-Zn mixed sulfide minerals

Selective flotation separation of Cu-Zn mixed sulfides has been proven to be difficult. Thus far, researchers have found no satisfactory way to separate Cu-Zn mixed sulfides by selective flotation, mainly because of the complex surface and interface interaction mechanisms in the flotation solution. Undesired activation occurs between copper ions and the sphalerite surfaces. In addition to recycled water and mineral dissolution, ancient fluids in the minerals are observed to be a new source of metal ions. In this study, significant amounts of ancient fluids were found to exist in Cu-Zn sulfide and gangue minerals, mostly as gas-liquid fluid inclusions. The concentration of copper ions released from the ancient fluids reached 1.02 × 10−6 mol/L, whereas, in the cases of sphalerite and quartz, this concentration was 0.62 × 10−6 mol/L and 0.44 × 10−6 mol/L, respectively. As a result, the ancient fluid is a significant source of copper ions compared to mineral dissolution under the same experimental conditions, which promotes the unwanted activation of sphalerite. Therefore, the ancient fluid is considered to be a new factor that affects the selective flotation separation of Cu-Zn mixed sulfide ores.

Theory analysis and vestigial information of surface relaxation of natural chalcopyrite mineral crystal

Abstract X-ray diffraction was used to measure the unit cell parameters of chalcopyrite crystal. The results showed that the chalcopyrite crystal is perfect, and the arrangement of its atoms is regular. A qualitative analysis of molecular mechanics showed that surface relaxation causes the chalcopyrite surface to be sulfur enriched. Atomic force microscope (AFM) was used to obtain both a microscopic three-dimensional topological map of chalcopyrite surface and a two-dimensional topological map of its electron cloud. The AFM results revealed that the horizontal and longitudinal arrangements of atoms on the chalcopyrite surface change dramatically compared with those in the interior of the crystal. Longitudinal shifts occur among the copper, iron and sulfur atoms relative to their original positions, namely, surface relaxation occurs, causing sulfur atoms to appear on the outermost surface. Horizontally, AFM spectrum showed that the interatomic distance is irregular and that a reconstruction occurs on the surface. One result of this reconstruction is that two or more atoms can be positioned sufficiently close so as to form atomic aggregates. The lattice properties of these models were calculated based on DFT theory and compared with the experimental results and those of previous theoretical works. On analyzing the results, the atomic arrangement on the (001) surface of chalcopyrite is observed to become irregular, S atoms move outward along the Z-axis, and the lengths of Cu—S and Fe—S bonds are enlarged after geometry optimization because of the surface relaxation and reconstruction. The sulfur-rich surface and irregular atomic aggregates caused by the surface relaxation and reconstruction greatly influence the bulk flotation properties of chalcopyrite.

First-principle study on the surface atomic relaxation properties of sphalerite

The surface properties of sphalerite (ZnS) were theoretically investigated using first principle calculations based on the density functional theory (DFT). DFT results indicate that both the (110) and the (220) surfaces of sphalerite undergo surface atom relaxation after geometry optimization, which results in a considerable distortion of the surface region. In the normal direction, i.e., perpendicular to the surface, S atoms in the first surface layer move outward from the bulk (d1), whereas Zn atoms move toward the bulk (d2), forming an S-enriched surface. The values of these displacements are 0.003 nm for d1 and 0.021 nm for d2 on the (110) surface, and 0.002 nm for d1 and 0.011 nm for d2 on the (220) surface. Such a relaxation process is visually interpreted through the qualitative analysis of molecular mechanics. X-ray photoelectron spectroscopic (XPS) analysis provides the evidence for the S-enriched surface. A polysulphide (Sn2−) surface layer with a binding energy of 163.21 eV is formed on the surface of sphalerite after its grinding under ambient atmosphere. This S-enriched surface and the Sn2− surface layer have important influence on the flotation properties of sphalerite.

Effect of lattice defects on the electronic structures and floatability of pyrites

The electronic structures of three types of lattice defects in pyrites (i.e., As-substituted, Co-substituted, and intercrystalline Au pyrites) were calculated using the density functional theory (DFT). In addition, their band structures, density of states, and difference charge density were studied. The effect of the three types of lattice defects on the pyrite floatability was explored. The calculated results showed that the band-gaps of pyrites with Co-substitution and intercrystalline Au decreased significantly, which favors the oxidation of xanthate to dixanthogen and the adsorption of dixanthogen during pyrite flotation. The stability of the pyrites increased in the following order: As-substituted < perfect < Co-substituted < intercrystalline Au. Therefore, As-substituted pyrite is easier to be depressed by intensive oxidization compared to perfect pyrite in a strongly alkaline medium. However, Co-substituted and intercrystalline Au pyrites are more difficult to be depressed compared to perfect pyrite. The analysis of the Mulliken bond population and the electron density difference indicates that the covalence characteristic of the S-Fe bond is larger compared to the S-S bond in perfect pyrite. In addition, the presence of the three types of lattice defects in the pyrite bulk results in an increase in the covalence level of the S-Fe bond and a decrease in the covalence level of the S-S bond, which affect the natural floatability of the pyrites.

Contribution of components from volume defect in natural pyrite and quartz to solution chemistry of flotation pulp

Abstract The volume defects in pure pyrite and quartz from a classical Cu–Pb–Zn–Fe sulfide deposit were investigated. The results indicate that a large number of volume defects exist in natural pyrite and quartz. The volume defects assume a variety of shapes, including long strips, oval shapes and irregular shapes, with sizes ranging from a few microns to dozens of microns. These volume defects are rich in metallogenic elements as a result of the capture of metallogenic and mineralizing fluid during the defect-forming process. The volume defects are fractured during the grinding process, and their chemical components are released into the solution, as confirmed by the abundant presence of various metal and non-metal components in the cleaning water and EDS results. Under the experimental conditions of 10 g pyrite or quartz with grinding fineness of d 90 =37 μm, which was cleaned in 40 mL of pure deionised water under an inert atmosphere, the total average concentrations of Cu, Pb, Zn, Fe, Ca, Mg and Cl − in the aqueous solution are 32.09×10 −7 , 16.51×10 −7 , 19.45×10 −7 , 516.52×10 −7 , 129.50×10 −7 , 35.30×10 −7 and 433.80×10 −7 mol/L, respectively, for pyrite and 19.20×10 −7 , 8.88×10 −7 , 8.31×10 −7 , 82.71×10 −7 , 16.21×10 −7 , 4.28×10 −7 and 731.26×10 −7 mol/L, respectively, for quartz. These values are significantly greater than those from the experimental non-oxidative dissolution of the pyrite or quartz, respectively. Therefore, the metallogenic fluid in volume defects of mineral crystal is concluded to represent the dominant contribution to the solution chemistry of sulfide flotation pulp. The present investigation will help to deeply understand the flotation theory of sulfide minerals.

Leaching characteristics and mechanism of copper flotation tailings in sulfuric acid solution

The copper deposit in Yangla zone of China is large, and its recovery is low only using flotation process. Therefore, the copper in the flotation tailings is leached by sulfuric acid can improve copper recovery. The factors affecting leaching process and the leaching mechanism were investigated in this study. Copper is leached at a rate of 53.8% when initial H2SO4 concentration is 0.428 mol/L, leaching temperature is 348 K, liquid-to-solid ratio is 3: 1, stirring speed is 300 r/min and leaching time is 60 min. Through combine the acid leaching process of tailings with the flotation process of raw ore, copper comprehensive recovery has been improved. Kinetics results show that the leaching process is controlled by internal diffusion with an activation energy of 9.796 kJ/mol. To characterize the mechanism of acid leaching, chemical analysis, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were used. The results indicate that the fine size of copper minerals and CaSO4 precipitation which generated during acid leaching process affected the leaching of copper minerals.