Abstracts:To improve the accuracy of microseismic inversion, seismic anisotropy and moment tensor source should be carefully considered in the forward modelling stage. In this study, 3D microseismic anisotropy wave forward modelling with a moment tensor source was proposed. The modelling was carried out based on a rotated-staggered-grid (RSG) scheme. In contrast to staggered-grids, the RSG scheme defines the velocity components and densities at the same grid, as do the stress components and elastic parameters. Therefore, the elastic moduli do not need to be interpolated. In addition, the detailed formulation and implementation of moment-tensor source loaded on the RSG was presented by equating the source to the stress increments. Meanwhile, the RSG-based 3D wave equation forward modelling was performed in parallel using compute unified device architecture (CUDA) programming on a graphics processing unit (GPU) to improve its efficiency. Numerical simulations including homogeneous and anisotropic models were carried out using the method proposed in this paper, and compared with other methods to prove the reliability of this method. Furthermore, the high efficiency of the proposed approach was evaluated. The results show that the computational efficiency of proposed method can be improved by about two orders of magnitude compared with traditional central processing unit (CPU) computing methods. It could not only help the analysis of microseismic full wavefield records, but also provide support for passive source inversion, including location and focal mechanism inversion, and velocities inversion.

Abstracts:When the traditional drill and blast method is applied to rock crushing projects, it has strong vibration, loud noise and dust pollution, so it cannot be used in densely populated areas such as urban public works. We developed a supercritical CO2 true triaxial pneumatic rock-breaking experimental system, and conducted laboratory and field tests of dry ice powder pneumatic rock-breaking. The characteristics of the blast-induced vibration velocity waveform and the evolution of the vibration velocity and frequency with the focal distance were analyzed and discussed. The fracturing mechanism of dry ice powder pneumatic rock breaking is studied. The research results show that: (1) The vibration velocity induced by dry ice powder pneumatic rock breaking decays as a power function with the increase of the focal distance; (2) The vibration frequency caused by dry ice powder pneumatic rock breaking is mainly distributed in 1–120 Hz. Due to the dispersion effect, the dominant frequency of 10–30 Hz appears abnormally attenuated; (3) The traditional CO2 phase change fracturing energy calculation formula is also applicable to dry ice pneumatic rock breaking technology, and the trinitrotoluene (TNT) equivalent of fracturing energy is applicable to the Sadovsky formula; (4) Dry ice powder pneumatic rock breaking is shock wave and high-energy gas acting together to fracture rock, which can be divided into three stages, among which the gas wedge action of high-energy gas plays a dominant role in rock mass damage.

Abstracts:The quantitative determination and evaluation of rock brittleness are crucial for the estimation of excavation efficiency and the improvement of hydraulic fracturing efficiency. Therefore, a “three-stage” triaxial loading and unloading stress path is designed and proposed. Subsequently, six brittleness indexes are selected. In addition, the evolution characteristics of the six brittleness indexes selected are characterized based on the bedding effect and the effect of confining pressure. Then, the entropy weight method (EWM) is introduced to assign weight to the six brittleness indexes, and the comprehensive brittleness index Bc is defined and evaluated. Next, the new brittleness classification standard is determined, and the brittleness differences between the two stress paths are quantified. Finally, compared with the previous evaluation methods, the rationality of the proposed comprehensive brittleness index Bc is also verified. These results indicate that the proposed brittleness index Bc can reflect the brittle characteristics of deep bedded sandstone from the perspective of the whole life-cycle evolution process. Accordingly, the method proposed seems to offer reliable evaluations of the brittleness of deep bedded sandstone in deep engineering practices, although further validation is necessary.

Abstracts:Copper ions (Cu2+) are usually added to activate the sulfidized surface of zinc oxide minerals to enhance xanthate attachment using sulfidization xanthate flotation technology. The adsorption of Cu2+ and xanthate on the sulfidized surface was investigated in various systems, and its effect on the surface hydrophobicity and flotation performance was revealed by multiple analytical methods and experiments. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterization demonstrated that the adsorption of Cu2+ on sulfidized smithsonite surfaces increased the active Cu—S content, regardless of treatment in any activation system. The sulfidized surface pretreated with NH4+–Cu2+ created favorable conditions for the adsorption of more Cu2+, significantly enhancing the smithsonite reactivity. Zeta potential determination, ultraviolet (UV)-visible spectroscopy, Fourier transform-infrared (FT-IR) measurements, and contact angle detection showed that xanthate was chemically adsorbed on the sulfidized surface, and its adsorption capacity in various systems was illustrated from qualitative and quantitative aspects. In comparison to the Na2S–Cu2+ and Cu2+–Na2S–Cu2+ systems, xanthate exhibited a higher adsorption capacity on sulfidized smithsonite surfaces in NH4+–Cu2+–Na2S–Cu2+ system. Hence, activation with Cu2+–NH4+ synergistic species prior to sulfidization significantly enhanced the mineral surface hydrophobicity, thereby increasing its flotation recovery.

Abstracts:In this work, the effect of ammonium sulfate on the adsorption characteristics of low-concentration Pb(II) ions on the sulfidized hemimorphite surface was comprehensively investigated. The results showed that ammonium sulfate could increase the maximum recovery of hemimorphite from 69.42% to 88.24% under a low concentration of Pb(II) ions. On the hemimorphite surface pretreated with ammonium sulfate, the adsorption of Pb(II) ions was enhanced and the main species of Pb adsorbed was changed from Pb―O/OH to PbS. This was due to the larger amount of ZnS providing more effective adsorption sites for Pb components to generate PbS. Meanwhile, the intensity of ZnS decreased with the formation of PbS, demonstrating that ZnS was covered by PbS which formed later on the mineral surface. It was beneficial for the adsorption of butyl xanthate on the hemimorphite surface to form more hydrophobic substances. As a result, ammonium sulfate played a crucial role in realizing the efficient recovery of hemimorphite.