Fragmentation Simulation Of Rocks And Minerals By High Voltage Pulsed Discharge In Water

The traditional mineral fragmentation and hard rock drilling method have high energy consumption and dust production,and the fragmented minerals have defects such as over-grinding of fine particles and under-grinding of coarse particles.However,the mineral fragmentation and hard rock drilling methods with the high voltage pulsed discharge technology in water as the core do not have these problems.So the high voltage pulsed discharge technology in water has considerable application prospects in the field of mineral fragmentation and hard rock drilling.But both mineral fragmentation and hard rock drilling involve multi-field coupling problems.At present,research methods are limited,and it is difficult to extract physical information during mineral fragmentation and hard rock drilling.Therefore,how to capture physical information in this process is an important and meaningful research topic.The finite element software is widely used in the analysis of multi-field coupling problems and involves impact deformation problems,which provides the possibility of analyzing high voltage pulsed discharge mineral fragmentation in water and hard rock drilling.Based on the above background,this paper studies the relevant theories of high voltage pulsed discharge fragmentation in water,The finite element software ANSYS/LS-DYNA is used to build a needle-plate impact magnesite simulation model to describe the impact characteristics during fragmentation.And supplemented by magnesite fragmentation experiments to verify the rationality of the simulation model.Based on this,a needle-needle electrode granite drilling failure model is established to study the effect of electrode spacing on hard rock drilling.Finally,the DMOL3 module in Materials Studio’s material calculation software is used to study the interaction between the fragmented dissociation surface of rocks and various particles generated by discharge in water.The main research contents and results are as follows:（1）Under the condition of clarifying the fragmentation mechanism of high voltage pulsed discharge in water,a simulation model of 5mm needle-plate electrode impact magnesite is established by ANSYS/LS-DYNA.The energy injected into the discharge channel is equivalent to the explosion source.The final simulation results show that the maximum impact load on magnesite is 241 MPa,and the average compressive strength of high-grade,medium-grade and low-grade magnesite is 60.298 MPa,98.447 MPa,141.2 MPa respectively.theoretically,three grades of magnesite can be fragmentated.The simulation results also show that the shock wave generated by the discharge propagates in the form of spherical waves.（2）Under the condition of 40kV discharge voltage and high-voltage electrode 5mm away from magnesite sample,three kinds of magnesite fragmentation experiments are carried out.A high-speed camera is used to record the development process of the shock wave.The experimental results show that under this experimental condition,three grades of magnesite can be effectively fragmented.The shock wave is propagated in the form of spherical waves,which proves that the simulation model of needle-plate electrode impact magnesite is correct.（3）Based on the above,Based on the research of needle-plate electrode impact magnesite,the ANSYS/LS-DYNA finite element software is used to establish four numerical simulation models of granite drilling under the discharge spacing of 2mm,4mm,6mm and8mm needle-needle electrodes.The simulation results show that under the condition of 38kV discharge voltage,the 2mm,4mm and 6mm discharge spacings can fragment granite,but the8mm discharge spacing has no fragmenting ability.Moreover,the drilling and fragmenting capacity of the 2mm discharge spacing and the 4mm discharge spacing are not much different,but they are all greater than the drilling and fragmenting capacity of the 6mm discharge interval.The results are consistent with the relevant experimental results.（4）Taking magnesite fragmentation as an example,the relationship between the active particles generated during the fragmentation process and the dissociation surface of rock ore is studied.The fragmentation results of magnesite are analyzed by SEM,BSD and EDS energy spectrum analysis,and the monomer particles of MgCO₃ are obtained when magnesite is fragmented.The hydroxyl radicals（·OH）generated by the discharge and the dissociation surface of magnesite（211）are studied.Materials Studio software is used to analyze the state density of magnesite（211）dissociation surface,and then the top position of Mg atoms in magnesite（211）dissociation surface is selected to establish·OH adsorption model.The simulation results show that the adsorption energy between magnesite and·OH is-4.381eV,and·OH can be adsorbed on the dissociation surface of magnesite（211）.Through the combination of numerical simulation and experiment,this paper describes the impact characteristics of high voltage pulsed discharge mineral fragmentation in water and the process of hard rock drilling,which provides a new research method for the study of pulsed discharge mineral fragmentation in water and hard rock drilling.The hydroxyl adsorption model analyzes the relevant properties of the disintegration surface of mineral fragmentation,and provides a certain reference for the flotation after mineral fragmentation.