Effect of particle gradation on pore structure and seepage law of solution in weathered crust elution-deposited rare earth ores

Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leaching.The results showed that the pore areas in four kinds of ore samples before leaching were mainly concentrated in 10^(4)–10^(7)μm^(2),whose pore quantities accounted for 96.89%,94.94%,90.48%,and 89.45%,respectively,while the corresponding pore volume only accounted for 30.74%,14.55%,7.58%,and 2.84%of the total pore volume.With the decrease of fractal dimension,the average pore throat length increased,but pore throat quantities,the average pore throat radius and coordination number decreased.Compared with that before leaching,the change degree of pore structure during leaching increased with the fractal dimension decreasing.For example,the reduction rate of the average coordination number of ore samples was 14.36%,21.30%,28.00%,and 32.90%,respectively.Seepage simulation results indicated that seepage paths were uniformly distributed before leaching while the streamline density and seepage velocity increased with the fractal dimension decreasing.Besides,the phenomenon of the streamline interruption gradually reduced during leaching while preferential seepage got more obvious with the decrease of the fractal dimension.

Effect of particle gradation of aluminum on the explosion field pressure and temperature of RDX-based explosives in vacuum and air atmosphere

To optimize the energy output and improve the energy utilization efficiency of an aluminized explosive,an explosion device was developed and used to investigate the detonation pressure and temperature of R1(A16)aluminum powder and the aluminum powder particle gradation of R2(Al6+Al13),R3(Al6+Al24)and R4(Al6+AI flake)in a confined space.By using gas chromatography,quantitative analysis and calculations were carried out to analyze the gaseous detonation products.Finally,the reaction ratios of the aluminum powder and the explosion reaction equations were calculated.The results show that in a confined space,the quasi-static pressures and equilibrium temperature of the aluminum powder in air are higher than in vacuum.In vacuum,the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R3>R4>R2 and R3>R4>R1>R2,respectively.In air,the quasi-static pressures and equilibrium telperatures of the samples in descending order are R1>R2>R4>R3 and R1>R4>R2>R3,respectively.R4(Al6+AI flake)and R3(Al6+A124)have relatively higher temperatures after detonation,which shows that the particle gradation method can enhance the reaction energy output of aluminum during the initial reaction stage of the explosion and increase the reaction ratio by10.6%and 8.0%,respectively.In air,the reaction ratio of AI6 aluminum powder can reach as high as 78.16%,and the reaction ratio is slightly reduced after particle gradation.Finally,the reaction equations of the explosives in vacuum and in air were calculated by quantitative analysis of the explosion products,which provides a powerful basis for the study of RDX-based explosive reactions.

2D IMAGE BASED SIEVING FOR PARTICLE AGGREGATE GRADATION

Acquiring the size gradation for particle aggregates is a common practice in the granule related industry,and mechanical sieving or screening has been the normal method. Among many drawbacks of this conventional means,the major ones are time-consuming,labor-intensive,and being unable to provide real-time feedback for process control. In this letter,an optical sieving approach is introduced. The two-dimensional images are used to develop methods for inferring particle volume and sieving behavior for gradation purposes. And a combination of deterministic and probabilistic methods is described to predict the sieving behaviors of the particles and to construct the gradation curves for the aggregate sample. Comparison of the optical sieving with standard mechanical sieving shows good correlation.

Mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradation

The mass-front velocities of granular flows results from the joint action of particle size gradations and the underlying surfaces.However,because of the complexity of friction during flow movement,details such as the slope-toe impedance effects and momentum-transfer mechanisms have not been completely explained by theoretical analyses,numerical simulations,or field investigations.To study the mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradations we conducted model experiments that recorded the motion of rapid and long-runout rockslides or avalanches.Flume tests were conducted using slope angles of 25°,35°,45°,and 55° and three particle size gradations.The resulting mass-front motions consisted of three stages:acceleration,velocity maintenance,and deceleration.The existing methods of velocity prediction could not explain the slowing effect of the slope toe or the momentum-transfer steady velocity stage.When the slope angle increased from 25° to 55°,the mass-front velocities dropped significantly to between 44.4% and59.6% of the peak velocities and energy lossesincreased from 69.1% to 83.7% of the initial,respectively.The velocity maintenance stages occurred after the slope-toe and mass-front velocity fluctuations.During this stage,travel distances increased as the angles increased,but the average velocity was greatest at 45°.At a slope angle of 45°,as the median particle size increased,energy loss around the slope toe decreased,the efficiency of momentum transfer increased,and the distance of the velocity maintenance stage increased.We presented an improved average velocity formula for granular flow and a geometrical model of the energy along the flow line.

Study on macro and micro shear strength of continuously graded and gap-graded sand

The particle gradation of sand has a significant influence on its shear strength,yet the similarities and differences between the effects of continuous and gap grading have yet to be fully explored.In this study,the discrete element method(DEM)was used to simulate biaxial tests on granular samples that were both continuously graded and gap-graded.The macroscopic analysis revealed that the shear strength of continuously graded sands increases initially and then decreases as the uniformity of particle size distribution decreases.On the other hand,the lack of medium particles in gap-graded sands amplifies the difference in particle size between coarse and fine particles,leading to a decrease in shear strength.Microscopically,both continuous and gap gradings affect the internal packing structure of the particle assembly,which consequently affects particle stress distributions,contact forces,coordination numbers,stress-induced anisotropies,and contact force networks,thus having an impact on the macroscopic shear strength.The global uniformity of particle size distribution was unidirectionally affected by continuous grading,while gap grading had a locally bidirectional influence.These findings provide a better understanding of the effects of particle grading on the macroscopic shear strength of sands.