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 104–107 μm2, 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.