## 3 Microscopic Characterization of Tailings Particles
### Three-Dimensional Pore Throat Model and Parameter Analysis  
At present, the most widely used method for extracting 3D pore throat models is the \"maximum sphere method\", which is simple, stable, and can accurately preserve the distribution and connectivity features of pore throats [19]. The largest ball method is used to simplify the hole throat to obtain a model composed of a large number of balls and sticks, which is called the \"ball stick model\". The model includes pores and throats, and finding out the relationship between the two can provide further understanding of the microscopic characteristics inside the specimen. The pore-network modeling analysis module was used to calculate the maximum spherical model in AVIZO, and the pore-throat model of the tailings sample was established, as shown in Figure 12, where the sphere represents the connected pores in the soil sample and the cylinder represents the throat between the pores. The number, radius, coordination number, and number, radius, and length of the roar are the key parameters of the model, which all restrict the permeability of tailings. Pore coordination refers to the number of roaring channels connected to the pores, which is a key parameter to reflect the connectivity of the pore throat-network model. In general, it is believed that the larger the average coordination number, the stronger the connectivity between the pores, and the greater the permeability, as shown in Figure 13.  
From Figure 13, it can be seen that the number of coordination pores of CLT, FCT and SCT is small and all of them are distributed in the range of 0-15, while the number of STT and SDT is greater and mainly distributed in the range of 5-25. The permeability characteristics of the tailings samples are closely related to the distribution of the throat radius, and when the radius distribution of the throat is concentrated and the frequency value at the peak is high, it can be inferred that its permeability is poor. When the radius distribution of the larynx is dispersed and the frequency at the peak is low, it can be inferred that its permeability is good [20]. The probability distribution of the throat radius of three tailings samples with the representative throat numbers of CLT, STT and SDT is plotted as shown in Figure 14.  
Figure 11: Fractal dimensions of tailings sample. Figure 12: Model of tailing specimens and balls. As can be seen from Figure 14, the probability distribution of the laryngeal radius tends to be normally distributed, and the peak frequency and concentration of the radius distribution decrease from CLT to STT and then to SDT, and the permeability should tend to increase, which is in line with conventional thinking. The length and distribution of the throat is an important feature of the flow capacity, and when the throat radius is similar, the longer the throat, the greater the number of pores connected, the better the connectivity, and the corresponding permeability. The scatter plot of the throat length distribution of the tailing samples is shown in Figure 15.  
As can be seen from the scatter plot of Figure 15, the length of the roar of the SDT and STT specimens is widely distributed; a large number of roars are distributed from 500 to 3000 \(\upmu\)m, and the frequency distribution is very uniform. However, the number of roars of CLT, FCT and SCT samples was relatively small, and the length of CLT and SCT roars was longer, distributed between 2000 and 6000 \(\upmu\)m; the longest roar of CLT reached 7500 \(\upmu\)m, while FCT was generally shorter, distributed between 500 and 1500 \(\upmu\)m.  
The pore-throat ratio is one of the key structural parameters of the tailings pore-throat model and is defined as the ratio of the pore radius to the average of the throat radius to which it is attached. With the decrease in the pore-throat ratio, the development of pore space becomes more balanced, and the permeability will also be improved.