## 5 Influence of Pressure Filtration Parameters on Mud Cake Deformation
### The Effect of Filtration Pressure on Mud Cake Deformation and Dewatering Time  
An increase in filter pressure is helpful for the rapid discharge of pore water, which can accelerate completion and reduce the required time to a certain extent. The influence of the filtration pressure on mud cake deformation and the dewatering time is analyzed below. In addition, the variation in the compression deformation of a mud cake over time under different filtration pressures is minimal, and the corresponding dewatering time is also similar as the deformation-time curve tends to flatten. In addition, the filtration pressure has some influence on the final mud cake thickness, but has little influence on the time required for the compression deformation to be stabilized, which is usually around 60 min.  
It can also be seen from Figure 11 that it takes a long time until the thickness of mud cake is basically unchanged under pressure, and the thickness of mud cake changes less at a later stage. The variation in the dewatering time with the filtration pressure obtained by taking a 70% water content in the mud cake after pressure filtration as a control index is shown in Figure 12. For each working condition under different initial cake thicknesses, the increase in pressure can effectively shorten the dewatering time when the filtration pressure is small, and when the filtration pressure is increased to the critical value, thereafter, the influence of the filtration pressure on the dewatering time is small, which is reflected in the gradual slowing down of the change trend of the curve of the filtration pressure-dewatering time. This law is similar to that given by theoretical calculations in reference [46]. This is because when the pressure increases, the excess pore pressure in the mud cake also increases, the discharge rate for the pore water increases, and the decrease rate of the void ratio accelerates, leading to a decrease in the pressure time. But at the same time, an increase in filter pressure also shortens the time when the void ratio of the mud cake decreases to the lowest, which results in a decrease in the filter pressure time.  
Figure 10: Variation in the time required for pressure filtration with initial cake thickness.  
After the filtration pressure reaches the critical value, a continuous increase in pressure has less influence on a reduction in the dewatering time; therefore, considering the comprehensive processing efficiency and the increase in processing energy consumption brought about by the pressure increase, it is more economical to adopt the critical filtration pressure for the pressure filtration process in engineering. It can be seen from Figure 12 that when the initial cake thickness reaches more than 300 mm, the dewatering time decreases greatly when the filtration pressure increases from 0.6 MPa to 1.0 MPa, whereas the dewatering time decreases greatly when the filtration pressure is increased from 0.4 MPa to 0.8 MPa for initial cake thicknesses below 300 mm. When the initial cake thickness increases, the corresponding critical filtration pressure also increases.