# Experimental Study on the Desalination of Waste Leachate Using the Combined Freezing Method
## 3 Results and Discussion
### The Desalination Effect of Different Desalination Methods on Waste Leachate  
#### 3.2.1 Research on the Desalination Effect of the FGM on Waste Leachate  
The experiments use the freezing method as the basis of the study and combine it with other methods. The ice matrix itself consists of pure ice grains (columns or flakes), and under gravity, salt ions erode the ice body and form brine channels that gradually penetrate downward until they detach from the ice body [26; 27]. The freezing temperature and solution concentration affect the formation of brine channels [28], and under different experimental conditions, the brine channels produced inside the ice body show different characteristics. Figure 4 shows the microstructural observation diagram of brine bubbles and brine channels at different stages under the microscope. By observing the micrographs, it can be seen that brine bubbles of different sizes and shapes with irregular distribution were formed inside the ice body under the four experimental conditions (Figure 4a-d). The brine channels looked like a regular arrangement in the ice body, which was generally in a tree-like structure accompanied by tiny branches. With the prolongation of the sampling time, it can be seen that the brine channels become wider, and the color of the ice body gradually tends to be transparent from yellowish brown. Under simulated winter average temperature conditions (5 \({}^{\circ}\)C), gravity desalination experiments were carried out on waste leachate at different ice production rates. The results are presented in Figure 5; the removal efficiency was 84.28% under the condition of the 40% ice production rate. At this time, it was observed that there were a large number of pores on the ice surface produced by brine erosion, and there were a small number of brown solids distributed above the ice body, which were precipitation as the organic matter adsorbed and formed, with a final detection of ice meltwater salinity of 0.64%. When the ice production rate was 50%, the salinity of the ice meltwater was 0.87%, and the salt rejection was 78.62%. When the ice production rate was 60%, the salt rejection decreased the most, the salt rejection was 57%, and the salinity of the ice meltwater was 1.75%. When the ice production rate continued to increase, reaching 70% and 80%, the salt rejection continued to decrease, falling below 50%, accompanied by the salinity of the ice meltwater increasing to 2.65%. This suggests that, at an ambient temperature of 5 \({}^{\circ}\)C, an increase in the ice production rate leads to an increase in the number of salt ions retained in the ice body, reducing the passage of salt channels, and fewer salt ions leaving the ice body, leading to a reduction in the salt rejection. Through the study of the salt rejection at different salt rejections under the simulated average winter temperature, it is found that longer times for brine channels to form at higher salt rejections and the formation of brine channels that do  
Figure 3: Changes in the water quality parameters at different salinities of the solution. not penetrate the entire ice sheet but only form short brine channels within the ice or a small number of narrow brine channels that penetrate the ice sheet result in a slow desalination process. A low salt rejection means that the desalination process takes longer. During this time, the brine channels are fully open, and salt ions are continuously discharged from the brine channels, reducing the salt retention rate in the ice body. At the average summer temperature, the trend in salt rejection with different ice production rates is roughly the same as at the average winter temperature. Under the  
Figure 4: Microstructural observation diagram of brine bubble vesicles and brine channels at different stages of microscopy: **(a)** 80% ice production stage, **(b)** 70% ice production stage, **(c)** 60% ice production stage, and **(d)** 50% ice production stage. Figure 5: The FGM desalination parameters at different ambient temperatures.