# 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
#### 3.2.2 Research on the Desalination Effect of the FCM on Waste Leachate  
Figure 6 shows the FCM desalination parameters at different centrifugal times (speed 2000 rpm). The surface area of the crushed ice crystals was larger and more concentrated brine was attached to the surface, and most of the concentrated brine was separated by centrifugal force after it was applied. When the centrifugal time was 1 min, the salt ions attached to the surface of the ice crystals were separated, and the salt rejection was 70.51%. The results show that 1 min of centrifugal force released most of the salt ions from the ice crystals. As the centrifugal time increases, the salt rejection increases from 70.51% to 75.18%. Although the salt rejection increased, the rate of was is slow, mainly due to the low melting tendency inside the broken ice crystals. The melted water is temporarily stored inside the ice crystals. Due to the small volume of the ice crystals, the salt ions carried inside are relatively small and are carried out under the action of centrifugal force [30]. The ice production rate continues to decrease from 64.87% to 58.68%, which is consistent with the FGM's conclusion that increasing the salt rejection reduces the ice production rate but reduces the pure water loss rate due to the relatively fast FCM process, which avoids losses due to the melting of ice crystals during operation. From the perspective of the salinity of the melted ice water, after 5 min of centrifugal force, the salinity of the melted ice water decreased from 4.07% to 1.01%, indicating that the salinity of the melted ice water decreased with the increase in the centrifugal time. These results indicate that centrifugal time, as an important parameter, has a significant effect on salt rejection, and salt rejection increases with the increase in centrifugal time. This result is consistent with the research of other scientists [31]. To further investigate the effect of the centrifugal speed on the salt rejection, experiments were carried out with the centrifugal speed as a variable. The effect of the centrifugal rotational speed on the salt rejection and ice production rate is shown in Figure 7. When the rotational speed was 1000 rpm, the salt rejection and ice production rates were 42.67% and 78.46%, respectively. At this time, the rotational speed was low, and the centrifugal force was not enough to overcome the friction and other hindrances, resulting in a lower salt rejection. When the rotational speed was 1500 rpm, the salt rejection was 55.48%, but the ice production rate decreased by 14.74% until the rotational speed was increased to 2000 rpm when the salt rejection was 70.36%. This indicates that, as the centrifugal rotational speed increases, the centrifugal force increases, which accelerates the settling rate of salt molecules, thus greatly improving the salt rejection. At 2000 rpm increased to 3000 rpm, the salt rejection increased from 72.52% to 73.16%, which was only a 0.64% increase in salt rejection. The centrifugal process observed that, when the rotational speed was continuously increased, a collapsed layer of gradually increasing thickness was formed at the bottom inside the centrifuge, causing ice crystals to collect on the bottom inner wall of the centrifuge. The experimental results and phenomena showed that most of the salts were discharged when the rotational speed was above 2000 rpm, the salt rejection changed slowly, and the surface of the ice crystals tended to be dry. Changes in the salinity of ice meltwater can more clearly reflect the relationship between salt rejection and rotational speed; before the centrifuge rotational speed of 2000 rpm, the trend of ice meltwater salinity is obvious, from 2.33% to 1.21%, and after that, the increase in the rotational speed of ice meltwater salinity will be 1.09% from 1.21%, and the ice production rate decreases to 57.41%.