# Experimental Study on the Desalination of Waste Leachate Using the Combined Freezing Method
## 3 Results and Discussion
### Freezing Parameter Settings
(2016) investigated the effect of freezing temperatures on Ca\({}^{2+}\) mobility and the removal rate in the process of PF, and the results showed that, when the freezing temperature was reduced from \(-5\)\({}^{\circ}\)C to \(-25\)\({}^{\circ}\)C, most of the Ca\({}^{2+}\) migrated to the concentrate, and the Ca\({}^{2+}\) removal rate of the ice meltwater was reduced from 98.18% to 90.35%, proving that the freezing temperature, as the main parameter, was not the lower the temperature, the better the desalination effect. The salinity of the concentrate with the reduction in temperature showed an upward trend, from \(-10\)\({}^{\circ}\)C with 6.91% gradually rising to 15.1%, with a concentration multiplication rate of 3.43. This experimental phenomenon is mainly the lower temperature of the ice produced by the heat capacity, and the heat conduction speed is slow, melting is slower, the salt ions migrate to the concentrate faster than the speed of the icicle melting, and the salt ions migrate to the concentrate in larger proportions ([PERSON] et al., 2016). From Figure 2, it can be seen that the highest salt rejection of 35.75% was achieved at a freezing temperature of \(-15\)\({}^{\circ}\)C. Therefore, \(-15\)\({}^{\circ}\)C is the optimum freezing temperature. Changes in the water quality parameters at different salinities of the solution are shown in Figure 3. In the process of ice formation, the ice constantly excludes salt ions, and the salinity of the formulated high-salt solution is in the range of 2-5%; with the increase in the initial salinity, the concentration of salt ions per unit area increases and the more salt ions are encapsulated, which makes it more difficult to separate the brine, resulting in a decreasing trend in the salt rejection, which is reduced from the beginning at 51.32% to 34.72%. [PERSON] et al. (2017), who carried out desalination studies on artificial seawater (35.6 g/L) and concentrated brine (2600 mg/L), showed that the salt removal rate was 74% and 97.7%, respectively, which also indicates that high-concentration brines are more difficult to treat. When the initial salinity was 5%, the salinity of the frozen treated meltwater was 2.99%, and all other conditions remained the same; the increase in the  
Figure 1: Changes in the water quality parameters at different freezing times. saliinity of the initial solution caused the brine channels to become overloaded, and the salt ions in the ice body could not be removed in time to be reintroduced into the solution as the ice body melted, increasing in the salinity of the meltwater. The salt in the solution interferes with the crystallization process of water molecules, resulting in lower freezing temperatures, low hardness, and easy loosening of block ice formed from solutions with higher salinity [18]. As in the experiment, the ice body at 6% initial salinity was loose and in the form of loose flakes when placed in a funnel, and similar results were reported in the study by [PERSON] et al. [19]. In this case, the short brine channel makes it very easy to separate the brine from the ice, and the desalination rate is 58.72%. Due to the faster melting rate of the ice flakes, the desalination is better compared to other initial concentrations, but the lowest ice formation rate is only 33.62%. In summary, by analyzing the change in the desalination rate and the special experimental situation, we believe that the lower the salinity of the solution, the better the desalination effect and the more difficult the treatment of high-concentration wastewater. The complexity of the water quality will directly affect the salt rejection, so the water quality indexes of waste leachate were tested [20]. Compared with the desalination study of [PERSON] et al. [21], the composition of seawater and waste leachate is very different, mainly because most seawater is soluble inorganic salts such as NaCl and the content of soluble organic matter (DOM) is only 0.2-2.0 mg C/L, which is very small and has a small effect on the salt rejection [22; 23].