# Experimental Study on the Desalination of Waste Leachate Using the Combined Freezing Method
## 2 Materials and Methods
### Experimental Methods and Processes  
To simulate the top-down freezing process in nature, the periphery of the container was wrapped with insulating cotton to prevent heat exchange between the container wall and the outside, and an opening was provided at the top to ensure that the cold air could only be applied to the solution from above. Take 1 L of the prepared high-saline solution (prepared with NaCl) and place it in a freezing container. Freeze at \(-\)10 \({}^{\circ}\)C for 12 h, 15 h, 18 h, 21 h, and 24 h, respectively. After freezing, remove the ice and place it on a stainless steel funnel. After gravity desalting for 100 min, the remaining ice crystals are collected. After the temperature of the melted ice water has risen to room temperature, its indicators are measured to obtain the optimum freezing time; the samples are frozen at \(-\)10 \({}^{\circ}\)C, \(-\)15 \({}^{\circ}\)C, \(-\)20 \({}^{\circ}\)C, \(-\)25 \({}^{\circ}\)C, and \(-\)30 \({}^{\circ}\)C for 12 h to obtain the optimum freezing temperature.  
The waste leachate was treated before the experiment and stored in a cool place after filtration to prevent water evaporation from affecting the detection of water quality indicators. Firstly, FGM was used to conduct desalination experiments on waste leachate using the ice production rate as an independent variable to explore the trend of the desalination effect under different ice production rates (40%, 50%, 60%, 70%, and 80%). In addition, the changes in salt rejection under the average temperatures in winter and summer were compared (based on the temperatures in Northern China, with an average temperature of 5 \({}^{\circ}\)C in winter and 28 \({}^{\circ}\)C in summer). The FCM uses an ice crusher to crush ice into small ice cubes about 6 mm in diameter. The crushed ice crystals are placed in a filtered centrifuge at a speed of 2000 rpm, and experiments are conducted at different centrifugal times (1 min, 2 min, 3 min, 4 min, and 5 min) and 2 min with different rotational speeds (1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, and 3000 rpm) as independent variables. The FBM includes the FGBM and FCBM. The FGBM involves placing ice on a blowing device for blowing after 100 min of gravitational action, with blowing times set at 5 min, 10 min, 15 min, and 20 min. The FCBM first crushes the ice in the ice crusher into small ice cubes of about 6 mm in diameter, places them in a funnel, and then applies a blowing effect. The blowing time is set to 1 min, 2 min, 3 min, 4 min, and 5 min. Finally, the treated ice crystals are collected, and the salinity of the meltwater is measured after it has melted to room temperature.  
All experiments were performed three times, with the data organized using Excel 2018 software and plotted using Origin2017 (OriginLab Corp, Northampton, MA, USA) and Visio2019 (Microsoft Corporation Corp, Redmond, WA, USA) software; SPSS Version 25.0 (IBM Corp, Armonk, NY, USA) software was used for data analysis and correlation and significance studies between variables. Polyfit and one-way ANOVA methods were used.