Treatment of brackish water with unipolar layered freezing method

Ice crystals of highquality can be obtained with high recovery rate in the process of brackish water desalination with unipolar layered freezing method. Brackish water with different concentrations of salt (500 mg/L, 1000 mg/L, 2000 mg/L, 3000 mg/L, 5000 mg/L) has been frozen at temperatures from -2°C to -20°C at a regular interval of 2°C and relationships between the factors including desalination rate, freezing temperature, freezing rate, ice growth rate, and concentration of brackish water have been analyzed. Analysis results show that desalination rate declines with the increase of freezing rate and concentration of the samples. Freezing rate mainly depends on freezing temperature. Ice growth rate is mainly determined by freezing rate and freezing time, while the solution concentration has no effect on freezing rate. The optimum freezing temperature ranges for the samples with concentrations of 500 mg/L, 1000 mg/L, 2000 mg/L, 3000 mg/L, 5000 mg/L are -6--10°C, -4--8°C, -6--10°C, -2--6°C and -2--8°C, respectively. At the optimum freezing temperature, with the ice growth rates of 9.5%, 9.3%, 7.0%, 7.8% and 8.5%, the desalination rates for the brackish water samples reach the maximums of 94.3%, 80.6%, 64.8%, 68.1% and 59.2%, respectively.