Theoretical Analysis of Saline Diffusion during Sodium Chloride Aqueous Solutions Freezing for Desalination Purposes

Abstract

Abstract:Considering the important demand of fresh water and its scarce availability, water 18 desalination is an interesting technology, producing about 44 Mm 3 /year worldwide, but, in general 19 the most common desalination techniques are highly energy demanding. Freezing-Melting (F/M) 20 desalination uses just up to 70% less thermal energy, but is the least used process mainly, due to the 21 difficulty of the salt separation. This study proposes a model able to analyses the thermodynamic 22 potential that allows the salt diffusion during the F/M process, using an aqueous solution of sodium 23 chloride. This should allow to obtain a sensitive analysis of the process to promote the separation 24 between the high concentration brine and the ice with liquid separation by physical process. The 25 unidimensional model is based on the evolution of both processes: thermal and mass diffusions, 26 depending on temperature and saline gradients, predicting whether the salt will remain inside the 27 ice or not. Thus, the thermal potential is adjusted to frozen only when the salt has been "pushed" 28 towards the brine. Mostly models have base their results on the assumption of a "certain value of 29 saline concentration of the liquid fraction", value in which there is great disagreement. In this paper 30 the calculations are based on the concentration in the solid-liquid interface, which has been 31 extensively studied and there is a coincidence in those results, being the main advantage of the 32 proposed model. 33Keywords: freezing/melting desalination process; aqueous solutions of sodium chloride; theoretical 34 diffusive models 35 36