Self-Sustaining Water Softening–Desalination Processes: Chloride–Sulfate Systems

The potential to organize steady-state self-sustaining processes of the softening–desalination of brackish water was studied in a numerical experiment on the example of multicomponent model solutions containing sodium and calcium chlorides and sulfates. In the steady-state, self-sustaining processes of softening, water is subjected to desalination by means of a cation-exchange resin, and the formed brine is used to regenerate this cation-exchange resin in repeated sorption–desorption cycles without the addition of any surplus reagents. The interest in self-sustaining processes is associated with new technological opportunities in the creation of a new generation of water-treatment systems, e.g., mobile, stand-alone setups or systems with a high degree of freshwater recovery. The calculations of ion-exchange dynamics have been carried out for dozens of consecutive softening–desalination cycles via changes in the varied parameters, in particular, the ratio of components in the initial solution and the composition of desalted water. The conditions under which no steady-state regimes are formed or attained are shown. Based on the results of numerical experiments, a criterial relationship for the preliminary estimation of the feasibility of self-sustaining processes is proposed.