Evaporation of a reverse osmosis discharge studied by Pitzer model and solubility phase diagrams

Water desalination by reverse osmosis necessarily leads to the production of concentrates which generates a serious challenge to operators. Indeed, disposal of concentrates in natural environment cannot be considered because of the nature of the chemicals contained and their high concentrations. Thus, a specific treatment has to be achieved, which increases the cost of softened water. To prevent this drawback it is proposed the enhancement of the discharge by extracting several valuable salts such as sulfates or chlorides salts of sodium, magnesium and potassium which may counterbalance the treatment additional costs. For this purpose isothermal evaporation at 25 °C is suggested. In the present study, in addition to X-ray diffraction used to identify the various salts recovered, quinary and hexary diagrams were establish to draw the experimental crystallization paths. In addition, because the tested solutions can exhibit very high ionic strength, Pitzer model has been applied to describe the multicomponent systems for calculation of solubility products of the various electrolytes. The results obtained show on one hand good agreement between theoretical and experimental studies and, on the other hand that most salts recovered from the brine are of a high potential use.