Investigation of cyclic self-sustaining ion exchange process for softening water solutions on the basis of mathematical modeling

Abstract

New possibilities of using ion exchange pretreatment of saline waters to desalination, with a view to removal of scale forming components, such as calcium and magnesium, are considered in the paper. A cyclic self-sustaining process driven by electro-selectivity effect is discussed. In this process, no additional chemicals, except for brines formed during desalination, are required for regeneration of ion-exchanger in operation cycles. The paper deals with the development of a computer model for description and prediction of the performance of ion exchange columns. Theoretical description and modeling assumptions included the set of differential equations of mass balance, initial, boundary and operational conditions. The impact of the phenomenon of isothermal supersaturation of solutions in ion exchange bed was taken into consideration. Correlations between observations and calculations were tested. The mathematical model was verified by experiments carried out with seawater and a model solution of brackish water and with modified zeolite of A-type which was used as a softening cation-exchanger. Experimental break-through curves (concentration histories) were fitted by calculation data with a good accuracy. Issues related to the choice of optimal parameters were addressed. The stability of the process was analysed in case of a leakage of solutions. The results of investigation demonstrate the possibility of maintaining the cyclic self-sustaining process in a wide range of compositions of raw solutions.