Predicting solid precipitation is critical for high-efficiency desalination systems because of associated impact on system performance. Among the mineral salts most often associated with scaling issues in membrane-based desalination systems, CaSO4 and CaCO3 are the major foulants that adversely impact membrane performance (i.e., fouling, wetting). Commonly used Debye-Huckel limiting law for predicting precipitation reactions with multiple salts is only valid for dilute solutions where the electrolyte ions were assumed to be mainly affected by the long-range coulombic interactions. Therefore, Pitzer model is widely adopted in desalination research as an extension of Debye-Huckel limiting law in predicting precipitation reactions at high salinities. Pitzer model has been shown to work well for predicting ion activities and saturation indices in high salinity solutions, but its accuracy in kinetically-limited conditions is still in doubt. Electrochemical Impedance Spectroscopy (EIS) is a surface sensitive measurement allowing the detection of minimal surface changes and has been used in various fields to study surface crystal formation. It uses impedance potential of a system determined from the response to an alternating current (AC) of varying frequency to detect crystallization of salts. In this study, we used synthetic solution at supersaturated condition as predicted by Pitzer model to study scale formation in membrane-based desalination system. The objective of this study is to provide insight into the precipitation of salts in high salinity aqueous solutions in the presence of membrane surface and investigate the impact of the kinetic constraints on the performance of high water recovery desalination processes.

Verification of Pitzer model in predicting calcium precipitation at high salinities with electrochemical impedance spectroscopy (EIS)

ACS Spring 2022

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