Assessment of the scaling potential for sparingly soluble salts in RO and NF units

• Published in: Desalination 2004-08, Vol.167 (1-3), p.247-256
• Main Author: Sheikholeslami, R.
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Membrane fouling; Nanofiltration; Pollution; Reverse osmosis; Scaling potential
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/j.desal.2004.06.134

This paper briefly discusses the current industrial practice for assessing the scaling potential of sparingly soluble salts and suggests a more theoretical approach which is expected to provide more accurate results. This theoretical approach is based on the use of Gibbs free energies of reaction for prediction of dissociation and solubility constants which have usually been estimated crudely through empirical means. In addition, this systematic approach incorporates determination of the activity coefficients by considering short and long ion-interactive forces through incorporation of thermodynamic electrolyte models. Furthermore, since the basic principles and individual ion-interactive forces are incorporated. The results demonstrate that total dissolved salts cannot be used to incorporate the effect of salinity on scaling potential. This has further implications in membrane modules as the individual ion-specific passages through the membranes are different for different salts and the relative composition of the feed stream changes from the inlet to the outlet. As such the specific ion composition within modules should be used for assessing the scaling potential along the modules. Advances in computational techniques enables us to asses the scaling potential of sparingly soluble salts from a more fundamental and theoretical basis as discussed in this paper. Further incorporation of computational techniques and basics of thermodynamics would allow incorporation of other factors and even interactive effects.