Abstract:

Membrane scaling is regarded as one of the key-problems for nanofiltration(NF) membrane separating performance during salt solution softening process. Most of the studies on NF membrane inorganic fouling were performed to comprehensively investigate the running conditions(such as NF permeate recovery and recycling ratio) on the scaling potential prediction and apply different techniques to characterize the NF membrane scaling morphology. However, only a few information was reported systematically about the mechanisms and processes of NF membrane surface dynamic scaling. The fundamental mechanisms and processes referred to sparing soluble precipitations and scaling are not cleared clarified. This paper focuses on the research progress for the mainly NF membrane scaling mechanisms(including crystallization and particulate fouling, bulk crystallization and surface crystallization), which play critical roles during scale formation on NF membrane surface. Besides, it is introduced in detail for the resistance(including membrane resistance, concentration polarization resistance, cake resistance and pore-block resistance) models used to quantify NF membrane inorganic fouling. In addition, the scaling processes including concentration polarization stage, nucleation stage, crystallization and deposition stage, respectively, on the NF membrane surface are introduced briefly. Finally, the further development as well as challenges on dynamic scaling mechanism on NF membrane surface for saline water softening are suggested.

Key words: nanofiltration membrane, saline water softening, scaling mechanism, membrane surface scaling resistance