Rejection of trace ionic solutes in nanofiltration: Influence of aqueous phase composition

The use of nanofiltration (NF) in water treatment has been proposed to improve the quality of the produced water and extend the options of concentrate valorization, taking the benefit of its different ions selectivity patterns. However, there is a need to understand and optimize the rejection not on...

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Bibliographic Details
Published in:Chemical engineering science 2013-12, Vol.104, p.1107-1115
Main Authors: Pages, Neus, Yaroshchuk, Andriy, Gibert, Oriol, Cortina, Jose Luis
Format: Article
Language:English
Subjects:
Aigua
aqueous solutions
Brackish
Cationic
Chemical engineering
Concentration (composition)
Cross-flow
Depuració
Dominant salt
electric field
Electrolytes
Enginyeria dels materials
inorganic ions
ions
Membranes
Nanofiltració
Nanofiltration
Negative rejection
Purification
Rejection
salts
Selectivity
Separació de membranes
solutes
Solution-diffusion-film model
surface water
Trace ion
Water
water treatment
Àrees temàtiques de la UPC
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Summary:The use of nanofiltration (NF) in water treatment has been proposed to improve the quality of the produced water and extend the options of concentrate valorization, taking the benefit of its different ions selectivity patterns. However, there is a need to understand and optimize the rejection not only of major components (e.g. NaCl or MgSO4) but also of minor components specially in brackish waters. The selectivity of ion rejection by NF membranes has been studied theoretically and experimentally. Theoretical analysis has been carried out within the scope of the solution-diffusion-film model (SDFM) recently extended to electrolyte mixtures. In this study, experimental ion rejection data of typical cationic and anionic species present in surface waters at various trans-membrane pressures and cross-flow velocities have been obtained with a NF membrane (NF270). Several combinations of dominant salts (NaCl, MgCl2, MgSO4, Na2SO4) with trace ions (Na+, Cl−, Mg2+, SO42−) have been used. The rejection of ions crucially depends on their environment. The dramatic differences in the rejections can be explained by the spontaneously arising electric fields generated in the membrane phase. Their effect gives rise to negative rejections of singly charged inorganic ions present as small additions to well-rejected dominant salts. As a result of theoretical interpretation the intrinsic membrane permeabilities to ions have been estimated for different aqueous solutions compositions. •Ions rejection in NF depends on their environment that is the dominant salt.•Dramatic differences in rejections can be explained by electric fields.•Their effect gives rise to negative rejections of singly charged inorganic ions.•Negative ions rejections are controlled by electric field rather than permeability.•Ion permeabilities have been estimated for different aqueous solutions compositions.
ISSN:0009-2509
1873-4405
DOI:10.1016/j.ces.2013.09.042