Influence of ion size and charge in nanofiltration

Three commercial nanofiltration membranes were studied: two negatively charged (NF 40 and NTR 7450) and one positively charged membrane (UTC 20). The membrane pore radii were estimated using filtration experiments with uncharged solutes. For the analysis of the results the Spiegler–Kedem equation an...

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Bibliographic Details
Published in:Separation and purification technology 1998-08, Vol.14 (1), p.155-162
Main Authors: Schaep, Johan, Van der Bruggen, Bart, Vandecasteele, Carlo, Wilms, Dirk
Format: Article
Language:English
Subjects:
Donnan exclusion
Ion size
Nanofiltration
Salt retention
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Summary:Three commercial nanofiltration membranes were studied: two negatively charged (NF 40 and NTR 7450) and one positively charged membrane (UTC 20). The membrane pore radii were estimated using filtration experiments with uncharged solutes. For the analysis of the results the Spiegler–Kedem equation and the steric hindrance pore model were used. Salt retention measurements were carried out for NaCl, MgCl 2, Na 2SO 4 and MgSO 4 at different concentrations. The experimental results were evaluated with the Donnan exclusion theory. For both NF 40 and UTC 20 the results could not be ascribed to charge effects alone and the retention sequence of the salt solutions was found inversely proportional to the salt diffusion coefficients in water. For the NTR 7450 membrane, which had larger pores, the Donnan exclusion theory could be used and salt retention was mainly determined by charge effects. It was also shown that transport by diffusion could not be neglected.
ISSN:1383-5866
1873-3794
DOI:10.1016/S1383-5866(98)00070-7