Md. Afonso et Mn. De Pinho, Transport of MgSO4, MgCl2, and Na2SO4 across an amphoteric nanofiltration membrane, J MEMBR SCI, 179(1-2), 2000, pp. 137-154
The transport of multivalent ions across an amphoteric nanofiltration membr
ane is described through an integrated model involving the extended Nernst-
Planck equations and the Donnan equilibrium at the membrane-solution interf
aces.
The membrane-forming aqueous phase consists of an amine and an ampholytic p
olymer containing quaternary amine groups and sulphonic acid groups. In the
permeation experiments of single solutions of MgSO4, MgCl2, and Na2SO4, th
e pressure ranges from 10 to 25 bar, the feed circulation velocity from 0.4
4 to 5.1 mis and the feed concentration from 1.8 to 193 mol/m(3).
The membrane active layer acquires a negative surface charge distribution,
by adsorption of anions from the solution, and this charge distribution mai
nly determines the membrane performance. The experimental evidence of the e
ffects of both ions valences and the feed concentration on the salt rejecti
ons is in agreement with the Donnan exclusion principle.
The relative errors between the experimental and the calculated permeation
fluxes and the salt rejections are lower than 22 and 12%, respectively. The
sole model parameter, the membrane effective charge, is found to depend on
the salt nature and concentration upon the correlation, C-M (mol/m(3)) = a
C-Sf(b) (mol/m(3)), where the parameters a and b are
Parameter MgSO4 MgCl2 Na2SO4
a (mol/m(3)) 91.9 22.3 50.7
b 0.904 1.06 0.704
The parameter b is related to the salt stoichiometry and the cation valence
by the equation: b = (v(C)z(C))(Z)c/(2)/2. (C) 2000 Elsevier Science B.V.
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