TRANSPORT OF ELECTROLYTES THROUGH A WEAK ACID NANOFILTRATION MEMBRANE- EFFECTS OF FLUX AND CROSS-FLOW VELOCITY INTERPRETED USING A FINE-POROUS MEMBRANE MODEL

A one-dimensional fine-porous membrane model has been exploited to det ermine the reflection coefficient, sigma, and the internal solute mass transport coefficient, k(m), for the nanofiltration of simple salts a nd dyes by two weak-acid membranes, HR and LR, differing in sigma for a NaNO3 solution. The rejection, r, was strongly dependent on the cros sflow velocity, u, and the flux, J, in these experiments. The dependen ce of the external solute mass transport coefficient; k(s) on u was al so determined. The dominant parameter in determining the limiting, low J and high u, rejection for the systems is sigma. It was influenced p rimarily by the charge of the colon for the simple sodium salts, NaNO3 and Na2SO4. The k(m) remained constant within experimental error, for NaNO3 and Na2SO4 using membrane HR and for the two dyes NaR4 and Na(2 )R1 using membrane LR even though the charge on the colons and their f ormula weights differed in each comparison. Transitions from regime I, i.e., decreasing r with increasing J at constant u, to regime II, i.e ., increasing r with increasing J at constant u, behavior were observe d at low u for a trivalent dye using membrane LR.