Tsou T.-YHsu J.-P.JYH-PING HSU2022-03-222022-03-22202203767388https://www.scopus.com/inward/record.uri?eid=2-s2.0-85115750395&doi=10.1016%2fj.memsci.2021.119869&partnerID=40&md5=0795d9484e77bca586c4dd31b0110812https://scholars.lib.ntu.edu.tw/handle/123456789/598236The rejection of symmetric (1:1 and 2:2), asymmetric (1:2 and 2:1), and mixed (1:1 + 1:2 and 1:1 + 2:1) salts by a polyamide membrane is investigated theoretically taking account of its pH-regulated and bipolar nature. We consider the most compact way of distributing pores (honeycomb-like) on the membrane surface so that the influence of pore-pore distance on rejection performance can be taken into account. Assuming large pore-pore distance (or low porosity) so that the concentration polarization effect is negligible, we can investigate the influence of the intrinsic properties of the membrane on its performance. The results of numerical simulation reveal that, due to high resulting surface potential and high ionic selectivity, asymmetric salts exhibit better rejection performance than symmetric salts. The variation of rejection with the applied pressure shows a local maximum, and the associated mechanism discussed. The variations of local pH and filtration potential are examined to help understanding the ionic transport mechanisms in nanofiltration. The separation of mixed monovalent and divalent ions of the same polarity under the conditions of low ionic strength and low applied pressure is discussed for assessing the feasibility of ion recovery and purification. ? 2021 Elsevier B.V.Bipolar chargeFiltration potentialIonic separationMultiple ionic speciesNanofiltrationIonic strengthNanofiltration membranesPurificationSaltsApplied pressureCylindrical nanoporesIonic separationsIonic speciesMixed saltsRejection performanceSymmetricshydronium ionhydroxideinorganic saltpolyamidepolymerArticledependent variabledeprotonationdiffusionelectric potentialgeometryhydrodynamicsion transportionic strengthisoelectric pointmembranenanofiltrationpHpolarizationporosityrate constantsimulationsurface chargethermodynamicsDistanceIonic StrengthPerformancePhPressureRejection[SDGs]SDG6journal article10.1016/j.memsci.2021.1198692-s2.0-85115750395