Theory of pressure-driven transport of neutral solutes and ions in porous ceramic nanofiltration membranes

Hindered transport theory and homogeneous electro-transport theory are used to calculate the limiting, high volume flux, rejection of, respectively, n eutral solutes and binary electrolytes by granular porous nanofiltration me mbranes. For ceramic membranes prepared from metal oxides it is proposed th at the membrane structural and charge parameters entering into the theory, namely the effective pore size and membrane charge density, can be estimate d from independent measurements: the pore radius from the measured hydrauli c radius using a model of sintered granular membranes and the effective mem brane charge density from the hydraulic radius and the electrophoretic mobi lity measurements on the ceramic powder used to prepare the membrane. The e lectro-transport theory adopted here is valid when the membrane surface cha rge density is low enough and the pore radius is small enough for there to be strong electrical double layer overlap in the pores. Within this approxi mation the filtration streaming potential is also derived for binary electr olytes. (C) 1999 Elsevier Science B.V. All rights reserved.