Separation of cadmium ions and estimation of membrane transport parameters of a nanofiltration membrane

Abstract

Nanofiltration (NF) has been widely used to separate solutes from dilute solutions where, in general, high rejection of the solute is not required. In the present work, performance of a commercial TFC-NF-300 membrane has been studied to separate cadmium salt from dilute synthetic wastewaters at different operating conditions. The operating variables studied are applied pressure (3-20 atm), feed salt concentration (10-250 ppm) and feed flowrates. The feed and permeates are analyzed for solute concentration by conductivity method, which represents well for the concentration of a single metal solute in a solution. It is observed that the rejection of cadmium ions increases with increase in feed pressure and decreases with increase in feed concentration at constant feed flowrate. The maximum observed rejection efficiency of the metal is found to be 75.76 and 61.47% for an initial feed concentration of 10 and 250 ppm, respectively. Membrane transport parameters are estimated using Spiegler-Kedem model based on irreversible thermodynamics.