Separation of binary heavy metals from aqueous solutions by nanofiltration and characterization of the membrane using Spiegler-Kedem model

Heavy metals are important sources of environmental pollution and are non-degradable, and therefore, continue to exist in water. Membrane technology is one option for the separation of heavy metals from wastewater without generating any pollution load. This paper presents the binary heavy metals (cadmium and nickel) separation capability of a commercial nanofiltration membrane from aqueous solutions. The influence of applied pressure. feed solute concentration, feed flowrate, feed pH and nature of anion on the retention of cadmium and nickel ions is studied. it is observed that the rejection increases with increase in feed pressure and decreases with increase in feed concentration at constant feed flowrate. The maximum observed solute rejection of nickel and cadmium ions are 98.94% and 82.69%, respectively, for an initial feed concentration of 5 ppm. The NF membrane is characterized by using the Spiegler-Kedem model based on irreversible thermodynamics coupled with film theory. Boundary layer thicknesses, as well as the membrane transport parameters are estimated by using the Levenberg-Marquardt method. The estimated parameters are used to predict the membrane performance and found that the predicted values are in good agreement with the experimental results. (C) 2008 Elsevier B.V. All rights reserved.