DESALINATION www.elsevier.com/locate/desal Desalination 247 (2009) 610–622 Rejection behavior of nickel ions from synthetic wastewater containing Na 2 SO 4 , NiSO 4 , MgCl 2 and CaCl 2 salts by nanofiltration and characterization of the membrane Z.V.P. Murthy*, Latesh B. Chaudhari Department of Chemical Engineering, S. V. National Institute of Technology, Surat 395007, Gujarat, India Tel: +0091-261-2201641; 2223371 to 2223374; Fax: +0091-261-2201641; 2227334 e-mail: zvpm2000@yahoo.com; zvpm@ched.svnit.ac.in Received 25 July 2007; accepted 12 October 2008 Abstract Nanofiltration (NF) has attracted increasing attention over the recent years due to the development of new applications. This paper presents the separation of heavy metal ions such as nickel from synthetic wastewater of nickel electroless plating industry. The wastewater from nickel electroless plating industry contains various metals such as nickel, sodium, magnesium and zinc. In order to ascertain the effect of ion rejection in a mixed salt system, the rejection behaviour of nickel ion in synthetic wastewater of Na 2 SO 4 , NiSO 4 , MgCl 2 and CaCl 2 is tested by using NF300. The maximum observed solute rejection of nickel ion is 97.96% and 96.87% for an initial feed concentration of 5 and 10 ppm, respectively. The NF300 membrane is characterized by using combined film theory–Spiegler–Kedem (CFSK) model based on irreversible thermodynamics and ion transport model based on the extended Nernst–Planck equation. Boundary layer thicknesses, enrichment factors, concentration polarization modulus as well as membrane transport parameters are estimated by using the Levenberg–Marquadt 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. Keywords: Nanofiltration; Electroless plating; Membrane transport model; Membrane characterization 1. Introduction NF membranes gain importance for the selective separation of multivalent ions. NF mem- branes are often called as ‘‘loose RO’’ mem- branes, which is considered to be intermediate between RO and UF has gained importance due to its selective separation. In general, NF mem- branes can achieve higher water fluxes at lower transmembrane pressure, though with generally lower rejection than RO membranes. NF mem- branes are composed of polymeric materials that often contain negatively charged surface groups (i.e. carboxyl and sulfonate). Therefore, the rejection of solutes by NF membranes is *Corresponding author. 0011-9164/09/$– See front matter Ó 2009 Elsevier B.V. doi:10.1016/j.desal.2008.10.009 Published by