Simultaneous rejection of chromium(VI) and fluoride [Cr(VI) and F] by nanofiltration: Membranes characterizations and estimations of membrane transport parameters by CFSK model

•To study on the feasibility of NF300 and PN40 nanofiltration membranes for rejection of Cr(VI) and F from binary solution.•Characterization of NF300 and PN40 membrane with FTIR, SEM, and AFM.•Rejection of Cr(VI) and F was enhanced with increasing pressure and significant influence by pH of feed solution.•Membrane transport parameter and mass transfer coefficient was estimated by using CFSK model.•Experimental observed rejection and true rejection by Cr(VI) and F show good arrangement.

The current work examines the performance of NF300 and PN40 nanofiltration (NF) membranes for simultaneous rejection of Cr(VI) and F.Experimental: results indicate that, Cr(VI) and F percentage of removal was improved with increasing operating pressure and declined with increasing feed concentration. Highest percent rejection of Cr(VI) and F were found 97% and 92% with NF300 and 88% and 82% with PN40 membranes for 5 ppm feed respectively. Maximum removal was found at pH 8 and above with NF300 membrane compared to PN40 membrane. Mass transfer coefficient (MTC) was found 6.88 × 104 cm/s and 5.74 × 104 cm/s and membrane transport parameters (MTPs) such as solute permeability was 4.03 × 105 cm/s and 6.23 × 105 cm/s and reflection coefficient was 0.9688 and 0.9223 using CFSK model for 5 ppm feed of Cr(VI) and F respectively for NF300 membrane. A Good correlation was found in experimental results (observed rejection for Cr(VI) and F was 0.97 and 0.92) and the model predicts results (true rejection for Cr(VI) and F was 0.9731 and 0.9222) for 5 ppm feed of Cr(VI) and F respectively for NF300 membrane.