Poly(vinylalcohol) coated/Cibacron Blue F3GA-attached polypropylene hollow fiber membranes for removal of cadmium ions from aquatic systems

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Dye-affinity adsorption is increasingly used for heavy metal removal from aquatic systems. Synthetic hollow fiber membranes have advantages as support matrices in comparison to conventional microbead adsorbents because they are not compressible and they eliminate internal diffusion limitations. The aim of this study was to explore in detail the performance of polyvinyl alcohol coated/Cibacron Blue F3GA-attached polypropylene hollow fibers for removal of Cd(II) ions. The internal matrix was characterized by scanning electron microscopy. Commercially available polypropylene hollow fiber membranes were coated with polyvinyl alcohol (PVA). The PVA adsorption conditions were optimized to increase the amount of PVA by changing the initial concentration of PVA, and adding NaCl. The maximum PVA adsorption capacity was 22.6 mg/g. These hollow fiber membranes carrying Cibacron Blue F3GA (87.9 μmol/g) were used in the Cd(II) removal from aqueous solutions containing different amounts of ions (10–500 mg/l) and at different pH values (2.0–8.0). Cd(II) adsorption capacity increased with time during the first 40 min and then leveled off toward the equilibrium adsorption capacity. Adsorption of Cd(II) ions on the PVA coated polypropylene hollow fiber membranes was 1.2 mg/g. Cibacron Blue F3GA-attachment significantly increased the Cd(II) adsorption (46 mg/g polymer). The adsorption of Cd(II) ions increased with increasing pH and reached a plateau value at around pH 5.0. Competitive heavy metal adsorption from aqueous solutions containing Cd(II), Cu(II), Pb(II) and Hg(II) was also investigated. The adsorption capacities are 1.75 mg/g for Cu(II); 3.46 mg/g for Hg(II); 5.86 mg/g for Pb(II) and 18.45 mg/g for Cd(II) ions. These results may be considered as an indication of higher specificity of the Cibacron Blue F3GA-attached polypropylene hollow fibers for the Cd(II) comparing to other ions. Modified hollow fibers can be regenerated by washing with a solution of nitric acid (0.1 M). The maximum regeneration value was as high as 95%. These modified membranes are suitable for repeated use for more than three adsorption–desorption cycles without considerable loss of Cd(II) adsorption capacity.