Adsorption of Cd(II) and Pb(II) by in situ oxidized Fe3O4 membrane grafted on 316L porous stainless steel filter tube and its potential application for drinking water treatment

Abstract

Removing heavy metal ions from aqueous solutions is one of the most challenging separations. In situ oxidized Fe₃O₄ membranes using 316L porous stainless steel filter tube have shown great potential for removing anion Cr(VI). Here we report the performances of the in situ oxidized Fe₃O₄ membranes for removing two toxic cations Cd(II) and Pb(II) commonly existing in water and their potential applications for drinking water purification. The membranes exhibited high removal efficiency: 97% at pH 9.0 for Cd(II) of 1.0 mg/L initial concentration and 100% at pH 5.0-6.0 for Pb(II) of 5.0 mg/L initial concentration. The maximum adsorption capabilities were estimated at 0.800 mg/g and 2.251 mg/g respectively for Cd(II) and Pb(II) at 318 K by the Langmuir model. Results of batch tests revealed the existence of electrostatic attraction and chemisorption. XRD and FT-IR analyses indicated that the chemisorption might be the insertion of Cd(II) and Pb(II) into the Fe₃O₄ crystal faces of 311 and 511 to form mononuclear or binuclear coordination with O atoms of Fe-O₆ groups. Competitive adsorption of Cd(II) and Pb(II) in binary solutions revealed a preferential adsorption for Pb(II). Na₂EDTA solution was used to regenerate the membranes, and the maximum desorption ratio was 90.29% and 99.75% respectively for Cd(II) and Pb(II). The membranes were able to efficiently lower Cd(II) and Pb(II) concentrations to meet the drinking water standards recommended by the World Health Organization and are promising for engineering applications aimed at drinking water purification.

Keywords: Adsorption; Adsorption mechanism; Competitive adsorption; Heavy metal; Inorganic membrane; Membrane separation.