Adsorption of Cd(Ⅱ) and Cd(Ⅱ) by in situ oxidized Fe_3O_4 membrane grafted on 316L porous stainless steel filter tube and its potential application for drinking water treatment

摘要

Removing heavy metal ions from aqueous solutions is one of the most challenging separations. In situ oxidized Fe_3O_4 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 Fe_3O_4 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(ll) 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 Fe_3O_4 crystal faces of 311 and 511 to form mononuclear or binuclear coordination with O atoms of Fe-O_6 groups. Competitive adsorption of Cd(II) and Pb(II) in binary solutions revealed a preferential adsorption for Pb(II). Na_2EDTA 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.