Removal Of Cd（Ⅱ） And Pb（Ⅱ） From Aqueous Solutions Using In Situ Oxidized Fe₃O₄ Membranes

Water pollution especially the heavy metal contamination is increasingly serious with the development of industrialization.Heavy metals in water are highly toxic and carcinogenic for human body. The in situ oxidized Fe₃O₄ membranes from 316 L porous stainless steel tubes were prepared in ourpreliminary study and the membranes shew great removal potential for anion Cr（VI）. Here we report the removal performances of the in situ Fe₃O₄ membranes for the two common toxic cations Cd（Ⅱ） and Pb（Ⅱ）. The main results of the study are as follows.1. The membranes exhibited high removal efficiency of 97% at pH 9.0 for Cd（Ⅱ） of1mg/L initial concentration and 100% at pH 5.0-6.0 for Pb（Ⅱ） of 5 mg/L initial concentration.The adsorption kinetics for the two cations followed the pseudo-second order model. The adsorption isotherms were well described by the Langmuir model. Thermodynamic results demonstrated that the adsorption processes were spontaneous and endothermic, and the adsorption of Cd（Ⅱ） and Pb（Ⅱ） could be regarded as a physical adsorption enhanced by chemical effect.2. The competitive adsorption of Cd（Ⅱ） and Pb（Ⅱ） in binary solutions indicated that the presence of one metal ion intervened with the adsorption of the other in the binary component system and the affinity between Pb（Ⅱ） and membranes was much higher than that between Cd（Ⅱ） and membranes.3. 0.01 mol/L Na₂ EDTA solution was used to regenerate the in situ oxidized Fe₃O₄ membranes and the desorption ratio were respectively 90.29% and 99.75% for Cd（Ⅱ） and Pb（Ⅱ）.4.The membranes exhibited high removal efficiency 99.25% and 100% for Cd（Ⅱ） and Pb（Ⅱ） in drinking water samples. After adsorption process, the concentrations of Cd（Ⅱ） and Pb（Ⅱ） meet the requirements of the WHO drinking water standards.5. The membranes show promise to efficiently remove of Cd（Ⅱ） and Pb（Ⅱ） from aqueous solutions.