Synthesis Of Fe₃O₄-NSO-EDTA Magnetic Composite And Its Selective Adsorption Property For Cu（Ⅱ）

Sources of copper-containing wastewater involve multiple industries,and huge emissions pose a great potential threat to natural ecology.The components in copper-bearing wastewater are complex and changeable.Wastewater containing copper ions treated with traditional adsorption materials,and the removal effect will be seriously reduced.In addition,after adsorption treatment,traditional adsorbent faces the problems of time-consuming and energy-consuming solid-liquid separation,which greatly increases the total operating cost.In the face of increasingly strict emission standards,it is of great significance to develop adsorption materials that can achieve high-efficiency and low-energy consumption to remove copper pollution sources in wastewater.In this paper,silane reagent TMS-EDTA（N-（trimethoxysilylpropyl）ethylenediamine triacetic acid）was used to functionalize Fe₃O₄-NSO,obtaining Fe₃O₄-NSO-EDTA adsorbent with high Cu（II）selectivity that can be magnetically separated.The as-synthesisied materials were characterized by XPS,XRD,FT-IR,TGA,SEM,TEM,BET,VSM,CHN elemental analysis,and Zeta potential test.Moreover,the removal effect of Fe₃O₄-NSO-EDTA on Cu（II）,Zn（II）,and Cd（II）was explored,and the selective adsorption performance of Fe₃O₄-NSO-EDTA on Cu（II）in the mixed system was studied in detail.Binary kinetics experiments were designed to illuminate the mechanism of selective adsorption of Cu（II）.The main conclusions are as follows:（1）Polycondensation occurs between the molecules after the hydrolysis of TMS-EDTA,and the resulting polymer condensed with the hydroxyl groups on the surface of Fe₃O₄-NSO to form Si-O-Fe or Si-O bonds.The TMS-EDTA content of the as-synthesied matirals is10.53%.The prepared Fe₃O₄-NSO-EDTA is superparamagnetic nanoparticles with a saturation magnetic strength of 39.7 emu/g,and the solid-liquid separation process takes no more than 60 s by using a magnet.（2）The TMS-EDTA polymer layer on the surface of Fe₃O₄-NSO-EDTA can effectively improve the selectivity of the material.Compared with Fe₃O4-NSO,the performance of Fe₃O₄-NSO-EDTA in the Cu（II）/Cd（II）and Cu（II）/Zn（II）mixed systems for selective adsorption of Cu（II）was enhanced by 2.8 and 2.1 times,respectively.The stability constant of log K and the radius of metal ion formed by the complex of metal ion and EDTA will affect the selectivity of Fe₃O₄-NSO-EDTA to Cu（II）.（3）The mechanism of selective adsorption of Cu（II）by Fe₃O₄-NSO-EDTA in Cu（II）/Cd（II）binary system can be explained as follows:Cu（II）quickly occupied the surface active adsorption sites on Fe₃O₄-NSO-EDTA via complex,and generated steric hindrance to restrain Cd（II）from approaching Fe₃O₄-NSO-EDTA.After the surface layer EDTA group is saturated with Cu（II）,the free Cu（II）can pass through the TMS-EDTA polymeric layer and be adsorbed by the surface hydroxyl groups.Cd（II）,formed unstable complexes with EDTA groups,will eventually be replaced by free Cu（II）and released back into the solution.