| In recent years,with the rapid development of economy,the problem of environmental pollution has become more and more serious.Especially,the pollution of wastewater containing Cd（Ⅱ）heavy metals seriously endangers people’s health.Therefore,How to remove Cd（Ⅱ）from wastewater is particularly important.Because of its advantages of simple operation and high removal rate,the separation method of adsorption has become the focus of researchers in recent years.The key of the adsorption method is to find a kind of adsorbent with low cost,easy operation and high adsorption rate.The starch magnetic microspheres（AA-MSM,AAM-MSM and AAM-MSMPM）grafted with acrylamide（AM）,acrylic acid（AA）and methyl methacrylate（MMA）respectively were prepared by inverse emulsion polymerization using activated cassava starch（MS）as raw material.The synthesis process conditions were optimized and the synthetic products were characterized by Fourier transform infrared spectroscopy（FTIR）and scanning electron microscopy（SEM）.The adsorption thermodynamics and kinetics of Cd（Ⅱ）were studied by static and dynamic methods,and the adsorption mechanism of Cd（Ⅱ）in wastewater by starch magnetic spheres was revealed.The main research contents are as follows:（1）Magnetic starch microspheres（AA-MSM）were prepared by inverse emulsion polymerization with mechanically activated cassava starch as raw materials and AM and AA as graft monomers.FTIR and XPS analysis showed that AA-MSM contained-NH2,-COOH and-OH functional groups,indicating that AM,AA and MS were successfully grafted.SEM results showed that AA-MSM was irregular spherical with slightly adhesion surface.The saturation magnetization of the microsphere was 13.9 emu·g-1 and 12.3 emu·g-1 after adsorption of Cd（Ⅱ）,which indicating that Cd（Ⅱ）had little effect on the magnetism of the microsphere before and after adsorption,and providing experimental support for magnetic separation of AA-MSM after adsorption of Cd（Ⅱ）by external magnetic field.The maximum adsorption capacity of AA-MSM was 25.5 mg?g-1 when the amount of AA and AM was 45 wt%and 25wt%.The Cd（Ⅱ）adsorption process of AA-MSM was in accordance with Langmuir isothermal adsorption model and pseudo-second-order kinetic model,and the Cd（Ⅱ）adsorption was monolayer chemisorption.（2）In order to further improve the sphericity and adsorption capacity of the adsorbent for Cd（Ⅱ）,the AAM-MSM adsorbent was prepared by adding MMA monomer.When the dosage of MMA was 4 m L,the maximum adsorption capacity of AAM-MSM was 39.98 mg?g-1,which was 36.22%higher than that of AAM-MSM.The results show that the surface of AAM-MSM is smooth,regular in shape,uniform in size and good in sphericity after adding MMA.The possible reason is that in the inverse emulsion system,the MMA monomer with weak polarity is conducive to the improvement of surface hydrophobicity of the microsphere and the reduction of surface energy,and make the microspheres better sphericity.（3）In order to improve the adsorption capacity of AAM-MSM for Cd（Ⅱ）,porous magnetic starch microsphere adsorbent（AAM-MSMPM）was prepared by using PEG/Me OH binary system as pore forming agent.BET results showed that compared with AAM-MSMPM,the particle size of AAM-MSMPM decreased by 7.32 nm from 19.21 nm,the specific surface area increased by35.23 m2?g-1 from 7.33 m2?g-1,and the pore volume increased from 0.03 cm3?g-1to 0.13 cm3?g-1.AAM-MSMPM provided more adsorption sites for Cd（Ⅱ）.When p H=5,the mass ratio of polyethylene glycol to methanol is 1:2.5,and the amount of pore forming agent is 20 wt%,the maximum adsorption capacity of AAM-MSMPM for Cd（Ⅱ）is 210.68 mg·g-1,which is 81.02%higher than that of AAM-MSMPM.After five cycles of adsorption and desorption,the adsorption capacity of AAM-MSMPM for Cd（Ⅱ）remained unchanged.The adsorption mechanism showed that there were enough functional groups（-NH2,-COOH,-OH）on AAM-MSMPM surface at the initial stage of adsorption,and the adsorption capacity increased rapidly to 210.68 mg·g-1,and Cd（Ⅱ）rapidly diffused to the fixed adsorption point of AAM-MSMPM surface.When most of the adsorption sites on AAM-MSMPM surface were occupied by Cd（Ⅱ）,the adsorption reached equilibrium. |
