Preparation Of New Ferromagnetic Materials And Remediation Mechanism Of Cadmium Contaminated Soil

Soil pollution of cadmium is becoming more and more serious,threatening the human health.In this paper,referring to the preparation principle of“molecular imprinting polymers”,a new magnetic material with low cost and high activity was prepared and the new material,MFe,was used to adsorb cadmium in contaminated soil.In this paper,the preparation process of MFe were systematically studied.The structure and properties of MFe and its selective adsorption mechanism for cadmium were characterized systematically studied.The application of MFe to the remediation of cadmium-contaminated soil has achieved remarkable results.The main results and innovations are as follows:（1）The new material,MFe,with high specific surface area and activity,was prepared based on the“molecular imprinting technology”and“strong complexation of ammonia and cadmium”.The preparation process is based on the idea of"pre-adsorption-desorption".Firstly,Cd is adsorbed on the surface of iron powder by pretreatment,and then adsorbed cadmium is desorbed by ammonia leaching to obtain a new adsorption material MFe.In the ammoniacal solution system,free-NH₃ combines with cadmium to form complexes dominated by[Cd（NH₃）₆]²⁺,which desorbs cadmium on the surface of the material,causing the surface holes of MFe.After modification,the structure and properties of the new material changed obviously:Iron（hydroxyl）oxide was generated in large quantities;The surface of the MFe appeared obvious roughness and porosity,and the specific surface area was clearly promoted;Moreover,the surface was modified with-NH₂ groups with complexing ability with cadmium,which provides more sites for Cd（Ⅱ）adsorption.（2）Compared with the mineral components of soil,MFe has a stronger adsorption capacity for cadmium.The main mineral components in the tested soil included quartz,kaolinite,muscovite and limonite,and the saturated adsorption capacity of Cd（Ⅱ）on the above mineral surface was only 4.76,9.3,5.5 and 14 mg/g,respectively.The adsorption capacity of MFe for cadmium is as high as 47 mg/kg,whose adsorption is closer to Freundlich model and belongs to stable heterogeneous adsorption.MFe can effectively compete for the adsorption of cadmium on the surface of soil mineral components.（3）MFe can effectively remove cadmium from actual cadmium contaminated soil.When the dosage of citric acid is 15 g/kg and MFe is3%,the cadmium removal rate of more than 70%can be achieved.The redistribution of cadmium form was realized,in which the proportion of weak acid extractable cadmium was reduced from 55.23%to 40.02%,the reducible cadmium increased from 21.22%to 26.5%and the residual cadmium from 6.5%to 10.56%.Cadmium changed into more difficult to be bio-utilized after remediation.（4）MFe-magnetic remediation for cadmium-polluted soil was developed,and pilot test was carried out.For the three plots of soil with different pollution levels（The initial cadmium content was 3.58,1.64 and1.07 mg/kg,respectively）,MFe-magnetic separation remediation could achieve a cadmium removal rate of more than 70%,while the effective cadmium content was significantly reduced to less than 0.15 mg/kg after remediation.The new technology provides a new technical solution for the purification of soil polluted by heavy metal and has a certain application potential.