Research On Chitosan-based Soil Heavy Metal Chelating Agent

Chitosan（CS）is a non-toxic and easily degradable natural polysaccharide.The structure is rich in amino and hydroxyl groups,which makes chitosan have the ability to adsorb heavy metal ions,at the same time,it can take place a series of chemical reactions such as esterification,acylation and so on.It provides favorable conditions for the introduction of functional groups with stronger chelating ability to heavy metal ions.In this paper,four kinds of modified chitosan products were prepared to elute and cure the lead-cadmium contaminated soil.The details are as follows:（1）Study on remediation of Pb-Cd contaminated soil by elution with chitosan modified eluentTheneutralsolublechitosanmodifierNMPCS,waspreparedby phosphonomethylation of chitosan with phosphite and formaldehyde.The structure and morphology of the product were characterized by FTIR,XPS,SEM,element analysis.The results of soil elution experiment showed that the content of exchangeable Pb and Cd in soil increased significantly,and the removal rates of Pb and Cd were 7.22%and 24.75%,respectively.After adding NMPCS,which indicated that NMPCS could contribute to the transition from insoluble state to soluble state of metal in soil.It is found that NMPCS chelates lead and cadmium mainly through N,P,O atom.（2）Study on curing remediation of Pb-Cd contaminated soil with chitosan modified adsorbentMPCS,TACS and TGACS,was prepared by means of phosphonomethylation,Mannich reaction and esterification,respectively.And the characterization on structure and morphology showed that the modification was successful.The curing effect of MPCS,TACS and TGACS on soil heavy metal Pb and Cd was better than that of chitosan.The curing rates of Pb were 62.48%,66.10%,69.06%,respectively.And the curing rates of Cd were 68.63%,73.11%,79.08%,respectively.The curing rate is also relatively fast,basically reaching equilibrium in 7 days.（3）Study on adsorption of Pb²⁺and Cd²⁺by MPCSThe adsorption experiments show that the adsorption capacity of MPCS for Pb²⁺and Cd²⁺is 188.68 mg·g^-1,105.26 mg·g^-1,respectively.And the adsorption is better than that of CS.The adsorption isotherms also conform to the Langmuir adsorption model,and the adsorption kinetics is in accordance with the pseudo-second order kinetic model.The adsorption mechanism of heavy metal by MPCS that Cd²⁺is mainly chelated by-NH and-P-OH,and Pb²⁺is mainly chelated by-P-OH.