Synthesis Of Phosphorylated Chitosan And Its Separation Performance For La(Ⅲ) And Ce(Ⅳ)

Rare earths,known as“industrial vitamins”,are widely used in petrochemical,electronic,military and other fields.Solvent extraction is a widely used rare earth separation method in industry,but it has some shortcoming,such as large consumption of organic solvent and acid-base,low separation efficiency,serious ammonia nitrogen pollution and so on.In view of the disadvantages of solvent extraction,complexation ultrafiltration（C-UF）and shear-induced dissociation coupling with ultrafiltration（SID-UF）were used to separate rare earths.A novel water-soluble polymer rare earth complexant phosphorylated chitosan（PCS）was designed and synthesized.The selective separation effect of rare earths using PCS by C-UF and SID-UF was studied in order to provide a new method for the separation and concentration of rare earths.The research contents and main results are as follows:In order to improve the rare earth separation efficiency,a rare earth oriented water-soluble polymer complexant phosphorylated chitosan was designed and synthesized.After testing and characterization,it can be obtained that the solubility in water of PCS synthesized under the optimized conditions is 2.7 mg mL^-1.Compared with chitosan,the water solubility has been significantly improved.The PCS was with grafting rate of 23%and well-distributed element distribution,which is consistent with the designed structure.The synthetic method has the advantages of simple operation,mild and controllable reaction conditions and high product purity.It is expected to realize large-scale production and application.The kinetics of complexation reaction between PCS and rare earth（La（Ⅲ）,Ce（Ⅳ））was preliminarily studied and the optimized experimental conditions of C-UF were determined by rotating disk membrane（RDM）.The results showed that at pH 7.0 and 25℃,the order of complex reaction rate factor（K₁）is Ce（Ⅳ）>La（Ⅲ）.Besides,the optimized conditions for single La（Ⅲ）and Ce（Ⅳ）were pH 7.0,P/RE（mass ratio of polymer to rare earth）10 and pH 7.0,P/RE 8 respectively,while that for mixed rare earths was pH 7.0,P/RE 10.Under the optimized conditions,the rejection rate of rare earth ions all could reach more than 99%.According to density functional theory and frontier orbital theory,the stable configuration and orbital energy of complexes were studied.At the molecular level,it is concluded that PCS-Ce is more stable than PCS-La complex.On this basis,the shear stability of PCS and PCS-RE complexes was investigated.In the shear field with rotational speed（N）of 0～3000 rpm,the complexant PCS could maintain stability,while PCS-RE complexes dissociated with the increase of N.The corresponding shear rate when the complex began to dissociate was the critical shear rate（γ_c）.At pH 7.0,theγ_c of PCS-La and PCS-Ce is 1.31×10⁵s^-1and1.63×10⁵s^-1,respectively.The comparison showed that PCS-Ce is more stable than PCS-La complex.According to the difference of shear stability,SID-UF was used to orderly selective separate La（Ⅲ）and Ce（Ⅳ）in solution,and the regenerated PCS was obtained by percolation.The study on the separation coefficients（β）of La（Ⅲ）and Ce（Ⅳ）showed that within the scope of the experiment,β_La/Cereached a maximum of 37.1 at pH 7.0 and1480 rpm.Under the optimized conditions,the selective separation of La（Ⅲ）and Ce（Ⅳ）and the regeneration of PCS were realized,and the regenerated PCS showed good rare earth complexation performance which could be recycled.To sum up,C-UF and SID-UF processes for rare earth separation have the advantages of simple operation,green and efficient,reducing resource waste.The novel complexant PCS is with good separation effect on rare earth,which provides the possibility for industrial application.