Study On Dissolution Behavior And Regulation Mechanism Of Rare Earth Extraction By P507-N235 System

P507-N235 dual solvent extraction system can directly achieve the unsaponifiable extraction and separation of rare earths.But it still exist dissolution lossing in the process of rare earths extraction by P507-N235 organic phase.The dissolution losses not only cause a large amount of oily wastewater generating and environmental pollution,but also bring serious resource lossing.It does not accord with the conception of sustainable development strategy in China.Therefore,it is important to clarify the dissolution behavior rules of the P507-N235 system in process of rare earth extraction,find out the essential reasons of dissolution lossing,and construct a new method to completely prevent the dissolution loss of organic phase from the source for the sustainable and healthy development of rare earth industry.In this paper,with the help of advanced methods such as Langmuir-Blodgett（LB）membrane analyzer,Fourier transform infrared spectroscopy（FTIR）,Brewster angle microscopy（BAM）and Atomic force microscopy（AFM）are used to investigate the existence states,interaction and dynamic aggregation behaviors of extractant molecules and their extractives at the in situ interface,and clarify the dissolution behavior rules of organic systems.The surfactant Span 80 is added into the organic phase to adjust solution structure and improve the stability of the oil-water interface.A new regulation method has been established to prevent the dissolution lossing of the organic phase during the process of rare earths extraction.The specific contents are as follows:（1）The dissolution behavior law of the P507-kerosene system was studied.The organic phase of P507 was dispersed on the surface of pure water（p H=3）.The changes of P507 single molecule filmπ-A curve and interfacial dilatational rheology（elastic modulus,viscous modulus,dilatational modulus and phase angle）were obtained.With the increasing of P507 concentration,a large number of aggregates were formed.The formation of aggregates would change the interfacial structure and the interfacial rheological properties.This would affect the stability of the water/oil interface.The oil content in the extracted residue increased.Theπ-A curves and interfacial expansion rheology of P507-N235 and P507 were significantly different when N235 was added to the organic phase.Characterization by FTIR,BAM and AFM confirmed that the interaction between N235 and P507 molecules could inhibit the formation of P507aggregates.The three-dimensional mesh structure was formed and the interfacial stability was enhanced.（2）P507-N235 was used as an extractant.Taking rare earth Er³⁺and impurities Al³⁺and Mg²⁺in aqueous solution as research objects,the dissolution behavior of metal ions during rare earths by 507-N235 was analyzed.The presence of Al³⁺in the feed solution was detrimental to the extraction of rare earth Er³⁺and increased the oil content of the extracted residue,while the presence of Mg²⁺in the feed solution was beneficial to the extraction of rare earth Er³⁺and decreased the oil content of the extracted residue.The effect of the change of metal ion loading in the organic phase on theπ-A curve of the single molecule membrane and the rheological properties of interfacial membrane expansion were investigated.And it was found that the combination of P507 molecules and rare earth Er³⁺promoted the rightward shift of theπ-A curve.With the increasing of rare earth Er³⁺loading,the extractants mocules formed aggregates,and led to the"abrupt change"of theπ-A curve.Compared with the organic phase loaded with only rare earth Er³⁺,theπ-A curves shifted to the left when the organic phase was loaded with Al3+and Mg²⁺.Theπ-A curves shifted further to the left as the loading of Al³⁺increased,but the opposite was true for Mg²⁺,which gradually shifted to the right as the loading of Mg²⁺increased.FTIR and AFM characterization results confirmed that the formation of aggregates between P507 and metal ions had obvious structural differences,which led to the interfacial behavior changing due to different degrees and sizes of molecular interactions,and thus affected the stability of the interface membrane.（3）Span 80 was added to the P507-N235 organic phase.The extraction reaction was carried out with rare earth Er³⁺,and the concentration of Er³⁺and oil content in the extracted residue were measured.Compared with the organic phase without Span 80,the extraction rate of rare earth Er³⁺was basically unchanged after adding Span 80.And the oil content of the extracted residue was reduced.The interfacial properties between P507-N235 and P507-N235-Span 80 systems had obvious differences.It was found that there were complex interactions between Span 80 and P507-N235molecules,which made the interfacial membrane exhibit different viscoelastic properties.That would improve the stability of interface membrane and reduce the oil content of the extracted residue.FTIR and AFM characterization results confirmed that the more stable three-dimensional network structure was generated.The addition of Span 80 can improve the stability of the interface membrane.Dissolution of the P507-N235 system during the extraction process would be reduced.（4）Taking Span 80 as the regulating agent,P507-N235 as the extractant,impurities Al³⁺and Mg²⁺in the aqueous solution as research objects,the dissolution behavior of the P507-N235-Span 80 system during metal ion extraction was investigated.The results found that the adding of Span 80 would not affect the extraction effect of rare earth Er³⁺,and the oil content in the extracted residue was significantly reduced.The effect on theπ-A curve and the rheological properties of interfacial membrane of the P507-N235-Span 80 system with changing metal ion loading were investigated.The differences between P507-N235 and P507-N235-Span80 organic phases were compared and analyzed.FTIR and AFM characterization results further confirmed that the adding of Span 80 changes the structure and aggregation behavior of the interfacial membrane.The changes of the rheological properties of the interfacial membrane improved the stability of the interfacial film and reduced the dissolution lossing of the organic phase.It is confirmed that Span 80 can regulate the bulk structure of the P507-N235 system and reduce the dissolution lossing of the organic phase.A new method was provided to completely prevent the generation of oil-containing wastewater in the process of extraction.That made an important contribution to promoting the green and sustainable development of the rare earth industry.