Preparation Of Polymer-based Solid Phase Extractant And Experimental Study On Extraction Of Light Rare Earths

Rare earth elements are widely used in military,agriculture,aerospace,medical and other fields,and they are strategic resources that determine the destiny of the country.The separation method of rare earth elements is usually solvent extraction.However,this method requires the use of more organic solvents and produces a large amount of ammonia nitrogen wastewater,which has an adverse effect on the ecological environment.The solid phase extraction method is a new type of extraction method with simple operation and green extraction technology.In order to realize the use of solid-phase extractants in the separation of rare earths,it is of great significance to develop preparations based on high-efficiency solid-phase extractants for green separation and purification of rare earths.In this thesis,the XAD-7 doped extractant was used to prepare solid-phase extractant to explore the extraction of rare earths,and the feasibility of solid-phase extraction of rare earths was analyzed.XAD-7-P204,XAD-7-P507 solid-phase extractant can effectively extract and separate La3+and Ce3+.The extraction time was 20 min,the temperature was 25℃,pH=4.017,the mass of solid-phase extractant is 0.5 g,and the doping ratio is at 0.5 mL·g-1,the extraction capacities of the two extractants for La3+ were 7.542 mg·g-1 and 5.684 mg·g-1.By adjusting the pH,the separation between rare earths can be promoted,andβLa3+/Ce-3+ can be increased from 1.47 to 2.01,laying a foundation for the exploration of polymer-based solid phase extraction.In this thesis,aniline,pyrrole,and thiophene were used as monomers,and three kinds of polymers were prepared by using different oxidants.The polymer-based solid phase extractant was prepared by doping the extractant,and the extraction experiment of light rare earth(La3+,Ce3+,Pr3+,Nd3+)was carried out,The following conclusions were obtained:(1)The comparative experiment of extracting rare earth by PANI-P204,PANI-P507,PPy-P204,PT-P204 and three polymer monomers without extractant showed that:The polymer matrix without extractant had no extraction capacity for rare earth elements.After doping,the extractant played a role in promoting extraction,and the extraction and separation effect of doped P204 was better.(2)Evaluate the extraction performance of the polyaniline-based solid phase extraction system PANI-P204 and PANI-P507.When the extraction time was 30 min,the temperature was 25℃,pH=4.017,the mass of the solid phase extraction agent is 0.5g,and the doping ratio is 0.5 mL·g-1,the extraction rates of PANI-P204 solid-phase extr doping actant for La3+,Ce3+,Pr3+and Nd3+were 70.06%,69.23%,78.65%and 85.53%;The extraction rates of PANI-P507 solid-phase extractant for La3+,Ce3+,Pr3+and Nd3+ were 65.42%,72.89%,74.14%and 82.72%.When the pH of the aqueous solution is 4.017,the distribution ratio of PANI-P204 for La3+,Ce3+,Pr3+and Nd3+ is 1.52,2.17,3.42,5.32,and the distribution ratio of PANI-P507 extractant component to light rare earth was lower than that of PANI-P204.When pH=5.041,the mass of the solid phase extraction agent is 0.5 g and the ratio was 0.5 mL·g-1,βLa3+/Ce3+ was 9.47,when the pH of the water phase was adjusted to 1.026,βPr3+/Nd3+ was 6.83.It was beneficial to the separation of rare earth elements.(3)PPy-P204 extracts and separates rare earth La3+/Ce3+,the results showed that:when the temperature was 25℃,the extraction time was 30 min,mPPy-P204=0.2g,the doping ratio was 0.5 mL·g-1,c(Ce3+)=0.01mol·L-1,pH=5.041,The extraction rate of Ce3+was 79.2%;pH=4.017,c(La3+)=0.01 mol·L-1,other conditions were the same as above,the extraction rate of La3+was 77.01%.The optimal conditions for extracting La3+with PT-P204 were as follows:the temperature was 25℃,the extraction time was 30 min,c(La3+)=0.015 mol·L-1,mPT-P204=0.2g,the doping ratio is 0.5 mL·g-1,pH=3.086,the extraction rate reached 33.25%;The best conditions for extracting Ce3+were as follows:c(Ce3+)=0.01 mol·L-1,mPT-P204=0.2g,the doping ratio is 0.5 mL·g-1,pH=4.017,the extraction rate is 41.49%;(4)Combining FT-IR,SEM,EDS and other methods to explore the extraction mechanism,the P=O double bond stably existed in the solid phase extractant,and achieved the extraction of light rare earths.Analyzed by extraction thermodynamics and kinetics,the four polymer-based solid phase extractants extract light rare earths were all exothermic reactions(ΔH<0),entropy increases(ΔS>0),and the temperature rise was not conducive to the forward progress of the extraction reaction.The process of extracting rare earth ions conformed to the second-order kinetic model adsorption and Langmuir model.(5)Through repeated stripping and extraction experiments on the solid phase extractant with hydrochloric acid,the regenerated solid phase extractant was basically in line with the original extractant,and the regenerated solid phase extractant still had a good extraction effect and could be recycled.It had realized no emulsification and avoided the third phase in the solid-liquid extraction process.