| Solvent extraction is widely used in separation and purification for rare Earth elements.Nowadays,although more and more extractants have been developed,P204 and P507 are still the most common extractants.P204 is not only cheaper but also has better extraction performance than P507 in acidic media.However,due to its high stripping acidity,it is difficult to strip rare earth ions,making its application seriously hindered.In this paper,three kinds of additives with large steric resistance are proposed to be added to P204: TBP,P350 and n-octanol.By modifying the extractant or changing its extraction environment to solve the problem of difficulty in stripping rare earth ions for P204,reducing the concentration of stripping acid at the same t ime.The main research contents and results are as follows:(1)Study on the extraction conditions of Nd and Gd ions in P204-TBP,P204-P350,and P204-n-octanol extraction systems,reach factors as oscillation time,ion concentration,hydrochloric acid concentration,ratio of organic phase to aqueous phase,additive content,etc.And compared extraction rate with P204 extractant.The order of extraction rate is P204>P204-TBP>P204-P350>P204-n-octanol.The optimal extraction conditions are: CNd3+/Gd3+=0.1mol/L,O/A=1:1,35%P204,oscillation time is 9min.(2)Study on the distribution ratio and separation coefficient of Nd and Gd ions in P204-TBP,P204-P350 and P204-n-octanol extraction systems.It is concluded that the distribution ratio is inversely proportional to the concentrations of rare earth ions,hydrochloric acid,and additives,and is proportional to the ratio.Under the same conditions,the Gd ion distribution ratio is larger than that of Nd ions which belongs to the positive sequence extraction.?Gd/Nd decreased with the increase of ion concentration,hydrochloric acid concentration and additive content,because the distribution ratio of each component decreases.The increase of hydrogen ion concentration hinders the cation exchange reaction.The increase of additive content leads to the modification of the extractant and the change of the extraction environment,and weakens the ability of rare earth ions to coordinate with the extractant.P204-TBP separation performance is better,the maximum separation factor is 4.The best separation condition is: CNd3+/Gd3+=0.1mol/L,O/A=1:1,35%P204,oscillation time is 5min.(3)The stripping performance of P204-TBP,P204-P350,P204-n-octanol extraction system for Nd and Gd ions was studied and compared with P204 s ystem.The experimental results show that the stripping rate of P204 and P204-TBP,P204-P350,and P204-n-octanol extraction systems is proportional to the oscillation time and reach the equilibrium after 15 minutes.With the increase of stripping acid concentration,the stripping rate of Nd ions in each extraction system reaches equilibrium at low acidity.The Gd ions need higher stripping acid,and the stripping rate is less than that of Nd ions under the same conditions.The addition of additives makes the stripping rate higher than that of P204.With the increase of additive content,the stripping rate of P204-TBP extraction system increased significantly.The stripping properties of P204-TBP are superior to those of other extraction systems.The stripping rates of Nd and Gd were 95% and 90% respectively,which was much higher than that of P204 extractant.(4)The optimal extraction system P204-TBP was selected,and its extraction mechanism and thermodynamic analysis were studied.Infrared spectroscopy and slope method proved that the extraction mechanism of P204-TBP extraction system belongs to cation exchanges reaction.TBP forms an intermolecular hydrogen bond with P204 which modifies the extractant P204.With the presence of steric resistance effect,the stripping rate is greatly increased and the concentration of stripping acid is reduced. |
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