Study On Separation And Extraction Of Rare Earths By Nitrogenous Phosphoric Acid

Rare earths(REs)play an important role in various fields such as electronics,magnetism,metallurgy,phosphors,catalysts,glass,laser and ceramic technology.Nowadays,solvent extraction is the most popular technology for separation of rare earths because of their physical and chemical similarities.In recent years,designing and synthesizing of novel extractants which exhibit high efficiency and high selectivity toward metals have received more and more attentions.In this thesis,an ?-aminophosphonic acid extractant,(2-ethylhexylamino)methyl phosphonic acid mono-2-ethylhexyl ester(HEHAMP),has been synthesized by two steps,and the optimum reaction conditions were determined by temperature,reaction time and material ratio.The reaction product extractant was charactered by ESI-MS,1HNMR,HPLC.The yield was 78.9%and purity was about 96.7%.Solvent extraction and separation of rare earths(La-Lu,plus Y and Sc)by a novel synthesized extractant,HEHAMP,were investigated in chloride medium.The larger separation factors(?)between adjacent heavy REs suggested that HEHAMP has a better performance than HEHEHP.This extractant also exhibits good separation ability to separate Sc from REs.The extracted complex of trivalent REs was determined to be REClH2A4 by the slope analysis method.Thermodynamic parameters(?H,?G and ?S)of Lu and Yb were determined to be 7.47 kJ mol-1,-6.05 kJ mol-1,45.37 J mol-1 K-1 and 11.87 kJ mol-1,-4.96 kJ mol-l,56.49 J mol1 K-1 at 298K,respectively,which indicate that the extraction reaction of Lu is an endothermic process.The 30%loading capacity towards Yb(?)was about 14.46 g Yb2O3/L.HCl was the most efficient stripping acid and 92%of the loaded Yb(?)can be stripped by one stage stripping with 2 mol/L HCl.Synergistic extraction of trivalent rare earths by mixtures of HEHAMP and HEHEHP had also been investigated in chloride media.It was demonstrated that mixtures of HEHEHP and HEHAMP have an evident synergistic effect for heavy RE(?)and the maximum synergistic enhancement factors are 2.89,2.76,2.54,2.14,2.14 and 2.06 for for Lu,Yb,Tm,Er,Y and Ho separately at a HEHAMP mole fraction of 0.5.In the extraction step,the separation factors of the heavy rare earths with synergistic mixtures were obtained(?Y/Ho=1.31,?Er/Y=1.61,?Tm/Er=1.78,?Yb/Tm=1.76,?Lu/Yb=1.20).The extracted complex was determined as REAB2·HA·2HB.The loading capacity of the mixture of 15%HEHAMP and 15%HEHEHP for Yb(III)and Lu(III)was about 23.59 g Yb2O3/L and 24.25 g Lu2O3/L,respectively.In addition,HCl was the most efficient stripping acid,over 95%Yb(III)could be stripped by one stage stripping with 1 mol/L HCl.