Syntheses Of Amino Organo-Phosphorus Extractants With Different Steric Hindrances And Their Application In The Extraction Of REs

Three kinds of amino organophosphorus extractants including ?-aminophosphonate,a-aminophosphonic acid and ?-aminophosphonates were synthesized and applied in the extraction and separation of rare earths.The extraction performance of the extractants with different molecular structures towards rare earths was compared and the effect of steric hindrance was discussed.In addition,the synergistic effect of a-aminophosphonic acid H2A2 and P204 on the rare earth extraction was also studied.The main results are as follows.1.a-Aminophosphonate extractant di(2-ethylhexyl)(2-((2-ethylhexyl)amino)propan-2-yl)phosphonate(DEHAMEP,B)was synthesized and applied in the extraction and separation of Ce(?),Th(?)and RE(?)in sulfate medium.This extractant exhibits excellent selective extraction towards Ce(?),minor extraction for Sc(?)and poor extraction for other RE(?)and Th(?).The extraction of Ce(?)by DEHAMEP was compared with that obtained with other neutral phosphorus extractants such as DEHEHP,Cyanex 925 and Cyanex 923.The Ce(?)extraction decrease in the order:DEHAMEP>Cyanex 925>Cyanex 923>DEHEHP at aqueous acidity<1.5 mol/L H2SO4.The extraction complex of Ce(?)was determined to be Ce(HSO4)2SO4·2B.Different from Cextrant 230,DEHAMEP can separate Ce(?)and Th(?)at low aqueous acidity due to its larger steric hindrance on the methylene group between the N and P atoms.Fractional extraction experiment was processed to separate and recover Ce(?)from sulfuric acid leaching of the bastnaesite using DEHAMEP.CeO2 product with a purity>99.5%was obtained,in which the thorium content is<0.063%.So DEHAMEP would have a favorable application foreground in the selective recovery of Ce(IV).2.The acidic extractant 2-ethylhexyl-3-(2-ethylhexylamino)pentan-3-yl phosphonic acid(HEHAEPP,H2A2)was studied for the extraction and separation of trivalent rare earths in chloride medium.The extractability of HEHAEPP is superior to that of P507 and Cyanex 272.Even at high aqueous acidities,HEHAEPP remains higher extraction ability and selectivity towards heavy rare earths,indicating that HEHAEPP would be a promising extractant for the extraction and separation of heavy rare earths at high aqueous acidity.Compared to the extractants without some side chains on the methylene group between the N and P atoms,HEHAEPP have both higher extraction ability and better separation performance towards rare earths due to its larger steric hindrance.The extraction reaction was a cation exchange process and the extracted complexes were determined to be REA3.3.The extraction of rare earths by the mixture of HEHAEPP(H2A2)and P204(H2B2)was studied in chloride medium.A remarkable positive synergistic effect was observed for the rare earth extraction.However,the separation efficiency of rare earths in this mixed extractant system was inferior to that for the sole HEHAEPP system but superior to that for the P204 system,which is comparable with or a little higher than other reported synergistic extraction systems.Chloride anion was involved in the extraction reaction and the extracted complexes were determined to be RECl2H4A3B2.4.The extraction and separation for rare earths by four P-aminophosphonate extractants with different steric hindrance was studied and compared in chloride medium.These extractants have better separation performance towards heavy rare earths at relatively higher aqueous acidities.And the increasing steric hindrance can improve the extraction selectivity towards heavy rare earths.Furthermore,?-aminophosphonate extractants have stronger extraction ability towards RE3+ than?-aminophosphonate extractant Cextrant 230 at the same condition.