Syntheses of DEHHAMP and Its Derivatives and Their Applica-Tion in the Extraction and Separation of REs and Thorium

Author:Wei Hai Qin

Supervisor:liao wu ping


Degree Year:2019





Solvent extraction is one of the most commonly used methods for the mineral treatment and separation of rare earths and their recovery and enrichment.Due to the rapid development of high-technology and rare earth industry,the environmental problems caused by traditional extraction processes must be solved urgently and the products of rare earths with higher and higher quality are required.So it is urgent to develop some novel extractants and high efficiency green separation processes for rare earths.In this thesis,a novel extractant DEHHAMP and its derivative were synthesized and applied in the extraction and separation of rare earths and thorium.The synergistic effect of mixed HEHHAMP and Cyanex272 extractants was also studied in the extraction and separation of rare earths.The main contents can be stated as follows.1.The separation and extraction of Ce(Ⅳ)and Th(Ⅳ)from RE(Ⅲ)by di(2-ethylhexyL)-N-heptyL-aminomethylphosphonate(DEHHAMP)in sulfate medium were studied.The effect of some factors such as aqueous acid concentration,extractant concentration in the organic phase and temperature of the system were investigated.The extraction of metal ions by DEHHAMP decreases following the order:Ce(Ⅳ)>Th(Ⅳ)>Sc(Ⅲ)>other RE(Ⅲ).The extraction mechanism was proposed to be solvation mechanism and the extracted complexes were deduced to be Ce(SO4)2·2L and Th(HSO4)2SO4·L by the slope analysis method.The extraction reactions of Ce(Ⅳ)and Th(Ⅳ)were both exothermic processes.The loaded Ce(Ⅳ)in the organic solution can be stripped efficiently by 3%H2O2 while the loaded Th(Ⅳ)by 4 mol/L HC1.The extraction capacities of 0.63 mol/L DEHHAMP towards Ce(Ⅳ)and Th(IV)are 30.0 g/L CeO2 and 24.4 g/L ThO2,respectively.Furthermore,an extraction process based on DEHHAMP was proposed to selectively extract and separate cerium(ⅣV)and thorium from the bastnaesite leaching.The cascade extraction test of the laboratory scale gives the cerium product with the purity of 97.2%and a yield of 85.4%,and the thorium product with the purity of 96.5%and a yield of 98.8%.2.The acidic extractant n-heptylaminomethyl phosphonic acid 2-ethylhexyl ester(HEHHAMP)was obtained by the hydrolysis of DEHHAMP and applied for the extraction and separation of trivalent rare earths from chloride medium.The extraction of heavy REs by HEHHAMP was higher than that of the light ones as in the order:La<Gd<Ho<Y<Er<Tm<Yb<Lu.The extraction reaction was a cation exchange process and the extracted complexes were determined to be REClH2L4.The extraction reaction of RE(Ⅲ)by HEHHAMP was an endothermic process.The separation factors between heavy REs and yttrium by HEHHAMP,i.e.βEr/Y,βTm/Y,βYb/Y and βLu/Y,were determined to be 2.18,9.36,14.9 and 24.3,respectively,which are higher than those of the sole HEHEHP or D2EHPA system,indicating that HEHHAMP is a more efficient extractant for the separation of yttrium from heavy REs.The extraction capacities of HEHHAMP towards Yb(Ⅲ)and Lu(Ⅲ)were determined to be 12.76 g/L and 15.43 g/L,respectively.3.The extraction of heavy rare earths by the mixture of HEHHAMP and Cyanex272 from chloride solution was studied and the synergistic effect between HEHHAMP and Cyanex272 was observed.Furthermore,the separation factors between the adjacent rare earths are higher than those for the sole HEHHAMP or Cyanex272 system.A cation exchange mechanism was deduced for this mixed extractant system by the methods of slope analysis and constant mole.The synergistic extraction of heavy rare earths was an endothermic and spontaneous process.The loaded rare earths in the organic phase can be stripped efficiently,that is,more than 90%REs in the loaded organic phase can be stripped by 1 mol/L HCl.4.The extraction kinetics of thorium(IV)by di(2-ethylhexyl)-[N-(2-ethylhexyl)aminomethyl]phosphonate(Cextrant230)from sulfate medium was investigated using a constant interfacial cell with laminar flow.Based on the effect of stirring speed and temperature on the rate of thorium extraction,the mass transfer process is suggested to be a mixed chemical reaction-diffusion controlled one with the apparent activation energy(Ea)being of 38.10 kJ/mol.The linear relationship between the extraction rate and the interfacial area along with the strong interfacial activity of Cextrant230 suggests that the extraction reaction occurs at the liquid-liquid interface.Moreover,the effect of concentrations of H+,SO42-,HSO4-,metal ion and extractant in aqueous and organic phases were investigated,and the extraction rate equation for the thorium extraction by Cextrant230 was obtained.The apparent forward extraction rate constant was calculated to be 10-2.58.