Separation And Enrichment Of Heavy Rare Earth Ions In Complex Rare Earth Leaching Solution

Rare earth elements in weathering crust elution-deposited rare earth ores are mainly adsorbed on the surface of clay minerals in the form of ionic phase.The distribution of light,medium and heavy rare earth elements is complete.Weathering crust elution-deposited rare earth ores are rich in medium and heavy rare earth elements closely related to high-tech and new material industries.They are the main sources of medium and heavy rare earth elements in the world and the important strategic resources in China.At present,the industrial mining method of weathered crust elution-deposited rare earth ores is in-situ leaching process.And then,ammonium bicarbonate is used to remove the impurity in leachate.The rare earth precipitate is obtained by precipitation of rare earth with ammonium bicarbonate or oxalic acid.The precipitate is calcined to rare earth oxide at high temperature,and then the rare earth oxide or carbonate is dissolved into rare earth solution by acid to separate and purify the single rare earth according to the subsequent separation requirements or application requirements.This process needs a lot of chemical reagents and energy.Therefore,how to separate rare earth from rare earth leachate directly has been a hot research field.Solvent extraction is one of the most important methods for rare earth extraction and separation.It is suitable for large-scale continuous production,high separation efficiency and simple process.It can not only separate rare earth from most impurity ions,but also enrich rare earth without introducing new impurity ions.Furthermore,the research and development of new efficient extractant are an important link in solvent extraction.3-Oxyglutaramide is a new green environmental extractant developed in recently years.It adds ether-oxygen bond to the structure of diamide,in which its physical and chemical properties are changed,and showed good extraction ability of rare earth.Three kind of 3-oxyglutaramide extractants,N,N,N',N'-tetrabutyl-3-oxyglutaramide?TBDGA?,N,N',N',N'-tetrahydro-3-oxyglutaramide?THDGA?and N,N,N',N',N'-tetraoctyl-3-oxyglutaramide?TODGA?,were synthesized.Their chemical structures were characterized by infrared spectroscopy?IR?and nuclear magnetic resonance?NMR?after purification by column chromatography.The extraction properties and reaction mechanism of rare earth ions by 3-oxyglutaramide extractants were studied in ammonium sulfide,ammonium sulfate and ammonium nitrate media solutions.The effects of contact time,ammonium ion concentration,rare earth ion concentration,extractant concentration,temperature and diluent type on extraction behavior was investigated by single factor variable method.The extraction equilibrium time,composition of extractant and thermodynamic parameters were obtained from experiment results.The main contents were as follows:1.In three ammonium salt solution of NH₄Cl??NH₄?₂SO₄ and NH₄NO₃,different diluents have different effects on the extraction performanc of TBDGA,THDGA and TODGA.?1?In ammonium chloride solution,n-octane/n-octanol(V_octane:V_octanol=7:3)as a mixed diluent had the highest extraction rate,and the single-stage extraction rates of Y and Gd ions can reach 89.54%and 91.28%by THDGA.The reason was that the polarity of mixed diluent n-octane/n-octanol(V_octane:V_octanol=7:3)was the greatest compared with other extractants,which was conducive to forming rare earth complexes.At the same time,the presence of n-octanol as a cosolvent was conducive to the extracted species into the organic phase and increased the extraction effect.?2?In ammonium nitrate solution,n-octane/n-octanol(V_octane:V_octanol=7:3)and dichloromethane as diluents were suitable for the extraction of rare earth ions by TBDGA.The single-stage extraction rates of La,Y and Gd ions were up to 85.85%,98.56%and 97.24%.The seven diluents investigated had a little effect on the extraction efficiency of THDGA and TODGA,and the single-stage extraction rates were all above90%.In addition to the polarity of the diluent,the steric hindrance effect and the polymerization of the extractant in the diluent could influence the extraction effect of the extractant.?3?In ammonium sulfate solution,the seven diluents had a little effect on the extraction performance of TBDGA,THDGA and TODGA.Divalent sulfate ions formed rare earth sulfate precipitation with rare earth ions at the interface of two phases.These precipitations hindered the extraction mass transfer process and the coordination reaction between rare earth ions and extractant molecules which seriously affected the extraction performance of TBDGA,THDGA and TODGA.The highest single-stage extraction rate of La?III?,Y?III?and Gd?III?is only 29.96%.2.In three ammonium salt solution of NH₄Cl??NH₄?₂SO₄ and NH₄NO₃,n-octane/n-octanol(V_octane:V_octanol=7:3)was used as diluent,the single-stage extraction rates of La?III?,Y?III?and Gd?III?ions by TBDGA,THDGA and TODGA increased with the increase of oscillation time and ammonium ion concentration in aqueous phase,but decreased with the increase of rare earth ion concentration.?1?In ammonium chloride solution,the extraction rate of three extractants was very fast and could be reached extraction equilibrium within 15 minutes.In tested concentration range,the single-stage extraction rate of Y?III?and Gd?III?by TBDGA was better than THDGA and TODGA,reaching 87.86%and 98.53%in 2 mol/L ammonium solution containing 700 mg/dm³ rare earth ion.But the maximum extraction rate of La?III?was only 25.38%.?2?In ammonium nitrate solution,the three extractants had high extraction rate and fast extraction efficiency for rare earth ions,and the extraction equilibrium could be reached within 20 minutes.In tested concentration range,the highest single-stage extraction rate of La?III?,Y?III?and Gd?III?reached 81.54%,97.85%and 99.18%in 2mol/L ammonium solution containing 1000 mg/dm³ rare earth ion.?3?In ammonium sulfate solution,the extraction efficiency of three extractants for rare earth ions was very poor.The existence of divalent sulfate ion was not conducive to the coordination of rare earth ions and extractant molecule,which seriously affected the extraction rate of rare earth ions.The maximum single-stage extraction rate of La?III?,Y?III?,Gd?III?were only 22.98%.3.In three ammonium salt solution of NH₄Cl??NH₄?₂SO₄ and NH₄NO₃,n-octane-n/octanol(V_octane:V_octanol=7:3)was used as diluent.When the concentration of ammonium ion and initial rare earth ion was constant,the extraction distribution ratio increased with the increase of the concentration of extractant,and the composition of extractant formed by TBDGA,THDGA and TODGA with rare earth ion were calculated.The effects of temperature on the extraction of La?III?,Y?III?and Gd?III?rare earth ions by three extractants were investigated in the range of 303-331 K.The thermodynamic functions of the extraction reaction were calculated.The results showed that the extraction partition ratio decreased with the increase of temperature and these extraction reactions were exothermic.Reducing the temperature was beneficial to the extraction reaction.4.Infrared spectroscopy results certificated that 3-Oxyglutaramides coordinated with rare earth ions through carbonyl and ether-oxygen bonds.5.Water,DTPA and EDTA were selected as three stripping agents.The results improved that water had a little stripping effect on rare earth ions.Both EDTA and DTPA had fast stripping rates for Y?III?and Gd?III?,among which DTPA had better stripping effect than EDTA.In addition,the stripping rate of Gd?III?by the two stripping agents was higher than that of Y?III?after reaching the stripping equilibrium.This study showed that TBDGA,THDGA and TODGA had good extraction ability towards Y?III?and Gd?III?in ammonium chloride and ammonium nitrate solutions.In ammonium sulfate solution,the extraction efficiency of rare earth ions by three extractants was very weak.The order of extraction efficiency of three extractants for rare earth ions was Gd?III?>Y?III?>La?III?.Using same experimental parameters,the single-stage extraction efficiency of 3-Oxyglutaramide extractants for the same rare earth ion was TBDGA>THDGA>TODGA.It was mainly due to the interaction of electron-induced effect and steric hindrance effect of alkyl groups connected to N atoms in the amide structure.From all experimental results,an alternative new idea and technical guidance for industrial production of separation and enrichment rare earth from rare earth leachate was proposed.