Effect Of Impurity Ion On Extraction Behavior Of Rare Earth Ions From Complex Ammonium Salt Leachate

Weathering crust leached rare earth（RE）ore is rich in ionic form RE that adsorbed on clay minerals.The ore has abundant reserves and complete distribution of light,medium and heavy RE（Ⅲ）,is an important source of medium and heavy rare earth in China,even in the world.It is a superiority mineral ore resource and a key metal mineral resource in our country because of its unique characteristic,has widely used in the high-tech field.In industry,the main mining method for weathering crust leached rare earth ore in China is in-situ leaching.The technological process is as follows:Leaching mine with ammonium salt to obtain leachate rich in RE（Ⅲ）;Removing impurity from the rare earth leachate;Enriching the RE（Ⅲ）in precipitation using ammonium bicarbonate or oxalic acid;Getting REO by roasting the precipitation at high temperature;Purifying rare-earth by using acid dissolution.The procedure of the process needs massive reagent and energy,which is a complicated process.Moreover,amounts of acid-solution and Alkaline solution containing in the effluent will make problems in wastewater treatment.Therefore,how to establish a simplify technological procedure becomes a hot research subject in the world to reduce the cost and to rich rare-earth ion from leachate by the one-step way.This dissertation used 3 kinds of acid phosphine extractants,2-Ethylhexyl phosphate mono-2-Ethylhexyl ester（P507）、Bis（2-Ethylhexyl）phosphate（P204）、2-Ethylhexyl Phosphate（Mono-and Di-Ester mixture,P0261）to separate RE from leachate by solvent extraction.Effect of RE ion concentration,aluminum ions concentration,magnesium ions concentration,ammonium ions concentration on the extraction behavior of typical rare-earth ions La（Ⅲ）,Nd（Ⅲ）and Gd（Ⅲ）were researched.Then,the extraction behavior about rare-earth ions in real leachate contains impurity ion from mines using 3kinds of extractants was discussed.The feasibility extraction process for the separation of rare earths from ammonium salt leachate by the one-step method and the effect of impurity ions on the extraction behavior were investigated.The main results are as follows:1.The extraction behavior of rare-earth ions extracted by extractants in the ammonium salt solution without impurities.In the NH₄Cl and NH₄NO₃ solution with 0～0.1 mol·dm^-3 of RE（Ⅲ）,all three tested REs（Ⅲ）can be extracted by three extractants under 1:1 O/A ratio.RE（Ⅲ）extraction rate decreased with the increased of the RE（Ⅲ）concentration when the concentration of RE（Ⅲ）higher than 0.1 mol·dm^-3.RE（Ⅲ）extraction capacity is followed:Gd（Ⅲ）>Nd（Ⅲ）>La（Ⅲ）.While,the maximum extraction capacities of Gd（Ⅲ）extracted by P507,P204,and P0261 are 0.21,0.27,and0.24 mol·dm^-3 respectively.The extraction capacity of RE（Ⅲ）from the NH₄NO₃ solution is higher than that value from the NH₄Cl solution.2.The influence and mechanism of impurity ions aluminum and magnesium on the extraction behavior of rare earth.（1）When Al³⁺concentration exceeding to 1500 mg·dm^-3,the existence of impurity Al³⁺in aqueous solution shows affect on the extraction rate of RE（Ⅲ）under 1:1 O/A ratio and 0.05 mol·dm^-3RE（Ⅲ）concentration.While,the extraction rate of RE（Ⅲ）decreased slowly when Al³⁺concentration increased from 1500 to 1800 mg·dm^-3,and become quickly when Al³⁺concentration increased from 1800 to 3000 mg·dm^-3.In（NH₄）₂SO₄solution with 1800 mg·dm^-3 of Al³⁺,the extraction rates of La（Ⅲ）for the three kinds of extractants（P507,P204,and P0261）are 87.76%,95.71%and 100%,which are the lowest extractant rate along with 0～12.24%largest loss in all ammonium salts solution.In contrast,RE（Ⅲ）extraction loss rates for the three kind of extractants are 0%,0%and1.60%～2.48%in NH₄NO₃ solution with 1800 mg·dm^-3 Al³⁺,which has minimal loss.The lowest extraction rates of La（Ⅲ）are 7.61%,82.41%,and 75.59%while Al³⁺concentration reached 3000 mg·dm^-3.So the high concentration of impurity metal ions has a significant effect on RE（Ⅲ）enriched process.And at the same time,if the concentration of Al³⁺is below 1800 mg·dm^-3,there is less effect on the extraction behavior of RE（Ⅲ）extracted by three extractants.（2）When P0261 used,the existence of Al³⁺will affect the extraction of RE（Ⅲ）under O/A=3:7 with 0.05 mol·dm^-3 RE（Ⅲ）.While the extraction rate of RE（Ⅲ）decreased slowly when Al³⁺concentration increased from 0 to 300 mg·dm^-3,and become quickly when Al³⁺concentration increased 300 to 2000 mg·dm^-3.The best extraction rates of La（Ⅲ）and Nd（Ⅲ）are 69.38%and 74.86%,reducing 8.23%and 9.51%respectively,which can be obtained from the NH₄Cl solution containing 300 mg·dm^-3 of Al³⁺.The lowest extraction rate of Nd（Ⅲ）in（NH₄）₂SO₄ solution is 39.54%,with a 44.65%loss when the concentration of Al³⁺is 1000 mg·dm^-3.The extractant will be emulsified to cause the difficulties of phase separation after the concentration of Al³⁺reached 2000mg·dm^-3.Therefore,to ensure the effect that Al³⁺concentration on extraction behavior of RE（Ⅲ）is acceptable.And the concentration of Al³⁺must be controlled below 300mg·dm^-3under the 3:7 O/A ratio.（3）The La（Ⅲ）,Nd（Ⅲ）and Gd（Ⅲ）extraction rates both can reach 100%when Mg²⁺as impurity ions in the NH₄Cl,（NH₄）₂SO₄ and NH₄NO₃ solution.The water and oil phases well separated after extraction.Therefore,the impurity Mg²⁺at the 0～60 mg/dm³will neither affect the 0.05 mol·dm^-3RE（Ⅲ）extracted completely nor cause the emulsification of the extractants.（4）Effect of NH₄⁺concentration on RE（Ⅲ）extraction behavior is obvious when the concentration of RE（Ⅲ）and metal impurity ions are constants.The extraction rate of RE（Ⅲ）decreases with the increase of NH₄⁺concentration in the extraction process.（5）According to the infrared spectrum analysis of the organic phase containing RE（Ⅲ）,RE（Ⅲ）interacts with two kinds of bonds during the extraction process:1)RE（Ⅲ）exchanges with hydrogen ions of P-OH,P-OH groups consumed,so the peak strength of P-OH weakened or even disappeared;2)RE（Ⅲ）and P=O to form P=O→RE coordination bond.The metal impurity ions will compete with RE（Ⅲ）to interact with P-OH or P=O,which reduces the number of P=O→RE coordination bonds.3.The influence of the stripping-agent type and concentration,impurity ion concentration on the back-extracted of RE（Ⅲ）from the loaded organic phase.（1）The results show that distilled water,2.0 mol·dm^-3 EDTA solution,and 1.0mol·dm^-3 DTPA solution cannot work to RE（Ⅲ）back-extracted.（2）The concentration of HCl above 0.6 mol·dm^-3 can be work on back-extracted of RE（Ⅲ）and metal impurity ions when O/A=1:1.The maximum back-extracted rates of La（Ⅲ）from P507,P204,and P0261 are 100%,94.70%,and 89.07%.The RE（Ⅲ）back-extracted rate increased with the increase of HCl concentration.The existence of Al³⁺and Mg²⁺will prevent the RE（Ⅲ）back-extracted completely.The higher concentration of metal impurity ions,the lower the maximum back-extraction rate of the RE（Ⅲ）.To compare the types of RE（Ⅲ）under the same experimental conditions,the maximum stripping rate follows Gd（Ⅲ）<Nd（Ⅲ）<La（Ⅲ）,which reveals that the easier the RE（Ⅲ）extracted,the more difficult to stripped.To compare the three kinds of extraction,RE（Ⅲ）from the P507 organic phase is the easiest to be back-extracted,that from P204 is the easier,that from P0261 is the most difficult to be back-extracted.4.Research of extraction behavior of RE（Ⅲ）from real leachate by three kinds of extractants and the evaluation of the feasibility of separating and enriching rare earth from leachate by the one-step method.The result of RE（Ⅲ）enriched from the real leachate from Jiangxi area and the south of Yunnan area Weathering crust leached rare earth ore in China showed:the aqueous phase and oil phase are easily separated after extraction both 1:1 and 3:7 O/A ratios.To analyze the extraction rate of RE（Ⅲ）and main metal ions in the aqueous phase under 1:1O/A,REs（Ⅲ）can be extracted completely with 100%extraction rates.At the same time,the extraction rates of Ca²⁺and Mg²⁺are above 95.86%,the extraction rates of Fe³⁺and Al³⁺are located in the range of 73.75%～98.92%and 7.40%～100%.From the extraction behavior of RE in real leachate,the concentration of each major impurity ion from the real leachate is low and there is no obvious effect on the extraction behavior even the process of RE（Ⅲ）enrichment.This dissertation provides an alternative and potential method for the industrial RE（Ⅲ）separation from complex rare earth leachate for weathering crust leached rare earth ore.