The remaining percentage of four LREEs in the aqueous phase with change in the number of extraction stages (0.5M PC88A, extraction OA ratio = 4, four stages). The purity of four LREEs in the aqueous phase with changing the number of extraction stages (0.5M PC88A, extraction OA ratio = 4, four stages). The remaining percentage of four LREEs in the organic phase with change of the number of phases in the first stripping (0.10 M HCl, stripping OA ratio = 7/4, three phases).
Purity of the four LREEs in the organic phase by changing the number of stages in the first stripping (0.10 M HCl, stripping ratio OA = 7/4, three stages). The remaining percentage of the four LREEs in the organic phase by changing the number of stages in the second removal (0.15 M HCl, OA removal ratio = 3/2, seven stages).
Introduction
Research background
This similarity of electronic configurations leads to the same chemical behavior for all REEs (Zhang et al., 2016). Several traditional separation methods have been adopted, including solvent extraction, ion exchange, fractional precipitation, fractional crystallization, selective oxidation, selective reduction, gravity separation and magnetic separation (Voncken, 2016; Jordens et al., 2014; Lucas et al., 2015). Hydrogen storage, nickel lanthanide battery electrodes, optical lenses, phosphors, liquid cracking catalyst Cerium polishing powders, phosphors, liquid cracking catalyst Praseodymium magnets, lasers, X-ray scintillators.
These compounds are transferred from one liquid solvent to another, generally from the aqueous phase to the organic phase. Furthermore, the specification of the final product has one of the biggest impacts on the decision on the solvent extraction method (Rane et al., 2006).
Recent studies
Although there are a number of studies on the solvent extraction of REEs, only a few papers deal with the next process, stripping (Wang et al., 2011; Tian et al., 2013; Chen et al., in press; Nasab et al. al ., 2011). This process consisted of repeating solvent extraction and stripping twice with D2EHPA diluted with kerosene. In this study, McCabe-Thiele diagrams for La and Nd stripping were drawn and it was concluded that there is a high OA ratio for removing co-extracted material.
2015) studied a co-extraction and selective purification method for the separation of Pr and Nd with 50% saponified 0.15 M PC88A as the extractant and pure Nd solution as the purification fluid. Considering the fact that many researchers are conducting experiments on the separation of other metals by selective removal and the results are often used in real industrial processes to increase the separation efficiency, the selective removal of LREE should be investigated (Paria and Sarma). , 2000; Taghizadeh et al., 2010.
Research purpose
Based on the optimization results, a semi-continuous counter-current process was established for the separation of La, Ce/Pr and Nd using selective stripping. In the first step, four extraction stages were tried to separate La, selectively extracting Ce, Pr and Nd. Finally, seven stages of selective stripping were performed to retain high-purity Nd in the organic phase while stripping Ce and Pr in the aqueous phase.
Background theory
The equilibrium isotherm can be drawn by mixing two phases in different volume ratios of OA. The slope of the operating line describes the flow ratio of the organic phase to that of the aqueous phase, which is needed to achieve a desired separation (Mular et al., 2002). By changing the slope of the operating line, selective extraction of a metal ion can be achieved (Rousseau, 1987).
Because the equilibrium constant can be used to determine the spontaneity of a specific reaction and maximize the yield of product, it is important to determine the stoichiometry and equilibrium constant of the extraction reaction. Additionally, a linear line can be made when log D is plotted against extractant concentration at a constant pH.
Experimental set-up and procedures
Reagents and apparatus
Solvent extraction and stripping process
Batch counter-current extraction and stripping
Results and discussion
Optimization of stripping in the two-LREE-component
- La and Ce system
- Effect of extractant type and concentration
- Slope analysis method
- Ce and Pr system
- Effect of extractant type and concentration
- Effect of Ce/Pr concentration ratio in the feed solution
- Effect of hydrochloric acid concentration of strip
- Effect of organic-phase-to-strip-liquor volumetric ratio
- Slope analysis method
- Pr and Nd system
- Effect of extractant type and concentration
- Effect of Ce/Pr concentration ratio in the feed solution
- Effect of hydrochloric acid concentration of strip
- Effect of organic-phase-to-strip-liquor volumetric ratio
- Slope analysis method
To determine the impact of the concentration ratio of two REEs on the stripping behavior, several experiments were performed with varying concentration ratios of La and Ce in the feed solution (Figures 9, 10). The stripping percentage of La and Ce with change of HCl concentration (La/Ce concentration ratio = 1, stripping OA ratio = 1). As the volumetric ratio of the organic phase to the stripping liquid increased, the stripping percentage of two LREEs decreased significantly due to the small amount of hydrogen ions in the stripping liquid.
Figure 16 shows the relationship between pH and D of La and Ce in the removal phase. The concentration ratio of Ce to Pr was varied from 1 to 4 at a fixed total concentration of Ce and Pr to investigate the relationship between the concentration ratio of the two LREEs in the feed solution and the removal percentage. As shown in Figures 18 and 19, there was little difference in the removal behavior of the two LREEs.
Therefore, the concentration ratio of Ce and Pr was determined to be 1 by considering two factors - the existing ratio in the leachate and the highest SF in the stripping stage. Percentage of Ce and Pr stripping with changing REE concentration ratio (0.05M HCl, OA stripping ratio = 1). Percent stripping of Ce and Pr with varying HCl concentration (Ce/Pr concentration ratio = 1, OA stripping ratio = 1).
As shown in the diagram, separation of Ce and Pr can be achieved with at least six countercurrent stripping stages at an OA ratio of 5:3. Figures 27 and 28 show the effect of the Pr/Nd concentration ratio in the nutrient solution on the stripping behavior of two LREEs with 0.5M PC88A and 0.05M HCl at an OA ratio of 1. Therefore, the optimal concentration of HCl in Pr and the system Nd was determined to be 0.15M.
Percent stripping of Pr and Nd with varying HCl concentration (Pr/Nd concentration ratio = 1, OA stripping ratio = 1). In Figure 33, a McCabe-Thiele diagram plots the concentration of Pr or Nd in the aqueous phase versus that in the organic phase.
Semi-continuous process using selective stripping of four
- Optimization
- Effect of extractant type and concentration
- Effect of organic-phase-to-feed-solution volumetric
- Effect of hydrochloric acid concentration of strip
- Slope analysis method
- Semi-continuous counter-current process
- The optimum conditions for extraction and selective
- The experimental results of a semi-continuous counter-
The extraction percentages of all LREEs in the four-component system were lower than those in the two-component systems. This is because a larger proportion of LREEs in the aqueous phase can complex with extractant if the OA ratio is higher. The purpose of the extraction stage is to keep La in the aqueous phase and extract only other LREEs.
This means that the percentage of REEs that form chloride complexes in the aqueous phase has increased in this system. In the extraction, high purity and yield of La was predicted to remain in the aqueous phase through a four-step extraction at an OA ratio of 4. Finally, Ce and Pr bands with 0.15 M HCl and high purity of Nd remain in the organic phase.
The main objective of the extraction step is to keep La in the aqueous phase with high purity while extracting most of the other three LREEs. The change of purity and residual percentage of LREEs in the aqueous phase with the number of stages is represented in Figures 42 and 43. Figures 44 and 45 plot the variation of residual percentage and purity of LREEs in the water phase against the number of stages.
Seven steps of stripping at OA ratio of 3:2 with 0.15 M HCl were necessary to keep only Nd in the organic phase. Figures 46 and 47 show the remaining percentage and purity of Nd in the organic phase. The purity of four LREEs in the organic phase with changing the number of steps in the second stripping (0.15 M HCl, stripping OA ratio = 3/2, seven steps).
Conclusion
The difference in the stoichiometric number of H+ ions participating in the stripping reaction can be explained by the HSAB theory. To completely remove the extracted La in the organic phase, the first selective stripping step was applied, three phases at an OA ratio of 7:4 with 0.10 M HCl. Seven stages of stripping at an OA ratio of 3:2 with 0.15 M HCl were followed to strip the extracted Ce and Pr, maintaining the high purity of Nd in the organic phase.
향후에는 다른 REE의 선택적 제거와 박리 반응 메커니즘에 대한 연구가 필요합니다. 이에 본 연구에서는 선택적 탈거를 통한 새로운 경희토류 분리 공정을 개발하였다. 네 가지 유형의 경희토류 원소에 대한 선택적 박리를 도입하기 전에 주기율표에서 서로 옆에 위치한 두 가지 경희토류 조합에 대해 박리 공정의 최적화가 수행되었습니다.
경희토류와 추출제 사이의 복잡한 구조를 파악하고 추출 및 탈거 과정에서 화학량론을 조사하기 위해 구배 분석법을 적용했습니다. 결과적으로 경희토류 비료는 유기상에 염화물 이온을 포함합니다. 동일한 변수에 대해 4개의 경희토류 시스템에서 박리 공정의 최적화 조건을 결정하기 위한 실험을 수행하고 그 결과를 2개의 경희토류 시스템에서 얻은 값과 비교했습니다.
또한, 선택적 박리를 위한 역류 박리 공정에서 단위수와 유기상과 수상의 부피비를 결정하기 위해 McCabe-Thiele 방법을 사용하였다. 최적화 실험 결과와 McCabe-Thiele 다이어그램을 기반으로 선택적 스트리핑을 이용한 반연속 역류 공정을 4가지 경희토류 시스템에 도입했습니다. 본 연구에서는 경희토류 시스템에서 스트리핑을 위한 최적의 조건을 찾아내고 선택적 스트리핑을 이용한 새로운 반연속 역류 공정을 개발했습니다.
