{"title":"Solvent extraction systems for selective isolation of light rare earth elements with high selectivity for Sm and La","authors":"Hossein Salehi, Samane Maroufi, Rasoul Khayyam Nekouei, Veena Sahajwalla","doi":"10.1007/s12598-024-03019-7","DOIUrl":null,"url":null,"abstract":"<div><p>This study details a comprehensive approach focusing on the effective separation of light rare earth elements (REEs) via solvent extraction technique. A stock solution containing lanthanum, cerium, neodymium, praseodymium, and samarium was prepared by dissolving their pure mixed oxide (reclaimed from spent Ni-MH batteries) in a diluted HCl solution. Key extractants, including bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272), Cyanex 572, trialkylphosphine oxide (Cyanex 923), and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC 88A), along with tributyl phosphate (TBP) as a phase modifier, were utilized to form organic systems. The extraction behavior and separability of these systems at various pH levels as well as their extraction mechanisms were investigated. The results demonstrated a direct relationship between the extraction trend and the experimental pH value, with enhanced selectivity when TBP was added. Notably, Nd and Pr exhibited similar extraction behaviors, with minor deviations from Ce, making their separation difficult to achieve. Sm extraction followed a distinct trend, allowing for its separation from other elements at pH ≤ 2. In contrast, La exhibited a low affinity for coordination with extractants when pH was ≤ 3.5, facilitating the separation of other elements from La, which could then be isolated in the raffinate. Among the studied organic systems, combinations of Cyanex 572 and PC 88A with TBP demonstrated superior performance in element separation. Optimum separation factors were calculated with <i>β</i><sub>Ce/La</sub> = 12, <i>β</i><sub>Nd/La</sub> = 87, <i>β</i><sub>Pr/La</sub> = 127, and <i>β</i><sub>Sm/La</sub> = 3191 for the former, and <i>β</i><sub>Sm/Ce</sub> = 54, <i>β</i><sub>Sm/Nd</sub> = 20, and <i>β</i><sub>Sm/Pr</sub> = 14 for the latter. These findings provide valuable insights for selecting extraction systems and designing experiments for the effective solvent extraction separation of light REEs from their mixture.</p><h3>Graphic Abstract</h3><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":749,"journal":{"name":"Rare Metals","volume":"44 3","pages":"2071 - 2084"},"PeriodicalIF":9.6000,"publicationDate":"2025-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s12598-024-03019-7.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Rare Metals","FirstCategoryId":"88","ListUrlMain":"https://link.springer.com/article/10.1007/s12598-024-03019-7","RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MATERIALS SCIENCE, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
This study details a comprehensive approach focusing on the effective separation of light rare earth elements (REEs) via solvent extraction technique. A stock solution containing lanthanum, cerium, neodymium, praseodymium, and samarium was prepared by dissolving their pure mixed oxide (reclaimed from spent Ni-MH batteries) in a diluted HCl solution. Key extractants, including bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272), Cyanex 572, trialkylphosphine oxide (Cyanex 923), and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC 88A), along with tributyl phosphate (TBP) as a phase modifier, were utilized to form organic systems. The extraction behavior and separability of these systems at various pH levels as well as their extraction mechanisms were investigated. The results demonstrated a direct relationship between the extraction trend and the experimental pH value, with enhanced selectivity when TBP was added. Notably, Nd and Pr exhibited similar extraction behaviors, with minor deviations from Ce, making their separation difficult to achieve. Sm extraction followed a distinct trend, allowing for its separation from other elements at pH ≤ 2. In contrast, La exhibited a low affinity for coordination with extractants when pH was ≤ 3.5, facilitating the separation of other elements from La, which could then be isolated in the raffinate. Among the studied organic systems, combinations of Cyanex 572 and PC 88A with TBP demonstrated superior performance in element separation. Optimum separation factors were calculated with βCe/La = 12, βNd/La = 87, βPr/La = 127, and βSm/La = 3191 for the former, and βSm/Ce = 54, βSm/Nd = 20, and βSm/Pr = 14 for the latter. These findings provide valuable insights for selecting extraction systems and designing experiments for the effective solvent extraction separation of light REEs from their mixture.
期刊介绍：
Rare Metals is a monthly peer-reviewed journal published by the Nonferrous Metals Society of China. It serves as a platform for engineers and scientists to communicate and disseminate original research articles in the field of rare metals. The journal focuses on a wide range of topics including metallurgy, processing, and determination of rare metals. Additionally, it showcases the application of rare metals in advanced materials such as superconductors, semiconductors, composites, and ceramics.
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