CAREER: The solution structure of lanthanide-extractant complexes across liquid-liquid interfaces

职业：跨液-液界面的镧系元素萃取剂配合物的溶液结构

• 批准号: 2041914
• 负责人: David Cantu
• 金额: $ 55万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2041914&HistoricalAwards=false
• 关键词: CAREER; solution; structure; lanthanide; extractant

Rare earth elements, including lanthanides, are vital to clean energy, defense, and consumer technologies, such as smart phones, wind turbines, lasers, guidance systems, and medical contrast agents. For most applications, specific lanthanides are needed in near-purified form. The purification process requires separating the elements from each other. The separation is particularly challenging due to the chemical similarity of the rare earth elements and thus requires substantial amounts of solvent and energy. Efficient rare earth separation processes are needed to ensure a reliable, sustainable supply of rare earth elements for the United States. Liquid-liquid, or solvent, extraction is the separation process by which most rare earth elements are obtained. The effectiveness of solvent extraction to separate rare earth elements lies in the selectivity of extractants, or ligands, to bind a particular rare earth element. Enhancing ligand selectivity and extraction capacity for particular lanthanides will improve the efficiency of the separation. This project seeks to resolve the structure of lanthanide-ligand complexes in solution and determine the mechanism by which ligands transport lanthanides from the aqueous to organic phase in solvent extraction. The connection between molecular structures and mechanisms at aqueous-organic interfaces with the extent and rate of rare earth solvent extraction will be determined. This CAREER project will incorporate rare earth separation research into an undergraduate chemical engineering separation course and will expand efforts to promote chemical engineering in Nevada high schools. The educational and outreach components of the project aim to bridge graduate student research and chemical separations instruction, introduce undergraduate students to the concepts of rare earth separations, and strengthen the chemical engineering workforce development pipeline in support of Nevada’s continued expansion toward technology-based employment.With joint support from the Interfacial Engineering program and the Established Program to Stimulate Competitive Research (EPSCoR), this project intends to generate fundamental knowledge to determine the connection between lanthanide-ligand complex structures in solution with their relative aqueous-organic solubility (separation extent), as well as to resolve how ligand structure affects the transport mechanisms of lanthanide ions (separation rate). The selectivity of most current lanthanide extractants can be improved because it is based on size exclusion alone, and lanthanide ion size differences due to contraction are small. This project will investigate multi-acidic ligands as lanthanide-specific extractants, leveraging their tunable binding strength arising from multiple protonation sites. A combination of ab initio molecular dynamics simulations with spectroscopy measurements will resolve lanthanide-ligand complex structures in aqueous and organic phases at varying protonation states. Binding specificity is necessary but not sufficient for effective lanthanide extraction; therefore, the transport of lanthanide ions across the aqueous-organic interfaces will be investigated as well. Classical molecular dynamics simulations with rare event simulation techniques will generate free energy profiles of lanthanide-ligand complex transport across aqueous-organic interfaces, which will be used to determine relative aqueous-organic solubilities and mechanisms of ligand-mediated lanthanide transport across aqueous-organic interfaces. Extraction measurements will be performed as well to verify predictions. Structural, mechanistic knowledge of lanthanide solvent extraction is limited, especially for multi-acidic ligands whose protonation state change with acidity. It is expected that the work in this project will identify the molecular characteristics that could make multi-acidic ligands selectively bind particular lanthanide ions and transport them to the organic phase. More broadly, structures in solution are understudied in liquid-liquid separations, and structural and mechanistic insights can lead to fundamentally understanding structure-function connections in solvent extraction, an important unit operation with a need for higher selectivity to improve efficiency and sustainability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

稀土元素，包括镧系元素，对清洁能源，国防和消费技术至关重要，如智能手机，风力涡轮机，激光，制导系统和医用造影剂。对于大多数应用，需要接近纯化形式的特定镧系元素。净化过程需要将元素彼此分离。由于稀土元素的化学相似性，分离特别具有挑战性，因此需要大量的溶剂和能量。需要高效的稀土分离工艺，以确保为美国提供可靠、可持续的稀土元素供应。液-液或溶剂萃取是获得大多数稀土元素的分离过程。溶剂萃取分离稀土元素的有效性在于萃取剂或配体结合特定稀土元素的选择性。提高特定镧系元素的配体选择性和萃取能力将提高分离效率。本研究旨在解析溶液中镧系元素-配体络合物的结构，并确定在溶剂萃取中配体将镧系元素从水相转移到有机相的机理。将确定水-有机界面处的分子结构和机理与稀土溶剂萃取的程度和速率之间的联系。这个CAREER项目将把稀土分离研究纳入本科化学工程分离课程，并将扩大在内华达州高中推广化学工程的努力。该项目的教育和推广部分旨在连接研究生研究和化学分离教学，向本科生介绍稀土分离的概念，并加强化学工程劳动力发展管道，以支持内华达州继续向技术型就业扩张。在界面工程计划和刺激竞争力研究既定计划（EPSCoR）的联合支持下，该项目旨在产生基础知识，以确定溶液中镧系元素-配体络合物结构与其相对水-有机溶解度（分离程度）之间的联系，以及解决配体结构如何影响镧系离子的传输机制（分离速率）。大多数当前镧系元素萃取剂的选择性可以得到改善，因为它仅基于尺寸排阻，并且由于收缩导致的镧系元素离子尺寸差异很小。本项目将研究多酸性配体作为镧系元素特异性萃取剂，利用其多个质子化位点产生的可调结合强度。从头算分子动力学模拟与光谱测量相结合，将解决镧系元素-配体配合物的结构在水相和有机相在不同的质子化状态。结合特异性是必要的，但不足以有效的镧系元素提取，因此，运输的镧系元素离子通过水-有机界面也将进行研究。经典的分子动力学模拟与稀有事件模拟技术将产生自由能的镧系元素-配体配合物的跨水-有机界面的传输，这将被用来确定相对水-有机溶解度和配体介导的镧系元素跨水-有机界面的传输机制。还将进行浸提测量，以验证预测。对于镧系元素的萃取，特别是对于质子化状态随酸度变化的多酸配体的萃取，其结构和机理的认识是有限的。预计本项目的工作将确定能够使多酸配体选择性地结合特定镧系离子并将其输送到有机相的分子特征。更广泛地说，溶液中的结构在液-液分离中研究不足，结构和机理的见解可以从根本上理解溶剂萃取中的结构-功能联系，这是一个重要的单元操作，需要更高的选择性，以提高效率和可持续性。该奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的支持影响审查标准。

项目成果

Analysis of the First Ion Coordination Sphere: A Toolkit to Analyze the Coordination Sphere of Ions

• DOI: 10.1021/acs.jcim.3c00294
• 发表时间: 2023-04
• 期刊: Journal of chemical information and modeling
• 影响因子: 5.6
• 作者: Stuart J. McElhany;Thomas J. Summers;Richard C. Shiery;David C. Cantu