Recycling and separation of critical elements using porous materials

锂、稀土元素、钴和铝等关键金属元素是不可再生的资源，对现代技术至关重要。例如，锂用于电子设备和电动汽车的电池，稀土用于喷气发动机和金属的防腐蚀涂层。一些关键元素，如锂和稀土，在美国并不天然丰富，其供应和成本可能会受到地缘政治因素的影响。了解如何分离和纯化关键元素将通过国内关键元素的开采和回收来促进国家的经济和安全。然而，通过现有方法实现高纯度的关键金属元素的分离是具有挑战性的。微孔钛硅酸盐材料具有独特的结构特征，适用于分离高纯度的关键金属元素。因此，本研究计画将利用一套实验与计算方法，设计微孔钛矽酸盐材料，以高选择性地分离关键元素。本研究项目的目的是通过连续离子交换/连续离子色谱（CIX/CIC），阐明微孔钛硅酸盐中离子吸附位点的空间排列如何促进具有非常相似性质的金属离子的高分辨率分离。钛硅酸盐在其微孔内具有长程有序的离子吸附位点，其中微孔是具有与水合金属离子类似的尺寸的通道。通过材料设计，这些有序的离子吸附位点可以提供对金属离子选择性的可调节性。研究人员将使用一套针对不同长度尺度（离子吸附位点、晶胞和颗粒尺度）的实验和计算方法来设计分离稀土和其他金属离子的材料。该项目将首先关注钛硅酸盐孔隙内的精细结构特征，如带电位点密度和分布，与稀土离子吸附和分离性能的关系。将合成和模拟具有不同带电位点密度的结构。离子吸附平衡常数将通过实验测量以及使用密度泛函理论计算来计算。将开发描述微孔内金属离子水合和脱水的计算方法。这些努力将导致分离稀土阳离子的结构特征的建议。然后，该项目将重点评估材料结构（化学成分，孔径和孔隙拓扑结构）对金属离子迁移速率和活化能的影响。这一结果将通过研究离子吸附和迁移的微孔材料的各种结构（钛硅酸盐，粘土和沸石）使用实验和计算方法。最后，该项目将侧重于确定粒度和形态对稀土吸附能力，强度和动力学的影响，这将是制备这些材料用于实际应用的重要一步。该项目将为设计用于分离化学性质相似的金属离子（如分离稀土元素或分离锂和钠）的微孔材料提供指导，也可以根据原料成分和杂质进行定制。该奖项反映了NSF的法定使命，通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Critical metallic elements, such as lithium, rare-earth elements (REEs), cobalt, and aluminum, are non-renewable resources that are vital to modern technologies. For example, lithium is used in batteries for electronic devices and electric vehicles, and REEs are used in jet engines and anti-corrosion coatings for metals. Some critical elements, such as lithium and REEs, are not naturally abundant within the United States, and their supply and cost can be affected by shifting geopolitical factors. Understanding how critical elements can be separated and purified will advance the Nation's economy and security through advancements in mining and recycling of domestic critical elements. However, it is challenging to achieve the separation of critical metal elements with high purities by existing methods. Microporous titanosilicate materials contain unique structural features that are suitable for separating critical metal elements with high purities. Therefore, this research project will use a set of experimental and computational methods to design microporous titanosilicate materials for the highly selective separation of critical elements. The project also involves training students of various educational levels as well as outreach activities that disseminate the research findings to a broader audience from diverse backgrounds.The goal of this research project is to elucidate how the spatial arrangements of ion-adsorption sites in microporous titanosilicates facilitate high-resolution separation of metal ions with very similar properties by continuous ion exchange/continuous ion chromatography (CIX/CIC). Titanosilicates have long-range order ion-adsorption sites inside their micropores, where the micropores are channels with sizes similar to hydrated metal ions. Through material design, these ordered ion-adsorption sites could offer tunability toward metal ion selectivity. The investigators will use a set of experimental and computational methods for different length scales (ion adsorption site, unit cell, and particle scales) to design materials for the separation of REEs and other metal ions. The project will first focus on relating the fine structural features inside titanosilicate pores, such as charged site density and distribution, to REE ion adsorption and separation performance. Structures with different charged site densities will be synthesized and simulated. Ion adsorption equilibrium constants will be measured experimentally as well as computed using density functional theory calculations. Computational methods describing the hydration and dehydration of metal ions inside micropores will be developed. These efforts will lead to recommendations for structural features for separating REE cations. The project will then focus on evaluating the effects of material structure (chemical composition, pore size, and pore topology) on metal ion migration rates and activation energies. This outcome will be achieved by studying ion adsorption and migration on microporous materials of various structures (titanosilicates, clays, and zeolites) using experimental and computational methods. Finally, the project will focus on determining the effect of particle size and morphology on REE adsorption capacity, strength, and kinetics, which will be an important step in preparing these materials for practical applications. This project will provide guidelines for designing microporous materials for separating chemically similar metal ions (such as separating REEs from each other or separating lithium and sodium), which can also be customized based on the feedstock composition and impurities.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.