zwitterionic membranes for rare earth element separations

This research focuses on overcoming limited ability of traditional membranes to separate solutes and ions of similar size and charge, with a specific target of developing membranes capable of REE separations. Membrane filtration, when applicable, offers high energy efficiency, easy scalability, simple operation. Unlike extraction, it does not require the use of solvents. However, the selectivity of today’s commercial membranes is insufficient for many separations, including separating REE ions from each other due to their comparable ionic radii, formal charge, and charge density. The objective of this project is to design membranes with functional nanopores, inspired by biological pores that combine nanoconfinement with selective interactions. This is based on the core premise that selective separation of aqueous solutions of REEs can be achieved in a membrane filtration system if 1) the nanoscale pores are slightly larger than the solute REE molecules; and 2) the pores are lined with zwitterionic (ZI) ligands that exhibit selective and reversible binding to the desired ion. The membranes will be constructed using the self-assembly of copolymers with ZI ligands that can selectively enrich and thus separate REEs. Using this system, selected for its tunability and easy scalability to roll-to-roll systems, the project will aim to link molecular-level insights to experimental thermodynamic, transport, and permeation data—laying the groundwork for the development of new models based on fundamental phenomena. To achieve these objectives, the team will (1) use polymer self-assembly to synthesize new membranes with < 3 nm tunable nanochannels with functional pore chemistries designed for selective interactions with REEs, (2) quantify the effect of nanoconfinement on ligand-REE thermodynamics using computations and experiments, and (3) interrogate REE transport mechanisms in bench scale experiments and simulations. 

polymeric ligands with tunable affinities to enable selective f-element separations

The f-elements (lanthanides and actinides) play a crucial role in several peaceful applications of nuclear technology, including electricity generation, clean energy technologies, and cancer treatment. These elements can be harvested from natural resources through traditional mining approaches or by processing industrial waste sources. In many cases, the lanthanides must be separated from the actinides, like uranium and thorium, before they can be used in the final application. Lanthanides and actinides are currently separated by solvent extraction approaches - a chemical process with large physical and carbon footprints and also generates mixed radioactive waste. Membrane-based separations are an alternative to solvent extraction that can have a smaller physical footprint and minimize the volume of waste generated. Thus, designing membrane materials that can selectively achieve these separations is a key step in improving the sustainability and cost-effectiveness of these processes. 

The goal of this research is to understand the molecular-level phenomena that underpin ion-ion selectivity in copolymer ligands used for f-element separations. This goal will be achieved by synthesizing polymer ligands with controlled compositions to serve as a platform for studying ligand-ligand and ligand-ion interactions. Molecular interactions will be investigated through a combined approach of computational modeling and spectroscopy. Finally, the polymer ligands will be coated on membrane surfaces. These studies will reveal the practical implications of intermolecular interactions on affinity, kinetics, and selectivity. This research will be integrated with a graduate-level radiochemistry course in which students will develop teaching tools to communicate radiochemistry concepts to non-scientific audiences. These tools will be deployed at outreach events that target K-12 students in Cleveland through partnerships with the Leonard Gelfand STEM Center and the Girl Scouts of Northeast Ohio. Finally, a new mentored-teaching experience for graduate students will serve as a practicum to integrate inclusive pedagogical techniques into their teaching portfolios.

rotating packed beds as a tool for process intensification in nuclear fuel reprocessing

Collaborator and Lead PI: Anna Servis (Argonne National Lab)

Nuclear energy is a robust, carbon-neutral source of power which already constitutes 20% of the US electrical grid and is poised to play a key role in mitigating climate change. To date, the US has accumulated over 80,000 metric tons of used nuclear fuel (UNF) from commercial reactors. Recycling UNF is a sustainable way to minimize radioactive waste accumulation in the US: however, current reprocessing schemes are not cost competitive with traditionally mined uranium. One of the major drivers of cost is the capital expenditures associated with shielding large separation processes.

This project explores the use of rotating packed bed contactors to increase separation process efficiency while minimizing the physical footprint of the process units. Prototype rotating packed beds will be applied for gas absorption, solvent extraction, and solid-phase extraction processes relevant to reprocessing nuclear fuel. Undergraduate students on this project received support through the CWRU SOURCE office.

Putting entropy to work: Leveraging the role of water organization in peptide binding events to selectively recover rare earths

Rare-earth elements are critical components in wind turbines, electric vehicles, and smart phones. The United States imports 100% of its rare earth elements from China, where they are mined and purified through time- and energy-intensive processes. This project, a collaboration between Case Western Reserve University, Clemson University, and Pennsylvania State University-University Park, will recover valuable rare earth elements (La, Ce, Nd, Pr) from phosphogypsum—a fertilizer mining waste mixed with radioactive impaired water. The vision for this project is to discover new separation mechanisms, materials, and processes to recover valuable resources (rare earth elements, fertilizers, clean water) from waste streams of the fertilizer industry, paving the way for a sustainable domestic supply of rare earth elements and a sustainable agriculture sector. Doing so will enable the recycling of an otherwise unusable waste stream and treat impaired waters that threaten local water supplies. Simultaneously, the next generation of engineers will be trained to tackle complex environmental engineering problems at the forefront of the food-energy-water nexus. Educational outreach programs will target the general public using the social media app TikTok and engage local high school students in research experiences and mentoring programs. In addition, interactive activities for K-12 outreach events focused on sustainability and water treatment will be developed.

A membrane-based approach to medical isotope purification

Ac-225 is a promising isotope for targeted alpha therapy (TAT, a personalized cancer treatment) that has shown excellent patient outcomes by avoiding whole body doses of radiation while successfully treating otherwise pervasive cancers. To date, all 225Ac used in domestic clinical trials was harvested from legacy nuclear waste at Oak Ridge National Laboratory. This legacy supply of 225Ac is so limited that only 1 in 5,500 people who qualify for the treatment are able to receive it. To produce clinically relevant quantities of 225Ac, 1) nuclear physicists need to develop new production routes in accelerators or cyclotrons and 2) separation scientists need to develop new purification processes. Resin-based extractive chromatography has long been the workhorse for medical isotope purification. While these separation materials perform well in bench-scale purification schemes—they cannot be scaled up for clinically relevant production. In this work, we develop a membrane-based approach using covalently tethered DGA ligands with the goal of reducing separation time from days to seconds.

electrocemical reprocessing of used nuclear fuel: reaction-diffusion modeling of americium

Nuclear energy is a robust, carbon-neutral source of power which already constitutes 20% of the US electrical grid and is poised to play a key role in mitigating climate change. To date, the US has accumulated over 80,000 metric tons of used nuclear fuel (UNF) from commercial reactors. Without a federal policy for long-term disposal of this waste, most UNF is stored locally at the power plants or in temporary storage locations offsite.

Electrochemical pyroprocessing is a promising technique for "upcycling" commercial nuclear waste and advancing the nuclear fuel cycle. It utilizes a series of electrochemical unit operations to convert spent nuclear fuel (e.g. uranium oxide fuels) into metal alloy fuel for next-generation fast neutron breeder (Gen-IV) reactors. A remaining obstacle for pyroprocessing is the lack-of-understanding of the fundamental electrochemical mechanisms that underpin the design of efficient, scalable electrorefiners. In this project, we use a combination of electroanalytical techniques and first-principles diffusion-reaction models to understand the electrochemical behavior of uranium and americium in high temperature, molten salt eutectics. This work is a collaboration with scientists in the Chemical & Fuel Cycle Technologies Division at Argonne National Laboratory and supported through a UNLP fellowship awarded to Bethany Kersten.

Single-molecule Imaging of f-element separations to advance purification design

Using single-molecule microscopy, we will study the fundamental molecular phenomena that occur at the surface of adsorbents during ion-exchange chromatography. This powerful tool will give us a deeper understanding of the interplay between mass transport and reaction kinetics at the interface of ligand-decorated adsorbents and the chromatography mobile phase. Understanding these complexation events at small length- and fast time-scales will resolve phenomena that contribute to chromatographic resolution and inform the future design of separation materials for highly-selective separations.