Selective electrochemical separation of cations for rare earth element recovery and water softening

Rare earth elements (REEs) play an essential role in our modern society, being critical resources for electronic devices and renewable energy technologies. Efficient platforms for REE recovery and purification are essential to resource security and environmental management. Imparting electrochemical control over an adsorbent system can lead to higher modularity and sustainability, by enabling chemical-free adsorbent regeneration. For the reversible capture and release of REEs, we design and synthesize a redox-copolymer, poly(ferrocenylpropyl methacrylamide-co-methacrylic acid) (P(FPMAm-co-MAA)), that combines an ion-exchange carboxylic group for REE adsorbent, and a redox-active ferrocene moiety for regeneration based on electrochemical control. By molecularly tuning the copolymer composition, efficient adsorption uptake could be achieved alongside electrochemically-regenerated adsorbent reuse. This work provided a proof-of-concept for electrochemically-regenerable ion-exchange copolymers for REE recovery that has to potential to be generalized for various applications of this concept for electrifying ion-exchange systems and cation-selective separations. This thesis will also consider the possibility of applying this ion-exchange redox system to other cation separation applications such as selecting divalent over monovalent separations for the use of water softening as part of this thesis. The thesis also explores the use of electrochemical metal oxide deposition as a method for selectively recovering Cerium over Lanthanum. A growing industrial demand for rare earth elements (REEs) and supply chain crises are making REEs more important. This thesis presents an electrochemical method for separating cerium and lanthanum from wastewater, reducing reliance on chemicals. Taking advantage of the oxidative property of cerium (III) and the difference in solubility of Ce- and La-(hydr)oxide in acids, we were able to selectively recover cerium on the electrode surface while leaving lanthanum in wastewater. From the equivalent of cerium-lanthanum, a successful recovery of cerium with a purity exceeding 90% was obtained by varying the solution conditions and electrical parameters. To validate the methods, an actual iron slag leachate was used as a model waste liquid. Our alternating current system achieved effective removal of cerium with ~90% purity. The proposed method holds promise for enhancing REE recovery through refining the electrochemical system. This system exhibits potential applicability to selective oxidation-based separation processes.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Vapnik, Haley R

Contributors dc:contributor

• Su, Xiao
• Kenis, Paul J. A.
• Yang, Hong
• Sankaran, R. Mohan

• Rare Earth
• Redox-copolymer
• Electrochemical Separation
• Rare Earth Element Extraction
• Separation Processes
• Electrochemical Processes
• Ion Exchange
• Electrodeposition
• Adsorption
• Water Softening

Statement dc:rights

• Copyright 2023 Haley Vapnik

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/122116

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F122116