Development of novel chitosan-based ion-imprinted polymers for selective recovery of rare earth elements from mine waste
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[EMBARGOED UNTIL 05/01/2026] This dissertation investigates the development of alkali/urea dissolved chitosan hydrogels (AUCH) for the selective recovery of critical rare earth elements (REEs) from mine waste. Through a systematic approach advancing from single-element to multi-element systems, the research demonstrates exceptional selectivity, high adsorption capacity, and robust performance across diverse environmental conditions. First, the AUCH platform was established by optimizing crosslinking strategies with glutaraldehyde (AUCH-G) and 1,2,7,8-diepoxyoctane (AUCH-D), achieving neodymium adsorption capacities up to 174.7 mg/g with maintained selectivity across pH 2-10. The research then expanded to target heavy REEs, with AUCH-D achieving maximal capacities of 162.53 mg/g for Tb(III) and 132.05 mg/g for Dy(III), revealing differences in adsorption mechanisms through thermodynamic and kinetic analyses. These investigations demonstrated that despite more favorable thermodynamic parameters for Dy(III), Tb(III) exhibited superior adsorption performance, highlighting the complex interplay between ionic radius, coordination geometry, and entropy-driven binding. Further advancing the technology, the study demonstrated ratio-controlled extraction of adjacent lanthanides through dualtemplate imprinting, maintaining specific Nd ratios (1:1, 2:1, and 4:1) that mirror commercially relevant didymium compositions. Thermodynamic analyses revealed consistently lower energy requirements for Nd(III) binding compared to Pr(III), providing mechanistic insights into selective adsorption. Finally, optimal regeneration protocols were established through comparative evaluation of mineral acids and chelating agents, where 0.05M EDTA achieved optimal balance between elution efficiency and material preservation, with degradation rather than binding site saturation identified as the primary mechanism of capacity loss. Collectively, this work advances fundamental understanding of selective REE binding mechanisms while demonstrating practical applications for critical materials recovery from secondary resources.
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Ph. D.