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theses

The rare earth carbonates in the broadest definition are an important class of insoluble rare earth solids that account for a large amount of the globe’s rare earth mineral resources and are precipitated as precursor materials in the preparation of other rare earth solids in industrial settings. Understanding how to best extract and utilize the rare earths from carbonate sources starts with a fundamental understanding of the properties of the pure rare earth carbonates, namely the normal carbonates (RE2(CO3)3·xH2O) and the hydroxycarbonates (RE(OH)CO3). This would allow us to improve the efficiency and sustainability of industrial rare earth refinement, find new ways to precipitate the carbonates, and enable important technologies that rely upon a stable supply of rare earths. Thus, a comprehensive review of the normal carbonates and hydroxycarbonates was conducted to find the values for their fundamental properties; crystallographic parameters, thermochemical values, thermal decomposition behavior, and aqueous solubility. Trends with respect to increasing atomic number were established based upon the available literature; lattice parameters shrink, are less thermodynamically stable, decompose at successively lower temperatures, and increase in solubility. These property values, namely the thermochemical and aqueous solubility values, may then be utilized in thermodynamic simulations to discover new processes by which rare earth carbonates can be precipitated from aqueous solutions of pure rare earth salts or mixed rare-earth/metal cation salts. We have predicted and verified the precipitation of the normal rare earth carbonates from concentrated aqueous solutions of rare earth chlorides using monoethanolamine (MEA) loaded with carbon dioxide (CO2). This precipitation methodology allows for the facile recovery and separation of the reaction products, the normal carbonate(s) and the water soluble MEA salt, the latter of which has applications in other industries. Finally, a technology/synthesis strategy that offers a low cost, relatively physically robust alternative to optically active components has been explored to demonstrate the necessity of a stable rare earth supply. Optically active, transparent composite materials were created by tuning the refractive index of the polymer matrix (CN551) using ZrO2 nanoparticles to match that of the optically active, micron sized rare earth LYEF phosphor (La0.92Yb0.075Er0.005F3) agglomerates. The nature of the polymer-ceramic composite means that the components are fairly mechanically robust, can load fairly large quantities of optically active components by volume, and are easier to synthesize than their single crystal/polycrystalline counterparts.

ETD_8806

Ph.D.

Includes bibliographical references

by Paul Kim

doi:10.7282/T3DB859D

ETD doctoral

The author owns the copyright to this work.