No description available.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2007. / Includes bibliographical references.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 205-214). Also available via the Internet.

Thesis (Ph. D.)--University of Hong Kong, 1991.

<p>Rare earth elements (REEs) are 15 elements in the lanthanide series plus scandium and yttrium. They are essential for clean energy, defense, and other high-tech industries. Production of high-purity REEs, however, is limited to a few countries, posing great supply risks. Separation of crude REE mixtures into individual REEs is the most challenging step because of similar physical and chemical properties of the REEs. Conventional REE purification processes are based on solvent extraction methods, which are inefficient, require thousands of separator units, and produce large amounts of waste. Chromatography methods are inherently more efficient than solvent extraction methods because of orders of magnitude higher interfacial area per unit volume. Low-cost chromatography sorbents, however, do not have sufficient selectivity for REE purification. </p><p>In this dissertation, ligand-assisted displacement (LAD) chromatography was developed for the separation and purification of REEs from complex mixtures. A ligand, which is selective for REEs, can be added in the mobile phase or immobilized in the sorbent to achieve REE separation and purification. Constant-pattern design methods and a general zone splitting strategy were developed for producing high-purity REEs with high yields and high productivities from complex mixtures. The new methods were tested for producing three high-value REEs, called the magnets REEs, which are the key ingredients in permanent magnets, neodymium (Nd), praseodymium (Pr), and dysprosium (Dy), from waste magnets, bastnäsite concentrates, and monazite concentrates. </p><p>A two-zone LAD was designed and tested for recovering high-purity <a>neodymium (Nd), praseodymium (Pr), and dysprosium (Dy) </a>from waste magnets. Three-zone LAD was designed to recover high purity Nd and Pr from bastnäsite and monazite concentrates. High purity REEs (>99.5%) were produced with high yields (>99%) and high productivities (>100 kg REEs/m³/day). </p><p>Compared to conventional solvent extraction methods, the LAD methods are inherently safer and greener, since they do not require flammable organic solvents or toxic extractants and generate much less waste. LAD methods require only a few zones with a small number of columns. They have more than 10 times higher productivity, or less than10 time the footprint, than solvent extraction. The LAD methods are also versatile and adaptable to a wide range of product purity requirement, feedstock composition, or production scale. </p><p>The LAD methods have the potential to transform the conventional solvent extraction methods with low efficiency and high environmental impact into more efficient and environmentally friendly chromatography methods. They can enable the production of the magnet REEs domestically and provide a driving force to change the current linear path of the REEs, from ores to permanent magnets, to landfills, into a more sustainable circular REE economy.</p>

Polybrominated diphenyl ethers belong to group of brominated flame retardants. Important property of these substances is their ability to reduce flammability or to prevent ignition of many products of daily use, such us televisions, carpets, mattresses and many others. Polybrominated diphenyl ethers however are characterized by high persistence and lipophility, leading to their accumulation in the environment. In recent years, concerns about the effects of organic halogen compounds on human health, suggesting their inclusion in the list of persistent organic pollutants in 2009. These contaminants are capable of long-range transport and accumulation in the environment. Therefore, the presence of polybrominated diphenyl ethers is systematically observed in the abiotic and biotic components of the environment worldwide. Their presence has been demonstrated in areas that are clearly very distant from sources of contamination. This thesis is focused on the use of gas chromatography to assess the level of contamination of selected components of the environment, especially of soil. For these purposes was used method of gas chromatography with electron capture detection mass spectrometry.