Preface

These elements perplex us in our reaches [sic], baffle us in our speculations, and haunt us in our very dreams. They stretch like an unknown sea before us—mocking, mystifying, and murmuring strange revelations and possibilities.

Sir William Crookes (February 16, 1887)

Volume 43 of the Handbook on the Physics and Chemistry of Rare Earths adds five chapters to the series, which span a broad range of subjects, from liquid-crystalline materials to extraction and separation from actinides, recycling technologies, and structural and thermodynamic properties of the elements. The volume is therefore in tune with some of the present concerns about worldwide rare earth supplies. Chapter 254 is devoted to lanthanidomesogens, which are lanthanide complexes with liquid-crystalline properties and/or lanthanide-doped liquid crystals. Lanthanidomesogens combine the exceptional luminescent or magnetic properties of lanthanide ions with the peculiar features of liquid crystals, anisotropy and response to electric and magnetic fields, for instance. The various liquid-crystalline phases are described for each category of compounds, as well as the experimental methods for characterizing them. The less-documented field of actinidomesogens is also covered. Chapter 255 deals with recycling of the rare earths, presently a hot topic in view of the limited availability of some of the critical elements and, also, of the rising environmental cost of extracting and separating rare earths. Reprocessing of permanent magnets, lamp and screen phosphors, nickel metal hydride batteries, and polishing powders is described. Classical technologies such as physical separation, hydrometallurgy, and pyrometallurgy are detailed, along with emerging techniques such as high-gradient magnetic separation. Difficulties inherent to each class of recyclable materials are pointed out and solutions outlined. In a way, Chapter 256 complements the preceding one in critically assessing the potential of ionic liquids as new extractant agents for the separation of lanthanides and of lanthanides from actinides in the context of nuclear waste management. Ionic liquids present advantages over classical solvents in that they are more resistant to radioactive damage, have very low vapor pressure, and are highly tunable with regard to their physical and chemical properties. The review carefully assesses the potential of ionic liquids in liquid–liquid extraction compared to conventional solvents, either as replacement solvents or additives and ends with a mechanistic description of extraction in ionic liquids. Chapter 257 focuses on structural changes induced in lanthanide elements by high hydrostatic pressure (up to about 200 GPa). Physical and chemical properties of the metals are governed by the nature of the 4f electrons, which, in turn, is sensitive to pressure: at high compression, the 4f shell delocalizes and participates in bonding, hence influencing crystal structures. The chapter details element by element the structural studies carried out over the last decade. The volume concludes with a comprehensive and critical compilation of the thermodynamic properties of all rare earth elements. Selected best values for heat capacity, enthalpy and entropy of formation, melting temperature, boiling point, enthalpy and entropy of melting, as well as sublimation enthalpy are listed element by element (Chapter 258). The availability of high-purity metals renders these values quite trustable; however, some areas for which further measurements are required are identified and experiments suggested.

CHAPTER 254. LANTHANIDOMESOGENS

By KOEN BINEMANNS

Katholieke Universiteit Leuven, Belgium

Liquid crystals (LCs) are a state of matter between liquid and solid and the corresponding compounds present at least two melting points, the first corresponding to the transition to the LC cloudy phase and the second being a clarification to pure liquid. Some LCs are seen in living systems; for instance, certain proteins and cell membranes are LCs. Technically, the properties of LCs are exploited in electronic displays (LCDs). Lanthanidomesogens can be defined as liquid-crystalline lanthanide complexes or lanthanide-containing LCs. These compounds combine the unique properties of lanthanide ions, luminescence and paramagnetism, with those of LCs: fluidity, anisotropy, and response to electric and magnetic fields. Lanthanidomesogens allow obtaining materials that emit linearly polarized light or that can be aligned by an external magnetic field. The reader is first introduced to the different types of mesophases and to the experimental methods used for identifying them. A detailed presentation of the different classes of lanthanidomesogens is then given, with the focus on their structural, luminescent, magnetic, and electric properties. The classes of compounds reviewed include Schiff’s base complexes, β-enaminoketonates, β-diketonates, bis(benzimidazolyl)pyridine complexes, phthalocyanine complexes, porphyrin complexes, lanthanide alkanoates, polyoxometalate-surfactant complexes, ionic liquid-crystalline lanthanide complexes, and lyotropic lanthanidomesogens. The chapter concludes with an overview of the less-documented actinide-containing LCs (actinidomesogens).

CHAPTER 255. RECYCLING OF RARE EARTHS FROM SCRAP

By MIKIYA TANAKA, TATSUYA OKI, KAZUYA KOYAMA, HIROKAZU NARITA AND TETSUO OISHI

National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba, Ibaraki, Japan

More and more attention is being paid to the recycling of rare earth elements from industrial scrap in order to help secure the supply of these elements, mostly because of their limited occurrence in minable primary resources and also because of the environmental concerns associated with mining and separation operations. The chapter presents a comprehensive review of the technologies developed for the recycling of rare earth elements from industrial scrap such as permanent magnets, phosphors, metal hydride batteries, and polishing materials. The review will be useful as reference material for researchers and engineers active in rare earth and other metal recycling communities.

The current situation of rare earth supply, the industrial practice of rare earth recycling, and rare earth material flows are first summarized. Studies covering fundamental and practical aspects for each material are then systematically described with respect to (i) pretreatment processes such as crushing and magnetic separation, (ii) hydrometallurgical methods including leaching, precipitation, solvent extraction (classical and advanced), adsorption, and molten salt electrolysis, (iii) pyrometallurgical methods including chemical vapor transport and selective reduction–distillation, and (iv) uses of the recovered products.

Since neodymium magnets are the most important targets of rare earth recycling at present, the corresponding procedures are described in detail along with the problem of removing the large amount of iron (ca. 70%) present in these magnets.

CHAPTER 256. IONIC LIQUIDS: NEW HOPES FOR EFFICIENT LANTHANIDE/ACTINIDE EXTRACTION AND SEPARATION?

By ISABELLE BILLARD

CNRS/IN2P3 and Université de Strasbourg, France

The cost induced by the off-shoring of rare earth mining and separation to China is generating a renewed interest in liquid–liquid extraction methods for these strategic elements. Moreover, recovery of actinides, in particular uranium and plutonium, by liquid–liquid extraction processes from nuclear wastes is at the heart of the development of the nuclear industry. In this context, new methods and new extractants are being intensely sought, and ionic liquids could be an alternative to classical solvents. Ionic liquids are defined as salts with melting temperatures below 100 °C. They are at present of great interest in all fields of chemistry and materials science. Apart from their “green” properties, their resistance to radioactivity and amazing chemical versatility offer a new playground to f-element researchers and engineers.

Following a brief summary of rare earth extraction and liquid–liquid extraction of actinides using molecular solvents, the author reviews and discusses the main properties of ionic liquids that are of importance to liquid–liquid extraction. The various ways in which ionic liquids are used for the extraction/separation of rare earths and actinides either as replacement solvents or as simple additives are then critically reviewed. The focus of the chapter is on the mechanisms of extraction in ionic liquids, and the differences between ionic liquids and molecular solvents are highlighted.

CHAPTER 257. STRUCTURE AND PROPERTIES OF LANTHANIDES AT ULTRA-HIGH PRESSURE

By GOPI K. SAMUDRALA AND YOGESH K. VOHRA

University of Alabama at Birmingham, USA

The nature of 4f electrons in lanthanides and their compounds, either “localized” or “itinerant,” is responsible for most of their physical and chemical properties. Localized states corresponding to tightly bound electron shells or to narrow bands of correlated electrons near the Fermi level are observed for all lanthanides. Pressure has a striking effect on the electronic structure, which, in turn, induces structural changes. For instance, crystal structure transitions from hexagonal closed packed (hcp) → samarium type → double hexagonal closed...