A comprehensive review is presented of the extractive metallurgy of rare earths. The topics covered are: world rare earth resources and production; ore processing and separation of individual rare earths; reduction, refining, and ultrapurification of rare earth elements; methods for rare earth materials analysis; and a selection of the numerous rare earth applications. World rare earth reserves are abundant and would last for well beyond the next century. However, all of the 16 naturally occurring rare earth elements are not equally distributed in the ore minerals. This, compounded with the problems specific to the isolation and recovery of each of the rare earths, sets the stage for an unequal rare earth availability. The close chemical similarity of rare earths looses its importance when divergent physical properties determine the processes for rare earth element reduction and refining. The rare earth metals, alloys, and compounds have been as pure as could be determined. Finally, the commercial...

Extractive Metallurgy of Rare Earths

Summary For many years scientists have considered the rare earth elements as a group of nearly identical elements, and if something was known about one of them it was generally assumed to be the same for all of them. As rare earth scientists continue to work on these metals more exceptions are found each day. Indeed the differences in many cases are greater than those found for elements which lie in the same group, e.g. the alkaline earth metals, or the noble metals - Cu, Ag and Au. The differences due to the divalency of Eu and Yb as compared to the normal trivalent rare earth metals are the most obvious in consideration not only of their physical properties, but also in the method of preparing the pure metals. For the trivalent rare earths there are four major methods used to prepare these 14 metals (sections 1.1.1 to 1.1.3 and 1.2), and within each group there are minor but significant differences. A comparison of the basic physical properties shows significant and widely varying behaviors in their crystal structures (fcc→dhcp→Sm-type→hcp), melting points, (a difference of a factor of two between Ce and Lu), boiling points (the “saw-tooth” characteristic so vividly displayed in fig. 2.10), and vapor pressures (a difference of a factor of one million in the vapor pressures of La and Tm at 1300°C). Even the smooth, regular and systematic variation as implied in the term “lanthanide contraction” is not found in the metallic radii which exhibit anomalies at La, Gd and Lu, and between the light and heavy lanthanides (fig. 2.7a). Although, as noted, wide differences exist in the properties between certain rare earth elements, the systematic variation from one neighboring rare earth to the next (especially for the lanthanides) does occur, and allows one to predict properties which have not been determined experimentally. In making these predictions one should be aware that anomalies can occur and exercise caution. In so doing the application of systematics to rare earth materials can be a powerful tool for understanding their nature and predicting their behaviors in new surroundings.

Chapter 2 Preparation and basic properties of the rare earth metals

The heat capacity of dysprosium has been measured over the range 15 to 300°K, and the thermodynamic functions have been calculated. Dysprosium had previously been found to exhibit two magnetic transitions and corresponding to these we have observed two maxima in the heat capacity, one at 174°K and a second at 83.5°K. Only the lower peak shows a dependence on the thermal history of the sample and this dependence was investigated. A correlation of the various contributions to the entropy at room temperature indicates that the magnetic contribution is R ln (2J+1). The value of S0298.16 is 17.87 cal (°K)—1 (g atom)—1.

Heat Capacity of Dysprosium from 15 to 300°K

The heat capacity of terbium has been measured in the temperature range 15 to 350°K. A lambda anomaly has been observed with the peak at 227.7°K. There is, in addition, an anomalous region near 220°K. The heat capacity in this region depends on the thermal history of the sample. The value of the entropy at 273.16°K is 17.50 cal/ (g atom‐deg) in agreement with the value predicted on the assumption that at room temperature the 4f electrons have the same configuration as in the free tripositive ion.

Heat Capacity of Terbium from 15 to 350°K

Chapter 45 Rare earth fluorides

http://jes.ecsdl.org/content/100/10/442.full.pdf

A. H. Daane

Papers

Preparation of Yttrium and Some Heavy Rare Earth Metals