Rare Earth Elements: Applications and Instrumental Determination

Abstract

Abstract. The applications of rare earth elements (REE) in various technological fields are reviewed, with emphasis on the importance of the knowledge of the chemical composition of the materials used. Nuclear neutron activation (NNA), atomic absorption spectrometry (AAS), inductively coupled plasma-atomic emission spectrometry (ICP-AES), inductively coupled plasma-mass spectrometry (ICP-MS) and x ray fluorescence spectrometry (XRF) are the most frequently used analytical techniques for determining REE. Complex matrices require the prior separation of the analytes by column chromatography. IntroductionRare earth elements (REE) have aroused growing technological interest over the past few decades [1]. In fact, these elements are frequently included in alloys, catalysts, special glasses, cathode-ray-tubes, electronic ceramics and advanced ceramics to substantially enhance their properties.As a rule, yttrium (Y) is included in the rare earth group. While its electron configuration differs from that of lanthanides, the volume contraction of the latter with increase in their atomic weight justifies inclusion of Y, the atoms of which are very similar in density and volume to those of the lanthanide series. This similarity is also reflected in nature, where REE and Y coexist in many minerals. In fact, rare earths are frequently referred to as "yttria earths".The following sections discuss the most significant technological applications of these elements. MetallurgyThe main use of REE in metallurgy is in the production of steel alloys and microalloys [2].Thus, depositing 0.5-4% of Yon the surface of chromium steel endows the material with a high resistance to increased temperatures and oxidizing gases.The addition of an appropriate amount of a mixture consisting of 60% Ce02, 25% La203, 10% Nd203 and 5% Pr20 3 (Misch metal) to iron stainless steel increases its resistance to oxidation [3]. Also, the presence of small amounts of this mixture favors the formation of sphenoidal graphite in carbon steel, thereby avoiding the release of toxic fumes.

X-ray fluorescence spectrometry

“…7 More targeted reviews included the work of Fitton, 8 who presented an overview of a range of X-ray techniques in geological applications. Fuentes et al 9 considered the role of various techniques, including XRF, in the determination of the REE, emphasizing the need for chromatographic separation in the analysis of complex matrices. Harada and Sakurai 10 described XRF analysis with high energy photons (40± 100 keV) and concluded that this approach had some attractive features, particularly in the determination of high-Z elements in medium-z matrices in environmental and materials applications.…”