The Lanthanides, Rare Earth Elements

Abstract

The lanthanides (or lanthanons) are a group of 15 elements of atomic numbers from 57 through 71 in which scandium (atomic number 21) and yttrium (atomic number 39) are sometimes included. The lanthanide series proper is that group of chemical elements that follow lanthanum in its group IIIB column position of the periodic table. Their distinguishing atomic feature is that they fill the 4 f electronic subshell. Actually, only those elements with atomic numbers 58–71 are lanthanides. Most chemists also include lanthanum in the series because, although it does not fill the 4 f subshell, its properties are very much like those of the lanthanides. The elements scandium and yttrium are also known as the “rare earths” because they were originally discovered together with the lanthanides in rare minerals and isolated as oxides, or “earths.” Collectively, these metals are also called rare earth elements (REEs). In comparison with many other elements, however, the rare earths are not really rare, except for promethium, which has only radioactive isotopes. Yttrium, lanthanum, cerium, and neodymium are all more abundant than lead in the earth's crust. All except promethium, which probably does not occur in nature, are more abundant than cadmium. The relative abundance and atomic numbers are provided. The more common lanthanide compounds are listed in Section 1. Scandium is a silvery white metallic chemical element, the first member of the first transition‐metal series in the periodic table. The name is derived from Scandinavia, where the element was discovered in the minerals euxenite and gadolinite. In 1876, L. F. Nilson prepared about 2 g of high purity scandium oxide. It was subsequently established that scandium corresponds to the element “ekaboron,” predicted by Mendeleyev on the basis of a gap in the periodic table. Scandium occurs in small quantities in more than 800 minerals and causes the blue color of aquamarine beryl. Yttrium is one of the four chemical elements (the others are erbium, terbium, and ytterbium) named after Ytterby, a village in Sweden that is rich in unusual minerals and rare earths. Yttrium is a metal with a silvery luster and properties closely resembling those of rare earth metals. It is the first member of the second series of transition metals. Yttrium is found in several minerals and is produced primarily from the ore material xenotime. Lanthanum is a white, malleable metal; it is the first member of the third series of transition metals, and the first of the rare earths. Lanthanum is found with other lanthanides in the ore minerals monazite, bastnaesite, and xenotime, and in other minerals. It was discovered in 1839 by the Swedish chemist Carl G. Mosander. Scientists have created many radioactive isotopes of lanthanum.

Gadolinium as an Emerging Microcontaminant in Water Resources: Threats and Opportunities

“…Generally, the mobility and bioavailability of LAs are governed by several factors, such as temperature, pH, as well as the concentration and type of organic and inorganic ligands [32,63]. According to Wells and Wells [150], nitrates, chlorides, and sulfates of LAs are soluble; however, their hydroxides, carbonates, and phosphates are insoluble. In river and estuarine waters, it is documented that pH, colloids, and salinity control the LA fractionation [32].…”

Urban mining as a contribution to the resource strategy of the Canton of Zurich

“…After oral uptake the LREE (smaller atomic numbers Z and larger atomic radius r) are more soluble and are favourably deposited in the liver, whereas the heavier (higher Z and smaller r) are enriched more in the bones due to the similarity of their r with that of the bivalent calcium-ion of the bone structure (U.S. EPA, 2012). Chlorides were found to be about half as toxic as nitrates (Wells and Wells, 2012), Sm-nitrate having the highest overall toxicity with a s-RFD of 0.00002 mg/kg/day as shown in Table 2. For REE-chlorides, Lu seems to have the highest toxicity with a s-RFD of 0.0009 mg/kg/day, while Nd, Pr-and Sm-chlorides have the lowest with a s-RFD of 0.5 mg/kg/day.…”

“…(Sneller et al, 2000). Toxicological studies have shown acute and chronic effects on animals, which strongly depend on the form and rate of admission as well as the concentration (Wells and Wells, 2012). For oral uptake Table 2 provides an overview of human health threshold values of the oral Reference Dose for life-long daily uptake (RfD) and for inhalation (RfC).…”

“…For REE-chlorides, Lu seems to have the highest toxicity with a s-RFD of 0.0009 mg/kg/day, while Nd, Pr-and Sm-chlorides have the lowest with a s-RFD of 0.5 mg/kg/day. The mean lethal dose LD 50 of chlorides for mice is about 300-600 mg/kg, whereas a daily uptake of 0.6 mg/kg is assumed to be allowable (Wells and Wells, 2012).…”

“…The ACGIH (American Conference of Governmental Industrial Hygienists) has defined an inhalation-threshold of 1 mg/m 3 for Y, which is assumed to be sensible for all REE (Wells and Wells, 2012).…”