Chapter 73 Chapter 73
1. The beginnings: yttrium and cerium
In tables representing the periodic system the element lanthanum (La) having the atomic number 57 is followed in most cases immediately by element 72, hafnium (Hf). The elements in between, i.e. cerium (Ce, 58), praseodymium (Pr, 59), neo- dymium "(Nd, 60), p r o m e t h i u m (Pm, 61), s a m a r i u m (Sm, 62), europium (Eu, 63), gadolinium (Gd, 64), terbium (Tb, 65), dysprosium (Dy, 66), holmium (Ho, 67), erbium (Er, 68), thulium (Tm, 69), ytterbium (Yb, 70) and lutetium (Lu, 71), are listed separately, usually somewhere at the b o t t o m of the table, just as if these elements existed only to annoy the constructors of the various types of periodic tables with the problem of how to place them in some acceptable manner. The elements cited - together with yttrium and scandium located above them in the periodic table - are collectively termed rare earth elements, on the one hand because most of them were found, in their oxide form, in two minerals, and were considered 'earths' as was usual at the time, and on the other hand because apparently they were rare. The latter attribute, however, is not fully correct. The rare earth elements are actually not very rare; moreover, some of them, e.g., yttrium, are more a b u n d a n t on our planet than c a d m i u m or mercury. Whereas, however, the latter elements occur in rather high concentrations in their minerals, the former are found in numerous rocks, but in very low concentrations. This was one of the reasons why it was so difficult to identify them. Since they usually occur together and their chemical behaviour - owing to their particular atomic structure - is extremely similar, their separation is a very exacting analytical task. This is the other reason why their discovery took so long; it was in fact a process that lasted over 160 years.
Rare earth elements are found mainly in two minerals: yttria and ceria, both of them contained in monazite sand. With much laborious work the chemists lured new element after element from these minerals, only to find out later that the new 'elements' were not homogeneous substances, but mixtures, which - after further wearisome separation operations - turned out to consist of two or more elements.
Whenever some novel method appeared in analytical chemistry and was applied to these substances, new elements were discovered in most cases.
DISCOVERY AND SEPARATION OF THE RARE EARTHS 35 1.1. Yttria
The history of rare earth elements began in 1787. Carl Axel Arrhenius, a lieutenant of the Swedish Royal Army, was a gifted, though amateur, Mineralogist.
At an excursion in the vicinity of Ytterby, a small Swedish town three miles away from Stockholm, he found a curious black mineral that had never before been mentioned by anyone: He just called it 'black stone'. Ever since, many rare earth elements bear the name of the town Ytterby. As new elements again and again turned up from analyzing the black mineral, the discoverers gave them names by varying the name Ytterby: yttrium, ytterbium, terbium, erbium all stem from it.
The new mineral was first studied by an acquaintance of Arrhenius, Bengt Reinhold Geijer. He was the first to report on it in the literature. He assumed that the asphalt-like mineral contained tungsten, by reason of its high density (Geijer 1788).
The next scientist who took interest in the mineral was a Finnish chemist, Johan Gadolin. He analyzed it in 1794 and found a new 'earth' in it that was similar in many respects to alumina and also to lime. It amounted to 38~o of the mineral;
Gadolin also found iron and silicate as constituents (Gadolin 1794, 1796).
Gadolin's statement was confirmed by the investigation of Ekeberg in Stockholm during the following year. Ekeberg found that the mineral also contained beryllium;
finally, it turned out to be iron-beryllium-yttrium silicate. Ekeberg's finding de- monstrates the surprising rapidity of scientific information in those years: beryllium had only just been discovered by the French chemist Vauquelin. (Vauquelin's discovery attracted much attention in Sweden, presumably because he discovered beryllium in the precious stones beryl and emerald which had earlier been analyzed by one of the greatest figures in Swedish chemistry: Torbern Bergman. This scientist maintained that he found aluminium in them. It was Vauquelin's discovery that exposed Bergman's error. Let it be said in Bergman's excuse that the properties of beryllium and aluminium are largely similar, the only analytical difference detectable with the techniques available at the time is that aluminium hydroxide is soluble in excess alkali and beryllium hydroxide is not.) It was Ekeberg who gave the name yttria to the new earth discovered by Gadolin (Ekeberg 1797, 1799). At the time, 'earths' were universally considered elements. Although Antal Ruprecht, professor at the Mining Academy in Selmecbfinya (Hungary) reported in 1790.that he obtained metals by reducing alkaline earths (i.e. alkaline-earth metal oxides) with carbon (Ruprecht 1790), Klaproth proved that Ruprecht's metal clumps were derived from impurities in the crucible used in the experiments (Klaproth 1791). The fact that 'earths' were not elements but compounds was conclusively demonstrated only from 1807 on, when Davy electrolyzed their melts and undisputably obtained metals from them.
Ekeberg again detected yttria in 1802 in another black mineral, yttrotantalite (found also close to Ytterby). However, in this mineral he also discovered another new metal: tantalum.
After Davy had separated numerous metals such as calcium, strontium and barium from alkaline earths in the first decade of the 19th century, chemists began to use the name yttrium for the metal instead of yttria, however, it still took a long
t i m e u n t i l t h e y w e r e a b l e t o p r o d u c e t h e e l e m e n t in t h e p u r e s t a t e .
W h e n t w o w e l l - k n o w n a n a l y t i c a l c h e m i s t s , K l a p r o t h (1801) a n d V a u q u e l i n (1801), c o n f i r m e d t h e e x i s t e n c e o f G a d o l i n ' s a n d E k e b e r g ' s n e w e l e m e n t , y t t r i u m o c c u p i e d its r i g h t f u l p l a c e a m o n g t h e e l e m e n t s , o r r a t h e r a m o n g t h e ' e a r t h s ' , still c o n s i d e r e d e l e m e n t s i n t h o s e y e a r s . K l a p r o t h t h e n g a v e a n e w n a m e t o t h e ' b l a c k s t o n e ' , t h e m i n e r a l f o u n d b y A r r h e n i u s : h e c a l l e d it g a d o l i n i t e , a f t e r t h e d i s c o v e r e r o f y t t r i u m , w h o w a s still a l i v e a t t h a t t i m e . ( T o n a m e m i n e r a l s a f t e r p e r s o n s b e c a m e a f a i r l y r e g u l a r h a b i t in m i n e r a l o g y . S i m i l a r s u g g e s t i o n s t o n a m e n e w e l e m e n t s a f t e r p e r s o n s a l s o c a m e u p i n c h e m i s t r y , b u t - m a i n l y d u e t o t h e o p p o s i t i o n o f B e r z e l i u s - w e r e n o t r e a l i z e d . I t is o f i n t e r e s t t h a t G a d o l i n ' s n a m e w a s t h e o n l y o n e l a t e r g i v e n t o a n a t u r a l e l e m e n t still b e a r i n g it.)
Carl Axel Arrhenius (1757-1824) did not care much for the military profession (he was an officer of the engineer corps), but was passionately interested in chemistry and mineralogy. He frequently visited the laboratory of the Mining Academy. During his stay in Paris he attended the lectures of Lavoisier and Fourcroy. He was one of the first champions in Sweden of the new antiphlogistic chemistry based on oxygen. When in Sweden, he attended the lectures of Berzelius and also worked in his laboratory. He terminated his military career as lieutenant-colonel, but parallelly he also made a remarkable scientific career: he was elected a member of the Swedish Academy of Science (Anonymous 1824).
Bengt Reinhold Geijer (1758-1815) was a member of the Swedish Royal Council of Mines, royal chief assayer, later director of the Royal Institute of Mining. He was a member of the Swedish Academy of Sciences (Anonymous 1816).
Johan Gadolin (1760-1822) was born in Abo (today Turku), an old Finnish university town which at the time belonged to Sweden. His father was professor of physics at the university. (After a great fire in 1828 the university moved to Helsinki and is still run there.) Johan Gadolin studied at the University of ,~bo and subsequently spent five years in Uppsala in Torbern Bergman's institute. It was there that he acquired extensive experience in mineral analysis. After Bergman's death he hoped to become his successor. Since, however, he was not appointed, he returned to the university of his birthplace. He travelled much all over Europe and became acquainted with the leading chemists of the age. It was he who published the first book in Swedish (Inleding till chemien, 1798) that was based on Lavoisier's new theory of chemistry. In 1797 he was appoint- ed professor of chemistry and mineralogy to the University of Abo and remained in this position un- til his death. Besides his activity in analytical chemistry, his papers dealing with specific heat are also noteworthy. Gadolin was active in politics too: he was one of the pioneers fighting for the independence of Finland. It took, however, another hundred years for independence to come true. Gadolin, anyhow,still lived to see Swedish rule over Finland change to Russian rule in 1809 (Ojala 1937).
Anders Gustaf Ekeberg (1767-1813) was born in Stockholm. He studied in Uppsala, Greifswald and Berlin. He began his career in the Swedish Mining Council and later became associate professor of chemistry at the University of Uppsala. In 1799, he was elected a member of the Swedish Academy of Science. Based on Lavoisier's chemical nomenclature he developed a Swedish chemical nomenclature (1795), he published it anonymously, however, because he feared his professor, who remained faithful to the phlogiston theory. Ekeberg is also significant as an analytical chemist. With the discovery of tantalum he acquired lasting merits (Boklund 1971).
Nicolas Louis Vauquelin (1763-1829) was born in the French village St. Andr& At the age of 14, he began to work as a pharmacist's apprentice in Rouen and, subsequently, as an assistant in Paris
DISCOVERY AND SEPARATION OF THE RARE EARTHS 37
Fig. 1. Johan Gadolin (Courtesy of the National Museum of Finlartd).
to a pharmacist who was, as it happens, the brother-in-law of Fourcroy, the famous chemist.
Fourcroy then employed Vauquelin as an assistant in his own laboratory. In 1794 he became associate professor at the new F~cole des Travaux Publiques (the later Ecole Polytechnique).
In 1797 he became professor of analytical chemistry at the ~Ecole des Mines, later professor of chemistry of the Coll6ge de France. Later he also taught chemistry at the Mus~e d'Histoire Naturelle and at the medical faculty. His activity in mineral analysis is very significant. He discovered two new elements: beryllium as mentioned above, and chromium (Cuvier 1833).
1.2. Ceria
T h e other basic m i n e r a l of the rare earth e l e m e n t s is the m i n e r a l t o d a y called cerite. It was also first f o u n d in Sweden, earlier t h a n gadolinite, a n d the chemists suspected as early as in the m i d d l e of the 18th c e n t u r y t h a t it c o n t a i n s some u n k n o w n 'earth'. T h e m i n e r a l occurred in the Bastn~isgrube m i n e close to R y d d e r h y t t a n . Very m a n y silicate-based related m i n e r a l s a n d f o u n d there, m o s t of
Fig. 2. Martin Heinrich Klaproth.
them containing rare earths and besides them other metals as well. Even their mineralogical systematization was rather a problem, no wonder that the chemists of that age were unable to cope with the task. Already Cronstedt, the famous discoverer of nickel (Cronstedt 1751), and thirty years later the greatest analyst of the age, Torbern Bergman (Bergman 1784) suspected something, but neither got farther than suspicion. Another twenty years had to pass until simultaneously Berzelius and Hisinger in Sweden and Klaproth in Berlin confirmed the suspicion, and separated the unknown 'earth' from the mineral. It proved to be the main component besides silicate. They achieved their results independently from one another and reported on them in one and the same year (Hisinger and Berzelius 1804, Klaproth 1804) in one and the same journal, namely in the Neues Allgemeines Journal der Chemie, cited after its editor, professor Gehlen, usually as Gehlen's Journal. They sent their papers so nearly simultaneously that Berzelius received a letter saying that Klaproth's paper on the same subject will appear in the cur- rent issue, his paper in the next. The fairness of the editor is characterized by
DISCOVERY AND SEPARATION OF THE RARE EARTHS 39 t h e f a c t t h a t i n t h e i s s u e i n w h i c h K l a p r o t h ' s p a p e r w a s p u b l i s h e d a n o t e a p p e a r e d a n n o u n c i n g t h a t a p a p e r o n a s i m i l a r s u b j e c t h a d a l r e a d y a r r i v e d a t t h e j o u r n a l s i m u l t a n e o u s l y . K l a p r o t h n a m e d t h e n e w e a r t h o c h r o i t e e a r t h , w h i l e B e r z e l i u s a n d H i s i n g e r n a m e d it c e r i u m a f t e r t h e s m a l l p l a n e t C e r e s d i s c o v e r e d a t t h e t i m e . ( I t is p e r h a p s u n f a i r t o c i t e B e r z e l i u s ' s n a m e first, s i n c e H i s i n g e r ' s n a m e s t a n d s first a s a u t h o r . H o w e v e r , a t t h e t i m e B e r z e l i u s w a s q u i t e a n o v i c e a s yet, w h i l e H i s i n g e r w a s a w e l l - k n o w n , r i c h f a c t o r y o w n e r w h o w a s m u c h i n t e r e s t e d in s c i e n t i f i c q u e s t i o n s a n d r e c o g n i z e d B e r z e l i u s ' s t a l e n t . T h e l a t t e r ' s c a r e e r m a k e s it s e e m p r o b a b l e t h a t it w a s h e w h o p e r f o r m e d t h e b u l k o f a n a l y t i c a l w o r k . B y t h e w a y , in t h a t s a m e y e a r B e r z e l i u s - w i t h H i s i n g e r ' s m a t e r i a l s u p p o r t - f o u n d e d a j o u r n a l 'Afhandlingar i Fysik, Kemi och Mineralooi' w h i c h a p p e a r e d f o r six y e a r s a n d i n v o l v e d a s i g n i f i c a n t f i n a n c i a l loss. H o w e v e r , H i s i n g e r w a s o n b a d t e r m s a t t h e t i m e w i t h t h e j o u r n a l o f t h e S w e d i s h A c a d e m y o f S c i e n c e . I n t h e first i s s u e of t h e n e w j o u r n a l , H i s i n g e r a n d B e r z e l i u s a l s o p u b l i s h e d t h e i r p a p e r o n t h e d i s c o v e r y o f c e r i a i n S w e d i s h . )
K l a p r o t h b e l i e v e d t h a t t h e n e w s u b s t a n c e w a s a n e l e m e n t , B e r z e l i u s , h o w e v e r , a l r e a d y a s s u m e d t h a t it w a s t h e o x i d e o f a n e w e l e m e n t .
Martin Heinrich Klaproth (1743-1817), the son of a country tailor, started his career, as so many great chemists, as a pharmacist's apprentice. He then worked as an assistant in Hannover, Danzig and Berlin in various pharmacies. While Klaproth worked in Berlin the owner of the pharmacy died unexpectedly and Klaproth led the pharmacy until the son came of age. Later Klaproth bought a pharmacy from the dowry of his wife. Meanwhile he was continually occupied with scientific problems, namely with the chemical analysis of minerals. In 1788, he was elected a member of the Scientific Academy in Berlin, and in 1800 he was charged with leading the chemical laboratory of the Academy. In 1809, he was appointed professor of chemistry at the University of Berlin then founded, and remained in this position until his death. Besides cerium he discovered the elements uranium and zirconium, and he was the first to study thoroughly the metals strontium, titanium and tellurium discovered by others. The name tellurium was given to the element by Klaproth (Szabadv;iry 1966, p. 117).
J6ns Jakob Berzelius (1779-1848) was the greatest and most important chemist of the first half of the past century. He was born in V~iversunda, his father was a school teacher. He was orphaned early and studied unaided to graduate as a medical doctor. He became an assistant and, in 1807, professor of chemistry in the Collegium Medicum in Stockholm, at the time still a school to train army surgeons, it was transformed into a medical university during Berzelius's professorship.
(Nowadays, it is called the Karolinska Institute, which up to the present day awards the Nobel Prizes in medicine and biology.) Berzelius was elected a member of the Swedish Academy of Sciences in 1808 and became its secretary in 1820. He also undertook several industrial ventures, most of which, however, were unsuccessful. In 1835, he was raised to the baronial rank in recognition of his merits in chemical science.
Berzelius was the first to determine the atomic mass of the elements with satisfactory accuracy.
It was he who introduced the chemical symbols still in use. His dualistic electrochemical hypothesis concerning the structure of compounds was a fundamental and progressive chemical theory for a long period. He was one of the pioneers of elemental analysis of organic substances.
Berzelius wrote numerous books. His manual of chemistry has been translated into several languages and was reprinted five times in Berzelius's lifetime. In his annual reports, entitled Jahresbericht, published from 1821 until his death he critically abstracted the scientific publi- cations of the year. The Jahresbericht was the ancestor of the numerous present scientific abstracting publications, all of them can be traced back to it. Besides cerium Berzelius discovered
thorium and selenium, the latter in the mud of his own sulfuric acid factory. He was the first to produce elemental zirconium, silicon and thorium (Szabadv/try 1966, p.125).
Wilhelm Hisinger (1766-1852) was born in Skinnskatteberg, where his father was proprietor of a thriving iron-works. Hisinger studied mining and subsequently took over the family enterprise.
He occupied himself with many branches of science, with chemistry, mineralogy, zoology and cartography. In 1804, he was elected a member of the Swedish Academy of Science.