Earth hafnium

Of special interest is the discovery of rare earths, noble (or inert) gases, and, finally, the elements predicted by 0. I. Mendeleev on the basis of the periodic system. Although these elements were discovered by means of chemical analysis and spectroscopic method, the histories of the above groups of elements are in many respects highly individual and separate chapters have been devoted to their presentation (Chapters 7, 8 and 9). No less peculiar is the history of the two stable elements which proved to be the last to be discovered on Earth—hafnium and rhenium (Chapter 10). The first part of the book ends with the history of radioactive elements (Chapter 11), which introduces the reader to the world of radioactivity, the world of unstable elements and isotopes the most of which were obtained artificially by means of nuclear reactions. 

Whereas zirconium was discovered in 1789 and titanium in 1790, it was not until 1923 that hafnium was positively identified. The Bohr atomic theory was the basis for postulating that element 72 should be tetravalent rather than a trivalent member of the rare-earth series. Moseley s technique of identification was used by means of the x-ray spectra of several 2ircon concentrates and lines at the positions and with the relative intensities postulated by Bohr were found (1). Hafnium was named after Hafma, the Latin name for Copenhagen where the discovery was made. 

Assay of beryUium metal and beryUium compounds is usuaUy accompHshed by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryUium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryUium content of the sample is calculated from the titration volume. Standards containing known beryUium concentrations must be analyzed along with the samples, as complexation of beryUium by fluoride is not quantitative. Titration rate and hold times ate critical therefore use of an automatic titrator is recommended. Other fluotide-complexing elements such as aluminum, sUicon, zirconium, hafnium, uranium, thorium, and rate earth elements must be absent, or must be corrected for if present in smaU amounts. Copper-beryUium and nickel—beryUium aUoys can be analyzed by titration if the beryUium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

Calcium metal is an excellent reducing agent for production of the less common metals because of the large free energy of formation of its oxides and hahdes. The following metals have been prepared by the reduction of their oxides or fluorides with calcium hafnium (22), plutonium (23), scandium (24), thorium (25), tungsten (26), uranium (27,28), vanadium (29), yttrium (30), zirconium (22,31), and most of the rare-earth metals (32). 

The discovery of hafnium was one of chemistry s more controversial episodes. In 1911 G. Urbain, the French chemist and authority on rare earths , claimed to have isolated the element of atomic number 72 from a sample of rare-earth residues, and named it celtium. With hindsight, and more especially with an understanding of the consequences of H. G. J. Moseley s and N. Bohr s work on atomic structure, it now seems very unlikely that element 72 could have been found in the necessary concentrations along with rare earths. But this knowledge was lacking in the early part of the century and, indeed, in 1922 Urbain and A. Dauvillier claimed to have X-ray evidence to support the discovery. However, by that time Niels Bohr had developed his atomic theory and so was confident that element 72 would be a... 

Titanium, which comprises 0.63% (i.e. 6320 ppm) of the earth s crustal rocks, is a very abundant element (ninth of all elements, second of the transition elements), and, of the transition elements, only Fe, Ti and Mn are more abundant than zirconium (0.016%, 162 ppm). Even hafnium (2.8 ppm) is as common as Cs and Br. 

The liquid-liquid extraction (solvent extraction) process was developed about 50 years ago and has found wide application in the hydrometallurgy of rare refractory and rare earth metals. Liquid-liquid extraction is used successfully for the separation of problematic pairs of metals such as niobium and tantalum, zirconium and hafnium, cobalt and nickel etc. Moreover, liquid-liquid extraction is the only method available for the separation of rare earth group elements to obtain individual metals. 

T.F. Levchishina, R.L. Davidovich, Complex fluorides of zirconium, hafnium, niobium and tantalum with cations of alkali earth metals, Dep. VINITI, No 3595-75 Dep 1975. 

The examination and analysis of minerals have provided x-ray emission spectrography with a challenge and an opportunity. This situation has arisen because of a great growth of interest in uranium and thorium minerals in the rare-earth oxides and in metals such as tantalum and niobium, or hafnium and zirconium. On the whole, x-ray emission spectrography has met the challenge successfully, and the investigations that prove this also demonstrate the versatility and the value of the method.70"72... 

Solvent extraction is often applied to separate two chemically similar metals such as nickel/ cobalt, adjacent rare earths, niobium/tantalum, zirconium/hafnium, etc. For the purpose of elaboration, the example of the separation of two chemically similar elements such as zirconium and hafnium from their nitrate solution, using TBP as an extractant is considered. The solvent extraction process in this case is chemically constant (K) is given by ... 

In the extraction and separation of zirconium from hafnium in a nitric acid system, using TBP, the system operates best if run at about 10% less than saturation [56]. As saturation of the solvent is approached, a zirconium compound precipitates in the presence of the solvent, causing cruds and emulsions. This problem is also encountered in rare earth circuits using DEHPA. 

ISOTOPES There are 44 known isotopes for hafnium. Five are stable and one of the unstable isotopes has such a long half-life (Hf-174 with a 2.0x10+ years) that it is included as contributing 0.16% to the amount of hafnium found in the Earth s crust. The percentage contributions of the 5 stable isotopes to the element s natural existence on Earth are as follows Hf-176 = 5.26%, Hf-177 = 18.60%, Hf-178 = 27.28%, Hf-179 = 13.62%, and Hf-180 = 35.08%. 

As the first element in the third series of the transition elements, hafnium s atomic number ( jHf) follows the lanthanide series of rare-earths. The lanthanide series is separated out of the normal position of sequenced atomic numbers and is placed below the third series on the periodic table ( La to 7,Li). This rearrangement of the table allowed the positioning of elements of the third series within groups more related to similar chemical and physical characteristics—for example, the triads of Ti, Zr, and Hf V, Nb, andTa and Cu, Ag, and Au. 

Bohr s theory received a striking confirmation when the element hafnium was discovered at his institute in 1923. During the early 1920s most chemists believed that element 72 would turn out to be a rare earth. But Bohr s theory implied that this element should have four electrons in its outermost shell, not three as the rare earths did. It should therefore have properties similar to those of the element zirconium. 

Hafnium was discovered in 1922 by Coster and deHevesy. They named it for Hafnia, the Latin word for Copenhagen. It is found in aU zirconium ores, such as zircon, (ZrSi04) and baddeleyite (Zr02). It occurs in the earth s crust at about 3 mg/kg. Its average concentration in sea water is 7 ng/L. 

Another approach to the "greening of catalysts has been the use of rare-earth compounds known as inflates. The term inflate is an abbreviation for the trifluoromethanesulfonate (SO3CF3) cation. Some typical triflates that have been used in research include the lanthanides, scandium, and hafnium. These triflates act as Lewis acids (electron acceptors) and can, therefore, be substituted for stronger mineral acids (such as sulfuric acid) with undesirable environmental... 

Georg von Hevesy. Hungarian chemist who, with Dr. Dirk Coster of the University of Groningen, discovered the element hafnium in zirconium ores and made a thorough study of its properties. Author of many papers on chemical analysis by X-rays, radioactivity, the rare earths, and electrolytic conduction. In 1943 he was awarded the Nobel Prize in Chemistry and in 1959 he received the Atoms for Peace Award. 

Olher mudern getter materials include cesium-rubidium alloys, tantalum. titanium, zirconium, and several of the rare-earth elements, such as hafnium,... 

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