Hafnium separation from zirconium

In the drying of compound intermediates of refractory and reactive metals, particular attention is given to the environment and to the materials so that the compound does not pick up impurities during the process. A good example is the drying of zirconium hydroxide. After the solvent extraction separation from hafnium, which co-occurs with zirconium in the mineral zircon, the zirconium values are precipitated as zirconium hydroxide. The hydroxide is dried first at 250 °C for 12 h in air in stainless steel trays and then at 850 °C on the silicon carbide hearth of a muffle furnace. 

Zirconium (and hafnium) have been separated from other metals by means of strongly acidic cation-exchangers, use being made of HCl [34], HCIO4 [35], and oxalic acid [36] media. In formic acid medium, metal ions form positive ions, except for Zr which produces anionic complexes [37]. Zirconium has been separated from hafnium on cation-exchangers by virtue of the differences in stability of their formate [38] and sulphate [39] complexes. Chelating resins have also been applied for separation of Zr and Hf [39]. 

Two recent patents [M2, M3] by J. A. Megy describe a process in which zirconium metal is reduced from a salt and separated from hafnium in the same step, thus shortening the long series of steps in present processes for producing reactor-grade rirconium from natural zircon. 

Uranium zirconium, and niobium ions or oxy ions are adsorbed by silica from nitric add solution down to pH 0 and niobium even for 10 3/ add. A weak oxalic acid solution removes the adsorbed metals (645). Zirconium can be separated from hafnium on silica gel (646). 

It was originally separated from zirconium by repeated recrystallization of the double ammonium or potassium fluorides by von Hevesey and Jantzen. Metallic hafnium was first prepared by van Arkel and deBoer by passing the vapor of the tetraiodide over a heated tungsten filament. Almost all hafnium metal now produced is made by reducing the tetrachloride with magnesium or with sodium (Kroll Process). 

Analyses of alloys or ores for hafnium by plasma emission atomic absorption spectroscopy, optical emission spectroscopy (qv), mass spectrometry (qv), x-ray spectroscopy (see X-ray technology), and neutron activation are possible without prior separation of hafnium (19). Alternatively, the combined hafnium and zirconium content can be separated from the sample by fusing the sample with sodium hydroxide, separating silica if present, and precipitating with mandelic acid from a dilute hydrochloric acid solution (20). The precipitate is ignited to oxide which is analy2ed by x-ray or emission spectroscopy to determine the relative proportion of each oxide. 

MIBK is a highly effective separating agent for metals from solutions of their salts and is used in the mining industries to extract plutonium from uranium, niobium from tantalum, and zirconium from hafnium (112,113). MIBK is also used in the production of specialty surfactants for inks (qv), paints, and pesticide formulations, examples of which are 2,4,7,9-tetramethyl-5-decyn-4,7-diol and its ethoxylated adduct. Other appHcations include as a solvent for adhesives and wax/oil separation (114), in leather (qv) finishing, textile coating, and as a denaturant for ethanol formulations. 

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). 

Hafnium Carbide. The need of pure zirconium [7440-67-7] for nuclear reactors prompted the large-scale separation of hafnium [7440-58-6] from zirconium. This in turn made sufficient quantities of hafnium dioxide [12055-23-17, Hf02, or Hf metal sponge available for production of HfC for use in cemented carbides (see Hafniumand hafnium compounds). 

There are many advantages of using metal chlorides as interprocess intermediates. One of the most important advantages is that the metal chlorides could be readily purified. In other words, co-occurring metals could be more readily separated from one another as chlorides. This is particularly important when the co-occurring metals have very different technological properties and the presence of one in another in the final product is detrimental to the intended commercial application. A famous example of such co-occurrence is that of zirconium and hafnium in the mineral zircon. Not more than 100 ppm hafnium should be present in the zirconium intended for use in the nuclear reactor core. The hafnium content of zircon is about 2.5%. 

K2HfF6> are special in that they are useful in a process for the separation of zirconium from hafnium by fractional crystallization. It is in general very difficult to separate zirconium from hafnium as they are chemically very similar. 

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. 

Zirconium was isolated from other compounds in 1824 by Baron Jons Jacob Berzelius (1779-1848), a Swedish chemist, but it was not produced in pure form until 1914 because of the difficulty in separating it from hafnium. 

Ammonium thiocyanate is used in the manufacture of herbicides, thiourea, and transparent artificial resins in matches as a stabilizing agent in photography in various rustproofing compositions as an adjuvant in textile dyeing and printing as a tracer in oil fields in the separation of hafnium from zirconium, and in titrimetric analyses. 

Hafnium is obtained commercially from mineral zircon, which is zirconium orthosilicate [14940-68-2]. Zircon usually contains hafnium oxide, Hf02, in an amount that ranges between 1 to 2%. Zircon sand is separated from heavy... 

Hafnium had lain hidden for untold centuries, not because of its rarity but because of its dose similarity to zirconium (16), and when Professor von Hevesy examined some historic museum specimens of zirconium compounds which had been prepared by Julius Thomsen, C. F. Rammelsberg, A. E. Nordenskjold, J.-C. G. de Marignac, and other experts on the chemistry of zirconium, he found that they contained from 1 to 5 per cent of the new element (26, 27). The latter is far more abundant than silver or gold. Since the earlier chemists were unable to prepare zirconium compounds free from hafnium, the discovery of the new element necessitated a revision of the atomic weight of zirconium (24, 28). Some of the minerals were of nepheline syenitic and some of granitic origin (20). Hafnium and zirconium are so closely related chemically and so closely associated in the mineral realm that their separation is even more difficult than that of niobium (columbium) and tantalum (29). The ratio of hafnium to zirconium is not the same in all minerals. 

In aqueous solution, zirconium(IV) and hafnium(IV) form complexes M(NCS)4-", where n = 1-8.104 Selective extraction of hafnium thiocyanate complexes from acidic aqueous solution by methyl isobutyl ketone is a widely used industrial method for the separation of zirconium and hafnium. Separation methods have been reviewed by Vinarov.105... 

Hafnium, determination of, in zirconium-hafnium solution, 3 69 extraction of, from cyrtolite and separation from zirconium, 3 67, 74... 

Most zirconium-containing minerals are 1 to 3 percent hafnium. Hafnium is a ductile metal with a brilliant silver luster. The properties of hafnium are often difficult to ascertain, as measurements of these properties are sometimes distorted by the presence of zirconium impurities. Of all the elements, zirconium and hafnium are two of the most difficult to separate from one another. Hafnium is a group IV transition element. 

The zirconium tetrachloride product must then be purified before reduction to metal. In particular, hafnium must be removed to less than 100 ppm Hf Zr because of the high neutron absorption cross-section it exhibits, and phosphorus and aluminum must be removed to even lower specifications due to their deleterious metallurgical impact on the final zirconium alloys. The tetrachloride product is first dissolved in water under carefully controlled conditions to produce an acidic ZrOCl2 solution. This solution is complexed with ammonium thiocyanate, and contacted with methyl isobutyl ketone (MIBK) solvent in a series of solvent extraction columns. Advantage is taken of the relative solubilities of Zr, Hf, and Fe thiocyanate complexes to accomplish a high degree of separation of hafnium and iron from the zirconium. 

To separate zirconium from hafnium, 2-thenoyltrifluoroacetone is less effective than the selenophene analog, which yields hafnium solutions of 98-99% purity thus, the two similar elements can be efficiently separated.133... 

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