Hafnium separation from

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). 

In France, Compagnie Europnene du Zirconium (CEZUS) now owned jointly by Pechiney, Eramatome, and Cogema, uses a separation (14) based on the extractive distillation of zirconium—hafnium tetrachlorides in a molten potassium chloride—aluminum trichloride solvent at atmospheric pressure at 350°C. Eor feed, the impure zirconium—hafnium tetrachlorides from the zircon chlorination are first purified by sublimation. The purified tetrachlorides are again sublimed to vapor feed the distillation column containing the solvent salt. Hafnium tetrachloride is recovered in an enriched overhead fraction which is accumulated and reprocessed to pure hafnium tetrachloride. 

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. 

In the initial thiocyanate-complex Hquid—Hquid extraction process (42,43), the thiocyanate complexes of hafnium and zirconium were extracted with ether from a dilute sulfuric acid solution of zirconium and hafnium to obtain hafnium. This process was modified in 1949—1950 by an Oak Ridge team and is stiH used in the United States. A solution of thiocyanic acid in methyl isobutyl ketone (MIBK) is used to extract hafnium preferentially from a concentrated zirconium—hafnium oxide chloride solution which also contains thiocyanic acid. The separated metals are recovered by precipitation as basic zirconium sulfate and hydrous hafnium oxide, respectively, and calcined to the oxide (44,45). This process is used by Teledyne Wah Chang Albany Corporation and Western Zirconium Division of Westinghouse, and was used by Carbomndum Metals Company, Reactive Metals Inc., AMAX Specialty Metals, Toyo Zirconium in Japan, and Pechiney Ugine Kuhlmann in France. 

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). 

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. 

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%. 

The pyrochemical process of zirconium-hafnium separation is particularly attractive not only because it makes the entire process of nuclear-grade zirconium metal production from zircon more economical than that involving a hydrometallurgical separation stage, but also... 

NN applications, perhaps more important, is process control. Processes that are poorly understood or ill defined can hardly be simulated by empirical methods. The problem of particular importance for this review is the use of NN in chemical engineering to model nonlinear steady-state solvent extraction processes in extraction columns [112] or in batteries of counter-current mixer-settlers [113]. It has been shown on the example of zirconium/ hafnium separation that the knowledge acquired by the network in the learning process may be used for accurate prediction of the response of dependent process variables to a change of the independent variables in the extraction plant. If implemented in the real process, the NN would alert the operator to deviations from the nominal values and would predict the expected value if no corrective action was taken. As a processing time of a trained NN is short, less than a second, the NN can be used as a real-time sensor [113]. 

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... 

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... 

In the optimization of conditions of hafnium extraction from tributylphosphate (TBF), these factors were analyzed X,-concentration of nitric acid in outlet water solution, [N] X2-concentration of TBF in e-xylol, % X3-ratio of phases, [1] and X4-time of extraction, min. The coefficient of hafnium separation was determined as the system response. 1/2-replica of full factorial experiment 24 (X4=X3X2X3) was chosen as the basic experiment. The outcomes of the experiment are given in Table... 

According to the results of different authors [61], the concentration of the sum of metals goes from 35 to 120 g/1. It is aggregate to chose values from 20 to 150 g/1 for the domain of concentration of the sum of metals. The other factor-concentration of nitric acid below 3 mol/1 has as a consequence poor extraction of zirconium and hafnium. With an increase of acid concentration above 5 mol/g, hafnium separates well in organic phase, but its separation falls. We choose the domain of nitric acid concentration from 3 to 8 mol/g. 

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. 

Photoelectron (PE) spectra have been measured for several (s-cis-diene)zirconocenes (5g, 51, 5s), for one example of the hafnium analogue (5n), and for (s-t/-ans-i7 -butadiene)Zr(C5Me5)2 (3c) (54). For both Cp and Cp series the highest occupied molecular orbital (HOMO) is separated from subsequent molecular orbitals (MO s) by a substantial energy difference. The observed PE spectra of 5 each exhibit a band around 6-6.5 eV (oi), well separated from several overlapping bands at 8-9 eV (6], f>2, fl2> bi). The PE spectrum of 3c shows a similar pattern [5.9 eV (aj) 7.1, 7.5, 7.5, 8.3 eV (fl2, i)]- The PE bands are in good accord with the... 

Lutecium is the heaviest, rarest, and most expensive lanthanoid element. The lanthanoids elements make up Row 6 of the periodic table between barium and hafnium. The periodic table is a chart that shows how chemical elements are related to one another. The lanthanoids are usually shown as a separate row at the bottom of the table. They are also called the rare earth elements. That name does not fit very well for most lanthanoids. They are not really so rare, but were once difficult to separate from each other. However, lutetium is both rare and difficult to separate from the other lanthanoids. 

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