Zirconium purification

Zirconium purification and conversion to zirconium dioxide. The zirconium-product stream leaving the HCNS recovery column D of Fig. 7.6 contained most of the metal impurities in the ZrCl4 feed other than hafnium. Purified zirconium was obtained by precipitating Zr(OH)4 at a pH low enough to prevent precipitation of other metal hydroxides. The precipitation procedure used by the Bureau of Mines was as follows. Zirconium content of the raffinate was diluted to 19 g/liter. To every cubic meter of diluted raffinate were added 5.7 liters of concentrated 33 N sulfuric acid, followed by sufficient 28% ammonium hydroxide to bring the pH to 1.2 to... 

Fig. 4.32. U.K. process for zirconium purification by hexone-thiocyanate route. Solvent A, bexone 2-7M in thiocyanic acid inititdly solvent B, texone...

The equihbrium is reversed at high temperature. The iodide is decomposed by passing the vapor over an electrically heated wire (1300—1400°C), yielding purified sohd titanium and iodine gas which is recycled. The iodide process also appHes to the purification of zirconium, hafnium, and siUcon. 

Uranium Purification. Subsequent uranium cycles provide additional separation from residual plutonium and fission products, particularly zirconium— niobium and mthenium (30). This is accompHshed by repeating the extraction/stripping cycle. Decontamination factors greater than 10 at losses of less than 0.1 wt % are routinely attainable. However, mthenium can exist in several valence states simultaneously and can form several nitrosyl—nitrate complexes, some for which are extracted readily by TBP. Under certain conditions, the nitrates of zirconium and niobium form soluble compounds or hydrous coUoids that compHcate the Hquid—Hquid extraction. SiUca-gel adsorption or one of the similar Hquid—soHd techniques may also be used to further purify the product streams. 

In the tributyl phosphate extraction process developed at the Ames Laboratory, Iowa State University (46—48), a solution of tributyl phosphate (TBP) in heptane is used to extract zirconium preferentially from an acid solution (mixed hydrochloric—nitric or nitric acid) of zirconium and hafnium (45). Most other impurity elements remain with the hafnium in the aqueous acid layer. Zirconium recovered from the organic phase can be precipitated by neutralization without need for further purification. 

Electron-beam melting of zirconium has been used to remove the more volatile impurities such as iron, but the relatively high volatiUty of zirconium precludes effective purification. Electrorefining is fused-salt baths (77,78) and purification by d-c electrotransport (79) have been demonstrated but are not in commercial use. 

The optimal choice depends on the total pressure of tire system, and on tire stoichiometty of tire reaction. As an example, the uansportation of zirconium as the tetra-iodide is made at low pressure, while the purification of nickel by tetracarbonyl formation is made at high pressure. These reactions may be written as... 

A more comprehensive purification procedure uses a sequence of steps as follows filtration at 200°C through a stainless steel powder compact filter of 10-jum pore size reduces the oxygen content and removes any solid impurities. Gettering with Zr foil for 46 h at 760°C reduces the oxygen concentration to 200 ppm. The weight ratio of K to Zr is 13 1 with a surface area to volume ratio of Zr to K 4 1. A second gettering with zirconium foil for 72 h at 800°C reduces the oxygen content 50 ppm. 

The phthalic anhydride/urea process may also be employed to convert tetra-chloro phthalic anhydride to green copper hexadecachloro phthalocyanine by condensation. In this case, titanium or zirconium dioxides, particularly in the form of hydrated gels, are used instead of the molybdenum salts which are used in the phthalic anhydride process [23]. There is a certain disadvantage to the fact that the products lack brilliance and require additional purification. 

A decrease in the number of uranium and plutonium purification cycles from three to two, or even one, would be highly advantageous. First-cycle decontamination factors of uranium from neptunium and from the fission products ruthenium and zirconium must be significantly improved to realize such a decrease. 

The decision about which HPLC column to choose is really controlled by the separation you are trying to make and how much material you are trying to separate and/or recover. I did a rather informal survey of the literature and my customers 15 years ago to see which columns they used. I found 80% of all separations were done on some type of reverse-phase column (80% of those were done on C18), 10% were size separation runs (most of these on polymers and proteins), 8% were ion-exchange separations, and 2% were normal-phase separation on silica and other unmodified media, such as zirconium and alumina. The percentage of size- and ion-exchange separations has increased recently because of the importance of protein purification in pro-teomics laboratories and the growing use in industry of ion exchange on pressure-resistant polymeric and zirconium supports. 

Fig. S. Apparatus for the synthesis and purification of halo(2,4-pentanedionato)zirconium(IV) complexes.

Separation and Purification. In the Purex process discussed here, the uranium, plutonium, and fission products are separated by solvent extraction into three different streams (Fig. 21.20). The plutonium stream goes through anion exchange (discussed later) to reduce traces of ruthenium, and the uranium stream goes through silica gel sorption to reduce traces of zirconium. The fission-product stream, which contains the fission products... 

From the second cycle the plutonium goes through anion exchange for final purification (Fig. 21.21). The principal problem here is due to ruthenium, which is difficult to remove because of its many valence states. The uranium stream goes through silica sorption primarily to remove zirconium, which seems to be carried along as a colloid. 

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