Aqueous zirconium chlorides

There have only been a few studies of the complexation of zirconium by the chloride ion [49CON/MCV], [56LEV/FRE], [62MAR/RYA], [70PRA/HAV], [76TRI/SCH] and the complexation has been found to be weak. All of the studies have used a mixture of perchloric and hydrochloric acids as the ionic medium, but of differing ionic strengths. 

Conniek and McVey [49CON/MCV] measured the extraction of zirconium into benzene as Zr(TTA)4, in the presence of chloride. Only two measurements were taken and were used to indicate the formation of ZrCP. However, due to the inadequacy of the number of data points used to derive the stability constant of the speeies, it has not been included in this review. Levitt and Freund [56LEV/FRE] studied the solvent extraction of zirconium with tributyl phosphate (TBP) in the presence of chloride (6.54 M HCIO4 25°C). They did not determine the stability of the zirconium chloride complexes formed but their data were subsequently used by [57SOL] as the basis for a determination of the stability constants for four complexes ZrCl, o = 1 to 

The reaction of zirconium with chloride can be represented by the equation  

Tribalat and Schriver [76TRI/SCH] reported a stability constant, in 4 M HCIO4, for Reaction (V.35)  

There is insufficient data to determine a stability constant at zero ionic strength for either ZrClj orZrC.  

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The Gibbs energy of formation for these aqueous zirconium chloride complexes are determined from the stability constant data given for 9 = 1 and 2 at zero ionic strength and the Gibbs energy of formation for Zr and d (Section V.2.1 and Chapter IV, respectively) ... 

All aqueous zirconium compounds have polymeric structures, sometimes with ligands bonded to the zirconium-based polymer. Whether ligands are bonded to the zirconium depends on the counterion. In very general terms, oxygenated ions such as carbonate and sulphate bond to the zirconium whilst halides such as chloride do not. 

There have been no reported measurements of either aqueous zirconium bromide or iodide complexes. However, on the basis of the stability of the complexes of zirconium with the chloride ion it is expected that the zirconium(IV) ion would form very weak complexes with either bromide or iodide. 

ZrOClj.SH O, white crystals that are soluble in water, insoluble in organic solvents, and acidic in aqueous solution used for textile dyeing and oil-field acidizing, in cosmetics and greases, and for antiperspirants and water repellents. Also known as basic zirconium chloride zirconyl chloride. 

Refractory Fibers Recently, zirconia-based insulating material with a low density and a low thermal conductivity has been developed in the form of fibers, paper, felt, board and shaped articles. The material is a cubic zirconia soHd solution stabilized with yttria, and has a maximum usable temperature of >2100 C. The innovative fabrication technique involves the use of an organic precursor fiber as a structural template, impregnated with an aqueous solution of zirconium chloride and yttrium chloride. The metallic salts are deposited within the organic fiber, which can subsequently be burned off by a controlled oxidation. The hollow remainder is then fired at a sufficiently high temperature (800-1300 °C) so as to induce crystallization, after which the oxide particles are sintered to develop a ceramic bond. Other techniques to produce refractory fibers involve phase inver-... 

Electrolysis. Electrowinning of zirconium has long been considered as an alternative to the KroU process, and at one time zirconium was produced electrolyticaHy in a prototype production cell (70). Electrolysis of an aH-chloride molten-salt system is inefficient because of the stabiUty of lower chlorides in these melts. The presence of fluoride salts in the melt increases the stabiUty of in solution, decreasing the concentration of lower valence zirconium ions, and results in much higher current efficiencies. The chloride—electrolyte systems and electrolysis approaches are reviewed in References 71 and 72. The recovery of zirconium metal by electrolysis of aqueous solutions in not thermodynamically feasible, although efforts in this direction persist. 

Hydroxyl Compounds. The aqueous chemistry of zirconium is complex, and in the past its understanding was compHcated by differing interpretations. In a study of zirconium oxide chloride and zirconium oxide bromide, the polymeric cation [Zr4(OH)g (H20)jg was identified (189) the earlier postulated moiety [Zr=0] was discarded. In the tetramer, the zirconium atoms are coimected by double hydroxyl bridges (shown without the coordinating water molecules) ... 

Oxide Chlorides. Zirconium oxide dichloride, ZrOCl2 -8H2 0 [13520-92-8] commonly called zirconium oxychloride, is really a hydroxyl chloride, [Zr4(OH)g T6H2 0]Clg T2H2O (189). Zirconium oxychloride is produced commercially by caustic fusion of zircon, followed by water washing to remove sodium siUcate and to hydrolyze the sodium zirconate the wet filter pulp is dissolved in hot hydrochloric acid, and ZrOCl2 -8H2 O is recovered from the solution by crystallization. An aqueous solution is also produced by the dissolution and hydrolysis of zirconium tetrachloride in water, or by the addition of hydrochloric acid to zirconium carbonate. 

A number of attempts to produce tire refractory metals, such as titanium and zirconium, by molten chloride electrolysis have not met widr success with two exceptions. The electrolysis of caesium salts such as Cs2ZrCl6 and CsTaCle, and of the fluorides Na2ZrF6 and NaTaFg have produced satisfactoty products on the laboratory scale (Flengas and Pint, 1969) but other systems have produced merely metallic dusts aird dendritic deposits. These observations suggest tlrat, as in tire case of metal deposition from aqueous electrolytes, e.g. Ag from Ag(CN)/ instead of from AgNOj, tire formation of stable metal complexes in tire liquid electrolyte is the key to success. 

The crude tetrachloride mixture of zirconium and hafnium is dissolved in ammonium thiocyanate solution. The solution is extracted with methyl isobutyl ketone (MIBK). MIBK is passed countercurrent to aqueous mixture of tetrachloride in the extraction column. Halhium is preferentially extracted into MIBK leaving zirconium in the aqueous phase. Simultaneously, zirconium tetrachloride oxidizes to zirconyl chloride, ZrOCb. When sulfuric acid is added to aqueous solution of zirconyl chloride, the chloride precipitates as a basic zirconium sulfate. On treatment with ammonia solution the basic sulfate is converted into zirconium hydroxide, Zr(OH)4. Zirconium hydroxide is washed, dried, and calcined to form zirconium oxide, Zr02. 

Water of crystallization may be measured by thermogravimetry. Zirconium may be analyzed in an aqueous solution by flame AA or ICP-AES. Sulfate may be identified in an aqueous solution by ion chromatography or by precipitation with barium chloride. 

No zirconium(III) complexes with oxygen donor ligands have been isolated. However, the electronic absorption spectra of aqueous solutions of Zrl3 have been interpreted in terms of the formation of aqua complexes (equation 4).29 The spectrum of a freshly prepared solution of Zrl3 exhibits a band at 24 400 cm-1, which decays over a period of 40 minutes, and a shoulder at 22000 cm-1, which decays more rapidly. The 24400 cm-1 band has been assigned to [Zr(H20)6]3+, and the 22000 cm-1 shoulder has been attributed to an unstable intermediate iodo-aqua complex. If it is assumed that the absorption band of [Zr(H20)6]3+ is due to the 2T 2Ee ligand-field transition, the value of A is 24 400 cm. This corresponds to a A value of 20 300 cm-1 for [Ti(H20)6]3+ 30 and 17 400 cm-1 for the octahedral ZrCl6 chromophore in zirconium(III) chloride.25... 

In all of the discussion of this chapter we have used an aqueous solution as the electrolyte, and electrodes suitable to those aqueous solutions. However, cells are not limited to aqueous solutions. Indeed, other solvents have been used for which liquid ammonia would be an example. Molten salts, such as mixtures of lithium chloride and potassium chloride, have been used for the study of cells at high temperatures. Some studies have been made at higher temperatures, in which solid electrolytes were used. Electrodes compatible with such solvents have also been devised. For example, a zirconium-zirconium oxide electrode stabilized with calcium oxide was used to measure the oxygen potential in nonstoichiometric metal oxides. However, no matter what the electrolytes or the electrodes are, the principles discussed in this chapter such as reversibility and proper measurement must be followed. 

Mix together on a spot plate 2 drops each (equal volumes) of a 0-1 per cent aqueous solution of alizarin-S (sodium alizarin sulphonate) and zirconyl chloride solution (0-1 g solid zirconyl chloride dissolved in 20 ml concentrated hydrochloric acid and diluted to 100 ml with water) upon the addition of a drop or two of the fluoride solution the zirconium lake is decolourized to a clear yellow solution. 

All salts of zirconium and hafnium tend to hydrolyze in aqueous solutions, though less so than those of titanium. In highly dilute solutions (<10 " M), Zr and Hf exist as the aqueous ions [M(OH) ] " " +, where n is pH-dependent. The hydration energies are 7001 and 7169kJ moU for Zr and Hf respectively. In chloride, perchlorate, and nitrate solutions, hafnium is less hydrolyzed than zirconium, while the reverse is true in sulfate solutions. This is connected with the lower solubility of hafnium compounds in sulfate solutions, even in only slightly acid media. It should be noted that the sulfate anion has a strong affinity for Zr and Hf... 

Zirconium and hafnium trifluoracetylacetonates were prepared by Larsen, Terry, and Leddy, who measured some of their properties. They prepared these compounds by the dropwise addition of the ligand to an aqueous solution of the metal oxide chloride, using intermittent addition of sodium carbonate to maintain the proper pH. 

Enones are reduced to saturated ketones by catalytic hydrogenation provided the reaction is stopped following the absorption of 1 mol of hydrogen. " A number of catalysts were found useful for this, including platinum, platinum oxide,Pt/C, " Pd/C, - Rh/C, " tris(triphenylphosphine)rhodium chloride, - nickel-aluminum alloy in 10% aqueous NaOH, and zinc-reduced nickel in an aqueous medium. Mesityl oxide is formed from acetone and reduced in a single pot to methyl isobutyl ketone using a bifunctional catalyst which comprised palladium and zirconium phosphate (Scheme 20). 

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