Aqueous zirconium fluorides

4 Group 17 (halogen) compounds and complexes V.4.1 Fluorine compounds and complexes V.4.1.1 Aqueous zirconium fluorides 

The step-wise reactions of zirconium with hydrogen fluoride can be represented by Eq.(V.23)  

The selected log K° determined from the weighted least squares analysis is  

The overall stability constants for the following reaction can be calculated from the step-wise constants given above and the selected auxiliary association constant for hydrogen fluoride (log /f = (3.18 0.02) see Chapter IV) 

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During the 1970s, aqueous solutions containing tin(IV) chloride and ammonium bifluoride found commercial application as flame-resistant treatments for woollen sheepskins and rugs, " - where they had the advantage over competitive titanium and zirconium fluoride systems of not imparting any yellow... 

VAS/KOZ] Vasil ev, V. P., Kozlovskii, E. V., Kokurina, G. L., Thermodynamics of the mononuclear formation of zirconium fluoride complexes in aqueous solution, Russ. J. Inorg. Chem., 21,(1976), 1826-1828. Cited on pages 143,312,313. 

Hexafluorozirconic acid [12021 -95-3]], H2ZrP, is formed by dissolving freshly prepared oxide, fluoride, or carbonate of zirconium in aqueous HP. This acid is produced commercially in a concentration range of 10 to 47%. The acid can be stored at ambient temperatures in polyethylene or Teflon containers... 

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. 

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. 

Fluoride, in the absence of interfering anions (including phosphate, molybdate, citrate, and tartrate) and interfering cations (including cadmium, tin, strontium, iron, and particularly zirconium, cobalt, lead, nickel, zinc, copper, and aluminium), may be determined with thorium chloranilate in aqueous 2-methoxyethanol at pH 4.5 the absorbance is measured at 540 nm or, for small concentrations 0-2.0 mg L 1 at 330 nm. 

A variety of peroxo and hydroperoxo complexes of zirconium(IV) and hafnium(IV) have been isolated from aqueous or aqueous methanolic hydrogen peroxide solutions that contain additional ligands such as sulfate, oxalate or fluoride. Examples of recently reported complexes are listed in Table 8 along with characteristic vibrational frequencies and the pH employed in the aqueous preparations. Earlier work on peroxo compounds has been reviewed by Connor and Ebsworth180 and by Larsen.5... 

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. 

Use may be made of the fact that even solid calcium fluoride reacts with the zirconium-alizarin-S reagent (compare Section IV. 17, reaction 6) and, in consequence, the fluoride test may be carried out in the presence of oxalate and phosphate, which interfere in aqueous solution. The calcium salts are precipitated in neutral or faintly basic solution. The precipitate is ignited and digested with dilute acid. The residue is then tested for fluoride by the zirconium-alizarin-S test the red hue of the reagent disappears and a yellow colouration results (see Section IV.17, reaction 6). 

It is known that non-aqueous synthesis has been effectively applied in the preparation of various metal phosphates, including amine-containing aluminum, gallium, indium, zinc and cobalt phosphates with three-dimensional open-framework structures [17-24]. Moreover, phosphates with a layered or chain structure can been crystallized from non-aqueous media [25, 26]. Since the fluoride ions mineralizer was introduced into the synthesis of zirconium phosphates, several zirconium phosphate fluorides with novel structures have also been developed. 

Zr-Al coprocess waste test, the feed, extractant, and scrub flows were 1, 0.5, and 0.1 mL/min, respectively. For the high sodium concentration waste, the feed, extractant, and scrub flows were 0.75, 1, and 0.25 mL/min, respectively. Samples of raffinate were drawn for analytical analysis approximately five hours after equilibrium had been reached. The resultant decontamination factors agreed reasonably well with our calculations. For the coprocess waste run, we expected an americium decontamination factor of 200. We purposely built in a large, overkillM in the sodium waste run by increasing the organic to aqueous flow rates. The sodium waste run produced a raffinate that, when calcined, would be well below the guideline for alpha-free waste with no allowance for decay. Analytical analysis of feeds and raffinates confirmed our batch results in that actinides were fractionated from major waste constituents such as aluminum, zirconium, sodium, and fluoride. 

Recent experimental work has indicated that the existing thermodynamic data on fluoride and chloride salts of zirconium and hafnium in a molten salt environment are unreliable. These data are required for the evaluation of non-aqueous processes for the separation of the two metals. ... 

Chapter 11 of Lustman and Kerze [LI] and Chap. 2 of ASTM Special Technical Publication 639 [S2] describe the generally excellent corrosion resistance of zirconium to most aqueous solutions. It is corroded, however, by hot concentrated sulfuric or phosphoric acids and is attacked by fluoride ion at concentrations as low as 0.001 percent [S2]. 

This is a study of the thermodynamics of the complexation of zirconium with fluoride using the calorimetric technique and measurement of the heat of solution of crystalline ZrCl4 in aqueous HF solutions. All experiments were conducted at a temperature of 25°C and in negligible ionic strength. Before and after each experiment, the calorimetric system was calibrated electrically. The initial concentrations of HF were varied from... 

Aqueous, chromium-free acidic solutions have also been developed for aluminum materials that may contain complex fluorides of titanium and zirconium, phosphate, and special organic compounds. These solutions are applied by spraying or dipping (up to 60 °C) and produce thin, almost colorless conversion layers with a surface weight < 0.1 g/m. ... 

Direct detection of even insoluble fluorides is also possible by means of the zirconium-alizarin test. Use is made of the fact that in the presence of small amounts of acid, precipitated or native calcium fluoride is readily soluble in warm aqueous solutions of salts that form complex fluorides. Pure calcium fluoride gives a clear solution impure products leave only the " gangue behind. 

The fact that solid calcium fluoride reacts immediately with zirconium alizarinate renders it possible to detect fluoride in a mixture with phosphates and oxalates. These salts interfere with the detection of fluoride in aqueous solution, because they form either insoluble or complex zirconium phosphates (or oxalates) and thus destroy the red zirconium-alizarin compound and also produce the yellow color. The fluoride in such mixtures may be isolated by treating the alkaline or neutral test solution with calcium chloride the precipitate is ignited and digested with dilute acid. The residue then may easily be tested for fluoride by the zirconium-alizarin solution. ... 

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