Aqueous zirconium sulphates

All of the experimental studies on the formation of Zr sulphate complexes have been re-interpreted in the present review (using a statistical (least squares) regression technique) since in the majority of cases either the model or the selected stability constants assigned by the authors are not supported by the data (see Appendix A) or no uncertainties were assigned in the original work. 

A summary of the available data, as reported in the original papers, together with the stability eonstants re-interpreted in the present review, is shown in Table V-28, whieh eontains eompiled experimental data for equilibria of the type  

NC Re-evaluation of the data in this review indicates that the formation of the species is not consistent with the data. 

Experimental data are available only at three different ionic strengths (2, 2.33 and 4 M perchloric acid solutions). As for zirconium complexes with other ligands, the limited number of available experimental data makes the extrapolation to infinite dilution relatively uncertain. 

Both the stability constant and interaction coefficient appear relatively consistent with the values of (4.87 + 0.15) and -(0.19 + 0.06) kg-mol found for NpSO [2001LEM/FUG]. The As value was used in conjunction with the interaction coefficient derived for s(Zr, ClOj) in this review (0.89 0.10) kg-mol, that for 

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Raman spectroscopic evidence has been obtained in support of the suggestion of over a decade ago that aqueous zirconium sulphate solutions do not contain a single preferred species stable over a range of composition. The equilibria shown in Scheme 2 were suggested to occur in sulphate solutions 0.1—0.4 mol 1 in zirconium. ... 

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. 

All of the members of the final review team contributed, if not text, then comments to all of the chapters of the book. Their primary responsibilities for the different sections/chapters were divided as follows. Paul Brown prepared the introduction, and the sections on elemental zirconium, the zirconyl ion, the gaseous zirconium oxides, zirconium hydride, the halogen compounds and complexes, the chalcogen compounds and complexes, the Group 15 compounds and complexes, zirconium carbides and silicates. He was assisted by Christian Ekberg in the interpretation of aqueous zirconium complexes in these sections. Some initial work was done by Ken Jackson on the zirconium sulphate, nitrate and phosphate compounds and complexes. Bernd Grambow was responsible for the drafting of the sections on zirconium hydrolysis, the ion and the section on crystalline and amorphous zirconium oxides. Enzo Curti drafted the section on the zirconium carbonates. 

Zirconium ( > 100 mg in ca /. M sulphuric acid solution). Add freshly prepared 10 per cent aqueous diammonium hydrogenphosphate solution in 50-100-fold excess. Dilute to 300 mL, boil for a few minutes, allow to digest on a water bath for 15-30 minutes and cool to about 60 °C. Filter through a quantitative filter paper, wash first with 150 mL of 1M sulphuric acid containing 2.5 g diammonium hydrogenphosphate and then with cold 5 per cent ammonium nitrate solution until the filtrate is sulphate-free. Dry the filter paper and precipitate at 110°C, place in a platinum crucible and carefully burn off the filter paper. Finally heat at 1000 °C for 1-3 hours and weigh as ZrP207 (Section 11.51). 

Sulphated zirconia was prepared by adding aqueous ammonia solution to zirconium oxychloride solution at a pH of 10. The precipitate was thoroughly washed with distilled water and freed from ammonium and chloride ions. It was dried in an oven at 120 C for 24h. The sulphation of the prepared zirconia was done with 1.0 N sulphuric acid (15 ml/g). It was dried at 110 C and calcined at 450°C for 3h. 

Although the solvent purification process is adequate for the production of say reactor-grade zirconium, it is possible to modify it so that pure hafnium may also be obtained. Distribution data are available for various solutions containing thiocyanate, sulphate and chloride from which it is possible, for example, to deduce that both hafnium and zirconium will extract into hexone provided the aqueous phase has a high thiocyanate concentration and a low chloride concentration. The zirconium may then be selectively backwashed in a second extractor using say an aqueous phase of high thiocyanate concentration and moderate sulphate concentration, where the separation factor of the system is high. The hafnium can then... 

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