Zirconium ionic strength

Other solvent degradation products derived from the diluent as well as from TBP may arise. Butyl lauryl phosphoric acid (HELP) has been used as a model for diluent derived diesters of phosphoric acid and at concentrations above 2xlO M enhances Zr extraction by TBP. HELP is not removed by alkali washing of the solvent but BLP is transferred into water at low ionic strength. Dialkylphosphorane complexes of Zr may also arise from irradiation and can stabilize emulsions. Diluent derived hydroxamic acids are present at too low a concentration (10 -10 M) to completely account for the extent of zirconium retention which occurs in... 

As shown in Table II, there was an increase in sorption with increasing ionic strength at pH 7.1, the opposite being obtained at pH 5. Such phenomena may be explained in terms of the types of sorbing species postulated earlier. It has been shown (20, 21, 22) that the nature of the sorption of radiocolloids from aqueous solutions differs from ionic sorption. For example, Schubert and Conn (23) found that the sorption of colloidal zirconium and niobium on a cation exchanger increased with increasing electrolyte concentration, while addition of electrolyte effectively competed with and reduced sorption of the ionic species. 

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. 

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) ... 

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. 

The complexation and dissociation data for Fe and H, respectively, were taken from the earlier work of [49DOD/ROL]. The data for the complexation with Fe are consistent with other literature data and the stability constants, when corrected for ionic strength, are consistent with the auxiliary data listed in Chapter II of this review for HF but not for HF . However, the latter species is unimportant in both the experimental solutions of [49DOD/ROL] and [62BUS] and, as such, will have negligible effect on the stability constants found for zirconium-fluoride complexes in the latter work. 

In their study of the complexation of zirconium by chloride, the ionic strength was 4 M (HCIO4, ElCl). Under these experimental conditions, the findings of the present review indicate that the dominant zirconium species would be Zr rather than ZrOH " ... 

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... 

Table A-32 Stability constants for zirconium(lV) hydrolysis at various ionic strength and temperature for the general reaction mZx + qWiO Zr ,(OH)J" ...

Nazarenko and Mandzhgaladze (1969) studied the hydrolysis of zirconium at 25 °C using either acidified NaClO or KNO3 media. In both media they used four ionic strengths, 0.1, 0.3, 0.5 and 1.0 moll". They studied the hydrolysis reactions via utilisation of competition with coloured organic complexes. They obtained stability constants for the first four monomeric species of zirconium and found that the species were very stable (see Table 10.6). The pH range that they used in their study was quite narrow and cannot justify the selection of constants for four... 

The speciation of zirconium has been determined relative to an ionic strength of 1.0 mol 1 (H,Na)C104 due to the very low pH at which zirconium hydrolyses. Similar calculations for zero ionic strength are relatively meaningless due to the ionic strength induced whilst the hydrolysis reactions take effect. Figure 10.15 shows the speciation of zirconium under the stated conditions and at 25 "C. 

Peshkova and Ang (1962) studied the hydrolysis of hafniumflV) using solvent extraction at 25 °C and in 1.0 and 2.0 mol 1 HCIO. They postulated the formation of the polymeric species, Hf3(OH)4 and Hf4(OH)g. Both of these species have been observed for zirconium hydrolysis. The stabUity constants found by Peshkova and Ang (1962) were log j =4.41 and log 4g = 8.11 in 1.0 mol 1 HCIO4 and log 34 = 4.71 and log = 8.85 in 2.0 mol 1 HCIO4. These constants were used to determine stability constants at zero ionic strength, assuming Ae 2 = 0, and the values found were... 

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