Zirconium speciation

A solubility constant (logn, ) was determined from the data at pH 4.2, being approximately - 52. However, the true concentration of zirconium in solution was not measured nor was the zirconium speciation. As such, the solubility constant measured cannot be accepted in this review. 

Lomenech, C., R. Drot, and E. Simoni. 2003. Speciation of uranium(VI) at the solid/ solution interface Sorption modeling on zirconium silicate and zirconium oxide. Radiochim. Acta 91 453-461. 

Substitution at polynuclear aqua-ions is often much slower than at the respective parent mononuclear aqua-ions, as has been demonstrated for, e.g., aluminum(III), iron(III), zirconium(IV), and hafnium(IV). A further example has been provided by aluminum, where the Al,3 polynuclear oxo-aqua-species takes several months to equilibrate with lactate. Very different rates of complex formation are used to sort out speciation in multicomponent polynuclear/mononuclear aqua-cation systems. The problems involved in this approach are well illustrated by a Al NMR study of the numerous reaction pathways in the Al " /ferron [ferron = 7-iodo-8-hydroxyquinoline-5-sulfonic acid, (18)] reaction. The slowness of reaction of polynuclear species can cause difficulties in the determination of total metal content, e.g., of aluminum by ferron or Alizarin S (19), in natural waters. In certain situations these... 

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. 

Figure 10.15 Predominance diagram for the speciation of the zirconium(IV) ion at 25 °C and in 1.0 mol 1 (H,Na)CI04. The behaviour in the region of 0 > -log [H ] > 12 should be treated with caution due to changes in activity coefficients.

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