Zirconium solubility constant

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. 

The thermodynamic values determined for the phases and species of zirconium are listed in Table 10.4. There is reasonable agreement between the values chosen in the present review with those selected by Brown, Curti and Grambow (2005). The main differences arise from the differing value chosen for the Gibbs energy of the zirconiumflV) ion. This difference is due to a different solubility constant chosen in the present review for Zr02(s) with respect to that chosen by Brown, Curti and Grambow (2005). 

Zirconium tetrachloride is a white crystalline solid with specific gravity 2.803.4 The solid sublimes under atmospheric pressure at 331° [log pBin. = — (26,000/4.57T) + 12.30] but melts at 437° under its own pressure, which is about 25 atm. at this temperature.18 The vapor density shows normal behavior up to 500°, at which point dissociation is suspected.16 Electron-diffraction results show tetrahedral symmetry with the Zr-Cl distance 2.33 A.17 Todd18 has recently determined the heat capacity of zirconium tetrachloride at low temperatures (extrapolated below —222°) and calculated the usual thermodynamic constants for the compound. The melting point of hafnium tetrachloride has been estimated as 432° under its own pressure, but the solid sublimes under atmospheric pressure at 317°.12 Both metal chlorides are extremely hygroscopic. They are easily soluble in water, although extensively hydrolyzed. All high-purity samples should be desiccated as well as possible. 

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