Titanium IV , Zirconium, Hafnium and Thorium

Titanium can exist in solution in a number of oxidation states. The trivalent and tetravalent states are stable in aqueous solution. Data for the trivalent oxidation state are given in Chapter 11. 

There have only been a few studies that have examined the hydrolytic reactions of titanium(IV), with many obtaining unreliable solubility or stability constant data. Data for the monomeric species TiOOH to TiO(OH)g are available, with the neutral complex having a large pH region of stability. Although polymeric species have been postulated in a number of studies, the stoichiometry of the species is widely different in each of the studies and, as such, none of the data for these species are retained. 

Hydrolysis of Metal Ions, First Edition. Paul L. Brown and Christian Ekberg. 

More recent solubility studies, on either rutile or anatase (Ti02(s)), have shown that these phases are much less soluble than the amorphous titanium hydroxide phase. Knauss etal. (2001) studied the solubility of rutile from 100 to 300 C and found that the minimum solubility across this range was temperature independent, with log ranging between —7.57 and —7.93. These values are almost 

Schmidt and Vogelsberger (2009) also measured the solubihty for Ti02(s) at zero ionic strength and obtained a solubility constant that is described by reaction (2.13) (M = TiO +, X = 1). The corresponding solubility constant obtained was 

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I W Titanium(IV), Zirconium, Hafnium and Thorium Table 10.8 Literature thermodynamic data for baddeleyite and Zr(s) at 25 °C. 

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