blogfast25
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Seeking K: hydrolysis of titanyl ion
For the hydrolysis of TiO(2+) salt solutions (Ti +IV), acc.:
TiO(2+) (aq.) + 3 H2O (l) ↔ TiO2 (s) + 2H3O(+) (aq.)
Does anyone have the equilibrium constant K = [H3O(+)]^2/[TiO(2+)]
Or alternatively the pH at which titanyl salts begin dropping out of solution as TiO2?
[Edited on 15-1-2010 by blogfast25]
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JohnWW
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I found about 153 results for "titanyl salts" on Google, including a World Patent on making them, although none were sufficiently specific to give
details such as the pH at which they hydrolyse to TiO2. It appears that TiO2 can be made to dissolve, with difficulty, by strong concentrated acids,
particularly hot concentrated H2SO4, as "TiO++" salts, although they more correctly contain hydrated cations like [Ti(OH)2(H2O)4]++, which in solution
are readily hydrolyzed to TiO2 on raising the pH. Even so, the pH at which this hydrolysis occurs is very low, probably less than 1, although a salt
[TiO]SO4.H2O can be isolated by crystallization.
BTW: Crude TiO2 is most often extracted from ilmenite/perovskite sands, (Fe,Ca)TiO3, which often occur in association with magnetite beach sands,
formed by the weathering of basalt, and may contain SiO2 even after magnetic or electrostatic separation. It would be separable as above by
dissolution with hot concentrated H2SO4, in which SiO2 is insoluble. The solution would also contain Fe(II) and (III), which would precipitate at
different pHs.
[Edited on 16-1-10 by JohnWW]
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kmno4
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Informations you sought about Ti(IV) hydrolysis can be found in these articles:
http://dx.doi.org/10.1016/0022-1902(81)80279-5
http://www3.interscience.wiley.com/journal/114238437/abstrac...
.... and in this book:
Бусев А.И., Типцова В. Г.,
Иванов В.М. "Руководство
по аналитической химии
редких металлов"( М.: Химия,
1978)
[Edited on 16-1-2010 by kmno4]
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blogfast25
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Thanks both JohnWWW and kmno4!
John, I've seen the patents too and all mention the precipitation of TiO2 from the ferrous/titanyl sulphate solution by titrating the solution to pH =
7, using strong NaOH. I actually worked in a 'sulphate process' TiO2 plant some 20 years ago and can confirm that this is the practice used.
Unfortunately this says little about the pH up to which TiOSO4 (or equivalent) stays in solution and above which it starts dropping the pigment...
The first link kmno4 provided, which strictly should have been:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi...
... must be the bees knees but at $30 somewhat outside my budget. Interesting how the abstract mentions quite a variety of TiO-type species...
I'll probably do some crude tests myself, involving various concentrations of TiOSO4, titrating till cloudiness and measuring pH.
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