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Phase Transformations, Ion-Exchange, Adsorption, and Dissolution Processes in Aquatic Fluorapatite Systems

Bengtsson, Asa; Shchukarev, Andrei; Persson, Per LU and Sjoberg, Staffan (2009) In Langmuir 25. p.2355-2362
Abstract
A synthetic fluorapatite was prepared that undergoes a phase transformation generated during a dialysis step. A surface layer with the composition Ca(9)(HPO(4))(2)(PO(4))(4)F(2) is formed, which is suggested to form as one calcium atom is replaced by two protons. A surface complexation model, based upon XPS measurements, potentiometric titration data, batch experiments, and zeta-potential measurements was presented, The CaOH and OPO(3)H(2) Sites were assumed to have similar protolytic properties as in a corresponding nonstoichiometric HAP (Ca(8.4)(HPO(4))(1.6)(PO(4))(4.4)(OH)(0.4)) system. Besides a determination of the solubility product of Ca(9)(HPO(4))(2)(PO(4))(4)F(2), two additional surface complexation reactions were introduced; one... (More)
A synthetic fluorapatite was prepared that undergoes a phase transformation generated during a dialysis step. A surface layer with the composition Ca(9)(HPO(4))(2)(PO(4))(4)F(2) is formed, which is suggested to form as one calcium atom is replaced by two protons. A surface complexation model, based upon XPS measurements, potentiometric titration data, batch experiments, and zeta-potential measurements was presented, The CaOH and OPO(3)H(2) Sites were assumed to have similar protolytic properties as in a corresponding nonstoichiometric HAP (Ca(8.4)(HPO(4))(1.6)(PO(4))(4.4)(OH)(0.4)) system. Besides a determination of the solubility product of Ca(9)(HPO(4))(2)(PO(4))(4)F(2), two additional surface complexation reactions were introduced; one that accounts for a F/OH ion exchange reaction, resulting in the release of quite high fluoride concentrations (similar to 1 mM) that turned out to be dependent on the surface area of the particles. Furthermore, to explain the lowering of pH(iep) from around 8 in nonstoichiometric HAP suspensions to about 5.7 in FAP suspensions, a reaction that lowers The surface charge due to the readsorption of fluoride ions to the positively charged Ca sites was introduced: CaOH(2)(+) + F(-) -> CaF + H(2)O. The resulting model also agrees with predictions based upon XPS and ATR-FTIR observations claiming the formation of CaF(2)(S) in the most acidic pH range. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
25
pages
2355 - 2362
publisher
The American Chemical Society
external identifiers
  • scopus:63249100904
ISSN
0743-7463
DOI
10.1021/la803137u
language
English
LU publication?
no
id
afd08dc7-7a3c-4cf2-86e4-f01d703900fe (old id 4332381)
date added to LUP
2014-03-04 09:46:58
date last changed
2017-12-10 03:48:18
@article{afd08dc7-7a3c-4cf2-86e4-f01d703900fe,
  abstract     = {A synthetic fluorapatite was prepared that undergoes a phase transformation generated during a dialysis step. A surface layer with the composition Ca(9)(HPO(4))(2)(PO(4))(4)F(2) is formed, which is suggested to form as one calcium atom is replaced by two protons. A surface complexation model, based upon XPS measurements, potentiometric titration data, batch experiments, and zeta-potential measurements was presented, The CaOH and OPO(3)H(2) Sites were assumed to have similar protolytic properties as in a corresponding nonstoichiometric HAP (Ca(8.4)(HPO(4))(1.6)(PO(4))(4.4)(OH)(0.4)) system. Besides a determination of the solubility product of Ca(9)(HPO(4))(2)(PO(4))(4)F(2), two additional surface complexation reactions were introduced; one that accounts for a F/OH ion exchange reaction, resulting in the release of quite high fluoride concentrations (similar to 1 mM) that turned out to be dependent on the surface area of the particles. Furthermore, to explain the lowering of pH(iep) from around 8 in nonstoichiometric HAP suspensions to about 5.7 in FAP suspensions, a reaction that lowers The surface charge due to the readsorption of fluoride ions to the positively charged Ca sites was introduced: CaOH(2)(+) + F(-) -> CaF + H(2)O. The resulting model also agrees with predictions based upon XPS and ATR-FTIR observations claiming the formation of CaF(2)(S) in the most acidic pH range.},
  author       = {Bengtsson, Asa and Shchukarev, Andrei and Persson, Per and Sjoberg, Staffan},
  issn         = {0743-7463},
  language     = {eng},
  pages        = {2355--2362},
  publisher    = {The American Chemical Society},
  series       = {Langmuir},
  title        = {Phase Transformations, Ion-Exchange, Adsorption, and Dissolution Processes in Aquatic Fluorapatite Systems},
  url          = {http://dx.doi.org/10.1021/la803137u},
  volume       = {25},
  year         = {2009},
}