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A solubility and surface complexation study of a non-stoichiometric hydroxyapatite
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
2009 (engelsk)Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, nr 2, s. 257-267Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The dissolution and surface complexation of a non-stoichiometric hydroxyapatite (Ca8.4(HPO4)1.6(PO4)4.4(OH)0.4), (HAP) was studied in the pH range 3.5 – 10.5, at 25 ºC in 0.1 M Na(Cl). The results from well-equilibrated batch experiments, potentiometric titrations, and zeta-potential measurements were combined with information provided by Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The information from the analyses was used to design an equilibration model that takes in to account dissolution, surface potential, solution and surface complexation, as well as possible phase transformations. The results from the XPS measurements clearly show that the surface of the mineral has a different composition than the bulk and that the Ca/P ratio of the surface layer is 1.4 ± 0.1. This ratio was also found in solution in the batches equilibrated at low pH where the dominating reaction is dissolution. In the batches equilibrated at near neutral pH values, however, the Ca/P ratio in solution attains values as high as 25, which is due to re-adsorption of phosphate ions to the HAP surface. The total concentration of protons as well as the total concentration of dissolved calcium and phosphate in solution were used to calculate a model for the dissolution and surface complexation of HAP. The constant capacitance model was applied in designing the following surface complexation model.

sted, utgiver, år, opplag, sider
Elsevier, 2009. Vol. 73, nr 2, s. 257-267
HSV kategori
Identifikatorer
URN: urn:nbn:se:umu:diva-10985DOI: 10.1016/j.gca.2008.09.034OAI: oai:DiVA.org:umu-10985DiVA, id: diva2:150656
Tilgjengelig fra: 2008-12-29 Laget: 2008-12-29 Sist oppdatert: 2018-06-09bibliografisk kontrollert
Inngår i avhandling
1. Solubility and Surface Complexation Studies of Apatites
Åpne denne publikasjonen i ny fane eller vindu >>Solubility and Surface Complexation Studies of Apatites
2007 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Apatites are a diverse class of phosphate minerals that are important in a great variety of natural and industrial processes. They are, for example, used as raw material in fertiliser production and in the remediation of metal-contaminated soils. Hydroxyapatite Ca5(PO4)3OH, (HAP) and fluorapatite Ca5(PO4)3F, (FAP) are similar to the biological apatite that is the main constituent of mammalian bone and teeth, and they are therefore promising materials for artificial bone and tooth implants.

This thesis is a summary of four papers with focus on dissolution and surface complexation reactions of HAP and FAP in the absence and presence of both organic ligands and the natural and commonly occurring iron oxide goethite (α-FeOOH).

The dissolution and surface complexation of HAP and FAP was investigated with a combination of different techniques. Potentiometric acid/base titrations and batch experiments were combined with X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectroscopy to generate dissolution and surface complexation models for both apatites. The results from these studies showed that both apatites form surface layers that are different from their bulk compositions when equilibrated in aqueous solutions. The modeling efforts predicted speciation of these surfaces as well as the concentration of the dissolution products in the solution.

The interaction between organic ligands and the apatite surfaces was also investigated and the results from this study show that the organic ligands form outer-sphere complexes on the apatite surfaces over a large pH interval, and that this adsorption enhances the dissolution of apatites.

The presence of goethite also enhances the dissolution of FAP as it acts as a sink for the phosphate released from FAP. Phase transformation in this system was detected using ATR-FTIR as the phosphate adsorbed to the goethite surface precipitates as FePO4 (s) after approximately 15 days of reaction time. This changes the speciation, and possibly also the bioavailability of phosphate in this two-mineral system.

sted, utgiver, år, opplag, sider
Umeå: Kemi, 2007. s. 56
Emneord
apatite, dissolution, calcium, phosphate, fluoride, goethite, surface complexation, speciation, outer-sphere complexation, FTIR, XPS, potentiometry
HSV kategori
Identifikatorer
urn:nbn:se:umu:diva-1408 (URN)978-91-7264-425-0 (ISBN)
Disputas
2007-11-16, KB3B1, KBC, Umeå Universitet, Umeå, 10:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2007-10-29 Laget: 2007-10-29 Sist oppdatert: 2018-01-13bibliografisk kontrollert

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