Effects of humic material on the precipitation of calcium phosphate

Alvarez, R; Evans, LA; Milham, PJ; Wilson, MA

Effects of humic material on the precipitation of calcium phosphate

Alvarez, R Evans, LA

Milham, PJ Wilson, MA

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Publication Type:: Journal Article
Citation:: Geoderma, 2004, 118 (3-4), pp. 245 - 260
Issue Date:: 2004-01-01

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Field	Value	Language
dc.contributor.author	Alvarez, R	en_US
dc.contributor.author	Evans, LA https://orcid.org/0000-0003-1544-6868	en_US
dc.contributor.author	Milham, PJ	en_US
dc.contributor.author	Wilson, MA	en_US
dc.date.issued	2004-01-01	en_US
dc.identifier.citation	Geoderma, 2004, 118 (3-4), pp. 245 - 260	en_US
dc.identifier.issn	0016-7061	en_US
dc.identifier.uri	http://hdl.handle.net/10453/3627
dc.description.abstract	Soil organic acids such as humic and fulvic acids can play an important role in influencing inorganic phosphate availability in P-fertilized soils by inhibiting formation of thermodynamically stable calcium phosphates. Calcium phosphate phases which are important in these systems may include amorphous calcium phosphate (Ca9(PO4)6·nH 2O; ACP), dicalcium phosphate dihydrate (CaHPO4 ·2H2O; DCPD, also known as brushite), octacalcium phosphate (Ca8H2(PO4) 6·5H2O; OCP) and the thermodynamically most stable phase, hydroxyapatite (Ca5(PO4)3OH; HAp). In this study, the formation of these phases in the presence of soil humic acids derived from the Sydney Basin in New South Wales, Australia has been examined using the combined techniques of pH-stat autotitration, Fourier transform infrared (FTIR) and laser Raman spectroscopy, as well as X-ray diffraction (XRD) and elemental analyses. Under conditions of high supersaturation at a pH of 7. 4 and a temperature of 25°C, it was found that these soil humics delay the transformation of unstable ACP to thermodynamically more stable OCP and thence to an apatitic phase resembling poorly crystalline HAp. At the lower pH of 5.7, and in the presence of humic acids, ACP was also precipitated initially. However, this was in contrast to the humic-free solutions which produced DCPD. ACP produced in the presence of humic materials persisted longer than DCPD in their absence, before ultimately hydrolyzing to OCP. Modes of humic-calcium phosphate interaction are discussed. It has been concluded that humic materials are geologically relevant inhibitors of calcium phosphate transformation and that they may modify the availability of phosphorus in soils by changing crystallisation behaviour from solution. © 2003 Elsevier B.V. All rights reserved.	en_US
dc.relation	http://purl.org/au-research/grants/arc/C29920006
dc.relation.ispartof	Geoderma	en_US
dc.relation.isbasedon	10.1016/S0016-7061(03)00207-6	en_US
dc.subject.classification	Agronomy & Agriculture	en_US
dc.title	Effects of humic material on the precipitation of calcium phosphate	en_US
dc.type	Journal Article
utslib.citation.volume	3-4	en_US
utslib.citation.volume	118	en_US
utslib.for	0602 Ecology	en_US
utslib.for	05 Environmental Sciences	en_US
utslib.for	06 Biological Sciences	en_US
utslib.for	07 Agricultural and Veterinary Sciences	en_US
dc.location.activity	Joensuu, FINLAND
pubs.embargo.period	Not known	en_US
pubs.organisational-group	/University of Technology Sydney
pubs.organisational-group	/University of Technology Sydney/Faculty of Science
pubs.organisational-group	/University of Technology Sydney/Faculty of Science/School of Mathematical and Physical Sciences
utslib.copyright.status	closed_access
pubs.issue	3-4	en_US
pubs.publication-status	Published	en_US
pubs.volume	118	en_US

Abstract:

Soil organic acids such as humic and fulvic acids can play an important role in influencing inorganic phosphate availability in P-fertilized soils by inhibiting formation of thermodynamically stable calcium phosphates. Calcium phosphate phases which are important in these systems may include amorphous calcium phosphate (Ca9(PO4)6·nH 2O; ACP), dicalcium phosphate dihydrate (CaHPO4 ·2H2O; DCPD, also known as brushite), octacalcium phosphate (Ca8H2(PO4) 6·5H2O; OCP) and the thermodynamically most stable phase, hydroxyapatite (Ca5(PO4)3OH; HAp). In this study, the formation of these phases in the presence of soil humic acids derived from the Sydney Basin in New South Wales, Australia has been examined using the combined techniques of pH-stat autotitration, Fourier transform infrared (FTIR) and laser Raman spectroscopy, as well as X-ray diffraction (XRD) and elemental analyses. Under conditions of high supersaturation at a pH of 7. 4 and a temperature of 25°C, it was found that these soil humics delay the transformation of unstable ACP to thermodynamically more stable OCP and thence to an apatitic phase resembling poorly crystalline HAp. At the lower pH of 5.7, and in the presence of humic acids, ACP was also precipitated initially. However, this was in contrast to the humic-free solutions which produced DCPD. ACP produced in the presence of humic materials persisted longer than DCPD in their absence, before ultimately hydrolyzing to OCP. Modes of humic-calcium phosphate interaction are discussed. It has been concluded that humic materials are geologically relevant inhibitors of calcium phosphate transformation and that they may modify the availability of phosphorus in soils by changing crystallisation behaviour from solution. © 2003 Elsevier B.V. All rights reserved.

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