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Formation of Precursor Calcium Phosphate Phases During Crystal Growth of Apatite and Their Role on the Sequestration of Heavy Metals and Radionuclides

Borkiewicz, Olaf J.
http://rave.ohiolink.edu/etdc/view?acc_num=miami1292008822

Abstract Details

2010, Doctor of Philosophy, Miami University, Geology and Environmental Earth Science.
Due to increasing risk associated with the contamination of the environment with heavy metals and radionuclides, societies worldwide are facing a pressing need for new more efficient environmental remediation techniques. One approach that gained considerable attention over the last two decades is in situ metal stabilization by phosphate amendments – a technique based on the coprecipitation of contaminant species with phosphates and the formation of insoluble metal(M)-substituted minerals, such as apatite Ca5-xMx(PO4)6(OH,Cl,F). One of the major results of this dissertation is that formation of apatite at Earth-surface conditions is preceded by crystallization of other less stable calcium phosphates (precursors) that ultimately transform to apatite. The first part of this dissertation investigates formation and evolution of calcium phosphate precursors under conditions simulating those found in Earth-surface environments. The pathways of phase development in the Ca(OH)2-H3PO4-H2O system were studied using conventional ex situ as well as in situ time-resolved X-ray diffraction. The results clearly indicate formation of precursors under conditions found at the Earth-surface, which may be relevant not only in the context of natural soil environments, but also in the context of engineered conditions, like those found during metal stabilization by phosphate amendments. In the second part of the dissertation, pathways of calcium phosphate development in the presence of different metal ions (Zn, Cd, Sr, U, and Th) are studied by time-resolved X-ray diffraction. The results clearly indicate a significant influence of contaminant species on the pathways of phase development in the Ca(OH)2-H3PO4-H2O system. Secondary metal-bearing phases, far more soluble than hydroxylapatite, were often formed in the presence of the metals studied. Finally, the role of precursor formation on the heavy metal sequestration and fate during crystal growth of apatite was studied by a combination of powder X-ray diffraction, SEM/EDS and ICP-AES. The results indicate significant reduction in the solution concentration of metals during formation of precursor phases and relative stability of the contaminant species during structural transformation of phases involved in low-temperature crystallization of hydroxylapatite. Fluctuations in the concentration of elements observed during structural changes in the system suggest a dissolution-recrystallization mechanism of transformation of amorphous phases to brushite and parascholzite.
John Rakovan, PhD (Advisor)
Hughes John, PhD (Committee Member)
Cahill Christopher, PhD (Committee Member)
Dong Hailiang, PhD (Committee Member)
Rech Jason, PhD (Committee Member)
Sommer Andre, PhD (Committee Member)
143 p.
Mineralogy
calcium phosphates; precursor phases; hydroxylapatite; time-resolved in situ X-ray diffraction; synchrotron

Recommended Citations

Citations

  • Borkiewicz, O. J. (2010). Formation of Precursor Calcium Phosphate Phases During Crystal Growth of Apatite and Their Role on the Sequestration of Heavy Metals and Radionuclides [Doctoral dissertation, Miami University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=miami1292008822

    APA Style (7th edition)

  • Borkiewicz, Olaf. Formation of Precursor Calcium Phosphate Phases During Crystal Growth of Apatite and Their Role on the Sequestration of Heavy Metals and Radionuclides. 2010. Miami University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=miami1292008822.

    MLA Style (8th edition)

  • Borkiewicz, Olaf. "Formation of Precursor Calcium Phosphate Phases During Crystal Growth of Apatite and Their Role on the Sequestration of Heavy Metals and Radionuclides." Doctoral dissertation, Miami University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1292008822

    Chicago Manual of Style (17th edition)

miami1292008822
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© 2010, all rights reserved.
This open access ETD is published by Miami University and OhioLINK.