The influence of thermodynamic and kinetic factors on the formation and dissolution of calcium phosphates in complex geochemical systems

• Applicant: Dr. Julian Oxmann
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry ; Oceanography
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 283810620

Formation of calcium phosphate (Ca-P) is an important process in removing phosphorus (P) from natural waters, with carbonate fluorapatite (CFAP) being a major sink for reactive P in the ocean. Local conditions may either favor direct apatite formation or nucleation of apatite precursors. In situ precipitation and dissolution of these minerals are, however, difficult to predict owing to the interplay between thermodynamic and kinetic factors. This project assesses effects of these factors on Ca-P precipitation and dissolution by combining conventional sediment and pore-water analyses, experimental approaches and geochemical modelling with state-of-the-art techniques for determining solid-phase P speciation. Main objectives are to (i) determine P speciation in Baltic Sea sediments; (ii) estimate the time of Ca-P precipitation in sea and brackish water under different experimental conditions using a nucleation assay; (iii) determine solubilities of Ca-P phases in sediment-water systems using a dissolution assay that mimics marine, brackish and freshwater conditions; (iv) identify the role of apatite precursors during P diagenesis; (v) verify results using geochemical models and cross-validate analytical methods. Techniques for determining Ca-P phases include chemical and synchrotron-based methods with accompanying scanning electron microscopy and electron microprobe analysis. These approaches will, together with the method validation, contribute to better understand P dynamics and P diagenesis in complex natural environments.

• DFG Programme: Research Grants
• International Connection: Netherlands, New Zealand
• Co-Investigator: Professor Dr.-Ing. Klaus Wallmann
• Cooperation Partners: Dr. Peter Kraal; Dr. Stefan Krause; Dr. Luitgard Schwendenmann