In-Situ Studies of Phosphate Surface Adsorption and Precipitation.

Phosphate is an important macronutrient required by organisms in soil, but often becomes the limiting factor in growth or biological production.   Because phosphate associates strongly with Fe, Al, and Ca minerals in soils, or can precipitate into its own mineral phase, phosphate can easily become unavailable.  Organic acids in soil add an interesting variable to the process by interfering with the geochemical cycle of phosphate; they can complex with Fe, Al, and Ca preventing the formation of minerals, or they can directly compete with phosphate for bonding sites.  Understanding the mechanisms of phosphate sorption to minerals found in soil and the precipitation of new phases while in competition with organic acids will ultimately allow for optimization of phosphate availability.  Aqueous soft X-ray synchrotron spectroscopy and Fourier Transformed infrared spectroscopy are utilized to discover the mechanisms of phosphate bonding to the surface of miinerals, the precipitation of Ca-P mineral phases, and the effect of citric acid on these mechanisms will be highlighted.