XAFS study of adsorbed and mineral forms of phosphate

The solubility of inorganic phosphorus in soils is regulated by surface-ads orbed phosphate or phosphate minerals. The objective of this study was to d etermine whether different phosphate species of relevance to soils showed d istinguishing XAFS spectral features. Phosphorus K-XANES spectra for Fe-pho sphates were characterized by a unique pre-edge feature near -3 eV (relativ e energy) that increased in intensity with increasing mineral crystallinity and was very weak for phosphate adsorbed on goethite. Spectra of Ca-phosph ates and a soil sample exhibited a distinct shoulder on the high-energy sid e of the absorption edge. Spectra of Al-phosphates were characterized by a weak pre-edge feature at -1 eV.