Application of Differential Atomic Pair Distribution Function Analysis in Determining Nutrient Fixation Mechanisms on Mineral Surfaces.

Adsorption and precipitation reactions on mineral surfaces regulate bioavailability, fate, and transport of ions in soils. EXAFS spectroscopy has been the most powerful technique for determining surface speciation for heavy metals and metalloids. However, EXAFS is not as effective for light elements, such as sulfate (S), phosphate (P) and silicate (Si), because of the weak X-ray scattering of the elements, hence difficulties in the EXAFS data collection and analysis. Thus, speciation of these oxyanions on mineral surfaces has remained quite ambiguous. Recently, differential X‑ray atomic pair distribution function (d-PDF) analysis based on total X-ray scattering, has risen to become an alternative surface speciation approach without having the challenges as EXAFS spectroscopy does. In this presentation, I will briefly introduce the d-PDF analysis, demonstrate its applications in determining surface speciation using S, P and Si adsorption on ferrihydrite surfaces, and discuss its limitations.