Speciation of Phosphorus on Sorbing Materials for Stormwater Filtration Using K-Edge X-Ray Absorption Near Edge Structure.

Stormwater filtration structures are a structural best management practice designed to help reduce dissolved phosphorus (P) losses from agricultural and urban areas. A variety of industrial by-products are suitable for use as P sorbing materials (PSMs) for storm water filtration. However, the ability of PSMs to sorb P will vary with the physical and chemical properties of the material. Knowledge of P speciation on reacted PSMs will provide insight into the P sorption mechanisms, aid in selection of appropriate PSMs for use as media in filtration structures, and guide disposal decisions for spent materials. Previously, researchers have only focused on bulk chemical analysis, typically using chemical extractions. Phosphorus K-edge X-ray absorption near edge structure (XANES) is an in-situ method that can be used for determination of P species in mixed environmental samples like PSMs. The objective of our study was to determine speciation of P on PSMs after sequential reaction with a 5 mg L^-1 P solution under batch conditions to achieve a P loading of ≥32 mmol kg^-1. Phosphorus K-edge XANES spectra of all PSMs samples and nineteen known P standards were collected in Advanced Photon Source in Argonne, Illinois. Phosphorus speciation in unknown samples was determined by linear combination fitting spectra collected from known P standards. Based on results of linear combination fitting, we suggest that the P forms a variety of calcium-, aluminum-, and/or iron-phosphate minerals and sorbed phases on the reacted PSMs. Overall, P speciation information will be used to improve P removal efficiency of stormwater filtration structures, and evaluate potential disposal options for spent materials (e.g., fertilizer potential).