Assessment of Hedley’s Sequential Extraction Method for Phosphorus Forms in Biosolids Using P K-edge X-ray Absorption Near-edge Structure Spectroscopy

We determined P species in biosolids and their residues after applying Hedley’s sequential extractions using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. HCl extraction successfully removed P associated with Ca minerals from the biosolids. The majority of P associated with Fe minerals (FeP) was extracted by the NaOH fluid. However, recalcitrant FeP phases remained persistent even after the final extraction process, suggesting that NaOH-extracted P fractions may be underestimated in biosolids with abundant Fe. The XANES technique is essential to identify secondary P phases in biosolids, which could not be detected by an XRD technique.