Early-Stage Investigation of Potential Phosphorus Recovery Pathway from Dredged Sediments: Case of Malmfjärden Bay,...

Metal and nutrients can be extracted and recovered from sediments for beneficial use. The aim of the current study is to extract phosphorus (P) from dredged sediments from Malmfjärden bay through chemical extraction, targeting the determination of the best conditions to extract P from the studied sediments with minimal contamination from metals. The chemicals used for the extractions include citric acid (C₆H₈O₇), sulphuric acid (H₂SO₄), sodium hydroxide (NaOH) and ethylenediaminetetraacetic acid (EDTA) at 0.01 M or 0.1 M. The acids were at pH 5, and NaOH at pH 12. The pH was also varied for 0.01 M EDTA at pH 2, and 0.1 M H₂SO₄ at pH 1. A single extraction was carried out with each reagent at the varying concentrations and pH. One test had a sequential two-step extraction of EDTA as the first step, followed by H₂SO₄ as the second step. The elements were analysed using inductively coupled plasma sector field mass spectrometry (ICP-SFMS). The results showed that the extraction efficiencies were significantly higher at 0.1 M than 0.01 M of the reagents, as well as at more acidic conditions for the reagents with a varied pH, in most cases. H₂SO₄ at pH 1 extracted the most P (46.4%), together with most of the other elements. EDTA also exhibited a high extraction efficiency for the elements and can be used as a pre-step to remove metal before extraction with H₂SO₄. Alternatively, although it had lower P extraction efficiencies, NaOH can be used as the extractant, since it extracted less of the other elements. The P/metal extraction ratios further indicated that NaOH achieved high selectivity, as well as the second step sequential extraction H₂SO_4. Hence, the recovered P will be less contaminated. P extraction from sediments can indeed become one way of recovering the finite element, which would otherwise be normally lost as waste with the sediments.