Phosphorus recovery from municipal sludge-derived ash: influence of incineration temperature and heavy metal ion on ash mineralogy

With the implementation of the “carbon neutrality” strategy, waste resource-utilization technologies have become the focus of future research. P recovery from excess sludge (ES) is of great significance. In this paper, P recovery in excess sludge ash (ESA) of different incineration temperatures was studied. The experiment results showed that the optimal incineration temperature of ESA was 750 °C, and its total phosphorus content was 90.7 mg/g, which were three times heavier than the original sludge. As the incineration temperature increased from 650 °C to 850 °C, the more crystals appeared to be agglomerated and there was melting phenomenon on the surface of ESA. Higher temperatures were conducive to the AIP formation. The new minerals such as Ca₄(Mg.Fe)₅(PO4)₆ and (Ca.Mg)₃(PO4)₂ were produced in ESA of 800 °C and 850 °C. Under the optimal acid-leaching conditions that were leaching time of 90 min, liquid–solid ratio of 50:1 (mL/g), and sulfuric acid (H₂SO₄) concentration of 1 M, P leaching efficiencies could reach 100% in ESA of 700 °C and 750 °C, where P leaching contents were the most abundant and more suitable for P recovery. The research results provided theoretical basis and operational conditions for P recovery of excess sludge.