Thermochemical Evaluation of Elemental Phosphorus Recovery from Sewage Sludge
DOI:
https://doi.org/10.17159/Abstract
The FlashPhos process aims to recover elemental white phosphorus (P4) from sewage sludge through drying, flash combustion/gasification, and carbothermic refining. This study evaluates the material behavior of sewage sludge ash during melting and reduction in a refining furnace designed for the FlashPhos process. Thermodynamic modeling in FactSage 8.2, combined with experiments from a tube furnace, assesses potential phosphorus recovery and minor element behavior.For the two types of sewage sludge analyzed, yields of 40% and 75% white phosphorus were achieved after 1 hour at 1600°C, with losses of 60% and 25% to the metal phase. These results slightly exceed the calculated equilibrium yield of 28-73%, primarily dependent on the iron-to-phosphorus (Fe/P) ratio of the sludge. Temperature significantly influences phosphorus yield, especially with incomplete ash melting.The process produces clean slag free of heavy metals, suitable as a cement-like binder material. However, heavy metals such as Zn, Pb, As, Sb, and Sn co-evaporate with phosphorus, requiring additional processing for pure P4 production. The final slag consists of CaO, SiO2, MgO, and Al2O3, effectively removing phosphorus and heavy metals. This version maintains the essential details while meeting the word count requirement.
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Copyright (c) 2026 Andrea Kotze, Sander Arnout, Els Nagels, Yannick Cryns, Davide Messina
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