Investigation on emission control of NO x precursors and phosphorus reclamation during pyrolysis of ferric sludge

Keke Xiao, Zecong Yu, Hui Wang, Jiakuan Yang*, Sha Liang, Jingping Hu, Huijie Hou, Bingchuan Liu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


In this study, a method to reduce the emission of NO x precursors (e.g., hydrogen cyanide (HCN) and ammonia (NH 3 )) while simultaneously reclaim more plant-available P was proposed through pyrolyzing ferric sludge (sludge conditioned by Fenton's reagents) rather than raw sludge. The nitrogen and phosphorus transformation at different pyrolysis temperatures was investigated. The results indicated that in comparison with the pyrolysis of raw sludge, the remaining iron compounds in ferric sludge can fix char-N in more stable forms (e.g., appearance of pyrrole-N at 900 °C). The secondary cracking of amine-N compounds in tar-N (e.g., 81.67% increase of amine-N at 900 °C) can be inhibited. Hence, more amine-N was remained and less heterocyclic-N and nitrile-N compounds were generated in tar–N. Less generation of NH 3 -N and HCN-N was also observed in NO x precursors (e.g., 5.46% decrease of NH 3 -N and 6.91% decrease of HCN-N at 900 °C). Moreover, the results of X-ray diffractometry, liquid 31 P nuclear magnetic resonance spectroscopic, X-ray photoelectron spectroscopic, and chemical analyses collectively indicated that iron present in ferric sludge also favored reclamation of more plant-available P. In comparison with the pyrolysis of raw sludge, an increase in the total phosphorus pool was noted (18.06–36.26 versus 15.54–30.59 mg g −1 dry solids). A decrease in mobility with the predominant P as sodium hydroxide (NaOH)-P, and an increase in plant-available P can be also obtained. This study indicated that pyrolysis of ferric sludge was a feasible way to simultaneously reduce emission of NO x precursors, reclaim plant-available P, and reuse ferric sludge.

Original languageEnglish
Pages (from-to)932-940
Number of pages9
JournalScience of the Total Environment
StatePublished - 20 Jun 2019
Externally publishedYes


  • Ferric sludge
  • Iron-rich char
  • NO precursors
  • Phosphorus recovery
  • Pyrolysis


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