Removal of phosphate from water by paper mill sludge biochar

Ming Zhang, Kun Lin, Xiaodian Li, Lijun Wu, Jie Yu, Shuang Cao, Dong Zhang, Liheng Xu, Sanjai J. Parikh, Yong Sik Ok

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


Biochar modification by metals and metal oxides is considered a practical approach for enhancing the adsorption capacity of anionic compounds such as phosphate (P). This study obtained paper mill sludge (PMS) biochar (PMSB) via a one-step process by pyrolyzing PMS waste containing ferric salt to remove anionic P from water. The ferric salt in the sludge was transformed into ferric oxide and zero-valent-iron (Fe0) in N2 atmosphere at pyrolysis temperatures ranging from 300 to 800 °C. The maximum adsorption (Qm) of the PMSBs for P ranged from 9.75 to 25.19 mg P/g. Adsorption is a spontaneous and endothermic process, which implies chemisorption. PMSB obtained at 800 °C (PMSB800) exhibited the best performance for P removal. Fe0 in PMSB800 plays a vital role in P removal via adsorption and coprecipitation, such as forming the ≡Fe–O–P ternary complex. Furthermore, the possible chemical precipitation of P by CaO decomposed from calcite (CaCO3; an additive of paper production that remains in PMS) may also contribute to the removal of P by PMSB800. Moreover, PMSBs can be easily separated magnetically from water after application and adsorption. This study achieved a waste-to-wealth strategy by turning waste PMS into a metal/metal oxide-embedded biochar with excellent P removal capability and simple magnetic separation properties via a one-step pyrolysis process.

Original languageEnglish
Article number118521
JournalEnvironmental Pollution
Publication statusPublished - 2022 Jan 15

Bibliographical note

Funding Information:
This research was financially supported by the Natural Science Foundation of Zhejiang Province (Grant No. HZ22E083129 ).

Publisher Copyright:
© 2021 Elsevier Ltd


  • Adsorption
  • Biochar
  • One-step process
  • Paper mill sludge
  • Phosphate
  • Waste-to-wealth strategy
  • Zero-valent iron (ZVI)

ASJC Scopus subject areas

  • Toxicology
  • Pollution
  • Health, Toxicology and Mutagenesis


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