Unraveling iron speciation on Fe-biochar with distinct arsenic removal mechanisms and depth distributions of As and Fe

Zibo Xu, Zhonghao Wan, Yuqing Sun, Xinde Cao, Deyi Hou, Daniel S. Alessi, Yong Sik Ok, Daniel C.W. Tsang

Research output: Contribution to journalArticlepeer-review

50 Citations (Scopus)


Tailored manipulation of iron speciation has become a critical challenge for the further development of Fe-biochar as an economical and eco-friendly amendment for arsenic (As) immobilization. Herein, a series of Fe-biochars with manipulated iron speciations were fabricated by controlling the carbon structures and pyrolysis conditions. Results revealed that abundant labile-/amorphous-C induced more reductive-Fe(0) formation (10.9 mg g−1) in the Fe-biochar. The high Fe(0) content resulted in the effective As immobilization (4.34 mg g−1 As(V) and 7.72 mg g−1 As(III)) as evidenced by Pearson correlation coefficient (PCC) analysis. The hierarchical depth distributions of As and Fe on the Fe-biochar caused by the redox reaction and concomitant sorption of As proved the decisive role of Fe(0). An iron-oxide shell (~10–20 nm) with a high arsenic accumulation was revealed on the surface, while deeper within the particles, Fe(0) was found to be associated with elemental As (As(0), up to 19.4%). By contrast, pyrolysis with the stable-/graphitic-C generated more amorphous-Fe (61.9 mg g−1) on the Fe-biochar, which accounted for the high As removal (10.1 mg g−1 As(V) and 7.70 mg g−1 As(III)) despite the limited Fe(0) content. In comparison to the reductive Fe(0), distinct depth distribution was observed that the As/Fe ratio was marginally changed within 200 nm depth of the amorphous-Fe biochar after As decontamination. Co-precipitation of As with Fe released from amorphous-Fe contributed to this depth distribution, as evidenced by the high correlation between released-Fe and As immobilization capacity (PCC as 0.84–0.95). This study unveiled a crucial role of iron speciation on distinct mechanisms for As removal, guiding the application-oriented design of multifunctional Fe-biochar for broad environmental remediation.

Original languageEnglish
Article number131489
JournalChemical Engineering Journal
Publication statusPublished - 2021 Dec


  • Arsenic immobilization
  • Co-precipitation
  • Engineering biochar
  • Green and sustainable remediation
  • Iron transformation
  • Redox reaction

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry
  • Chemical Engineering(all)
  • Industrial and Manufacturing Engineering


Dive into the research topics of 'Unraveling iron speciation on Fe-biochar with distinct arsenic removal mechanisms and depth distributions of As and Fe'. Together they form a unique fingerprint.

Cite this