Synthesis of Fe3O4@rice Husk Biochar for As(V) Remediation by Adsorption: Is Sodium Silicate Formation Involved?
ORCID
Abeysinghe: https://orcid.org/0000-0002-3842-0217; Mlsna: https://orcid.org/0000-0002-4858-1372
MSU Affiliation
College of Arts and Sciences; Department of Chemistry
Creation Date
2026-07-30
Abstract
Rice husks (RH) were pretreated by premixing with aqueous FeCl3 and 4 M NaOH at pH 10, then pyrolyzed at 600 °C for 1 h to generate Fe3O4-deposited on biochar, Fe3O4@RHBC, used to remediate aqueous As(V). The iron oxide phase was mostly Fe3O4 after pyrolysis with small amounts of Fe2O3 and α-FeOOH. Exposing RH to aqueous NaOH raises the possibility that RH's SiO2 content could generate sodium silicate, affecting its adsorption behavior. However, we demonstrate the absence of evidence for detectable sodium silicate formation on Fe3O4@RHBC as probed by FT-IR, XPS, and PZC studies. Since many silica-rich biochars have been pretreated with alkali, we were prompted to examine silica-to-silicate transformations by premixing 4 M NaOH with RH, without iron oxide modification, and heating to a series of individual temperatures, from 100 to 700 °C. Each sample was analyzed by FT-IR to determine if sodium silicate had formed from silica. As(V) uptake was determined as a function of pH, adsorbate-adsorbent contact time, initial As(V) concentration, adsorbent dose, and temperature. Optimized As(V) adsorption occurred at pH 5. As(V) adsorption kinetics on Fe3O4@RHBC best fit the pseudo-second-order model, and adsorption isotherms (5, 25, and 40 °C) were endothermic and fit the Langmuir isotherm model, with a maximum adsorption capacity of 5.56 mg/g at 25 °C. Competitive PO43−, SeO42−, MoO42−, Cr2O72−, CO32−, and F− adsorption during As(V) removal was investigated. The As recovery from the exhausted Fe3O4@RHBC by aqueous NaOH stripping gave ∼9.0% and ∼13.8% reductions in adsorption capacity after three batch As(V) regenerations.
Publication Date
6-20-2026
Publication Title
Biomass & Bioenergy
Publisher
Elsevier
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License
Rights
© 2026 The Author(s)
Recommended Citation
Abeysinghe, H. P., Sullivan, E. P., Rodrigo, P. M., Pittman, C. U., & Mlsna, T. E. (2027). Synthesis of Fe3O4@rice husk biochar for As(V) remediation by adsorption: Is sodium silicate formation involved? Biomass and Bioenergy, 216, 109652. https://doi.org/10.1016/j.biombioe.2026.109652
