Fe3O4-modified sewage sludge biochar for U(VI) removal from aqueous solution: performance and mechanism

Sewage sludge-derived biochar (SSB) was prepared at 600 °C pyrolysis temperature and modified by co-precipitation with Fe3O4 to obtain Fe3O4@SSB. The adsorption process of U(VI) onto the Fe3O4@SSB was accurately described by the pseudo-second order and Langmuir isotherm model. The maximum removal capacity of U(VI) was 149.15 mg/g at 303 K and initial pH of 4.0 by Langmuir isotherm model analysis. The removal mechanisms included complexation, ion exchange, reduction and electrostatic attraction. The U(VI) removal efficiency by Fe3O4@SSB remained above 90% after five adsorption–desorption. This work provided a reference for sewage sludge resource utilization and biochar modification for uranium-containing wastewater treatment.