Utilizing cost-effective biochar for highly efficient U(VI) removal from uranium-containing wastewater

Residual sludge (RS) from a wastewater treatment plant was used to prepare sludge-based biochar (RS-BC) by pyrolysis to treat U(VI)-containing wastewater. The findings revealed that RS-BC had exceptional adsorption performance, with a theoretical maximum adsorption capacity for U(VI) of 455.69 mg g⁻¹. The pseudo-second-order and Langmuir isotherm adsorption models effectively fit the adsorption process, and the thermodynamic parameters confirmed that the adsorption process was endothermic and spontaneous. The adsorption efficiency of U(VI) onto RS-BC exhibited remarkable stability and maintained a notable 90% retention even after five cycles of adsorption and desorption. Spectroscopic analyses revealed that ion exchange and complexation were the main adsorption mechanisms.