Adsorption performance of Cr(VI) using Fe-containing sludge biochar co-doped with nitrogen and sulfur

This work explored the adsorption performance of nitrogen and sulfur co-doped Fe-containing sludge biochar (SN@BC) for hexavalent chromium [Cr(VI)], highlighting its potential for practical applications. Biochar was prepared using Fe-containing municipal dewatered sludge as feedstock and chemically modified with ammonium persulfate [APS, (NH4)2S2O8] to optimize its morphological structures and functional group. Sorption experiment was conducted to examine the removal behavior of the modified biochar under various conditions, including different pH, material dose, Cr(VI) concentration, and contact times. The findings revealed that under an optimal pyrolysis temperature of 700 degrees C and a 1:1 mixing ratio, the SN@BC achieved a Cr(VI) removal efficiency of 98.76%. The sorption processes conformed to the pseudo-second-order model and Langmuir model. Thermodynamic studies revealed that the process was spontaneous and endothermic, favoring higher temperatures. Mechanistic analysis indicated that sorption was predominantly governed by electrostatic attraction, reduction, and complexation. Furthermore, SN@BC exhibited excellent regeneration performance, retaining 81.02% removal efficiency after five regeneration cycles, highlighting its stability and potential for long-term use in Cr(VI)-contaminated water treatment.