Effective removal of fluoride and lead ions from aqueous solutions using water treatment residue and rice straw co-pyrolysis biochar composites

The coexistence of fluoride and lead in the waste water often leads to compound pollution, and finding effective and cost-effective solutions remains a significant issue. In this study, water treatment residues biochar (WTR-BC) was synthesized for the first time through the co-pyrolysis of water treatment residues and agricultural wastes to remove fluoride and lead. The results indicated that WTR-BC demonstrated remarkable efficacy in adsorbing fluoride and lead, achieving a maximum capacity of 15.2 mg/g and 83.8 mg/g, respectively. The adsorption mechanism adhered to a pseudo-second-order kinetic model, which illustrated that it was primarily driven by chemisorption. Moreover, X-ray photoelectron spectroscopy analysis indicated the formation of new complexes, F-Al and F-C with F on the WTR-BC surface, and X-ray absorption fine structure spectroscopy showed that the lead in the WTR-BC samples mainly existed as lead ferrihydrite (64.7%) and Pb(C2H3O2)2 (35.3%). These results revealed that the binding of lead and fluorides to the WTR-BC surface was attributed to Fe-O-Pb, C-O-Pb-O-C, and Al-F bond structures. The successful preparation of WTR-BC provides a new approach for the treatment of complex fluoride and lead pollution and holds promise as a novel material for environmental remediation. Furthermore, it broadens the scope of reuse possibilities for both WTR and agricultural wastes.