To enhance the adsorption capacity of sludge-derived biochar for heavy metals in aqueous environments,this study prepared biomass-sludge mixed biochar(O-SBC)via co-pyrolysis of orange peel and municipal sludge,and explored the optimal preparation parameters.It systematically investigated the adsorption performance and mechanisms of O-SBC for Pb2+and Cd2+.Experimental results showed that O-SBC exhibited the highest adsorption capacity for Pb2+under the optimal preparation parameters(pyrolysis temperature:700℃,pyrolysis time:4 h,orange peel addition ratio:20%).In contrast,the optimal parameters for Cd2+adsorption were 700℃,4 h,and 40%orange peel addition ratio.After incorporating orange peel,the specific surface area of O-SBC was approximately twice that of pristine sludge-derived biochar(SBC),and the pore volume increased by 27%.The effects of reaction parameters on the adsorption of Pb2+and Cd2+showed similar trends.The optimal adsorption parameters were as follows:solid-liquid ratio of 2.5 g/L,initial solution concentration of 100 mg/L,pH 6,and contact time of 6 h.The adsorption processes of O-SBC for Pb2+and Cd2+both fitted well with the pseudo-second-order kinetic model;the adsorption isotherms of Pb2+and Cd2+were well described by the Langmuir model and Freundlich model,respectively.Mechanistic investigations indicated that the adsorption process involved multiple pathways,including chemical complexation,ion exchange,and pore filling.Among these,the surface functional groups of O-SBC dominated the adsorption process via complexation.Under competitive adsorption conditions,Pb2+exhibited a competitive advantage over Cd2+owing to its smaller hydration radius,and thus preferentially occupied the active adsorption sites.