Pb(II)adsorption by biochar from co-pyrolysis of corn stalks and alkali-fused fly ash

Numerous studies have reported the potential of silica as a biochar(BC)modifier.However,despite its high silica content,fly ash is rarely used for BC modification.Herein,modified BCs were produced by co-pyrolysis of corn stalks with alkali-fused fly ash(AFFA)at 200 and 600℃(denoted as AFFA/BC).The Pb(Ⅱ)adsorption mechanism and adsorption performance were investigated.The AFFA/BC had larger specific surface areas than the pure BC samples(2.54-137 vs.0.50 m2 g^(−1))owing to their stable carbon structure.The Pb(Ⅱ)adsorption capacity of AFFA/BC in water was approximately 6%higher than that of BC owing to the increased cation(Na+)exchange and new bonding sites,such as C-O and Si-O.AFFA/BC exhibited good Pb(Ⅱ)adsorption performance in high-concentration simulated wastewater(pH 4-6),with a maximum adsorption capacity of 110.29 mg g^(−1).The Pb(Ⅱ)adsorption mechanism was in accordance with the pseudo-second-order kinetic and Langmuir isotherm models.At 25℃and pH 5,the theoretical Pb(Ⅱ)adsorption capacities of AFFA200/BC and AFFA600/BC were 201.66 and 186.81 mg g^(−1),respectively,compared to 145.98 mg g^(−1)of BC.Physical adsorption,precipitation,cation exchange,and complexation were identified as the main Pb(Ⅱ)adsorption mechanisms through X-ray photoelectron spectrometry.