Improved Pb(II) removal in aqueous solution by sulfide@biochar and polysaccharose-FeS@ biochar composites:...

Novel biochars, namely nano iron sulfide@ walnut shell biochar (FeS@WNS), Starch-FeS@WNS and Chitosan-FeS@WNS, were prepared by WNS loaded with nano FeS and starch (or chitosan). Nano FeS can be effectively improved lead ions (Pb(II)) removal and starch (or chitosan) improved the stability of FeS and the defect of easy agglomeration. The materials were characterized by SEM, EDS, FTIR and XRD, and the preparation was successful. The adsorption capacity of Pb(II) reached 63.5, 80.0, 84.7 mg g^-1 under 0.5 g L^-1 of FeS@WNS, Starch-FeS@WNS and Chitosan-FeS@WNS. The adsorption of Pb(II) on the materials was more consistent with the pseudo-second-order kinetic model (K₂ = 0.001-0.005 g (mg·min)^-1, R² = 0.980-0.999) and Langmuir model (R² = 0.974-1.00), indicating that the adsorption of Pb(II) was mainly monolayer adsorption dominated by chemical adsorption. △G < 0 (-3.7~-6.97) and △H > 0 (1.56-20.49) indicated that the reaction was a spontaneous endothermic process. The mechanisms of Pb(II) removal from aqueous solutions involved electrostatic attraction, hydrogen bonding, physical adsorption, ion exchange and oxidoreduction. Additionally, stability and reusability of FeS@WNS, Starch-FeS@WNS and Chitosan-FeS@WNS was good. The novel sorbents of Starch-FeS@WNS and Chitosan-FeS@WNS can be used in Pb(II) wastewater treatment.