Influences of chemical treatment on sludge derived biochar; Physicochemical properties and potential sorption mechanisms of lead (II) and methylene blue

Unlike agricultural biomass, sludge-derived biochar is rich in nutrients, comprising exchangeable cations and various surface oxygen functional groups with carbonaceous structures. In this study, the influence of different activating reagents such as H₃PO₄, H₂O₂, K₂CO₃, and NaOH on the physicochemical properties of biochar was investigated. It was found that the biochar elemental composition remains nearly the same, while the surface Fe and Si were induced for H₃PO₄modification. The pH of the original biochar was varied from acidic to alkali (3.60-10.06) along the chemical treatment process. The surface-active sites of biochar and their nature were dramatically tuned based on their chemical modification. To interpret the relationship between each of the parameters obtained via chemical modification, adsorption of different pollutants, such as Pb(II), Cd(II), Cr(VI), V(V), As(III), and methylene blue (MB) were conducted. Among the biochars, NaOH-modified biochar was revealed as the optimum candidate with maximum uptake capacity for Pb(II) (195.75 mg/g) and MB (160.78 mg/g). Based on the adsorption kinetics and isotherm study, the adsorption process endorsed chemical sorption with multiple interactions along the heterogeneous surface. This study offered a comprehensive approach to manipulating the physicochemical properties of biochar.