Mn oxide-modified biochars with high adsorption capacity for Pb(II) in wastewater: Preparation and adsorption mechanisms

The occurrence of excessive levels of bivalent plumbum (Pb(II)) in wastewater poses a notable threat to both human health and ecological safety. In this study, orthogonal experiments were conducted to prepare coprecipitation-modified biochar (C-BC) and impregnation pyrolysis-modified biochar (I-BC) via potassium permanganate (KMnO₄) for removing Pb(II) from wastewater. Three types of modified biochars (BCs) (Mn-BCs) namely, C-BC₄₀₀, I-BC₄₀₀, and I-BC₇₀₀, were selected as high-efficiency adsorbents on the basis of their high removal rates (87.2%, 88.0%, and 91.2%, respectively) for 400 mg/L Pb(II) solutions. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM)‒energy-dispersive X-ray spectroscopy (EDS) analysis results indicated that Mn elements were distributed only on the outer surfaces of the C-BC₄₀₀ particles but occurred on the outer surface and were stably embedded in the I-BC₄₀₀ and I-BC₇₀₀ particles. Compared with those of the pristine (BCs), the Pb(II) adsorption rates of C-BC₄₀₀, I-BC₄₀₀, and I-BC₇₀₀ increased by factors of 3.75, 2.09, and 5.70, respectively. The Pb(II) adsorption capacities of C-BC₄₀₀, I-BC_400, and I-BC₇₀₀ (182.28, 133.16, and 69.25 mg/g, respectively) were significantly greater than those of the pristine BCs produced at 400 °C (45.43 mg/g) and 700 °C (40.71 mg/g). The excellent adsorption ability of Mn-BCs for Pb(II) depends on various adsorption mechanisms, including complexation, electrostatic attraction, surface adsorption, and ion exchange. These results suggest that Mn-BCs exhibit high application potential in the remediation of Pb(II)-contaminated wastewater.