Recycling of Mn oxide-loaded AMD sludge composite for the removal of As(V) and Sb(V) from wastewater: Adsorption performance and mechanisms

The remediation of arsenic (As) and antimony (Sb) contaminated water is now a global research priority. The concept of "treating waste with waste" by modifying and recycling acid mine drainage sludge (AMDs) for treating As and Sb-contaminated wastewater is widely supported by scholars worldwide. In this study, a novel composite material (MnOx@AMDs) was synthesized via co-precipitating Mn oxides with AMDs. Characterization and adsorption results indicated that, after optimal Mn oxide loading (Mn²⁺: MnO₄^- = 0.075: 0.05 (mol)), MnOx@AMDs-1 exhibited a significant increase in specific surface area and surface positive potential, as well as the formation of abundant mesoporous structures and functional hydroxyl groups. The adsorption of As(V) and Sb(V) onto MnOx@AMDs-1 was best described by the Pseudo-second-order (R² = 0.96 and 0.95) kinetics and Langmuir (R² = 0.99 and 0.96) models, indicating a monolayer homogeneous chemisorption process. The maximal theoretical adsorption capacities at 25°C were 49.31 mg g⁻¹ for As(V) and 155.12 mg g⁻¹ for Sb(V). Post-adsorption characterization revealed that the predominant adsorption mechanisms include complexation, electrostatic attraction, and hydrogen bonding. Furthermore, MnOx@AMDs-1 sustained a removal efficiency exceeding 75 % for As(V) and Sb(V) over five consecutive adsorption-desorption cycles, while the maximum concentration of dissolved Mn (1.87 mg L⁻¹) remained under the 2 mg L⁻¹ threshold set by GB 18918–2002 standards. In conclusion, MnOx@AMDs-1, as a novel adsorbent with high efficiency and environmental friendliness, demonstrates significant potential for application in treating As(V) and Sb(V) contaminated wastewater.