A manganese dioxide-modified red mud (Mn-RM) was developed as an adsorbent for the effective removal of lead ions (Pb²⁺) from wastewater. Various methods were used to characterize the prepared Mn-RM, analyze its adsorption performance, and evaluate the associated environmental risks post-adsorption. The results revealed that Mn-RM has a large surface area (38.91 m²/g) and a developed porous structure (0.02 cm³/g). The adsorption process exhibited good agreement with the Langmuir isotherm and pseudo-second-order kinetic models, showcasing a theoretical maximum saturation adsorption capacity of 721.35 mg/g. The adsorption mechanism primarily involves electrostatic attraction, ion exchange, and chemical precipitation. The optimal treatment conditions were determined by utilizing a response surface model, resulting in a maximum Pb²⁺ removal efficiency of 87.45% at pH 5.21, a dosage of 0.83 g/L, and an initial concentration of 301.04 mg/L. The risk assessment code (RAC) for each heavy metal in Mn-RM was less than 1%, indicating low environmental risk. Furthermore, the synthetic toxicity index (STI) values showed a significant decrease post-treatment. This study introduces the concept of “controlling waste with waste”, offering a cost-effective approach to both utilizing red mud and removing aqueous Pb²⁺ while ensuring environmental safety and minimal ecological impact.

Two new dioxidomolybdenum(VI) complexes of [MoO₂L(EtOH)] with aroylhydrazone ligands N'-(2-hydroxyl-3-methoxybenzylidene)-3-methylbenzohydrazide (H₂L¹) or 4-fluoro-N'-(2-hydroxylbenzylidene)benzohydrazide (H₂L²) were prepared in ethanol under ambient temperature in air. Both complexes were characterized by elemental analysis, IR and UV-Vis spectroscopy, as well as single crystal X-ray determination. The Mo atoms in the complexes are in octahedral coordination. Crystal structures of the complexes are stabilized by hydrogen bonds. The catalytic property for epoxidation of styrene by both complexes was studied.