Physicochemical characteristics and Mn2+ adsorption of annealed red mud were investigated in this study. The annealing temperature (105–900 °C) changed the mineralogical components and the point of zero charge of red mud. By comparison, annealed red mud at 700 °C (ARM700) had a better adsorption effect than other annealed samples, associated with the activated components of available Fe2O3, Al2O3, SiO2 and Na5Al3(SiO4)3CO3 (natrodavyne). The removal efficiency of Mn2+ by ARM700 was dependent on initial pH, contact time, and initial Mn2+ concentration of aqueous solution and was ∼56.5% with initial Mn2+ concentration 385 mg/L at initial pH > 5. The kinetics process was predicted better by the pseudo-second-order model. The Langmuir isotherm displayed a better fitting model than the Freundlich isotherm and the Mn2+ maximum adsorption capacity of ARM700 was 88.3 mg/g. The competing effects of Cu2+ and Zn2+ on Mn2+ removal were most obvious. There was efficient Mn2+ removal at the application of ARM700 to the leachate of electrolytic manganese residue.