Graphene nanosheets are produced in mass by Hummers method, accompanied with the emission of waste acid effluent with Mn2+, which should be reasonably recycled. Herein, Mn2+ was extracted into Mn3O4 nanoparticles by oxidation precipitation. Desirably, Mn3O4 powders were the spinel crystal phase and the particle size was 100–150 nm. The reversible discharge capacities of Mn3O4 anode maintained 528 mA h/g at 0.5 A/g for 100 cycles and 423 mA h/g at 1.0 A/g for 300 cycles, with high capacity retention ratios of 93.4% and 91.1%, respectively. Obviously, this work may promote the development of the circular economy.