Effective removal of Pb2+ from water by a novel magnetic Fe3O4-MnO2 composite prepared from steel pickling waste liquid: Adsorption behavior and mechanism

The high-value utilization of steel pickling waste liquid (SPWL) is an important direction in the resourceful utilization of hazardous waste. In this study, nano-Fe3O4 prepared from SPWL (S-Fe3O4) was hydrothermally compounded with MnO2 as Fe3O4-MnO2 (SFM), which were compared with Fe3O4-MnO2 (CFM) prepared by chemical reagents. The synthetic materials were evaluated by SEM, VSM, BET, XRD, and zeta potential, the results show that the spherical S-Fe3O4 was encapsulated by spiny spherical shell-like MnO2, and the SFM has a high saturation magnetization and specific surface area (159.91 m2/g). The adsorption experiments demonstrated that the adsorption effect of SFM on Pb2+ is highly similar to that of CFM. The maximal adsorption capacity of SFM reached 129.74 mg/g under ideal composite ratio and pH conditions, and the adsorption process was unaffected by competing heavy metal ions coexisting in the environment. Moreover, the high saturation magnetization strength of the SFM makes it simple to separate materials under a magnetic field. The pseudo-second-order kinetics and Langmuir isotherm models provided a good description of the Pb2+ adsorption on SFM. XPS and FTIR analysis provided evidence that the adsorbent surface has a high concentration of -OH functional groups, and that O atoms serve as Pb2+ binding sites, suggesting that ion exchange occurs during the SFM adsorption process. In this paper, we developed a cheap SFM with high adsorption performance and provided a novel approach to the high-value application of SPWL. [Display omitted] •Removal of Pb2+ from water by Fe3O4-MnO2 prepared from steel pickling waste liquid.•The maximum adsorption capacity of Fe3O4-MnO2 for Pb2+ reached 129.74 mg/g.•Ion exchange plays a major role in the removal process of Pb2+.•The cost of Fe3O4-MnO2 prepared from steel pickling waste liquid is 60 % lower than that prepared by chemical reagent.