Optimization of Preparation of Fe3O4-L by Chemical Co-Precipitation and Its Adsorption of Heavy Metal Ions

To address the serious pollution of heavy metals in AMD, the difficulty and the high cost of treatment, Fe3O4-L was prepared by the chemical co-precipitation method. Based on the single-factor and RSM, the effects of particle size, total Fe concentration, the molar ratio of Fe2+ to Fe3+ and water bath temperature on the removal of AMD by Fe3O4-L prepared by chemical co-precipitation method were analyzed. Static adsorption experiments were conducted on Cu2+, Zn2+ and Pb2+ using Fe3O4-L prepared under optimal conditions as adsorbents. The adsorption properties and mechanisms were analyzed by combining SEM-EDS, XRD and FTIR for characterization. The study showed that the effects of particle size, total Fe concentration and the molar ratio of Fe2+ to Fe3+ are larger. Obtained by response surface optimization analysis, the optimum conditions for the preparation of Fe3O4-L were a particle size of 250 mesh, a total Fe concentration of 0.5 mol/L, and a molar ratio of Fe2+ to Fe3+ of 1:2. Under these conditions, the removal rates of Cu2+, Zn2+, and Pb2+ were 94.52%, 88.49%, and 96.69% respectively. The adsorption of Cu2+, Zn2+ and Pb2+ by Fe3O4-L prepared under optimal conditions reached equilibrium at 180 min, with removal rates of 99.99%, 85.27%, and 97.48%, respectively. The adsorption reaction of Fe3O4-L for Cu2+ and Zn2+ is endothermic, while that for Pb2+ is exothermic. Fe3O4-L can still maintain a high adsorption capacity after five cycles of adsorption-desorption experiments. Cu2+, Zn2+ and Pb2+ mainly exist as CuFe2O4, Zn(OH)2, ZnFe2O4 and PbS after being adsorbed by Fe3O4-L, which is the result of the combination of physical diffusion, ion exchange and surface complexation reaction.