Feasible reutilization of sorbents was crucial to the waste water treatment process cost-effective and environmental friendly. Magnetic Fe 3 O 4 /MnO 2 composites as sorbents were recycle utilized to remove heavy metals ions [Pb(II), Cu(II), Cd(II) and Zn(II)] from industrial wastewater. In this paper, The Fe 3 O 4 /MnO 2 composites structure and interface adsorption mechanism were investigated by chemical affinity, Zero potentials combining with XRD, FTIR and TEM. The adsorption, desorption and recycle experiments were explored. The results indicated that Fe 3 O 4 /MnO 2 composites were nano structure with consisting of two layers with Fe 3 O 4 in the core and amorphous MnO 2 on the shell. The adsorption mechanism was that the heavy metals substituting for H of Mn-O-H and forming the structure of Mn-O-Me which meant the metals removal was the process of ion exchange. The sorbent removal efficiency of Cu, Cd, Pb and Zn were 99.81%, 99.76%, 98.1%, 83.25%, respectively. The equilibrium data analysis indicated that the Langmuir model was the most appropriate model to describe the adsorption of on the surface of Fe 3 O 4 /MnO 2 composites. The kinetics studies showed that the adsorption kinetics of heavy metal ions on the surface of Fe 3 O 4 /MnO 2 composites was significantly appropriate to pseudo-second-order model. The experiments verified that the Fe 3 O 4 /MnO 2 sorbent being separated from water by external magnetic field for recycling was feasible for environmental friendly and efficient remove heavy metal ions.

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The goal of the paper is to study the charge transfer and reactions at the columbite-(Fe) (FeNb2O6) mineral surface during the HF leaching process. In this paper, X-ray photoelectron spectroscopy (XPS), leaching experiments, and density functional theory (DFT) calculations were used to study the surface element adsorption, charge distribution, chemical state, and energy changes of the mineral surface during the process of leaching columbite–(Fe) with different concentrations of hydrofluoric acid. The results showed that as the concentration of F atoms was increased during the acid leaching process, the Nb–O bond was more likely to be broken than the Fe–O bond; the amount of charge transferred from Nb atom to F atom (0.78 e–0.94 e/atom) was greater than that from Fe atom to the F atom (0.25 e–0.28 e/atom), so it was determined that compared to Fe atoms, it was easier for the Nb atoms to bind to F. The results of XPS analysis showed that the electron binding energies of Nb5+–O, Fe3+–O, and Fe2+–O bonds on the mineral surface increased sequentially, and the M–O bond broke during the acid leaching process, forming more stable M–F bonds. Therefore, the Nb5+–F bonds were easier to form a stable structure. Combined with the ICP results, it was found that in the filtrate after 5M HF and 10M HF acid leaching minerals, c(Nb)/c(Fe) were 2.69 and 2.95, respectively, and the concentration ratio of Nb to Fe element in the mineral was 2 which was lower than 2.69 and 2.95, confirming the result of DFT calculation and illustrating that Nb atoms in columbite-(Fe) mineral were more soluble than Fe atoms.