LAUSR

Abstract The adsorption remediation of radioactive contamination from wastewater was of great scientific and economic significance. In this paper, we synthesized α-MnO2, β-MnO2, γ-MnO2 and δ-MnO2 with different crystalline structures via hydrothermal method, and investigated their adsorption performance towards U(VI). SEM, FT-IR XRD, BET and XPS were adopted to determine the surface properties and pore structures. The pseudo-second-order model and the Langmuir model were better suited for the adsorption process. The maximum adsorption capacities (pH 6, 298 K) were in order of δ-MnO2 (304.92 mg/g) > α-MnO2 (289.42 mg/g) > γ-MnO2 (277.09 mg/g)> β-MnO2 (257.84 mg/g), owing to the different specific surface area and crystallinity. δ-MnO2 possessed layered structure, poor crystallinity, as well as the largest surface area and pore volume, which were conducive to the diffusion of U(VI) ions between layers, and the effective use of the adsorption sites, thus promoting the adsorption capacity of U(VI) ions. Besides, the adsorption mechanism of MnO2 towards U(VI) was principally attributable to electrostatic attraction and the surface complexation ((Mn-O-U(VI))) due to various oxygen-containing functional groups. Consequently, the low-priced, simple preparation and highly efficient endowed δ-MnO2 with wide application for U(VI) removal from wastewater.