Preparation of core-shell composite materials capable of slowly releasing phosphate and their remediation performance of uranium-contaminated groundwater.

Acid in-situ leach uranium mining significantly alters the geochemistry of the ore zone, and leaves uranium, residual acid, as well as other potential contaminants in groundwater, which bring harm to human health and ecological environment. Many investigators have been trying to propose remediation strategies for the uranium-contaminated groundwater. Phosphate is an effective immobilization reagent of uranium in the groundwater. However, direct injection of phosphate tends to quickly form precipitates, resulting in fast blockage of the seepage passages in the ore zone around the injection holes and hindering its diffusion. In this paper, HAP@SiO2-600, HAP@SiO2-600@25SA, and HAP@SiO2-600@75SA with core-shell structures were prepared. Their slow-release of phosphate, the effects of pH, contact time, initial uranium concentration, and coexisting ions on their removal rate and efficiency of uranium, and their function of remediating uranium-contaminated groundwater were investigated. It was found that the increase of SA content in the outer layer of HAP@SiO2-600@25SA and HAP@SiO2-600@75SA resulted in the slow release rate of phosphate, decreasing the removal rate of uranium. The adsorption capacities of HAP@SiO2-600, HAP@SiO2-600@25SA, and HAP@SiO2-600@75SA from the aqueous solution at pH = 3.0 and 303 K were up to 582.6, 558.5, and 507.3 mg g-1, respectively. In addition, the materials showed excellent uranium removal performance in experiments where multiple ions coexisted. For actual acidic uranium-contaminated groundwater, HAP@SiO2-600, HAP@SiO2-600@25SA, and HAP@SiO2-600@75SA effectively increased the pH from 2.75 to 4.40, 3.87, and 3.72, respectively, and decreased the uranium concentration from 5.12 to 0.0062, 0.0065, and 0.0058 mg L-1, respectively. The FT-IR, XRD, TEM and XPS characterizations were performed to further clarify the uranium removal mechanism, and it was found that the elimination of U(VI) was ascribed to dissolution-precipitation, adsorption and ion exchange. The results show that the core-shell composite material capable of slowly releasing phosphate is effective in remediating uranium-contaminated groundwater.

Experimental and theoretical investigations of four 3d-4f butterfly single-molecule magnets.

The syntheses, structures, and characterization of four 3d-4f butterfly clusters are described. With different polyhydroxy Schiff-base ligands 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propanediol (H4L1) and 2-(2,3-dihydroxpropyliminomethyl)-6-methoxyphenol (H3L2), three heterotetranuclear NiLn complexes (NiDy-L1 (1), NiTb-L2 (2), NiDy-L2 (3)) and one heterohexanuclear CoDy complex (4) were obtained. The three heterotetranuclear NiLn complexes display a central planar butterfly topology. The heterohexanuclear complex was built from butterfly CoDy clusters and two Dy(III) ions by the bridging of pivalate. The vertices of the body positions of the butterfly are occupied by transition metal ions in all four complexes. Magnetic analyses indicate that the complexes exhibit typical single-molecule magnet behaviour with anisotropy barriers of 33.7 cm(-1), 60.3 cm(-1), 39.6 cm(-1), and 18.4 cm(-1) for 1-4, respectively. Ab initio calculations were performed on these complexes, and the low lying electronic structure of each Ln(III) (Ln = Dy, Tb) ion and the magnetic interactions were determined. It was found that the two Ln ions may have much more contribution to the total relaxation barrier through the stronger 3d-4f exchange couplings compared to weak Ln-Ln interactions.