Brannerite MnV2O6 with plate-like shape is successfully synthesized by hydrothermal method. Its crystal structure and morphology are investigated by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, tra...Brannerite MnV2O6 with plate-like shape is successfully synthesized by hydrothermal method. Its crystal structure and morphology are investigated by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscope （TEM）, high resolution transmission electron microscopy （HRTEM） and select area electronic diffraction （SAED）. The results show that the brannerite MnV2O6 with monoclinic structure has a uniform plate-like shape with a diameter of about 5-8μm and a thickness of about 500 nm. SAED patterns further confirm the structure of the brannerite MnV2O6 and the single crystalline character of the plate crystal. Magnetic properties are measured by superconducting quantum interference device （SQUID） in a temperature range of 2-300 K under a magnetic field of 1 T. The magnetic measurement results indicate that the material undergoes an antiferromagnetic transition with a Neel temperature of 17 K. Above 50 K, the inverse susceptibility is fitted well to the Curie-Weiss law with a calculated moment of 5.98μB. Finally, the origin of antiferromagnetic behaviour in the brannerite MnV2O6 is explained by means of Anderson model.展开更多
A synthetic coffinite was hydrothermally prepared and characterized before conducting a series of acid sulfate leach tests under conditions of relevance to uranium extraction.The results were then compared with simila...A synthetic coffinite was hydrothermally prepared and characterized before conducting a series of acid sulfate leach tests under conditions of relevance to uranium extraction.The results were then compared with similar studies on synthetic versions of the related U4+minerals uraninite(UO2)and brannerite(UTi2O6)to identify and differentiate the rate and U extraction among these important uranium minerals.Tests examining the influence of residence time on uranium dissolution from synthetic coffinite,uraninite and brannerite showed that under similar experimental conditions,complete dissolution of uranium from coffinite was obtained between 36 and 48 h.The activation energy for this reaction was calculated to be 38.4 kJ/mol.This represented a significantly slower rate of dissolution than that indicated for uraninite which dissolved in 3 h(Ea=15.2 kJ/mol).The synthetic brannerite was leached at a much slower rate than the coffinite and reached a maximum dissolution of^18%U in 144 h(Ea=42-84 kJ/mol).The clear differentiation in rates and U extraction among the three minerals is consistent with previous literatures which suggest that in terms of leachability,uraninite>coffinite>brannerite.It is expected that the presence of impurities in natural coffinites would further inhibit leachability.展开更多
文摘Brannerite MnV2O6 with plate-like shape is successfully synthesized by hydrothermal method. Its crystal structure and morphology are investigated by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscope （TEM）, high resolution transmission electron microscopy （HRTEM） and select area electronic diffraction （SAED）. The results show that the brannerite MnV2O6 with monoclinic structure has a uniform plate-like shape with a diameter of about 5-8μm and a thickness of about 500 nm. SAED patterns further confirm the structure of the brannerite MnV2O6 and the single crystalline character of the plate crystal. Magnetic properties are measured by superconducting quantum interference device （SQUID） in a temperature range of 2-300 K under a magnetic field of 1 T. The magnetic measurement results indicate that the material undergoes an antiferromagnetic transition with a Neel temperature of 17 K. Above 50 K, the inverse susceptibility is fitted well to the Curie-Weiss law with a calculated moment of 5.98μB. Finally, the origin of antiferromagnetic behaviour in the brannerite MnV2O6 is explained by means of Anderson model.
文摘A synthetic coffinite was hydrothermally prepared and characterized before conducting a series of acid sulfate leach tests under conditions of relevance to uranium extraction.The results were then compared with similar studies on synthetic versions of the related U4+minerals uraninite(UO2)and brannerite(UTi2O6)to identify and differentiate the rate and U extraction among these important uranium minerals.Tests examining the influence of residence time on uranium dissolution from synthetic coffinite,uraninite and brannerite showed that under similar experimental conditions,complete dissolution of uranium from coffinite was obtained between 36 and 48 h.The activation energy for this reaction was calculated to be 38.4 kJ/mol.This represented a significantly slower rate of dissolution than that indicated for uraninite which dissolved in 3 h(Ea=15.2 kJ/mol).The synthetic brannerite was leached at a much slower rate than the coffinite and reached a maximum dissolution of^18%U in 144 h(Ea=42-84 kJ/mol).The clear differentiation in rates and U extraction among the three minerals is consistent with previous literatures which suggest that in terms of leachability,uraninite>coffinite>brannerite.It is expected that the presence of impurities in natural coffinites would further inhibit leachability.
