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
Ores of infiltration sandstone-hosted uranium deposits in the sedimentary cover are ubiquitous composed of dispersed soot powder mineralization of black,brownish-black colour.Longterm studies of such loose U-ores by a...Ores of infiltration sandstone-hosted uranium deposits in the sedimentary cover are ubiquitous composed of dispersed soot powder mineralization of black,brownish-black colour.Longterm studies of such loose U-ores by analytical transmission electron microscopy(ATEM)proved their polymineral nature.Uranium blacks are composed by at least three different U-mineral forms:oxide(uraninite),silicate(coffinite)and phosphate(ningyoite)which are present in various proportions of ore compositions.Such high dispersed friable uranium formations are difficult to diagnose by traditional mineralogical methods(optical,XRD,IR and X-ray spectroscopy,etc.)which analyze total sample composition(phases mixture);their results characterize the dominant sample phase,omitting both sharply subordinate and X-ray amorphous phases.All research results are based on ATEM methods(SAED+EDS),which are optimal for crystallochemical diagnostics in the mineralogical study of such uranium ores.The article presents the diagnostic characteristics under electron microscope(EM)of uranous minerals from different sandstone deposits with their origin being discussed.展开更多
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.
基金financial support from the IGCP 675 of International Union of Geological Sciences(IUGS),UNESCO and China Geological Survey(Tianjin Center)。
文摘Ores of infiltration sandstone-hosted uranium deposits in the sedimentary cover are ubiquitous composed of dispersed soot powder mineralization of black,brownish-black colour.Longterm studies of such loose U-ores by analytical transmission electron microscopy(ATEM)proved their polymineral nature.Uranium blacks are composed by at least three different U-mineral forms:oxide(uraninite),silicate(coffinite)and phosphate(ningyoite)which are present in various proportions of ore compositions.Such high dispersed friable uranium formations are difficult to diagnose by traditional mineralogical methods(optical,XRD,IR and X-ray spectroscopy,etc.)which analyze total sample composition(phases mixture);their results characterize the dominant sample phase,omitting both sharply subordinate and X-ray amorphous phases.All research results are based on ATEM methods(SAED+EDS),which are optimal for crystallochemical diagnostics in the mineralogical study of such uranium ores.The article presents the diagnostic characteristics under electron microscope(EM)of uranous minerals from different sandstone deposits with their origin being discussed.
