| Scandium is a scatter rare metal.With its attractive application prospects in aviation industries,National defense-related scientific industries and new energy industries,it has been listed as one of the national strategic metals,which are extremely vital to economic and national security,by Russia,European Union and the U.S.A.Globally,the main scandium resources come from hydrothermal scandium deposits,for instance,in Bayan Obo deposit?China?,which supplies approximately90%of the world`s scandium production,scandium is hosted mostly by aegirine.Besides,the main scandium-bearing minerals in the Zhovti Vody deposit and Kumir deposit?Russia?are aegirine and thortveitite,respectively.Thus,hydrothermal Sc deposits has been regarded as the main objects for research and exploration and it is commonly believed that the hydrothermal metasomatism plays an important role in scandium`s metallogenic process.Moreover,all the three deposits above are characterized by the close relationship between Scandium mineralization and fluorine-bearing minerals,which suggested that hydrothermal fluids containing fluorine may play a key role in the metallogenic process of scandium metals.By now,due to the lack of thermodynamic data,the mechanism of migration and enrichment of scandium in fluorinated hydrothermal solution is still not clear.In view of the vital of this problem,in this study 1)simulation experiments are carried out,to determine the solubility of Sc in fluorine-containing fluids at high temperature and pressure?100-250?,saturated vapor pressure?;2)Thermodynamic parameters,such as the structures and the formation constants of the main complexes in fluorine-containing hydrothermal fluids,were obtained by the relevant thermodynamic calculation;3)Based on the thermodynamic data obtained,the role of fluorine-containing hydrothermal fluids in hydrothermal mineralization is discussed.4)metallogenic mechanism for the typical scandium deposits is modeledAccording to result of the simulation experiments,it is suggested that the ScF2+and ScF3o are the dominant species in solution and the solubility of scandium in fluorine-containing hydrothermal fluids is mainly controlled by these complexes`structure.The logarithms of the formation constant for ScF2+(Sc3++2F-?ScF2+)range from 12.09±0.02 to 14.76±0.01 at 100 to 250?,and from 17.24 to 19.81 for ScF3o(Sc3++3F-?ScF3o)at the same temperatures.Based on the thermodynamic parameters we obtained in this study and the data in previous studies,we simulated the metallogenic process of Baiyun Obo REE scandium deposit and Australian Nyngan lateritic scandium deposit.It is inferred that:1)the temperature for scandium`s deposition and enrichment is 400-300?in Baiyun Obo REE scandium deposit;2)Sc migrates mainly as Sc-F complexes in fluorine-bearing acidic hydrothermal fluids,while it migrates mainly in Sc-OH complex form after hydrothermal fluid and surrounding dolomite rock reacted,which is also the mainly precipitation and enrichment stage for scandium.Besides,it is also inferred that during the lateritic scandium deposit metallogenic process,if the source of surface water is atmospheric precipitation,the scandium migrates mainly as Sc-OH complex in weathering crust;while if the source is fluorine-rich rivers or lakes,it will migrate as both Sc-OH and Sc-F complex. |
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