Study On Efficiently Extraction Technology And Mechanism Of Vanadium From Black Shale Based On Alkaline Fusion System

Vanadium-bearing shale is a unique vanadium ore resource in China,and the total reseve of vanadium-bearing black shale is abundant.It is widely distributed in many provinces of China.Most of the vanadium in shale exists stably in the structures of mica group minerals in the form of V(?).High roasting temperature and long roasting time is usually used to destroy the structures of mica minerlas,which contributes to enhancing the leaching efficiency of vanadium.The alkaline fusion is researched and applied in extraction and utilization of complex and refractory mineral resources due to its energy-efficiency characteristic.The process of roasting with NaOH has been studied in this paper by using vanadium-bearing shale in Hubei province as raw material,the optimum process parameters in the roasting and leaching process on the leaching efficiency of vanadium has been investigated.Combining with the thermodynamic analysis,phase and microstructure changes of the roasting reaction process,the decomposition reaction process of vanadium-bearing muscovite and the migration and transformation process of vanadium in the alkaline fusion were studied.The dynamical behavior and reaction mechanism of roasting reaction were also investigated in the paper.The mechanism of enhanced vanadium extraction from shale by alkaline fusion was revealed via all of the above analysis.The results showed that under the conditions that the mass ratio of NaOH to raw ore was 1:1(g/g),the roasting temperature was 500 °C,leaching at normal temperature,the roasting time was 60 min and the liquid to solid rate was 4.0 mL/g.Under the optimum conditions,the vanadium leaching efficiency was 84.63%.Compared with the conventional roasting-leaching process,when the vanadium leaching efficiency was similar,the roasting temperature was reduced to 500 °C,the roasting time was shortened to 60 min.The mechanism results showed that the structural disintegration of muscovite and phase transformation of vanadium were strengthened under alkaline fusion system.During the roasting process,the structural of muscovite was decomposed into nepheline accompanied by the reaction with NaOH,and vanadium was liberated from the muscovite lattice.The decomposition product nepheline and the calcite in the black shale interacted with the molten alkali to produce a structurally stable aluminum stellite,which promoted the completely destruction of mica structure.However,due to the encapsulation of sodium silicate,vanadium is difficult to release completely.Compared with the conventional roasting process,the Gibbs free energy of the mica decomposition reaction was lower and the mica structure was more completely destroyed during the alkaline fusion process.The results of kinetics analysis showed that the roasting process was controlled by chemical reaction in the early stage of the whole roasting process.The related chemical changes of vanadium were completed at this stage,and the phase transformation process of vanadium was strengthened.Combined with the leaching behavior and chemical bond change analyses of the characteristic elements of muscovite,the reaction process muscovite structure in alkaline fusion could be described as: diffusion of molten alkali,dehydroxylation of muscovite,disintegration of muscovite structure and formation of alkali metal salt.