Process And Transfer Behavior Of Extracting Vanadium Existed In Muscovite From Stone Coal By Activating Roasting

The vanadium has been widely applied in metallurgical industry, astronavigation, chemical industry and new energy due to its special physical, chemical and mechanical properties. As a kind of important vanadium mineral resources, the stone coal is distributed widely in China, so it is an important method of extracting V2O5from stone coal. The stone coal of which the vanadium exists in the muscovite is a typical kind because of its wide distribution and large reserves, where the vanadium mostly presents in the form of Ⅴ(Ⅲ) and V(IV) embedded in the crystal lattice of aluminosilicate minerals. This lattice structure is very hard to be broken down, leading to high difficulty for the extraction of vanadium from the stone coals. At present, the relevant technology researches mainly focus on the process of vanadium extraction from stone coal, but not the corresponding mechanism analysis. Furthermore, the low water leaching rate of vanadium, environment pollution and high acid consumption of leaching process are existed in the process.Therefore, this kind of stone coal collected from Hubei was used as the research object in this article. The adding amount of sodium chloride could significantly reduce and the water leaching rate of vanadium could increase by using new roasting activators. The process of activating roasting-cooperating leaching-concentration and precipitation of vanadium was investigated in order to decrease the acid consumption and increase the leaching rate of vanadium. The operation was simple and the vanadium recovery might improve with the method of ion exchange for processing the mixed leaching solution. Furthermore, the mechanism between stone coal and additives and the transfer rule of vanadium during the roasting process were confirmed with detailed analysis of phase change and thermodynamics. The mechanism of cooperating leaching was determined by exploring and studying the dissolved law of main elements and minerals. The related leaching kinetics and thermodynamics of vanadium were investigated and improved to effectively guide the process of leaching, enrichment and precipitation.The results of vanadium extraction technology show that the water and acid leaching rate of vanadium were56%and16%, furthermore, the total leaching rate of vanadium was more than72%under the conditions of roasting with adding4% sodium chloride and8%potassium sulfate for60min at950℃, and then leaching with water for45min at90℃with the solid-liquid ratio of2.5mL/g. The water residue was leached by using1%H2SO4for60min at30℃with the solid-liquid ratio of2.0mL/g. The vanadium recovery rate could reach70.1%and the purity of V2O5production was more than99%with the ion exchange using D201resin and vanadium precipitation using acid ammonium salt for the mixed leaching solution.The results of mechanism analysis on roasting activation show that the main effect of NaCl was to accelerate damaging lattice structure of muscovite. The microcline and anhydrite appeared due to the reaction of SO2and CaO, and then the reaction of Na2O, K2O and V2O5, Al2O3, SiO2during roasting process with using K2SO4, which restrained and decreased the generation of anorthite and increased the water-soluble vanadate compound to enhance the water leaching rate of vanadium. The analysis of roasting thermodynamic shows that the SO2decomposed from K2SO4could react with CaO to generate CaSO4, the△GTθ of which was lower than calcium feldspar; therefore it would inhibit the generation of calcium feldspar and promote the formation of sodium potassium feldspar. The similar AGTθ of3CaO-V2O5and Na2O·V2O5suggests that the two kinds of vanadate could be generated together in the roasting process with high content of calcium in stone coal.The results of mechanism analysis on the leaching process show that the water leaching process of vanadium included the dissolved process of water-soluble vanadate and others. The dissolved process of acid-soluble vanadate and others could take place by aicd leaching with1%-10%H2SO4. The Ⅴ(Ⅳ) could dissolve and several kinds of feldspar might be destroyed with20%H2SO4. The particle morphology of roasted sample was regular and existed in sphere shape. The water leaching slag was porous morphology. The particle morphology of acid leaching slag was more irregular and the particle size was obviously decreased.The results of kinetics on cooperating leaching show that the control step about water leaching kinetics of roasted stone coal was divided into two stages, internal diffusion control and liquid film unsteady control. The acid leaching process was mainly affected by joint control of the chemical reaction and internal diffusion. Furthermore, the leaching kinetics for21n(1-x)/7+[(1-x)-7-1]=Kt was established. And then it was controlled by liquid membrane unsteady diffusion model, meanwhile, the chemical reactions were basically completed and stable.The thermodynamics of vanadium solution indicate that Ⅴ(Ⅳ) and V(V) were the main existence valence vanadium in leaching solution. VO2+and VO2+were the main forms under acidic condition, but Ⅴ(Ⅳ) would form HV2O5-and V4O92-under alkaline conditions. When the concentration of dissolved V(V) was low, the simple forms such as H2VO4-, HVO42-and VO43-could appear. While the concentration of dissolved V(V) was high, the complex forms such as V4O124-, H3V2O7-, H2V6O172-and H2V10O284-would generate. In sulfuric acid medium, the new vanadium species such as VSO4+, VOSO4and VO2SO4-could form, which would change the original stability range of the species, so the possibility of vanadium leaching was improved. The thermodynamics provided the theoretical foundation and scientific basis for ion exchange and vanadium precipitation with ammonium saltammonium under acid medium as the subsequent process of leaching solution.