| Stone coal is a typical abundant vanadium resource in China. Acid leaching is a common technology for extracting vanadium from stone coal, while the study of leaching mechanism is not comprehensive. The technology of blank roasting–acid leaching to extract vanadium of a typical mica-type vanadium-bearing stone coal from Hubei province was applied in this paper. The effects on the leaching rate of vanadium were evaluated. The transition of mineral phase, vanadium valence in the roasting process and the occurrence state of vanadium in the residue were analysed to uncover the leaching mechanism. It analyzed the dynamics of vanadium, aluminum and the relevance of vanadium-potassium, vanadium-magnesium in the leaching process. The main conclusions are as follows:(1) The stone coal from Hubei in which V2O5 grade is 0.71% is a typical low-grade mica-type vanadium-bearing stone coal. The result of vanadium valence distribution is that V(III) is dominant which accounts for 61.8%, and V(IV) accounts for 38.2%, while V(V) is undetected. Vanadium replace aluminum from dioctahedral structure as isomorphism in mica and clay minerals. The structure of vanadium-bearing mica go through three stages in the roasting process of stone coal:before 800?, the results indicated that the structure of mica was distorted and trivalent vanadium was oxidated to tetravalent vanadium because of dehydroxylation; Between 800? and 900?, the structure of mica was broken for the generation of pentavalent vanadium; When the temperature up to 950?, the pentavalent vanadium was wrapped by partially sintered.(2) For this stone coal, under the conditions of roasting temperatue 850?, roasting time 1h, leaching time 12 h, leaching temperature 95?, concentration of sulfuric acid 20%, ratio of liquid to solid 2:1, the leaching rate of vanadium reached to 91% by the technology of blank roasting–acid leaching to extract vanadium. Vanadium-bearing mica minerals and quartz embedded complex was an important factor that lead to vanadium was hard to be extracted. Raising sulfuric acid concentration not only aggravated the corrosion of the surface of minerals and improved the leaching rate of vanadium, but also restrained the formation of silica colloidal which could cause vanadium loss, and it was beneficial to form the alum, as a result, the concentration of aluminium ion in the leachate decreased obviously.(3) The results indicate that the leaching kinetics of vanadium interrelate with the valence of vanadium. At 25?-45? and 0-120 min, the leaching process of vanadium is controlled by the chemical reaction with the apparent activation energy of 36 k J/mol, and the leached vanadium mainly consist of V(V) and V(IV) on the particle surface. At 25-45? and 120-480 min, the reaction boundary moves into the inside of particles, and the leaching process of vanadium which is mainly V(?) turns to be controlled by internal diffusion with the apparent activation energy of 63 k J/mol. At 55?-95?, as V(III) is activated, the leaching process of vanadium is controlled by the internal diffusion with the apparent activation energy of 91 k J/mol. The leaching process of aluminum is controlled by the internal diffusion for its occurrence state is simply [Al O6] octahedron and [Al O4] tetrahedron, and the apparent reaction activation energy is 68 k J/mol.(4) The facts that vanadium-potassium and vanadium-magnesium both show a poor leaching correlation at low temperature, but vanadium-potassium and vanadium-magnesium both present a good leaching correlation at the high temperature further confirmed that V(V) existed in the form of free state, easy to extract, V(III) and V(?) mainly existed in the form of lattice bound state, hard to extract. |
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