| Extraction of vanadium is an important aspect of the compositive utilization of stone coal resource.From 1960s on,studies and applications about extraction of vanadium from stone coal have been carrying out in China.Generally speaking,the technical level of extraction of vanadium is out-dated,and has lots of problems,such as low recovery of vanadium,high consumption of reagents,high cost,and producing pollution.Theoretical researches of extraction of vanadium from stone coal are few,especially for the theoretical researches about roasting process and acid leaching process.The poverty of theoretical research seriously restricts the technology development of extraction of vanadium from stone coal.Besides,existing studies are mostly aimed at sodium salt roasting process,and few studies are aimed at oxidizing roasting process.Based on the research results of previous literatures, through lots of modern testing technologies and a great deal of theoretical analyses and experiments,correlative theories with oxidizing roasting of stone coal process and acid leaching of roasted stone coal process were studied detailedly in this dissertation.The main conclusions are as follows:1.Effect of roasting on crystal structure variation of illite and dissolution behavior of illite in acid solutionVariation rules of crystal structure of illite under 1050℃range were studied.The results indicated that adsorbed water and interlayer water are removed under about 100℃,and hydroxylation takes place between 600～800℃,and under 1050℃,the layered structure of illite collapses and begins to transform into mullite.Roasting makes the structural of tetrahedron and octahedron deformed and adjusted,which weakening the binding force of Al,K and Si got and strengthening their dissolution abilities in acid.2.Thermodynamic analysis of oxidizing roasting process and physical chemistry variation in oxidizing roasting processThermodynamic analysis of oxidizing roasting process was carried out,and Gibbs free energy diagrams of organic matter,pyrite, vanandium and calcium carbonate were figured.Oxidation reactions of organic matter and pyrite are easier to proceed than oxidation reaction of vanadium,thus,the presence of organic matter and pyrite in stone coal can restrain the oxidation of V(Ⅲ).In the oxidizing roasting process,organic matter,pyrite and vanadium(V(Ⅲ) and V(Ⅳ)) are oxidized,and calcite decomposed. When roasting temperature reaches 850℃,crystal structure of illite be destroyed,and roasting temperature reaches 1050℃,ridymite formed. Particles begins to sintering under 750℃,and with the roasting temperature increased,sintering intensified.The particular material of low melting point will form in a certain roasting temperature,and when roasting temperature is higher than the melting point,liquid phase forms, resulting in vanadium be encapsulated.3.Mechanism of vanadium oxidation in roasting process and the relationship between vanadium oxidation and vanadium leachingThe process of vanadium oxidation can be divided into three stages: at the first stage,V(Ⅲ) is oxidated into V(Ⅳ);at the second stage,V(Ⅳ) is oxidated into V(Ⅴ);at the final stage,the oxidations of V(Ⅲ) and V(Ⅳ) reach a balance.V(Ⅲ) should be oxidated into V(Ⅳ) or V(Ⅴ) before it be leach out into solution,and if vanadium is encapsulated in roasting process,it is hard to be leach out.4.Thermodynamic analysis of the process of acid leaching of the roasted stone coalPotential-pH equilibrium diagram of vanadium in aqueous solution was figured,and existence state and solubility of vanadium in aqueous solution was studied.Existence state of vanadium in aqueous solution is extremely perplexing,and under the condition of high potential and low pH,vanadium exists on the form of VO2+ orVO2+ in aqueous solution.Concentration logarithmic diagrams of dissolution of quartz,illite and kaolinite in aqueous solution were figured,and standard reaction constants of leaching reaction of illite,kaolinite and hematite were calculated.The results indicated that leaching reaction of illite and kaolinite can proceed spontaneously,and the solubility of kaolinite in acid solution is much better than illite.Hematite is very hard to dissolve in acid solution.5 Acid leaching kinetics of roasted stone coal and mechanism of vanadium leachingA "flake"-type kinetic model for vanadium leaching reaction was proposed.The apparent activation energy of the reaction is 99.52 kJ/mol. The kinetic result shows that the reaction rate is determined by chemistry reaction.Results of leaching experiments indicated that there are good correlation between leaching behavior of Al and V.When Al is leached out,V is leached out,too;and vice versa.Leaching rate of vanadium is determined by the damage degree of illite's crystal structure, and the increase of damage degree is beneficial to vanadium leaching. Mechanism of vanadium being leached out is in accord with the transition state theory of surface chemistry.Firstly,H+ adsorbs onto the surface of illite;secondly,H+ exchanges with V which in crystal structure of illite;finally,V desorbs from the surface of illite,thus,V goes into the solution.That is to say,vanadium is leached out from illite.
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