【作者】 周雪娇；

【导师】 魏昶；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2010， 硕士

【摘要】 钒是一种重要的合金元素,具有许多优良性能,广泛应用于钢铁工业、化工、电池以及医药等领域。随着钒生产及应用领域的逐渐扩大,钒二次资源的开发以及钒污染日渐受到人们的关注。钒是一种多价态元素,能生成+2、+3、+4、+5氧化态化合物,其中+4、+5价钒具有较强的毒性。调查发现,钒的毒性除与总钒含量外,还与钒的化合特性和赋存形态有关。钒在水溶液中的赋存形态主要取决于溶液的pH值、电势E等,这些都可以很方便的在E-pH图上显示出来。此外,钒系E-pH图还可以用于分析湿法提钒工艺条件的选择,预测钒金属的腐蚀性能,指导含钒废水处理中离子交换树脂的选择。本论文在全面综述钒研究进展及电位-pH图应用的基础上,绘制了V-S-H20系以及升温条件下V-H2O系E-pH图,分析了其热力学性质。同时本文还探讨了钒二次资源中一种主要附存状态—三氧化二钒的溶解动力学行为。V-H2O以及V-S-H2O系的热力学分析采用较为权威的数据(其中涵盖了诸多物种的吉布斯自由能)。室温条件下(25℃)V(Ⅲ),V(Ⅳ)和V(Ⅴ)的活度-pH图及V-H2O和V-S-H2O系电位-pH图表明：在自然界水中,低浓度的钒主要以单核离子形式存在,而在污染较为严重的含钒水中则可能存在多核钒酸盐的稳定优势区；SO42-和HSO4-离子可以显著扩大V3+,VO2+以及VO2+离子的稳定区域,形成VSO4+,VOSO4(aq)和VO2SO4-,并且其优势区随着钒活度的减小而增加；随着硫活度的降低,SO42-和HSO4-离子对钒区域的影响减小甚至消失,可溶钒物种转变为固相。升温条件下V-H2O系E-pH图显示：在不同的活度(100,10-2,10-4和10-6)条件下,钒水系电位-pH图显示腐蚀区在整个酸度范围内随着可溶钒物种活度的减小而增加；25℃及150℃条件下,五氧化二钒消失的临界值分别为10-3.17和10-3.51。在不同温度(25,50,75,100,125,150℃；活度=1)条件下,钒水系E-pH图表明随着温度的提高钒氧化物稳定区增加,而钒的稳定区基本不受温度影响。在这种较低的温度条件下,钒表现出较好的抗腐蚀性能。钒的腐蚀-免蚀-钝化图(活度=10-6)则表明在低的电势条件下,钒将不会被腐蚀。钒的腐蚀区及钒的稳定性基本不受温度的影响。在这种条件下,钒的钝化/免蚀性能一般,可能是活度较低时五氧化二钒消失的缘故。同时,本文还研究了V2O3溶解动力学,探讨了搅拌转速、温度、氧气分压、硫酸浓度以及矿物粒度对其溶解速率的影响。研究表明：当搅拌转速大于800 r/min时,外扩散已不再成为限制步骤；V203溶解速率随着温度和氧气分压的增大以及粒度的减小显著增加,而酸浓度对其基本没有影响。V203溶解过程受表面化学反应控制,反应的活化能为43.68 kJ/mol。更多还原

【Abstract】 Vanadium is an important alloying element that is used in the steel industry, chemical industry, battery and drug domain due to its excellent properties. With the ceaseless production and application of vanadium, increasing attention is being paid to the exploitation of vanadium secondary resources and vanadium contamination. Vanadium is a multiple valence element and exists in the+2,+3,+4 and+5 oxidation states in the nature, in which the+4 and +5 oxidation states possess a higher toxicity. It is found that the toxicity of vanadium compounds is not only affected by their total concent, but also affected by their combination properties and combined forms. The combined states in aqueous solution are mainly dependent on pH value and potential, which can represent in the Pourbaix diagrams (potential-pH) expediently. Meanwhile, the Pourbaix diagrams for V-H2O system can be used to analyze the extraction of vanadium by hydrometallurgy, predict the vanadium anticorrosive property, guide the selection of ion exchange resin in the effluent treatment.On the basis of describing the development in researching vanadium and application of Pourbaix diagrams, the potential-pH diagrams for the vanadium-water and vanadium-sulphur-water systems were depicted and the thermodynamical properties was analyzed. Meanwhile, this work studied the dissolution kinetic of vanadium trioxide, which is one of the main states in the vanadium-bearing secondary resources.The thermodynamics of vanadium are calculated from the most recent critically assessed reviews, which publish standard Gibbs energies of formation for the various species and phases considered. The Pourbaix diagrams for vanadium systems at 25℃show that:1) Vanadium mainly exists as mononuclear ions at low concentrations in nature waters and polyvanadates replace the mononuclear oxyanions as the preponderant species in more concentrated solutions.2) Comparison of the potential-pH diagrams for V-S-H2O with simple V-H2O system displays that SO42- and HSO4- ions obviously enlarge the regions of stability of V3+, VO2+ and VO2+ ions, forming VSO4+, VOSO4(aq) and VO2SO4-. The predominance areas for vanadium sulfates (VSO4+, VOSO4(aq), VO2SO4-) increase with the decrease on the vanadium activities.3) The activity-pH diagrams for each of the stable vanadium oxidation states indicate that an increase on the activity of sulfuric acid from 0.1 to 1.0 results in an increase on the predominance areas for vanadium sulfates and decrease on the stability areas for solid phases, such as V2O3, V2O4 and V2O5, etc.The Pourbaix diagrams for the V-H2O system at elevated temperature indicated that:1) The Pourbaix diagrams for vanadium with the activities of 100,10-2, 10-4 and 10-6 show that the corrosion area enlarges over the whole pH range with decreasing the soluble vanadium activity. Vanadium pentoxide (V2O5) disappears lower than the activity of 10-3.17 and 10-3.51 at 25℃and 150℃, respectively.2) The Pourbaix diagrams for the V-H2O system at 25-150℃with the activity of 100 indicate that the stability regions of vanadium oxides extend with the elevation of the temperature and the vanadium stability region is independent of temperatures. Vanadium represents a good corrosion resistance with this activity at low temperature.3) The Corrosion-Immunity-Passivation diagrams (10-6 activity of all dissolved vanadium species) show that the vanadium will not be corroded at lower potential. The corrosion domain minishes slightly and the stability region of vanadium is hardly changed with rising the temperature. At this condition, the immunity/passivation performance of vanadium is infirm due to the dissolution of vanadium pentoxide (V2O5) at low activity.Simultaneously, the kinetics of dissolution of vanadium trioxide in sulphuric acid-oxygen media was presented. The various parameters considered in this work were stirring speed, concentration of sulphuric acid, temperature, partial pressures of oxygen and particle size. The results showed that the negative effect of boundary layers was eliminated when stirring speed exceeded 800 r/min. The dissolution rate of vanadium trioxide increased with temperature and partial pressures of oxygen, but decreased with increasing particle size. No effect of concentration of sulphuric acid was observed on the conversion. The dissolution kinetics was controlled by the chemical reaction at the surface with the estimated activation energy of 43.46 kJ/mol.更多还原