Studies On Predominance Diagrams And Pourbaix Diagrams For V-Cl-H₂O System

E-pH diagram is a kind of indicator diagram which describe the relationship between the precenced forms of the elements and E, pH. It can easily deduce the possibility of the reaction keeping, the stability of products, the reaction extent and the predominance region of dissolved species, and has been widely used in the region of material, chemical industry, chemistry and metallurgy.The core of vanadium hydrometallurgical process is to make vanadium dissolve from raw material and deposition from the solution. Vanadium species have a series of complex equalized reaction. With difference in E and pH, there is difference between the main existing forms of vanadium and the types of ions.According to the principle of simultaneous equilibrium, thermodynamic analysis were carried out in V-H₂O, Cl-H₂O and V-Cl-H₂O systems at 25℃. Besides, a mathematical model of species concentrations, Eh and pH was constructed. By using the concentration comparison method and a graphic algorithm which absorbs the advantages from convex polygon method and scan point by point method, predominance diagrams and Pourbaix diagrams for V-H₂O, Cl-H₂O and V-Cl-H₂O systems were generated in this paper by computer.The predominance diagram for V-H₂O system shows that the valence states of predominance areas of dissolved species will rise while the figure of E gets high. A higher total concentration of vanadium results in more polycondensation reactions of the vanadium (â…¤) species and vanadium (â…£) species. Meanwhile, the multicore vanadium radical anions are predominance in high potential region. The stable areas of dissolved species change with E, pH value and the total vanadium concentration in the solution. Comparisons made between predominance diagrams CT(V)=1.0×10-3 mol·L-1 and CT(V)=1.0×10-5 mol·L-1 show that at a specific temperature and pressure the total concentration of vanadium has little effect on the stable predominance regions of the vanadium cation V²⁺, V3+, VO+, VOH²⁺ and VO²⁺. But, the stable predominance region of VO²⁺ reduces evidently. At high potential, the reactions changed toward the production of dicore vanadium radical anion from monocore vanadium radical anion and multicore vanadium radical anion from dicore vanadium radical anion with the acidification. This phenomenon illuminates that protonnation can promote polymerization. At the same potential and acid condition, the higher concentration of vanadium system take place polymerization, while the lower concentration system has not. So, high concentration of vanadium is another condition for polymerization.The comparisons made between Pourbaix diagrams for CT(V)=1.0×10-3 mol·L-1 and CT(V)=1.0×10-5 mol·L-1 show that there is no V2O5 in Pourbaix diagram at CT(V)=1.0×10-3 mol·L-1, In the Pourbaix diagram at CT(V)=1.0×10-3 mol·L-1, there are two liquid regions, which are divided by V6O13. Comparison made betweenâ… andâ…¢shows that they contain same dissolved species (V²⁺, V3+, VOH²⁺, VO+, VO²⁺, VO43-, H2VO4-, HVO42-). When the total concentration of vanadium descrease, the stable liquid regions will increase. At the higher concentration of vanadium, multicore vanadium radical and di-core vanadium radical anion play important parts in five valence of vanadium radical anion.In Cl-H₂O system, all species are soluble components, and have a great solubility, no solid phase is formed. In low potential area, the main species is chloride ions. In high potential area, the predominant component is perchlorate radical anion.Hydrometallurgical process of vanadium and the waste water containing vanadium include a large number of chloridion. Through the V-Cl-H₂O System study, characteristics and occurrence patterns of vanadium and chlorine can be determined under certain conditions. The research results provide a scientific basis to analyse leaching-out process of extracting vanadium by wet methold and develop clean and efficient metholdology of hydrometallurgy.Predominance diagrams for V-Cl-H₂O system shows that in high potential region, with pH value increasing, the predominant species of vanadium are H2V10O284-, HV10O285-, V4O124-, HV2O73- and VO43- in sequence. The absolute predominance area of VOCl2 (aq) lies in low potential region. Chloridion is not strict with vanadium anion in high potential and reductive environment.The Eh-pH diagrams for V-H₂O system, Cl-H₂O system, V-Cl-H₂O system plotted in this papar provide an important theoretical basis to analyse the characteristics of chemical combination and species of vanadium in water, as well as vanadium hydrometallurgical methodology.