| This work was supported by the National Natural Science Foundation of China (No.51304090) and the Applied Basic Research Programs of Yunnan Province (No.2011FZ062).Clay vanadium ore is an important vanadium ore resource which can be an important material for extracting vanadium. Traditional vanadium extraction technologies bring serious environment pollution with low recovery of vanadium and cannot adapt to properties of clay vanadium ore well. The direction of study on vanadium extraction is acid leaching under normal pressure without roasting, however, some problems are not solved yet during the studies of extracting vanadium from clay vanadium ore by acid leaching under normal pressure without roasting, such as low leaching index and the difficulties in separating leaching residue and leaching solution caused by argillization generated by grinding. In addition, the weakness of current theoretical research on acid leaching without roasting technology and the lack of cognition, which makes it difficult to offer basis guidance to breakthrough, has become a more important problem. In view of this, a new technology of vanadium extraction by acid leaching under normal pressure without roasting, i.e. vanadium extraction from clay vanadium ore by activated acid leaching under normal pressure without grinding and roasting, was put forward in this paper according to process mineralogy properties of clay vanadium ore and effect of activator. The experimental and mechanical researches were carried out, in which the relation between process mineralogy properties of clay vanadium ore and extracting vanadium was firstly researched, the optimum leaching conditions of vanadium extraction from clay vanadium ore by activated acid leaching under normal pressure were confirmed and the mechanism of that was stated by analysis of thermodynamics, microstructure, compositional variation and dynamics.Process mineralogy properties of clay vanadium ore was firstly researched by chemical analysis methods and modern analysis instruments such as scanning electron microscope, X-ray diffractometer and so on. The results show that, content of V2O5in the clay vanadium ore is2.04%which indicates that this ore has higher utilization value, and content of SiO2, the main chemical composition, is higher as81.59%which shows that this ore is acidic ore and vanadium in it can be extracted by acid leaching. In order to leach out the vanadium, which mainly exists as V(Ⅲ) and accounts for90.18%in total vanadium, translation from Ⅴ(Ⅲ) into Ⅴ(Ⅳ) or Ⅴ(Ⅴ) has to be taken for Ⅴ(Ⅲ) is indissolvable in water and acid.90%of vanadium occurs in argillaceous illite and partly exists in lattice of mica in form of isomorphism, so mineral structures of illite and V-bearing mica have to be destroyed so that vanadium in which can be extracted by leaching.On the basis of analysis of process mineralogy and thermodynamics, the effects of main influence factors on acid leaching vanadium were investigated by single factor way, and immanent causes were analyzed. The results show that, with certain conditions, leaching temperature and dosage of sulfuric acid have significant effects on leaching rate, followed by leaching time and ratio of liquid to solid, and that of particle size is less. The leaching rate of activated acid leaching under normal pressure is higher as92.32%under optimum conditions of MnO2, the activator, dosage of1.5%, agitator speed of300r/min, sulfuric acid dosage of30%, leaching time of6h, leaching temperature of90℃and ratio of liquid to solid of1:1.Comparing with unactivated acid leaching, activated acid leaching not only improves leaching rate significantly, but also reduces acid consumption and shortens leaching cycle. In addition, acidity of activated acid leaching solution is relatively weak, which can reduce dosage of neutralization reagent used in pretreatment process of solvent extraction and lower production cost. Meanwhile, comparing with traditional vanadium extraction technologies, under the premise of ensuring higher leaching rate, the new technology leave out the processes of expensive grinding and complex roasting, which solves problems of the difficulties in separating leaching residue and leaching solution caused by argillization generated by grinding, simplifies operation, reduces cost and avoids roasting pollution, meeting the requires of modern chemical and metallurgical industry.Aiming at the problem of feeble basic theoretical research on vanadium extraction by acid leaching without roasting, mechanism of vanadium extraction by activated acid leaching under normal pressure without grinding and roasting was investigated and explained from aspects of thermodynamics, micro structure, compositional variation and dynamics comprehensively applying thermodynamics and dynamics principles and modern analysis methods such as X-ray diffraction analysis and electron microscope scanning analysis, etc.1) Thermodynamics of vanadium extraction by acid leaching:SiO2, the basic substance of the ore, is hardly dissolved and steadily remained during the sulfuric acid leaching process, showing that acid leaching is suitable for extracting vanadium from clay vanadium ore. Dissolution reaction of illite and V-bearing mica, the main V-bearing minerals, in acid solution can spontaneously and completely proceed, indicating that vanadium in these two minerals can be leached with acid in view of thermodynamics. Also, limonite is indissolvable in acid, causing difficulty for vanadium in it to be dissolved.2) Mechanism of activated acid leaching under normal pressure stated by analyzing change of the micro structure characteristics:With assistance of activator, sulfuric acid solution can destroy mineral structure more effectively and generate many fractures on the surface of particles, which is beneficial for lea’ching agent molecules to diffuse into centers of ore particles and leach vanadium furthest. Simultaneously increasing of specific surface area of ore particles makes sulfuric acid contact with minerals more sufficiently so that vanadium is leached more easily and the leaching rate is risen.3) Mechanism of activated acid leaching under normal pressure announced by analyzing chemical compositions and mineral interior:The large disappearance of diffraction peaks of illite and mica in the XRD atlas of activated leaching residue shows that during process of activated leaching, the capacity of oxidation and dissolution of minerals in leaching system is enhanced with assistance of activator so that most of minerals are dissolved and destroyed, further leading to the easier leaching of vanadium existing in mineral lattices. Contents of the main chemical compositions in activated acid leaching solution are higher than that in unactivated acid leaching solution, which indicates that activated acid leaching system can destroy mineral structure more exhaustively and make ore-forming elements released and thus higher leaching rate is obtained.4) Kinetics study of activated acid leaching under normal pressure:Leaching process fits the shrinking core model and both unactivated acid leaching and activated acid leaching submit to the kinetic equation controlled by chemical reaction. Though activated acid leaching does not change control steps, it makes the activation energy of leaching reaction reduces from66.1kJ/mol for unactivated acid leaching to45.91kJ/mol for activated acid leaching and reaction order falls from1.90to0.88, and thus decreases the influence of temperature and concentration of sulfuric acid and increases the leaching rate. |
PDF Full Text Request