The Experimental And Mechanism Reseach Of Improving The Leaching Ratio Of Vanadium

Vanadium is considered as one of the important rare metals which has been widelyused in many fields in modern society. Vanadium bearing slag plays a dominant role inthe sources of vanadium which is an important utilization of vanadic titano-magnetite.As is known to all, China is an important industrial countries of vanadium production,and allways attach importance to the technology vanadium extraction. At present,extraction of vanadium from vanadium slag has reached to a mature period, however, itis worthwhile to make further improvement.Based on the relevant research status of vanadium extraction from vanadium slag,this paper pays a significant attention to the roasting and leaching process of vanadiumslag with the purpose of improving the research of vanadium by some different contentand method so as to provide theoretical guidance for the production practice.Specifically, the following results have been achieved.(1) Thermodynamic analysis of oxidizing roasting of vanadium slagThermodynamic analysis of oxidizing roasting of vanadium slag was carried out,the gas partial pressure of reactions was take into consideration, and the Gibbs freeenergy giagrams of major reactions were figured under the roasting temperature. Withthe exist of Na2CO3, the sequence of the roasting process was iron, olivine, spinel andsome side reaction. It is also concluded that the oxidation process of vanadium slag wasdivided into two stages. The first stage was from345to600℃which was mainlydescribed as the oxidation of Fe3O4and the Fe2+in olivine phase. The second stageranged from600to925℃, and it was ascribed to the oxidation of the spinel phases.(2) The effect of alkaline additive in the roasting process of vanadium slagEffects of the sodium carbonate on the roasting process of vanadium was discussedby multiple means. It was concluded that the sodium carbonate did not decompose intoNa2O then react with the vanadium but directly, and the reaction temperature was about600℃. Adding a certain amount of Na2CO3could promote the oxidation reaction ofvanadium slag and lower the temperature of the formation of vanadates. The silicates inthe vanadium slag would compete to react with the sodium carbonate with the vanadium,which may affect the extraction of vanadium. Sufficient amount of Na2CO3can preventthe presence of vanadium bronzes, and enough Na2CO3is available for the formation ofsodium vanadates. When there is too much additives, the roasted slag would cohere together and form a honeycomb-like ball which would affect the extraction of vanadiumat last.(3) Mechanism of vanadium oxidation in the roasting processThe vanadium oxidation in the roasting process was simulating calculated byFactSage. Results shows that the oxidation of vanadium was different under variousroasting temperature. When the temperature was500℃and600℃, the spinel FeV2O4was oxidized to V3O5first, then was VO2and Fe(VO3)2and finally turn to V2O5. Whenthe temperature was700℃and800℃, the spinel FeV2O4was oxidized to VO2first,and then was the Fe(VO3)2. Fe2SiO4was oxidized before the FeV2O4, and it react withthe sodium carbonate to produce sodium silicates.(Na2O)(V2O5) was the majorproduction of vandium slag, and some liquid phases was detected when the roastingtemperature was800℃.(4) Mechanism of vanadium oxidation in the roasting processThe roasting, water leaching and ammonium carbonate leaching process wereinvestigated by single-factor experimental analysis. The effect of oxidation process andleaching process on leaching efficiency of vanadium, phase transition of vanadium slagin oxidation process and roasted samples in leaching were studied, etc. It was concludedthat the roasting temperature and addition amount of sodium carbonate were the majorfactors that affect the leaching ratio of vanadium. Suitable roasting process parameterswere roasting temperature800℃, roasting time90-120min, addition amount of sodiumcarbonate19%. Suitable water leaching process parameters were leaching temperature90℃, leaching time30min, liquid to solid ratio8.0ml/g, and under this conditions, theleaching ratio of vanadium approached90%, the vanadium content in the leachingresidue was1.17%. Suitable ammonium carbonate leaching process parameters wereleaching temperature60℃, leaching time20-25min, ammonium carbonateconcentration120g/L, and under this conditions, the leaching ratio of vanadium wasabove92%, the vanadium content in the leaching residue was1.03%. sodium roastingand ammonia leaching process was a practicable method to extract vanadium Under theammonia leaching process, most of the vanadates were leached to the leaching solution.