| Stone coal is black carbonaceous shale which contains vanadium. It is an alternative resource of vanadium in China, besides the vanadium and titanium magnetite ore. Our country is rich in stone coal resources, more than 20 around the province. This mineral extensively exists in Yunnan, Guizhou, Hunan, Zhejiang, Jiangxi, Guangxi, Gansu, Xinjiang, etc province or autonomous region. Total of vanadium reserves is about 118 million tons in stone coal vanadium mine, is 7 times of the vanadium total amount in China's vanadium and titanium magnetite, and is more than the sum of vanadium reserves in other countries. So how rationally to use the vanadium resources in the stone coal which has great significance.In our country, sodium salt roasting and water leaching is the traditonal technology of extract vanadium from stone coal.The brief flowof the classical technology includes chloridizing roasting, water leaching, deposition vanadium, alkali dissolution, ammonium salt precipitation vanadium and thermal decomposition. This classical technology has two main problems, low recovery of vanadium (<50%), high cost of the product and serious environment pollution.Serious poisonous gases, HCl and Cl2, are produced in the roasting process because sodium chloride is used as an additive, and the waste water and solid residues. Increasing environmental concerns and legislation concerning environmental protection, China banned the application of this technology in 2003, thus, the utilization of stone coal was limited. Therefore, it is extremely urgent to research and develop a new higher recovery of vanadium and no pollution to environment technology of extracting vanadium from stone coal.The aim of this paper is to research and develop a new process of extracting vanadium from stone coal, characterized by higher recovery of vanadium and which was environmentally-friendly. The new technology on vanadium extraction from stone-coal by sulfuric acid oxygen pressure leaching and solvent extraction was studied in this paper. Firstly, the mineralogy of the stone-coal from Tongren of Guizhou was investigated by various determination methods, scanning electronic microscope, electron probe analysis, energy spectrum analysis,Ⅹ-ray diffraction, thermogravimetric analysis, and so on. Based on the mineralogy, the investigative test was carried out. Then orthogonal and conditional experiments were designed. The effects of leaching time, leaching temperature, leaching agent concentration, leaching L/S, granularity of material, additive consumption, which were the influential factors of extraction of vanadium, were investigated. The results showed that under the conditions of leaching time for 3-4h, temperature at 150℃, sulfuric acid consumption was 25%-35%, ratio of liquid-solid was 1.2:1, the granularity was 0.074mm, Po2 was 1.2MPa and additive consumption was 3%-5%, vanadium leaching percent was over 90% by the method of two-step reverse flow oxygen pressurized acid leaching.At the same time, the technological process of extracting vanadium from the stone-coal oxygen pressure acid-leaching solution is reseached in this paper. Some parameters of extraction and anti-extraction, such as organic phase to aqueous phase (O/A), the composition of solvent, pH and the setting time, are optimized by a series of tests. The results show that after Pretreatment of acid recovery, removing iron by reduction process, adjusting pH to oxygen pressure acid leached solution, the extraction percent can be up to 95% under the conditions of 6-stage counter-flow extraction with 10%P204+5%TBP+85%coal oil, and the stripping efficiency will exceed 99% when 15%H2SO4 solution is taken as the stripping agent. By way of extraction, the concentration of vanadium can be raised to 37g/L or more, and the concentration of iron can be reduced to 0.6g/L or less. The mass ratio of V and Fe can be up to 60 in aqueous phase of stripping, the effect of separation is well.Ammonia was added to stripping liquor to precipitate vanadium, and then the precipitates (ammonium mult-vanadate) was calcined at 550℃for 3 h. The powdery V2O5 product with 99.5% in V2O5 content was obtained by this flowsheet. The total recovery efficiency of vanadium was about 80%.The advantages of this process are:short route, simple operation, high coefficient of recovery and with better economic efficiency, society benefits and environment acceptability. |
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