Experiment On Combustion Characteristics Of Stone Coal From Gansu Province In CFB And Extracting Vanadium From Stone Coal Ash

Stone coal containing vanadium is an important vanadium ore resources in our country, its reserves is extremely rich, extracting vanadium from stone coal has also become an important development direction of developing vanadium resources in China. At present, vanadium extraction process exists serious environmental pollution, heat energy cannot be fully utilized, vanadium recovery problems etc. In this paper, in view of a high carbon stone coal containing vanadium from the Gansu province, heat energy from stone coal obtained through the utilization of combustion technology of Circulating Fluidized Bed(CFB) was raised, and related experimental study of vanadium extraction would be carried out from ash containing vanadium with the characteristics of stone coal and Thermal Energy Engineering Research Institute of Zhejiang University in terms of technical advantages of vanadium extraction from stone coal. The purpose of these studies was to reduce the pollution of the environment, obtain high conversion rate of vanadium, and make full use of heat energy to improve the economic benefits of the comprehensive utilization of stone coal. The research content mainly included:experimental study of leaching characteristic of acid leaching for extracting vanadium and roasting stage in additive-free roasting technique for extracting vanadium from ash containing vanadium. The main research results are as follows:1.Stone coal from Gansu Subei is a very difficult ignition and burnout of coal. In the1MW CFB combustor, from the dense phase region to the furnace outlet along the furnace, temperature is uniformity and combustion condition is good. After the end of each combustion conditions, carbon content in bottom slag and fly ash basically can be controlled at about5%, the combustion efficiency is about70%, it proves that the full utilization of heat energy in stone coal is feasible using CFB combustion. After CFB combustion of stone coal, fly ash and bottom ash has a certain degree of vanadium enrichment, vanadium content of the fly ash amounts to about1.5%, while vanadium content of the bottom slag was more than0.8%.2.Study on acid leaching from ash containing vanadium is carried out with sulfuric acid as leaching agent, the average leaching rate of vanadium can reach87.83%, V2O5content of residue after the acid leaching decreases to0.14%, it shows that in high concentration of sulfuric acid and high temperature, leaching of vanadium in residue is feasible. In the process of leaching, leaching conditions of sulfuric acid concentration, leaching temperature, leaching time and liquid to solid ratio all affect vanadium recovery, but sulfuric acid concentration and leaching temperature play a greater impact. The appropriate parameters obtained are as follows:sulfuric acid concentration of6.0mol·L-1, leaching temperature of110℃, leaching time of2h, liquid to solid ratio of2.5:1, particle size of70μm.3.In the process of the direct acid leaching for vanadium extraction, recovery of vanadium will vary in order for different minerals containing vanadium, vanadium in free oxide is the first to be leached, then iron and aluminum oxides,vanadium in Roscoelite is the last, vanadium of mica minerals can be leached in high concentration of sulfuric acid and high temperature4.Fine grinding of mechanical activation pretreatment can reduce the stability of Roscoelite crystal, enhance the activity of Roscoelite crystal. Vanadium of ash containing vanadium mainly occurs in the mica crystal, mica crystal is dense, stable and hard to break. Mechanical activation pretreatment for ash containing vanadium can reduce the stability of Roscoelite crystal, Roscoelite crystal begins to decompose at low temperature and releases low valent vanadium.5.Some new rules are found from research on the effect of the oxidative atmosphere on vanadium conversion rate in roasting process.In the presence of non oxidizing atmosphere, Roscoelite crystal can still be destroyed, a small part of vanadium from Roscoelite crystal is released, however, in the absence of oxidative leaching agent, this part of low valent vanadium is difficult to be leached. At the same time, an oxidizing atmosphere contributes to oxidizing low valence vanadium to the high valence compound containing vanadium and accelerating the separation of low valent vanadium from Roscoelite crystal.6.1n the high temperature roasting process of ash containing vanadium, roasting factors of particle size of ash, roasting temperature, roasting time, air flow rate all play a great impact on conversion rate of vanadium. Under the appropriate roasting conditions, even in the low strength of acid leaching conditions of low sulfuric acid concentration and room temperature, vanadium conversion rate is still up to83.81%.7.Changes in pore structure will affect oxidation of low valence vanadium released after decomposition of Roscoelite crystal. Through the SEM analysis of surface morphology and analysis of Autosorb-1-C physical and chemical adsorption instrument, it is found that with the increasing of roasting temperature, the specific surface area of material and total pore volume decreases, the average pore size first increases and then decreases in the process of roasting. At the same time, with the increasing of roasting temperature, material sintering phenomenon is becoming more and more serious, the adsorption capacity of material for nitrogen is falling, closed hole which cannot produce adsorption curve increases gradually, and open hole is continuous reduction, a large number of closed hole cause that low valence vanadium released after decomposition of Roscoelite crystal cannot contact with the oxidizing gas and be oxidized into high valence vanadium compounds, the result is that vanadium is difficult to be leached.