Study On The Vanadium Extraction By Roasting From High Carbon Vanadium-bearing Shale By Using Composite Additives

This paper takes a certain vanadium bearing shale in Hubei as an object.In view of the characteristics of high silicon,high carbon and low vanadium content in the vanadium bearing shale,as well as the problems of large amount of chlorine salt in the roasting and leaching process of present vanadium processings and the low vanadium leaching rate,the extraction process of vanadium by preroasting,roasting with low-chlorine additive,leaching was studied and optimized.And the mechanism of destroying the crystal structure of vanadium-bearing minerals and affecting the oxidation of vanadium during the low-chlorine composite roasting process was explored.The study can provide theoretical basis and technical support for further improving the vanadium extraction rate of vanadium-bearing shale roasting and vanadium extraction process in an economical and environment-friendly manner.The main conclusions are as follows:A process of preroasting,low-chlorine composite additive roasting,water leaching,dilute acid leaching for treating vanadium-containing shale is proposed.process parameters are:preroasting temperature of 800?,preroasting time of 1 hour;roasting temperature of 800?,roasting time 3 hours;water leaching temperature of 80?,liquid to solid ratio of 10:1,water leaching time 120 min,Immersion cycle times of 4;acid leaching temperature of 80?,liquid to solid ratio of 10:1,pulp pH of 2,acid leaching time of 180 min.The final vanadium leaching rate was 90.26%.Mixing experiment results show that the low-chlorine composite additive obtained according to the principle of addition ratio of Na2SO4?Na2CO3>NaCl is optimized.In the preroasting process of vanadium-bearing shale,the carbonaceous and pyrite oxidation stages,the mica hydroxyl removal stage and the lattice vanadium oxidation stage occur in turn.After the removal of the hydroxyl group,the mica crystal structure is not destroyed,only the lattice distortion occurs at a high temperature,and it expands in the direction perpendicular to the cleavage plane.Under the effect of sodium salt,dehydrated mica is converted into melts that mainly contain elements such as Na,K,Al,Si,and O.During roasting,NaCl and Na2CO3 synergistically promote the further dissociation of the mica lattice and generate the microporous structure,so that the oxygen and vanadium are in full contact and the vanadium is oxidized.NaCl and Na2SO4 jointly promote the formation of chromium-containing hematite in melts,which partially fixed harmful elements of chromium and iron.In the early stage of the roasting process of low-chlorine composite additives,the oxidation reaction rate of low valance vanadium was relatively high.The addition of the composite additive promotes the low-valence vanadium oxidation reaction in the early stage of the composite roasting,so that the vanadium oxidation rate of the product is higher.In the later period of roasting,under the influence of ore sintering,while the oxidation rate of vanadium is further increased,it is difficult for oxygen to react with the low valance vanadium in the melts under the action of the composite additive,which results in a low oxidation rate of vanadium in the vanadium-containing shale.During roasting of the composite additive,potassium is mainly present in the melts or participates in the formation of soluble potassium salts and potassium feldspar.As the roasting temperature increases or the roasting time prolongs,the diffusion rate increases and the amount of potassium albite increases.This promotes the eutectic reaction of quartz and potassium albite,and accelerates the feldspathization of mica in the system,and promotes the formation of soluble vanadate.