Study On The Mechanism Of Vanadium Extraction From Pingtaishan Vanadium-Bearing Stone Coal By Multi-stage Roasting

Stone coal is an important vanadium resource in China with abundant reserves and great value in vanadium extraction.However,due to the influence of its formation environment,the composition of stone coal is very complex,the ore is impregnation with different degrees of carbonaceous,and vanadium occurs in the crystal lattice of silicate minerals with similar quality,which results in the difficulty of vanadium extraction from stone coal today,and the low efficiency of vanadium extraction.At present,vanadium extraction from stone coal mostly adopts the acid leaching process after roasting with compound additives,which can achieve better indexes,but different additives are used for different kinds of stone coal.Therefore,this paper proposes a two-stage oxidation roasting followed by acid leaching process of "Oxidation Crystallization+Decarbonization",aiming to reduce the selectivity of vanadium extraction process to stone coal,improve vanadium extraction efficiency,and reduce environmental pollution.And systematic research work is carried out around this process and mechanism.The process mineralogy study shows that the main composition of the ore is SiO2 and Al2O3,with mass fraction of 63.7%and 10.46%,respectively.The main valuable element is V,of which the content of V2O5 is 0.98%.The carbon content in the ore is higher,which is 14.15%.Vanadium mainly occurs in sericite with a distribution rate of 69.90%,which is atypical refractory vanadium-bearing stone coal.The thermodynamic calculation and analysis of the roasting process of vanadium-bearing stone coal were carried out by using HSC Chemistry 6.0 thermodynamic software.The results show that the roasting process of stone coal is a complex system.The order of the difficulty of forming the same type of vanadate with different metal oxides in stone coal and V2O5 is as follows:Na2O>CaO>MgO>Fe2O3;The difficulty of forming different vanadates with the same metal oxide and V2O5 is:vanadate>Pyrovanadate>Metavanadate.Based on the thermogravimetric analysis of stone coal with different heating rates,the results show that the optimal reaction kinetics model for the thermal decomposition of vanadium-bearing stone coal in the roasting process is Ginstling-Brounshtein equation.The reaction process is controlled by three-dimensional diffusion,and the integral form is(3/2)[1-2/3α-(1-α)2/3].The differential form is(1-α)1/3[1-(1-α)]-1.Apparent activation energy E=136.09kJ/mol and pre-exponential factor lnA=12.40s-1.The acid leaching rate of vanadium in stone coal after two-stage oxidation roasting can reach 51.42%.The specific process conditions are as follows:a roasting temperature of 800℃,roasting time of 20min,oxygen concentration of 20%atmosphere of 400mL/min;The second-stage roasting temperature was 700℃,the roasting time was 60min,the oxygen concentration was 20%,and the gas volume was 500 mL/min.The leaching conditions were as follows:temperature 90℃,time 3h,acid dosage 30%,liquid to solid ratio 1.25:1.By XRD,FTIR,BET,SEM after roasting on different conditions,the results showed that the sericite lattice was destroyed and a small part of carbonaceous was removed when the temperature reached 700℃ during the roasting process.In addition,calcite decomposition,goethite decomposition and other phase transition occurred,which is a key step to improve the leaching rate of vanadium.In the process of second-stage roasting,the carbon content decreased from 6.5%to 0.24%.In the roasted sample,the pore structure of the sample changed obviously,and the open holes at both ends gradually changed into closed holes at one end.At the same time,it can be seen that the surface of particles becomes more loose and porous,which is conducive to the gas-solid and liquid-solid reactions.The phase transition and migration behavior of the related elements were investigated by XRD and SEM-EDS scanning electron spectroscopy.The results show that vanadium exists in vanadium mica and schreyerite in raw ore.After two stages of roasting,part of vanadium is released and then leached in the form of vanadate.Part of vanadium remains in vanadium mica and schreyerite,while some of it enters into diopfeldspar.In addition,the Ca element was transferred from calcite to wollastonite and dodecalcium heptaaluminate,and the Fe element stably existed in hematite.