Fundamental Studies On The Pre-concentration And Separation Of Vanadium From Stone Coal Ore

Stone coal ore is an important vanadium-bearing resource in China,in which about 87%of the vanadium is reserved.However,the vanadium grade of stone coal ore is low and the occurrence states of vanadium are dispersive,which make it impossible be beneficiated by the conventional ore dressing methods.Therefore,of the existing techniques to extract vanadium from stone coal,the ore is directly used as feedstock.This causes the huge quantity of feedstock,and thereby high energy consumption,high reagent consumption as well as large amounts of residue and effluent.Consequently,the utilization of stone coal ore is restricted.As for the existing techniques to extract vanadium from stone coal ore,such as salt roast-leaching,calcification roast-leaching and blank roast-leaching etc,all of them are designed based on the same principle,i.e.oxidizing roast followed by liquid leaching.By the oxidizing roast,the V3+ occurred as isomorphism in mica minerals are oxidized to soluble V4+ or V5+.But the reducing minerals in stone coal,such as carbon and FeS2,will inevitably inhibit the oxidation of V3+ and greatly reduce the leaching rate of vanadium.In order to solve the above-mentioned problems,an innovative process was proposed in the present study to pre-concentrate and separate the vanadium from stone coal.At the first step,the dispersive vanadium in stone coal was enriched in an easy-separated V-rich phase through reducing roast.Subsequently,the V-rich phase was separated by physical separation method,and a high-grade vanadium concentrate was obtained.As the theoretical supports for this new process,the following fundamental studies were conducted firstly.(1)The phase relations in the CaO-SiO2-VOx system at 1873 K under the oxygen partial pressure of 6.9×10-11 atm and 1.7×10-9 atm were determined by the static equilibration method,and the isothermal section diagram of this system was constructed.Furthermore,the standard Gibbs energy of formation of the vanadium compounds CaV2O4,CaVO3,V2O3 and Ca2Si1-?V?O4(0<?<0.1)were measured by chemical equilibrium method.These results,on one hand,fill the blanks of thermodynamic and phase diagram data of V-bearing systems;on the other hand,provide the necessary fundamental information for the pre-concentration of vanadium from stone coal ore and V-bearing slags.(2)Based on the above results,the spinel phase Fe3-xVxO4 was pre-designed as the V-rich phase according to the mineral characteristics of stone coal ore.In this connection,the magnetic properties of the Fe3-xVxO4 were studied,and the phase diagram of the CaO(15 mass%)-SiO2-FetO-V2O3 system at 1623 K was constructed.The results indicated that the spinel phase Fe3-xVxO4 is an ideal V-bearing phase for the concentration of vanadium in stone coal,and it is suitable to be separated efficiently by the magnetic separation method.These results not only provide fundamental basis for the design of the V-rich phases from V-bearing resources,but also enrich the phase diagram data of vanadium oxide-containing systems.(3)The isothermal synthetic rate of Fe2VO4 from Fe2O3 and V2O3,as well as FetO and V2O3,in the temperature range from 1274 K to 1473 K under CO and CO2 mixture atmosphere(CO/CO2=0.05?1)were investigated by isothermal thermo-gravimetric method.The results showed that Fe2O3 reacted with V2O3 more quickly and easily than Fe,0.This indicated that Fe2O3 is a favorable addition for vanadium concentration in stone coal ore.Furthermore,the solid-state synthetic mechanism and kinetics of Fe2VO4 from Fe2O3 and V2O3 powder mixtures were investigated systematically.The kinetic model of the synthetic reaction was established,and some important kinetic parameters,such as the apparent activation energy and the reaction order,were determined.The obtained results can be used for the optimization of the conditions for vanadium concentration from stone coal ore.(4)Based on the above results,a novel approach for pre-concentrating and separating vanadium from stone coal was designed.The stone coal ore taken from Yichang City in Hubei Province was used as raw material in the present study.The environment-friendly Fe2O3 was selected as a capturer of vanadium in stone coal,the natural reducing property of stone coal was utilized to promote the formation of the magnetic V-rich phase-Fe3-xVxO4.Then,a high-grade concentrate containing vanadium higher than 12 mass%was obtained by magnetic separation method,and more than 90 mass%of the total vanadium was recovered.The new method provide a new way for the utilization of stone coal ore in an efficient and green manner.