Extraction Of Vanadium From Converter Vanadium Slag By High Pressure Acid Leaching Without Roasting

Vanadium is one of the most important rare metals,which is widely used in iron and steel industry,petrochemical,aerospace and new energy.There are valuable vanadium-titanium magnetite resources that are stocked in the Panxi area,Sichuan Province and Chengde,Hebei Province China.The converter vanadium slag that is produced in the iron and steel making process is one of the most important raw materials for extracting vanadium in the hydrometallurgical procedure.The traditional method for extracting vanadium from the vanadium slag is sodium chloride roasting and leaching process.The main principle of the process is to destroy the structure of vanadium-containing spinel and oxidize the V(?)to V(?)or V(?),which can be dissolved in the solution.However,it will consume a lot of energy and waste numerical chemical additions in the roasting procedure.Furthermore,large quantities of HC1 and Cl2 may be discharged into the air,which are also harmful to the environment.Although some advanced methods are developed for extracting vanadium,such as calcification roasting,mixture roasting and oxidation roasting,there are still some drawbacks that will cause the production process to be complexed,low metal recovery and slow reaction rates.Therefore,it is quite important to pay attention to develop a novel process for extracting vanadium in an efficient and environmental-friendly way,which may contribute to the utilization level of the vanadium-titanium magnetite resources in China.This research has proposed a novel process for extracting vanadium from the vanadium slag by high pressure acid leaching technology.The thermodynamic calculation for the high pressure leaching process,mechanism analysis for acid leaching vanadium from the slag,reasonable conditions for vanadium extraction and kinetics for the process have been researched.Moreover,based on the results obtained in the laboratory,an enlarged experiment has been researched.The main results are shown as fellow:Firstly,the mineral phases of the converter vanadium slag were characterized with XRD,SEM,BSE-EDS and EPMA techniques.And,a high pressure DSC technology was also employed to analysis the thermodynamic kinetics for the vanadium slag in the high pressure acid leaching process.The results indicate that:the vanadium-containing spinel,olivine and ilmenite are the main phases in the converter vanadium slag.The reaction of converter vanadium slag in the high pressure acid leaching process is a kind of endothermic reaction,which is in the range of 90-170 ?.The highest endothermic reaction DSC curve peaks is at 135 ?.Secondly,a series of elevated E-pH diagrams,such as S-H2O system,V-S-H2O system,Fe-S-H2O system,Mn-S-H2O system,Cr-S-H2O system and Ti-S-H2O system,have been calculated at 25,50,100 and 150 ? by the Factsage software,which shows the thermodynamic analysis in the high pressure acid leaching process.The results indicate that:the technology can extract vanadium from the converter vanadium slag into the solution.When the pH value is below 2,there are some soluble vanadium ions,such as V3+,VO2+ and VO2+.Because the E value of the pressure leaching system may increase,the V3+ will be oxidized,which cause the VO2+ and VO2+ leave in the solution.The other valuable elements,such as Fe,Mn and Cr will be dissolved into the solution,but Ti will be enriched in the leaching residues.Thirdly,the atmosphere acid leaching and pressure acid leaching are compared to explore the mechanism of extracting vanadium in the direct acid leaching process.The results indicate that:the structure of vanadium-containing spinel phase cannot be destroyed or release the vanadium from the lattice structure in the atmosphere acid leaching process,which causes that the vanadium cannot be extracted efficiently.In the high pressure acid leaching process,the structure of vanadium-containing spinel phase can be broke down along with olivine and ilmenite.And,the main phases of the leaching residues are TiO2,SiO2,FeTiO3 and Fe3O4.In order to extract vanadium from the vanadium slag,it is necessary to destroy the structure of the vanadium-containing spinel phase.Fourthly,the effect of oxygen pressure,leaching temperature,initial acid concentration,leaching time,liquid to solid ratio,particle size and stirring speed on the leaching process is investigated,and the reasonable condition for extracting vanadium is obtained.The results indicate that:there is no need to input the oxygen to the reaction system as the pressure can be achieved by the autoclave itself.The experiment result indicates that the leaching rate of V can reach 96.88%.Suitable technical parameters can be obtained by a shorter leaching time,a lower liquid to solid ratio and acid concentration.Under the condition of 30min leaching time,150 g/L initial acid concentration,8:1 mL/g liquid to solid ratio,400 rpm stirring speed,particle size less than 75 ?m at 140 ?,the leaching rate of V,Mn,Fe and Cr can reach 88.96%,80.68%,88.68%and 92.35%respectively.At the same time,the content of TiO2 in the leaching residues can research 26.06%.Fifthly,the kinetics of extracting vanadium from the vanadium slag by high pressure leaching process was researched,and the kinetics equation was also established.The results indicate that the leaching process obeys the rule of shirking core model,and the controlling step for the process is the chemical reaction.The apparent activation energy of leaching process is 47.69 kJ/mol,and the acidity coefficient is 0.48.Compared with the atmospheric leaching process and 350 ? microwave roasting-atmospheric acid leaching process,the apparent activation energy of pressure acid leaching is much lower than 77.65 kJ/mol of atmospheric leaching process and 66.68 kJ/mol of 350 ? microwave roasting-atmospheric acid leaching.The kinetics equation of extracting vanadium from vanadium slag by high pressure acid leaching process can be expressed as fellow:1-(1-x)1/3 = 0.0114 × r0-2 × CH2SO40.48×pO2×0.44 x exp(-47690/RT)At last,based on the results obtained in the laboratory,an enlarged experiment has been researched with a 100 L autoclave.The results indicate that:the process of extraction vanadium from converter vanadium slag by high pressure acid leaching process without roasting can be enlarged,which also obeys the rule that the leaching rate of vanadium can be more than 90%when the vanadium content in the leaching residues is below 2.26%.Under the condition of 90 min leaching time,250 g/L above initial acid concentration,8:1 mL/g liquid to solid ratio,300 rpm stirring speed,particle size less than 75 ?m at 150 ?,the leaching rate of vanadium can reach above 98%.With the two-stage high pressure acid leaching process,it can achieve a high leaching rate of vanadium with a low liquid to solid ratio and acid concentration.