Fundamental Study On The Optimization Of Vanadium Extraction From LD Converter Slag By Calcification Based Process And The Comprehensive Utilization Of Tailings

Vanadium,as an important strategic materials,is widely used in steel,chemical,aerospace,fabric,and chemistry,etc.Vanadium bearing converter slag is the main raw materials for the production of vandium in China and wordwide.Sodium salt roasting and calcification roasting are the most mature vanadium extraction processes at present,however,the former will be gradually replaced by the latter because it seriously affects the environment.Although the calcification roasting is a cleaner processs,it can not entirely displace the sodium salt roasting process,due to the fact concluded from the research and industry priactice that its leaching efficiency of vanadium is much lower.In this case,mechanical activation was proposed as the possible solution to enhance the effects of calcification roasting and leaching of vanadium bearing converter slag in this study.The influence of mechanical activation on the physical properties of vanadium slag,the oxidation roasting and leaching behavior were investigated.The strengthening mechanisms of mechanical activation were obtained.The comprehensive utilization of tailings from vanadium extraction process was also studied.All of these researches can lay the foundation for the cleaner and efficient vanadium extraction process.Firstly,the mineralogical and morphological characteristics of the converter slag were investigated,and the results shown that the major crystalline phases in the vanadium-bearing converter slag are vanadium spinel??Mn,Fe??V,Cr?₂O₄?,ulvospinel?Fe₂TiO₄?,olivine?Fe₂SiO₄?and metallic iron?Fe?.Most of metallic iron parcicles are surrounded by other phases.Based on the results of the variation of particle size,contents,mineral phase,and element distribution of the vanadium-bearing converter slag.An improved process which combined with grinding,sieving and magnetic separation steps,was proposed to separate metallic iron from vanadium-bearing converter slag efficiently.Spinel and olivine phases are the two major mineral phases in the beneficiated slag.Vanadium is enriched in the spinel phase but sparse in olivine phase,whereas chromium enriched in both phases.Secondly,the effect of mechanical activation on the physical properties of the vanadium-bearing converter slag was investigated.The results show that mechanical acitvation has a significant influece on the physical properties of the samples,the particle size of the samples directly decreased with the increase of activation time,then slightly increased as the aggregation.With the extending of activation time,the particles gradually shift from irregular shape to round with a porous surface,the specific surface area based on the BET model also significantly increased.It has been shown that mechanical activation also leads to the disorder of the crystal structure,the increase of the strain,and the decrease of the crystalline size of the samples.Both of isothermal and non-isothermal thermogravimetric investigations were performed to evaluate the kinetic and thermodynamic parameters of the oxidation of vanadium-bearing converter slag.Results indicate that the isothermal oxidation process consists of two distinct stages,i.e.,rapid oxidation stage?0min²0min?and slow oxidation stage?20min⁶0min?.Mechanical activation significantly increased the contribution of the fast oxidation stage to the entire process.Mechanical activation exhibited a significant effect on the oxidation rate of vanadium-bearing slag in low-temperature?300°C⁶00°C?during non-isothermal thermogravimetric analysis.It not only decrease the complete oxidation temperature,but also significantly decreased the apparent activation energy.The effects of calcium dosage,roasting temperature,leaching temperature,liquid to solid ratio,particle size,agitation speed,and acid concentration on the leaching efficiency of non-activated vanadium-bearing converter slag were investigated.A calcium/vanadium mole ratio of 1:1,roasting temperature of 900°C,leaching temperature of 50°C,liquid/solid ratio of 20:1?m L/g?,particle size of roasted sample smaller than 75?m,agitation speed of 200 rpm,leaching soulution with a p H value of 2.5 are identified as the optimal process parameters.For the non-activated vanadium-bearing converter slag,approximately 86% of vanadium can be dissolved after 60 min of leaching under the above optimal technological conditions.The effect of mechanical activation on the vanadium extraction process was investigated based on the calcification roasting-acid leaching process.The results showed that extending mechanical activation can significantly decrease the roasting temperature,increase the vanadium leaching efficiency,and decrease the leaching time.The roasting temperature can be decreased by 100°C with 80 min of mechanical activation.Furthermore,after 20 min of leaching,the leaching efficiency of vanadium can be incrased from 75% to 90% with increasing activation time from zero to 80 min.The leaching kinetic analysis showed that the diffusion through product layer was the rate–determining step in the course of the dissolution of vanadium.Mechanical activation can significantly decrease the corresponding apparent activation energy from 9.94 k J/mol to 7.63 k J/mol.The calcification roasting-two stages leaching process shows that the liquid/solid ratio,the consumption of leaching solution,and the leaching time can be significantly decreased by the two stages leaching process.Recycing of first-stage leaching liquor can double the concentration of vanadium in leaching liquor,and remarkably reduce the consumption of the leaching solution.The multiple use of the leaching liquor would significantly decrease the leaching efficiency of vanadium in the first stage leaching,however,the second stage leaching can make it up.A co-recovery process for recycling Fe,V,and Cr from vanadium tailings are poposed to fully recover valuable metals from vanadium tailings and realize the harmless treatment of final tailings.The feasibility of producing V and Cr-bearing ferroalloy through semi-molten reduction–magnetic separation process was investigated by theoretical calculations and physical measurements.The effects of reduction temperature,reductant?carbon?dosage,and time on the grain growth of metallic iron,magenetic separation efficiency,recovery rates of iron,chromium,and vanadium were studied.The result show that the co-recovery of Fe,V and Cr is feasible through high temperature reduction process.Approximately 99% of Fe,90% of V and 95% of Cr recovery in ferroalloy can be obatined at 1300°C reduction temperature,12% carbon dosage and 60 min.Ti was enriched in the non-magnetic tailings with a TiO₂ content of 27%.The hazardous assessment of the non-magnetic tailings was conducted according to the U.S.Environmental Proctection Agencey?EPA?Toxicity Characteristic Leaching Procedure?TCLP?.The results indicate that such kind of tailings is classified as non-hazardous solid waste,which can be safely used as secondary materials or stockpiled as an end-waste.In summary,the optimization of vanadium extraction from LD converter slag by calcification based process and the comprehensive utilization of tailings were investigated in this study.Such a comprehensive and clean utilization of vanadium-bearing converter slag has great potential for practical application.