| Vanadium is one of the national strategic metals.Due to its excellent mechanical,chemical,electrochemical,catalytic properties etc.,vanadium is widely used in fields like iron and steel making,chemical industry,electronics and painting.Vanadium slag is the major raw materials for vanadium production.At present,the most popular vanadium production process is sodium roasting-water leaching process.However,this technology has some disadvantages such as low overall resource and energy efficiency,as well as environmental pollution.In this thesis,a clean and efficient vanadium extraction process featuring oxygen-rich non-salt vanadium slag roasting,low temperature ammonium meta-vanadate conversion and leaching/cooling crystallization,was established.This new process is expected to be able to achieve high vanadium recovery,reduce exhaust gas and waste water at source,and realize comprehensive utilization of tailing in conjunction with iron-making process using blast furnace.It also provides scientific and technical support for comprehensive utilization of vanadium titano-magnetite resources in China.The following results and progresses were achieved:(1)Roasting process mechanisms show that vanadium spinel was transferred to inverse spinel at 500?;olivine was completely oxidized and inverse spinel was oxidized to Mg2VO4 at 700?;intermediate valence vanadates were oxidized to pentavalent vanadates at 700?1000 ? and solid solution(Fe0.6,Cr0.4)2O3 were generated at 900 ?,respectively.Thermodynamics calculation shows that vanadate reactions priority are vanadium spinel transformation,quadrivalent vanadates generation and pentavalent vanadates generation.Non-salt roasting process is an exothermic process.Non-salt roasting process was first adopted to oxidize vanadium selectively,avoid chromium oxidation and non-waste gas emissions.(2)A selectively leaching technology was first developed to selectively leach vanadium.Thermodynamics calculation shows that vanadates can be leached by ammonium bicarbonate.Silicon can be leached as an impurity but phosphorus would not be leached.Furthermore,leaching reactions are exothermic reactions.E-pH diagrams of V-H2O,Si-H2O,P-H2O,Fe-H2O,Ca-H2O,Mg-H2O,Mn-H2O were calculated.Kinetics of ammonium bicarbonate leaching shows that the first stage(t<30 min)and the second stage(t>30 min)are controlled by solid diffusion control and surface chemical reaction,respectively.Moreover,apparent activation energy for these two stages are 9.13 and 35.44 kJ/mol,respectively.The optimal ammonium bicarbonate leaching condition is roasted vanadium slag particle size of 75?48 ?m,ammonium bicarbonate mass concentration of 35%,leaching temperature of 50?,leaching duration of 150 min and L/S of 10:1.Under the optimal leaching condition,leaching efficiency for vanadium is 85%and the leaching efficiencies for phosphorus,silicon,calcium,magnesium and manganese are really low.Thus,the selective leaching goal was achieved.Phases transform of leaching residual shows that intensity of the strongest peak of vanadates are weakened in the leaching process.Characteristic peaks of leaching product carbonate are strengthened as leaching duration extends.Solid solution(Fe0,6,Cr0.4)2O3 was stable and could not be leached in the ammonium bicarbonate solution.(3)Vanadium slag oxidation kinetics were studied systematically.Roasting experiment shows that reducing particle size,increasing oxygen partial pressure,reducing heating rate,extending holding time can improve vanadium oxidation rate.Besides,optimal roasting conditions of particle size of 100?75 ?m,air atmosphere,heating rate of 4?/min,roasting temperature of 900?950? and holding time of 15 min were obtained.Non-isothermal oxidation kinetics for roasting process shows that vanadium spinel oxidation is controlled by chemical reaction,and reaction order,apparent activation energy and pre-exponential factor are 0.69,60.7 kJ/mol and 24.68 min-1,respectively.(4)The effects of different leaching ammonium reagents on leaching process were studied systematically.Kinetics of ammonium oxalate leaching shows that the leaching process is controlled by solid diffusion control and apparent activation energy is 26.7 kJ/mol.The optimal ammonium bicarbonate leaching condition is roasted vanadium slag particle size of 75?48?m,ammonium oxalate mass concentration of 13%,leaching temperature of 70?,leaching duration of 120 min and L/S of 10:1.Under the optimal leaching condition,leaching efficiency for vanadium is 90.3%,and the selective leaching goal was achieved.Phases transform of leaching residual shows that intensity of the strongest peak of vanadates are weakened as ammonium oxalate concentration increases.Characteristic peaks of leaching product oxalate are strengthened as ammonium oxalate increases.Solid solution could not be leached in the ammonium oxalate solution.When the leaching reagents are triammonium phosphate and diammonium hydrogen phosphate,the leaching solutions are weak alkaline and the leaching efficiencies are all above 85%.When the leaching reagent is ammonium dihydrogen phosphate,the leaching solution is acidic,and the leaching efficiency of manganese impurity increases substantially.After comprehensive analysis,ammonium bicarbonate was chosen as leaching reagent in the process of non-salt roasting and ammonium leaching.(5)Purification process of vanadium leaching solution,crystallization process and calcining process were studied systematically.The optimal purification condition is:CaO additive of 0.8 g,temperature of 70?,purification duration of 30 min,standing time of 30 min.The decomposition mechanisms for crystallization production of ammonium metavanadate at room temperature?1000 ? was studied.The non-salt roasting and ammonia leaching process was optimized by low temperature ammonium metavanadate conversion and high temperature vanadium dissolution.Through dephosphorization,desilication,cooling crystallization and calcining process,high-pure V2O5 product of 99.5%was obtained. |
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