Solution Chemistry & Separation Technology Of Aluminum, Vanadium And Molybdenum In Alkaline Solution

About 500,000～700,000 tons of spent catalysts are produced each year in the world,large amounts of precious metal,nonferrous metal or its' oxides are used to the preparation of catalyst, the metal content of spent catalyst is not lower,even higher than the content of raw ore.Recovery of valuable metals from spent catalyst shows great economic benefit and environmental benefit.Spent Al₂O₃-based catalyst is a kind of catalyst using Al₂O₃ as the carder and vanadium/ molybdenum as active constitutent but can not be regenerated again.To date,some investigations had been conducted to recover valuable metals in spent catalyst,but the main difficulty was the efficient separation of valuable metals in solution.This dissertation had made comments on the status of comprehensive utilization of spent catalyst,carded out a great deal of theoretical analyses and experiments with the reference of literature.By the calculation of solution chemistry of Al-V-Mo system,thermodynamic calculation,molecular dynamic simulation and some testing methods,the solution chemisty of Al-V-Mo system in alkaline solution and the separation technology had been studied detalledly,the basic theory and process engineering for the comprehensive utilization of spent catalyst had been researched systematacially.Main conclusions are obtained as follows:1.Research on the solution chemistry of Al-V-Mo system in aquous solutionAccording to the calculation of solution chemistry,the solubility and existing status of Al,V and Mo in acidic and alkalic solution had been analysed in theory.The concentration logarithmic diagram of Al-V-Mo in aquous solution with different concentration and pH had been plotted,the concentration and pH on the distribution of three elements had been analysed.The concentration logarithmic diagram provides some basic data for the separation of Al,V and Mo.The solubility of V and Mo in NaOH and sodium aluminate solution had been determined, which indicated that temperature had little effect on the solubility of Mo in sodium aluminate solution,but showed great effect on the solubility of V.The solubility of V in sodium aluminate solution is about 1g/l at 20℃but 50g/l at 80℃.The potential-pH equilibrium diagram of three kinds of system had been figured according to the data in literatures,the transformation of different valent state ions had been discussed.The diagrams provided theoretical foundation for the comprehensive utilization of spent catalyst.Material Studio was firstly used to molecular dynamic simulation of Al-V-Mo in aqueous solution.The results indicate that the formation of clustering of aluminates in solution,and the clusters are stabilized by sodium ions.Furthermore,the clusters make a contribution to the formation of polyaluminate.The molecular dynamic simulation results of V and Mo at three kinds of pH are in good accordance with spectroscopy results reported in the literatures.2.The concentration logarithmic diagram and potential-pH diagram of Ca(Ba)-V(Mo)-H₂O was firstly studied,the following are the results:The concentration logarithmic diagram of Ca-V(Mo)-H₂O indicated that the stable region of calcium vanadate and calcium molybdate enlarged,the residual concentration of V and Mo in soulution lowered with the increasing of temperature.The concentration logarithmic diagram of Ba-V(Mo)-H₂O indicated that the stable region of barium vanadate and barium molybdate enlarged,the residual concentration of V and Mo in soulution lowered with the increasing of temperature.In constrast to the diagram of Ca-V(Mo)-H₂O,barium showed better effect on the precipitation of V and Mo than calcium under the same condition,the residual concentration of V and Mo in soulution can be down to 10^-7.3and 10^-7.0mol/l in the system of Ba-V(Mo)-H₂O when temperature is 100℃.The potential-pH diagram of Ca(Ba)-V(Mo)-H₂O indicates that the stable region of calcium vanadate and barium vanadate are larger than that of calcium molybdate and barium molybdate. When vanadium and molybdenum coexist in the solution,calcium and barium will be inclined to react with vanadium firstly.3.The precipitation separation of alumina,vanadium and molybdenum had been conducted in the simulated solution,results are listed in the following:CaO,Ba(OH)₂ and CaCl₂ showed good effect on the precipitation of vanadium and molybdenum in the solution of V(Mo)-H₂O,the precipitation of vanadium and molybdenum can be 98%under suitable reaction conditions.In the solution of V(Mo)-Al-H₂O,the effect of CaO and CaCl₂ on the precipitation of vanadium and molybdenum was bad,however,Ba(OH)₂ still showed good effect on the precipitation of vanadium and molybdenum.Thermodynamic calculation indicated that the bad effect of CaO and CaCl₂ was ascribed to the formation of many kinds of calcium aluminate which was formed by calcium and large amounts of aluminate ion in the solution,but Ba(OH)₂ can not react with aluminate ion in solution.Ba(OH)₂ was firstly brought forward and used to separate vanadium,molybdenum and alumina successively in the sodium alumination solution.Under optimum condition,the precipitation of V and Mo can be 92%and 98%respectively,at the same time sodium aluminate solution was purified.Thermodynamic calculation indicated,with the increasing of temperature,the Gibbs free energy of reaction between Ba(OH)₂ and VO₄^3-slightly rose.However,the Gibbs free energy of reaction between Ba(OH)₂ and MoO₄^2-lowered to a more negative value,equilibrium constant of reaction between Ba(OH)₂ and MoO₄^2-enlarged.Hence,increasing temperature was good to the reaction between Ba(OH)₂ and MoO₄^2-.That is why Ba(OH)₂ can be used to separate vanadium and molybdenum successively in the sodium aluminate solution.4.Research on the kinetics of cobalt leaching from spent catalystKinetics of cobalt leaching from spent catalyst was investigated.A kinetic model was suggested to describe the leaching process of cobalt from spent catalyst,leaching kinetics indicated that diffusion through the product layer is the rate controlling process during the reaction. The activation energy was determined to be about 10.0kJ/mol.Leaching rate of about 98.5%of cobalt and 99.0%of nickel were achieved using -150+200 mesh particle size at a reaction temperature of 80℃for 240min reaction time with 30%(w/w)sulfuric acid concentration and the solid/liquid ratio of 1:8g/ml.5.New technology had been developed to recover valuable metals from one kind of spent catalyst on the basis of theoretical research,the results are listed as follows:With regard to a kind of a-Al₂O₃ based spent catalyst(V 0.55%,Mo 0.48%,Al₂O₃70.95%), the purity of alumina is 99.9%produced with carbonation decomposition process,the recovery of alumina can reach 90.6%in the whole process,the recovery of vanadium and molybdenum is 94.8%and 92.6%,respectively.