Research Of Efficient Separation And Recovery Molybdenum And Cobalt From Spent Hydrodesulfurization Catalyst

Hydrodesulfurization catalyst are widely used in crude oil refining processes and produce huge amounts annually.During the long-term operation of the catalyst,due to poisoning,aging,clogging and other problem,the activity of the catalyst decreased,and could not meet the operation requirements,finally formed spent catalyst,it was incorporated into hazardous waste for management.These spent hydrodesulfurization catalysts contain a large amount of valuable metals such as molybdenum and cobalt.Recycling the spent catalyst can not only prevent the loss and of valuable metals,but also reduce the environmental pollution,which has important Environmental and economic significance.In this research,we focus on key problems such as the difficulty of metal leaching and poor selectivity in the separation and recovery process,and carries out systematic research covering the process of leaching-extraction-strippingproductization.The main results are as follows:(1)Aiming at the difficulty in leaching molybdenum,cobalt,and aluminum in spent catalyst,the mechanism of the metal morphology of molybdenum,cobalt,and aluminum in spent catalysts during the pretreatment process was explored,an ultrasonic external field strengthening method was proposed,and the leaching parameters were optimized.The results show that through the pretreatment process,the metal in the spent catalyst can be converted from the hard leached sulphur state to the easily leached oxidation state,and the leaching rates of molybdenum and cobalt can be increased by 36.5% and 37.3%,respectively.The study found that the cavitation effect of ultrasonic is the key to improving the metal leaching rate.The ultrasonic cavitation effect can reduce the thickness of the diffusion layer and enhance the mass transfer process of metal ions,the leaching rates of molybdenum and cobalt can be increased by 12.1% and 9.2%,respectively.Under the optimal leaching conditions,the leaching rates of molybdenum and cobalt can reach 98.3% and 99.1%,respectively.(2)Aiming at the problem of high-efficiency and selective separation of molybdenum in molybdenum,cobalt,and aluminum containing leaching solutions,the morphological changes of molybdenum,cobalt,and aluminum ions in the solution were studied,and the mechanism of metal binding ability with different functional group was explored.The influence of different extraction conditions was explored.The results show that the change of metal ion form is the key factor affecting the metal extraction rate.Under the condition of p H value is 1.5,molybdenum mainly exists in the form of polymolybdate anion,which can form a stable extraction complex with the extractant containing quaternary ammonium salt functional group,while other metals mainly exist in the form of cations and do not react with the extractant.Therefore,the extractant containing quaternary ammonium salt functional group methyl trioctyl ammonium chloride has a good extraction effect on molybdenum.Under the optimal extraction conditions,the molybdenum extraction rate is 98.7%,the molybdenum-cobalt t and molybdenum-aluminum separation coefficient are 2541 and 2274,respectively,which realizes efficiencive separation of molybdenum.(3)In view of the toxicity,volatility,and pollution of traditional extractants,with quaternary ammonium salts as hydrogen bond acceptor and linear natural fatty acids as hydrogen bond donor,the influence of the structure and composition of hydrogen bond acceptor and hydrogen bond donor on the extraction capacity of metals was studied.The results show that the quaternary ammonium salt with benzyl groups exhibit greater steric hindrance and strong metal encapsulation ability,it can form a deep eutectic solvent with better molybdenum extraction ability with linear natural fatty acid.With deep eutectic solvent composed of benzyl tributyl ammonium chloride and n-nonanoic acid,the molybdenum extraction rate can reach 98.6%,the molybdenum-cobalt and molybdenum-aluminum separation coefficient are 1751 and 1543,respectively,which can achieve selective separation of molybdenum.(4)Aiming at the problem of extraction cobalt efficiently in cobalt and aluminum containing raffinate,a binary extraction system was used to extract cobalt.The influence mechanism of the binary extraction system was explored,and the influence of different extraction conditions were investigated.The results show that cobalt can form a stable extraction complex with the two extractants.At the same time,under weak acid conditions,the two extractants can form complementary synergistic effects,and increasing the cobalt extraction capacity.The co-extraction coefficient can reach 2.8,showing an obvious positive synergistic effect.Compared with a single extractant,the cobalt distribution ratio increased from 5.5 to 10.2.With the binary extraction system,the cobalt extraction rate can reach 92.4% and the cobalt-aluminum separation coefficient can reach 207 under the optimal extraction conditions,an efficiencive separation of cobalt was realized.(5)Aiming at the problem of efficient stripping molybdenum and cobalt from loaded organic phase and transform these metals to products,the influence mechanism of different strpping agents was explored,and the influence of different stripping conditions was investigated,research on molybdenum and cobalt productization has been carried out.The results show that the type and concentration of the stripping agent are the key factors affecting the metal stripping rate.Due to the polar effect of the stripping agent,the metal extraction compound in the loaded organic phase can be effectively destroyed to realize the efficient stripping of molybdenum and cobalt.Using ammonia as the stripping agent,molybdenum strpping rate was 95.6%,using evaporated crystalline for productization,ammonium molybdate product with purity of99.1% can be obtained.Using sulfuric acid as the stripping agent,the cobalt stripping rate was 95.8%,the obtained cobalt stripping solution is crystallized with oxalic acid,cobalt oxalate product with purity of 98.8% can be obtained.Based on the results of experiments and theoretical research,the whole process of efficient recovery and utilization of spent catalyst has been designed and developed.It lays a foundation for the industrial application of molybdenum and cobalt separation and extraction.