Study On Tungsten Recovery Process From Spent Catalyst

Abstract:In the production of the catalyst, tungsten, molybdenum and other nonferrous metals are added to improve the activity, selectivity and toxicity. Because of the carbon depositing on the surface of catalyst, catalyst poisoning and Active component oxidizing etc., Catalyst activity decreases gradually and becomes disabled during use.But most tungsten of the spent catalyst still keep its original form, and tungsten content in the spent catalyst is much higher than that in Tungsten Ore, so it has a high recovery value.Spent catalyst usually contains organics, so decarburization is prior in the process of recovery. Therefore, the traditional tungsten metallurgy is not suited to the recovery process. Because of the above issues, this study was based on the comprehensive utilization of secondary resources and the actual production conditions of the factory, combined with the characteristics of raw material composition, decided to use the sodium roasting-water leaching process to dissolve the spent catalyst, vulcanizes the water leaching to precipitate molybdenum, then extracts tungsten from the molybdenum removing leaching, finally implement separation of tungsten and molybdenum and comprehensive recovery of tungsten.In this paper, the properties of the raw material was studied by several analysis methods such as XRD and XRF. In the meantime, the principle of the experiment was expounded. This study researched different technological parameters on Sodium roasting-water leaching process, vulcanizing the water leaching to precipitate molybdenum and extracting Tungsten from the Molybdenum removing leaching, then got the following conclusions:Tungsten, Molybdenum, Aluminum of raw material is mainly exists in the form of WO3, MoO3and Al2O3. By thermodynamics calculation, WO3, MoO3and Al2O3in the process of roasting with sodium carbonate is endothermic reaction. The roasting reaction between WO3、MoO3and Na2CO3could be spontaneous,because of the gibbs free energy less than zero under the temperature427℃～727℃; And the roasting reaction between Al2O3and Na2CO3could be spontaneous because of the gibbs free energy less than zero when the temperature higher than527℃.The optimum process condition of sodium roasting-water leaching process is listed as follows. Raw materials mixed with sodium carbonate of1.3times, then roasted2hours at650℃.The roasted product leached for1.5hours in water at80℃.Solid-to-liquid was3:1.The Tungsten leaching rate was99.71%and the Molybdenum leaching rate was97.02%.The optimum process condition of vulcanizing the water leaching to precipitate Molybdenum is listed as follows. The leaching vulcanized75min in the pH7.5-8.0with vulcanizing agents of2.5times at70-80℃.Then add CuS of4.0times the pH7.5～8.0at30℃.After1.5hours, the Molybdenum removing rate was97.8%and the Tungsten recovery was98.30%.The optimum process condition of extracting Tungsten is listed as follows.The liquid was extracted8min by20%N235+15%TBP+sulfonated kerosene in the pH2.0.The O/A was1:4. In three stages countercurrent extraction experiment, the Tungsten recovery was99.82%. The loaded organic phase stripped by Ammonia concentration of4mol/L. The O/A was1.5:1. The stripping rate of the loaded organic phase was more than99%. The impurity content of the product which made by evaporation crystallization method could meet the standard of the zero grade in GBT/10116-2007.The comprehensive recovery of Tungsten was95.30%in the whole process.Figure32,Table18,Reference93in this thesis.