Recovery Of Valuable Metals From Spent Hydrogenation Catalysts

Catalysts are widely used in petroleum refining and chemical industry, about80%of the reactions in modern chemical production are dependent on the corresponding catalysts. The catalysts are usually consist of aluminum and silicon as the carrier and molybdenum, cobalt, vanadium, nickel and other rare metals as active constitutents, which have special structure and reactivity, so as to improve the impurity removing rate of raw materials. For example, vanadium can greatly promote the efficiency of hydrogenation desulfurization, denitrogenation and demetallization of the raw materials. In recent years, the ability of petroleum hydrogenation of catalysts was improved continuously in order to meet the increasing needs of ultra low sulfur fuel.However, the decreasing of activity or permanent poisoning of catalysts after being recycled for several times, result in losing a renewable utilization value. Thus, there are a large number of spent catalysts discharged every year. But the spent catalysts still contain quite a lot of non-ferrous metals or precious metals, sometimes the contents of them are much higher than lean ore. Spent catalysts as the major secondary sources of tungsten and nickel will not only cause a waste of resources, but also pollute the environment seriously if they are discharged directly. Carrying out the comprehensive recovery of spent catalyst is not only beneficial to reduce the pollution of the environment, but also beneficial to realize the recycle of resource.In this paper, the spent catalysts were studied which contained the considerable tungsten, followed by nickel and aluminum, therefore, the value of recycling and economic benefits were high. This research adopted the process of sodium-roasting and water immersion to extract tungsten, as well as acid leaching to recycle nickel and aluminum, its technological process was simple, low-cost, high-extraction and process feasibility. The influence factors of tungsten and nickel in recovery process and the optimum process conditions were ultimately determined. In order to explore the leaching mechanism of nickel, the dynamics of acid leaching process of extraction nickel were also investigated.The optimum technical conditions of extraction of WO3were determined by the experiments of sodium roasting-water immersion:The addition of Na2CO3was6times than theoretical amount of WO3, the mixture was sodium roasted at the reaction temperature of750℃for4h, then water leached under90℃for2h and the liquid-solid ratio of1:4, the leaching rate of WO3could reach more than95%, recovery rate of WO3was90.85%.The purity of the product was96.3%.Spent catalysts after extraction of tungsten as raw materials enriched in nickel oxide and compounds of aluminium, The residue was dissolved in sulphuric acid, nickel and aluminium were leached. The optimal leaching conditions of extraction of nickel and aluminum could be achieved:leaching rate of nickel about98.27%of nickel and90%of aluminum were achieved using sulfuric acid with the concentration of30%(mass fraction), and solid-liquid ratio1:8, at the reaction temperature of85℃for4h reaction time. The recovery of nickel reached94.3%, the total recovery of aluminum reached92.6%.The purity of nickel sulfate reached98.5%and met the industry quality standards, the purity of aluminium oxide reached94.5%.Kinetics of nickel leaching from spent catalyst was investigated. The results showed that the facrors of particle size,concentration of sulfuric acid,temperature of reaction had a great impact on the leaching rate of nickel. A kinetic model was suggested to describe the leaching process of nickel from spent catalyst, leaching kinetics indicated that the diffusion was the rate controlling process during the reaction, which was consistent with diffusion controlled kinetic equation and the leaching activation energy was determined to be15.95kJ/mol.