Research On Comprehensive Recovery Of Valuable Metals From Spent HDS Catalysts

Spent HDS catalyst is a hazardous solid waste produced in the petroleum refining hydrodesulfurization,which is rich in valuable metals such as molybdenum and nickel,and is an important secondary resource.The existing pyrometallurgical and hydrometallurgical processes are usually only for the separation and extraction of certain or some metals in the spent HDS catalysts,so it is difficult to achieve the complete harmless treatment and resource utilization of the spent HDS catalysts.In this paper,the separation and extraction of valuable metals from spent HDS catalysts were systematically studied,aiming at the comprehensive recovery of molybdenum,aluminum,nickel,cobalt,and aluminum.A novel cyclic metallurgical technique was developed to selectively separate and extract molybdenum from spent catalysts.Nickel,cobalt,and aluminum were leached from molybdenum extraction residue by hydrochloric acid,and then the two-stage extraction method is used to realize the separation and recovery of nickel,cobalt,and aluminum.The main research results of the paper are as follows:（1）A comparative study of molybdenum extraction from spent HDS catalysts was carried out by using phosphate complex acid leaching and pressure alkali leaching.The results showed that pressure alkali leaching was more effective.Compared with phosphate complex acid leaching,pressure alkaline leaching can realize selective leaching of molybdenum,and obtain a high leaching of Mo,while enriching nickel,cobalt,and aluminum in molybdenum extraction residue.Compared with sodium hydroxide,sodium carbonate as the leaching reagent has the advantages of low cost and low leaching of impurity aluminum.Under optimized conditions,the leaching of molybdenum reaches 95.4%,and the leaching of aluminum is only 0.7%.（2）Using CO₃^2-type N263 to separate and extract molybdenum in the soda pressure leachate of blank roasting spent HDS catalyst.The extraction of molybdenum can reach 99.8%after four-stage countercurrent extraction with an organic phase consisting of 35 vol.%N263+25 vol.%2-octanol+40 vol.%sulfonated kerosene while keeping the contact time 1 min,O/A ratio of 3.The extraction of Al,P,and Si is only 2.85%,4.0%,and 1.6%,respectively.After extraction,molybdenum can be separated from most impurities.The molybdenum-loaded organic phase was washed with water and stripped with NH₄HCO₃.Under the conditions of the NH₄HCO₃concentration of 3 mol/L,the contact time of 30 s,O/A ratio of 2:1,and room temperature,after four-stage countercurrent stripping,the stripping of Mo reaches more than 99.5%.The raffinate can be returned to the leaching process after being treated with sodium hydroxide,and the leaching of molybdenum is about 94%,which is basically equivalent to the leaching rate of molybdenum in the soda pressure leaching process.（3）Using hydrochloric acid to decompose the molybdenum extraction residue to extract nickel,cobalt,and aluminum.Under the conditions of HCl concentration of 5 mol/L,leaching temperature of 95°C,liquid to solid ratio of 10:1 ml/g,and leaching time of 4 h,the leaching of nickel,cobalt,and aluminum is 98.4%,99.1%,and 83.5%,respectively.The leaching process of Ni and Al is controlled by the surface chemical reaction,and the apparent activation energy is 90.52 KJ/mol and 73.63 KJ/mol,respectively.（4）Using N235 to separate and recover cobalt and molybdenum from the hydrochloric acid leaching solution.At room temperature,the extraction of cobalt and molybdenum reaches more than 99%after two-stage countercurrent extraction with an organic phase composition of 25vol.%N235 and 15 vol.%TBP in sulfonated kerosene,while keeping the O/A ratio of 1:1,the contact time of 2 min.Pure water and ammonia water can be used to achieve the stripping of Co and Mo,respectively.（5）The nickel in raffinate after extraction of cobalt and molybdenum was extracted and separated by HBL110.Under the condition of the organic phase composition of 45 vol.%HBL110 in sulfonated kerosene,the solution p H of 2,O/A ratio of 1:2,the contact time of 5 min,after four-stage countercurrent extraction,the extraction of nickel is over 99.6%,and the extraction of aluminum is only 0.3%.The nickel-loaded organic phase was stripped with sulfuric acid.Under the condition of H₂SO₄concentration of 2 mol/L,O/A ratio of 8:1,and contact time of 1 min,after four-stage countercurrent stripping,the stripping of nickel can reach 99.5%.