A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation catalysts: Part I: Metallurgical processes

Abstract

Catalysts are widely used in petroleum refining and chemical industries. Among secondary resources, spent catalysts are undoubtedly very important because of not only their large amounts and enormous economic values, but also because of the environmental concerns if disposed off. Spent hydrodesulphurisation catalysts usually consist of molybdenum sulphide mixed with sulphides of vanadium, cobalt and nickel on an alumina carrier. A wide variety of metallurgical processes are used to treat these catalysts. The processes vary in their selectivity for metals and complexity of operation, but adopt one of the following approaches: 1. acid leaching with either H 2SO 4, HCl or (COOH) 2, often after roasting; 2. caustic leaching with NaOH, sometimes after roasting; 3. salt roasting with Na 2CO 3, NaCl or NaOH followed by leaching with water or Na 2CO 3; 4. smelting either directly or after calcination; 5. anhydrous chlorination; 6. bioleaching. Roasting followed by sulphuric acid leaching seems to be the best option since all of the valuable metals dissolve. However the downstream processes to produce separate products with high purity are relatively complex. Sodium carbonate roasting followed by water leaching is a good option since molybdenum and vanadium are selectively extracted over aluminium, nickel and cobalt. Bioleaching offers good prospects for recovering valuable metals and at the same time, generates much less environmental pollution. However, much more research work is needed before it can be commercialised. After leaching, the metals in leach solutions have to be separated and purified by conventional separation techniques such as precipitation, adsorption, ion exchange and solvent extraction. Part II of this review considers the application of these methods, especially, solvent extraction for treating such leach solutions.