Spent hydro-refining catalysts mainly consists of 20-22% MoO3, 5-6% NiO, 4-5% S, 1-2% CO3O4, 1.3-1.5% Fe2O3, 3-4% SiO2, and the balance is Al2O3. In the present study, one such spent catalyst was roasted with sodium chloride to recover molybdenum by converting it into sodium molybdate. The sodium molybdate was further purified by chemical treatment to obtain a pure grade molybdenum trioxide. Various parameters like temperature, time and NaCl addition have been studied, and conditions for the maximum recovery of molybdenum have been established. (c) 2004 Elsevier B.V. All rights reserved.