148 Waste Management & Research Waste Manage Res 2005: 23: 148–154 Printed in UK – all right reserved

Nickel recovery from spent nickel catalyst A process for nickel recovery from a spent catalyst of definite composition has been developed using the hydro-metallurgi-cal route. The processing steps includes direct sulphuric acid leaching followed by separation of iron as well as silica and other impurities. For a 152 µm particle size catalyst, extrac-tion of about 98 % nickel was achieved at 363 K in 2 h using a sulphuric acid concentration (v/v) of 8 % and a pulp density of 10%. The dissolution of nickel followed diffusion-control-led leaching kinetics. Increase in temperature and sulphuric acid concentration resulted in increase in the nickel recovery. The activation energy for nickel dissolution was calculated to be 62.8 kJ mol–1. Finally, nickel was recovered as value-added products such as sulphide and oxalate with overall recovery of 90 and 88 % of nickel, respectively