Waste-to-Resources: Leaching of Cobalt from Spent Cobalt Oxide Catalyst

This article presents studies on the recovery of cobalt from a spent cobalt oxide catalyst, left after the preparation of industrial catalysts. Apart from cobalt, the tested material contained iron, copper, zinc, and nickel. Leaching was proposed as a simple and feasible operation to treat the spent cobalt oxide. The 0.1-8.0 M H2SO4 solutions were applied as leaching agents at an ambient temperature and at 70 degrees C. An 8.0 M H2SO4 solution at 70 degrees C leached two-fold more Co(II) than a 0.1 M H2SO4 solution at the same temperature. Similar to Co(II), regardless of the leaching temperature, the Fe ion was leached more efficiently with 4.0 or 8.0 M H2SO4 than with a 0.1 M acid. It should be emphasized that the Co(II) content in the solution after leaching was predominant at >90% (similar to 4800 mg/dm(3)), compared to other metal ions. The ANOVA analysis indicated that both the sulfuric(VI) acid concentration and temperature had a significant effect on the leaching efficiency. An increase in acid concentration from 0.1 to 8 M and the temperature of leaching (from ambient to 70 degrees C) had a positive effect on the Co leaching efficiency (an increase from similar to 20 to almost 50%). The proposed hydrometallurgical treatment of the spent cobalt oxide catalyst is a response to the waste-to-resource (WTR) approach.