BIOLEACHING OF SPENT CATALYST AND APPLICATION OF ULTRASOUND

Abstract

This work examines the bioleaching of hydrodesulphurization spent catalyst (containing Ni, Mo and Al). Since conventional use of acidophiles in spent catalyst bioleaching typically results in low Mo extraction, the use of fermentative bacteria was attempted for enhanced recovery. Escherichia coli (E. coli) was used for the first time in spent catalyst bioleaching, and the effect of particle size, pulp density, and temperature was investigated. Bioleaching data was used to train an artificial neural network for prediction of metal extraction and examination of the impact of bioleaching parameters. Effect of ultrasound was also examined on the growth of bacteria and bioleaching. Discontinuous sonication was found to enhance bacterial growth and increase metal extraction. The mechanisms involved in bioleaching were also investigated. To achieve higher extraction of both Ni and Mo, a sequential 2-stage biological process was outlined where 99 percent Mo was extracted in the second stage using E. coli.