Effect of ultrasound on bioleaching of hydrodesulphurization spent catalyst

Bioleaching is recognized as a green process for the extraction of metal values from ores or metal-laden solid wastes. However, the slow rate of extraction is a major limitation which needs to be addressed. Application of ultrasound in bioleaching, also known as sonobioleaching, may achieve a higher rate and extent of metal extraction. Although fungal sonobioleaching has been examined, the use of ultrasound in bacterial bioleaching remains unexplored. In this study, bacterial sonobioleaching of spent catalyst (containing Mo, Ni, and Al) using Escherichia coli is reported for the first time In two-step bioleaching, the effect of ultrasound (at 37 kHz and 80 kHz) was examined using continuous and discontinuous sonication. Initiation time of sonication after addition of catalyst was varied (at day 2, day 4 and day 6) to examine its effect on metal extraction. Application of discontinuous sonication led to an increase in Mo leaching from 46% to 54%. Multiple time sonication resulted in a higher increase in metal extraction than one-time continuous sonication. The increase in Mo extraction is attributed to the cavitation effects of sonication which includes better mixing within the pores and low NaCl depositions. (C) 2019 Elsevier B.V. All rights reserved.