Enhanced bioleaching of metals from black shale using ultrasonics

The effect of ultrasonic treatment on the bioleaching of metals from black shale was investigated using an indigenous strain of Aspergillus niger. Maximum growth of fungus was achieved in up to 15 days of incubation in stationary as well as shaking flasks (with and without ultrasonic treatment). Culture filtrates contained oxalic, citric, tartaric and malic acids. Maximum leaching of Al (92%), Fe (83%), Cu (92%), Zn (87%) and Co (71%) was achieved within 24 days when the black shale was leached by culture filtrate and treated ultrasonically. Lower values with statistically significant differences were found in the maximum extraction of metals during leaching for 36 days in control experiments without ultrasonic treatment and in stationary flasks.