USE OF ULTRASOUND IN MICROBIAL LEACHING OF NICKEL FROM LATERITES

Abstract

The importance of ultrasound in nickel extraction from lateritic nickel ore using a strain of Aspergillus niger was studied. The parameters examined were the pulp density, the ratio of length to diameter (L/D) of an ultrasonic cell, ultrasonic frequency and intensity and duration of exposure. The optimum conditions for maximum nickel extraction were a pulp density of 8.7% with an ultrasonic cell having an L/D ratio of 0.75 using an ultrasound frequency of 20 kHz at an intensity of 1.5 W cm(-2) while the sample was exposed for 30 min. Ultrasound enhanced the teaching rate of nickel and maximum extraction of 95% nickel was obtained in 14 days, in contrast to 24.9% nickel with conventional in situ bioleaching. It was found that in the presence of A. niger ultrasound had a significant effect, because it enhanced the growth of organisms resulting in an increased extraction rate of nickel with selective leaching of nickel over iron. This beneficial effect may possibly be due to a combination of leachant pore penetration, boundary and product layer breakdown and localized temperature increase and growth of microorganisms.