Effect of ore particle size and mixed culture on fungal bioleaching

摘要

The following research aims at leaching of chromite ore which is an oxide ore of chromium by two species of fungi; Aspergillus niger and Rhizopus arrhizus. The effect of individual fungus and combination of fungi on leaching of various metals; Cr, Ni, Co, Zn, Mn was attempted. Also the effect of ore particle size on leaching is attempted. The particle sizes were; +600 jxm, +300 μm, +150 |xm and +75 |xm. Five different sets of shake flask experiments were carried out corresponding to each combination of fungus inoculated as (A. niger; R. arrhizus) 1:0,0:1, 1 :1, 1 : 2, 2:1. The ratio taken was in terms of number of spheres of A. niger biomass to mL volume of R. arrhizus cell broth in 50 mL of media with ore. The flasks were filtered, centrifuged and analyzed using A AS at the end of 8 days. The results indicated that the maximum leaching of Cr was by R. arrhizus as sole organism for - 300, +150 |xm particle size and for Ni is by the combination of fungus 2 : 1 which is at - 600, + 300 μm particle size. Whereas other metals, Zn, Mn, Co are by A. niger as sole organism. It is concluded from the research work that there is an optimum size of ore particle for leaching which is different for various metals and different combination of organisms. The very smaller size hinders growth of organism or the leaching efficiency and larger size because less available surface area also accounts for lower leaching efficiency. Mixed consortium of organisms may prove to be better for bioleaching of certain metals like Ni, but for most of metals sole culture itself is efficient.