Studies on bioleaching of silica from Indian chromite ore by a silica tolerant Aspergillus niger AB200 : Characterisation of some physical parameters and scanning electron microscopic studies

Department of Chemical Engineering, Biotechnology Division, Calcutta University,

92, Acharya Prafulla Chandra Road, Kolkata-700 009, India

E-mail: deblina.ball@gmail.com

Manuscript received 21 August 2009, revised 14 December 2009, accepted 18 December 2009

The bioleaching of silica from chromite ore was studied to remove silica from low grade chromite ore and therefore Increase the percentage of chromium In the ore. Three microorganisms Bacillus circulans, Saccharomyces cenvisiae and Aspergillus niger were used for bioleaching studies. The results showed that Aspergillus niger has higher potency of silica bioleaching (30%) from chromite ore, followed by Saccharomyces cerevisiae {20.3%) and Bacillus circulans (17.8%). The organisms were then grown in their respective growth media along with silica for development of silica tolerant strain. The silica adapted organisms were used for bioleaching studies. Silica tolerant Aspergillus niger grown with 90 mg/100 ml silica concentration in the growth media showed maximum bioleaching of silica (53%) from chromite ore. It was named Aspergillus niger AB₂₀₀ and selected for further studies. The structural changes in the ore after bioleachlng was studied along with morphological changes in Aspergillus niger during the process of bioleaching by scanning electron microscope. Physical parameters are optimized for proper cellular growth and effective silica bioleaching from chromite ore. The optimized bioleaching process was carried out at 33 ºC for 7 days with 6 ml inoculum having 1.5 x 10⁶ spores/mi. The initial pH of the fermentation media was maintained at 4.5.