A comprehensive study on the bioleaching of nickel and cobalt from the lateritic chromite overburden of Sukinda mines of Orissa was conducted using oxalic acid producing Aspergillus niger NCIM 548. Culture filtrate bioleaching was found to be the best possible leaching method among the three methods described. Three most important bioleaching parameters were optimized using RSM coupled with Box Behnken design keeping the best method and pulp density (2%) fixed. Optimal values of the three different parameters for the maximum recovery of 70.49% Ni and 66.93% Co were; temperature of leaching 80 degrees C, days of fermentation 21 days and sucrose concentration 10%. The leaching data of nickel fitted the "Ginstling Brounsthein" equation while for cobalt a mixed kinetic model consisting of "spherical geometry" and the "Ginstling Brounsthein" equation was followed. The activation energies of the leaching processes were found to be 55.84 kJ/mol for nickel and 24.9 and 46.91 kJ/mol for cobalt. (C) 2014 Elsevier B.V. All rights reserved.