BACKGROUNDLeaching kinetics of the roasted (at 600 degrees C) chromite overburden of Sukinda mines Orissa, India, was studied with optimized data generated through response surface methodology (RSM) coupled with Box-Behnken design (BBD). The effects of oxalic, citric and gluconic acid concentration (50-150 mmol L-1), reaction temperature (60 degrees to 80 degrees C) and period (up to 3 h) on metal (nickel and cobalt) dissolution were examined. RESULTSExtraction of nickel and cobalt to the extent of 63.61% and 44.33%, respectively, was achieved using 150 mmol L-1 oxalic acid at 80 degrees C in 3 h; compared with other acids, oxalic acid leached more of the metals. Associated apparent activation energy for Ni was 74 kJ mol(-1), and that for cobalt was 84.37 kJ mol(-1) during the first hour, and 80.99 kJ mol(-1) for the remaining period since cobalt leaching followed biphasic kinetics. CONCLUSIONDissolution of nickel and cobalt from the roasted chromite overburden was highly dependent on the amenability of ore minerals to organic acid attack. Nickel leaching data fit the three-dimensional diffusion mechanism of the type Ginstling Brounsthein (GB) equation while a mixed kinetic model consisting of spherical geometry and the GB equation was followed for cobalt. This work presents maximum recovery of nickel and cobalt from chromite overburden using organic acid reported to date. (c) 2013 Society of Chemical Industry