=+Uranium Ore Residue of the Leaching Stage using Statistical Experimental Design” (Annals of Nuclear Energy, 2013: 48–52) reported on a twostage bioleaching process of vanadium by using the fungus Aspergillus niger. In one study, the authors examined the impact of the variables x1 5 pH, x2 5 sucrose concentration (g/L), and x3 5 spore population (106 cells/ml) on y 5 oxalic acid