The use of microorganisms to dissolve metals from ores has offered an ecologically friendly and less expensive alternative to traditional methods. The dissolution of metals by this method can be done in a two-stage bioleaching process: (1) microorganisms are grown in culture to produce metabolites (e.g. organic acids) and (2) ore is added to the culture medium to initiate leaching. The article “Two-Stage Fungal Leaching of Vanadium from 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 1 pH, 2 sucrose concentration (g/L), and 3 spore population (106 cells/ml) on y oxalic acidproduction (mg/L). The accompanying SAS output resulted from a request to fit the model with predictors 1, 2, and 3 only.
Fitting the complete second-order model resulted in SSResid 5 541,632. Carry out a test at significance level .01 to decide whether at least one of the second-order predictors provides useful information about oxalic acid production.