Ferric ion is a strength oxidant and its precipitation is an undesired phenomenon in the bioleaching process. Previous studies showed that it considerably occurs in bioleaching operations even at optimum conditions. Although there have been many reports on the Fe3+ precipitation, no study has made a mathematical modeling of the affecting parameters. The aim of the present work is the development of a model that represents the impact of some parameters on the Fe3+ precipitation.The polynomial model was developed. The resulted model presents the positive effect of all parameters on minimization of Fe3+ precipitation; particularly, the effects of pH and iron concentration, which are more significant. The validation of model was confirmed using F-test(P<0.001) and the coefficient of determination(R2=96.84%).The optimum values of parameters were determined as : pH = 1.5,Temperature=35.5°C, iron concentration=20g/l, pulp density = 15% (w/v) . The non-linear nature of the modeled response for Fe3+ precipitation was explained by a second-order polynomial equation. Also it was observed that by increasing the considered parameters, precipitation rate was increased. The severity of the effects of the parameters at the studied range was as follows: pH and iron concentration> temperature> pulp density.
