The phosphate-dolomite separation has a limited separation selectivity using conventional flotation. The utilization of bacteria alone or in presence of collector offers a good solution in terms of increasing the separation selectivity. In this study, the bioflotation was tested using two bacterial strains (Corynebacterium-diphtheriae-intermedius, CDI, or Pseudomonas Aeruginosa, PA) in the presence of amphoteric collector. Statistical design of experiments (DOEs) was used to screen, optimize, and study the factors mutual interactions. The screening design indicated that the bacteria concentration, bacteria conditioning time, and collector dosage are the most significant parameters. In addition, full factorial design indicated that the presence of bacteria improves the separation selectivity. Moreover, it was found that the PA performs better than CDI in presence of collector in terms of lowering the MgO % and increasing P2O5%. A concentrate containing 0.69% MgO and similar to 30.8% P2O5 with a recovery of similar to 80% can be obtained at 11.4 x 10(7) cells, 20 min and 4.0 kg/t for pH, PA concentration, PA conditioning time, and collector dosage, respectively. (C) 2012 Elsevier B.V. All rights reserved.