Enhancement of Hematite Flocculation in the Hematite–Starch–(Low-Molecular-Weight) Poly(acrylic acid) System

In the iron ore industry, the flocculation of hematite with starch in the presence of a dispersant for gangue minerals is important for the production of high-grade concentrates. The sequence of reagent addition in this process has been considered negligible as starch was reported to have no significant effect on the adsorption of other reagents in the literature. In this work, the colloid stability of hematite with different reagent addition sequences was studied. The results demonstrate that, when hematite is preconditioned with starch, the subsequent addition of a low-molecular-weight poly(acrylic acid) does not show any dispersive effect on hematite at starch concentrations greater than or equal to 4 ppm, because the adsorption of poly(acrylic acid) is completely blocked by the starch molecules coated on the hematite surfaces. When hematite is preconditioned with poly(acrylic acid), the flocculation effect of the subsequently added starch is significantly affected, with strong steric stabilization observed because of the reduced number of adsorption sites available to starch molecules.