Mechanistic Study of Interface Regulation by Pullulan as an Eco-Friendly Depressant for Selective Flotation of Apatite from Hematite

The selective flotation of apatite and hematite in high-phosphorus oolitic iron ore is challenging due to the declining selectivity of reagents as the particle size decreases. This study explores pullulan as an eco-friendly depressant in combination with α-bromolauric acid (α-BLA) as a collector. Microflotation experiments showed that while α-BLA exhibited a strong collection ability, its selectivity was poor. Adding pullulan created a hydrophilic layer that suppressed hematite flotation while enhancing apatite recovery. Under optimal conditions (pH 9, α-BLA 28.57 mg/L, pullulan 1.43 mg/L), the phosphorus content in the concentrate decreased from 8.83 to 0.97%, while iron recovery reached 86.83%, confirming the effectiveness of this reagent combination. Interfacial characterization and extended Derjaguin-Landau-Verwey-Overbeek (E-DLVO) calculations revealed that pullulan preferentially adsorbs on hematite, altering its wettability and charge, simultaneously hindering α-BLA adsorption. Additionally, the active site density on the mineral surface influences reagent adsorption and bubble attachment. These results highlight the synergistic effect of α-BLA and pullulan, offering a sustainable phosphorus-containing iron ore beneficiation strategy.