Reverse anionic flotation of dolomitic collophanite using a mixed fatty acid collector : adsorption behavior and mechanism

Collophanite in south China generally has a high MgO level, which negatively impacts wet-process phosphoric acid production and cannot be utilized directly. A novel mixed fatty acid soap (GSWF01) was employed as a collector for dolomite. A single reverse flotation experiment was performed on a dolomitic collophanite from Guizhou, China under different pH and collector dosages. A phosphate concentrate with P2O5 grade of 33.73%, MgO content of 1.07%, MER value (ω(MgO+Al2O3+Fe2O3)/ω(P2O5)) of 4.86% and phosphorus recovery of 91.06% was obtained. The beneficiation indexes of GSWF01 were better than that of sodium oleate (NaOL). The adsorption behavior and mechanism of GSWF01 on dolomite surface were investigated using quartz crystal microbalance with dissipation (QCM-D), atomic force microscope (AFM), infrared spectrometer (IR), and zeta potentiometer. The results revealed that GSWF01 chemically reacted with metal ions (Ca2+, Mg2+, etc.) on the surface of dolomite to generate fatty acid salt precipitation (chemisorption). The adsorbed layer transitioned from dense to loose in two stages, resulting in a stable double-layer adsorption structure. Moreover, in a weak acidic solution environment, physical adsorption of fatty acid molecules (RCOOH ((aq)) and fatty acid ion-molecular association compounds (RCOOH• RCOO-) generated by hydrolysis can also occur on the dolomite surface. These are the main reasons for the hydrophobic floating of dolomite. This is of great significance to the development of a novel high-efficiency dolomite collector and the enhancement of flotation process for carbonate collophanite.