The separation of phosphate from carbonate gangue using flotation is extremely complex due to the similarities in surface properties. The acidic flotation process of carbonates at pH 4.5-5.0 followed by a direct phosphate flotation uses phosphoric acid as depressor of apatite during carbonate flotation. The mechanism of apatite depression is rather hypothetical because of lack of data on the surface speciation in such a complex mineral suspension. A real-time method for in situ control of surface compounds on the minerals (carbonated hydroxylapatite and calcite) using a submerged Raman analyzer probe is proposed in this work to collect the data on the nature and kinetics of phase formed. The carbonated hydroxyfluorapatite (C-HFAp) and calcite reactivity in phosphoric acid at concentrations between 0 and 1 M) during 15 minutes was studied. The Raman spectra collected in situ and ex situ showed the peak at 1085 cm-1 of calcium carbonate at 10-3 and 10-1 M on the surface of hydroxyfluorapatite that disappears at high acid concentration. Kinetics studies performed at 4.6 (±0.1) pH range during 15 minutes showed calcium carbonate formation after 2 minutes of conditioning and that disappears after three minutes (Figure 1). The infrared spectra of C-HFAp in presence of phosphoric acid showed at 10-3 and 10-1 M new peak at 713 cm-1 that belongs to calcium carbonate vibrations which seems to be due to C-HFAp surface conversion as observed on XRD patterns.
Please click Additional Files below to see the full abstract
