Hydrogen-bonding-driven synergistic effect of n-OPA/OHA for selective zircon flotation

Zircon is the primary mineral for zirconium and hafnium extraction. However, removing associated gangue minerals such as feldspar from fine zircon ore is challenging due to the limitations of utilizing a single collector. This paper proposed a mixed collector n-octylphosphonic acid (n-OPA)/octyl hydroxamic acid (OHA) to promote the separation of zircon and feldspar. Accordingly, solution chemistry calculations, zeta potential, surface tension measurements and density functional theory (DFT) calculations were performed to study the detailed adsorption mechanism of mixed collector on surface of zircon. Flotation results for single minerals demonstrated that the mixed collector effectively facilitated the separation of zircon from feldspar, achieving a maximum recovery difference exceeding 88.00%. Run-of-mine ore flotation tests indicated that the use of n-OPA/OHA as a collector resulted in a zircon concentrate with a ZrSiO 4 grade of 12.57% and a recovery of 82.21%. In contrast, when sodium oleate (NaOL) was used as the collector, the ZrSiO 4 grade and recovery were 8.33% and 66.01%, respectively. Solution chemistry calculations and zeta potential measurements indicated that at pH 2.0, the mixed collector exists in the forms of n-OPA molecules, n-OPA −1 , and OHA molecules. Following interaction with the mixed collector, the surface potential of zircon significantly decreased by 14.8   mV. Surface tension measurements demonstrated a positive synergistic effect between n-OPA and OHA. DFT calculations revealed that the intermolecular interaction energies between n-OPA-OHA and n-OPA −1 -OHA were 41.5 and 32.8   kJ/mol, respectively, primarily attributed to hydrogen-bonding between them.