Orbital symmetry matching study on the interactions of flotation reagents with mineral surfaces

The selectivity of reagents to minerals is extraordinarily important in flotation. However, the selective mechanism of reagents for minerals has not been completely clarified. Similar to other chemical reactions, the surface reaction of minerals is associated with orbital symmetry matching between flotation reagents and surface metals. Nevertheless, no research has been found on this topic. The present work performed density functional theory (DFT) calculations on orbital symmetry matching between flotation reagents and metal ions on sulfide mineral surfaces. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were calculated. The results suggest that the symmetry of xanthate LUMO perfectly matches the symmetry of pyrite Fe HOMO, while the symmetry of dithiophosphate (DTP) LUMO fails to match the symmetry of pyrite Fe HOMO, so xanthate has better collecting ability than DTP for pyrite. Moreover, the symmetry of xanthate LUMO does not match the symmetry of galena Pb HOMO, whereas the symmetry of DTP LUMO matches the symmetry of galena Pb HOMO, so DTP is a stronger collector than xanthate for galena. Copper can activate sphalerite mainly because the symmetry of the Cu HOMO matches the symmetry of the xanthate LUMO. Meanwhile, for pure sphalerite, the Zn HOMO makes no contribution, and the symmetry of the Zn LUMO does not match the symmetry of the xanthate HOMO. In the case of Z-200, the main factor that results in its weak collecting ability for pyrite is the steric hindrance existing between Z-200 and the pyrite surface instead of orbital symmetry matching. For CN– adsorption, both HOMO and LUMO of CN– and those of galena surface Pb do not follow symmetry matching, while the opposite holds for the HOMO and LUMO of CN– and those of pyrite surface Fe, which causes the depressing effect of cyanide on pyrite.