Synthesis of selective heteroatomic collectors for the improved separation of sulfide minerals

The separation of sulfide minerals has always been a difficult problem in the field of flotation due to their often-similar affinity to the collectors. It is therefore crucial to improve the selectivity of collectors and to clarify the mechanism of separation. In this study, chelating collectors based on heterocyclic thioketone framework, namely benzo[d]oxazole-2(3H)-thione (BOT), 1H-benzo[d]imidazole-2(3H)-thione (BIT) and 5-(butylthio)-1,3,4-thiadiazole-2-thiol (CSC-1), were synthesized. An industry standard collector ethyl xanthate (EX) was used as a reference to evaluate the flotation performances of the synthesized collectors. The flotation results show that the trend of selectivity is BIT ≈ BOT > CSC-1 > EX. Zeta potential measurements confirm the above trend. These results are further rationalized by theoretical investigations, namely the adsorption free energy, electrostatic potential energy surface (EPS), total atomic dipole moment corrected Hirshfeld (ADCH) charge along with the HOMO-LUMO topology modelled by DFT calculation. By introducing concepts that are capable of describing the ionic character (the total ADCH charge of the coordination sites (T-ADCH-C)) and the charge transfer character of coordination (the degree of electron transfer (DET)), a qualitative model can be derived to demonstrate the theoretical rational of selectivity. Strong ionic collectors (EX) with a higher DET have a stronger collecting ability and in turn, a worse selectivity. Non-ionic collectors (BOT and BIT) with lower DET, on the contrary, display a better selectivity and a weaker collecting ability. Weak ionic collectors (CSC-1) are at the intermediate level. This work not only reveals the potential of using thioketones as selective sulfide collectors, but also provides a selectivity model based on the bonding and charge transfer character that can guide further development of more selective sulfide collectors.