Molecular Design of Flotation Collectors: Impact of an Allyl Group on Thionocarbamate Adsorption

Thionocarbamates, particularly N-ethyl O-isopropyl thionocarbamate (IPETC), are widely used as collectors in froth flotation. The recently developed N-allyl O-isobutyl thionocarbamate (AIBTC) shows broader applicability and enhanced recovery for coarse and fine particles of energy-relevant minerals compared to conventional IPETC. In this study, we observed that AIBTC achieved greater recovery yet lower selectivity in copper ore flotation than IPETC. To understand this difference, we studied the adsorption of AIBTC and IPETC on Cu, Ag, and Fe sulfides using solution depletion, contact angle, single-mineral flotation, density functional theory (DFT), and FTIR methods. In addition, we compared the interfacial activity of these molecules at the air-water and metal-solution interfaces. To more accurately delineate the effect of the C═C double bond, some studies included the saturated analogue of AIBTC, O-isobutyl N-propyl thionocarbamate (IBPTC). We explain the enhanced adsorption of AIBTC by the stabilization of its cis conformation by the C═C double bond as well as reduced dipole-dipole repulsion between adsorbed ligands. This result demonstrates that the interfacial packing of a neutral amphiphilic ligand with a large headgroup and two hydrocarbon chains is governed not only by ligand-metal coordination and hydrocarbon chain structure but also by the isomerism of the ligand headgroup and lateral dipole interactions.