The structure-property relationship of cationic collectors: Effects of methyl and hydroxyl in polar head groups

Abstract

The structure of the flotation collectors determines their hydrophobicity and adsorption behavior on mineral surface. In this study, the flotation performances of four cationic collectors with different polar head groups, i.e., dodecylpropanolamine (NDPA), N-dodecyl-isopropanolamine (DMPA), N-(2-hydroxy-1,1-dimethylethyl) dodecylamine (DMEA), and N-(2,3-propanediol)-N-dodecylamine (DPDA), were compared in hematite reverse flotation for quartz removal. The micro-flotation tests showed that the four collectors had excellent collecting capacity for quartz, while their flotation performance on hematite varied considerably. The differences in flotation performance caused by the collector molecular structure were investigated using Fourier transform infrared spectroscopy (FTIR), adsorption amount measurements, surface tension measurements, and molecular simulations. From the perspective of adsorption mechanisms, the numbers of introduced methyl and hydroxyl in the polar head groups of the collectors did not change the adsorption mechanism on the mineral surface, but affected the surface activities of the collector molecules. Molecular simulations indicated that the larger polar head groups of the collectors, the greater the steric hindrance between the collector molecules, which could prevent other molecules from adsorbing onto the mineral surface once the collector was adsorbed. The increase in the number of hydroxyl groups would enhance hydrogen bonding, which would also strengthen the collector adsorption. This study could help deepen the understanding of the relationship between molecular structure and properties of cationic collectors and provide guidance for the design of new cationic collectors.