Adsorption behavior of mixed cationic/anionic surfactants and their depression mechanism on the flotation of quartz

Mixed cationic/anionic surfactants are generating increasing attention as effective collectors during the flotation of muscovite, feldspar and spodumene ores. Many papers have been published focusing on the flotation mechanisms of these valuable minerals. However, the depression mechanisms on gangue minerals such as quartz have rarely been reported. In this study, mixed dodecylamine (DDA)/sodium oleate (NaOL) surfactants were used in the flotation separation of muscovite and quartz, and their depression mechanisms on quartz were investigated. Compared to DDA alone, the use of mixed surfactants resulted in a significantly higher adsorption amount of surfactants on the quartz but a lower flotation recovery and contact angle with the quartz. This is attributed to the different molecular self-assembly mechanisms between solely DDA and mixed surfactants at the quartz/water interface, as revealed by molecular dynamics simulations. A hydrophobic monolayer coating forms for solely DDA, with the head groups adsorbing on the quartz via electrostatic interactions. In the case of mixed surfactants, DDA preferentially interacts with NaOL via electrostatic interaction through the oppositely charged head groups and hydrophobic interactions between their carbon chains. As a result, most DDA and NaOL molecules form hydrophilic spherical-like micelles near quartz, whereas only a few DDA molecules adsorb directly on the quartz via hydrogen bonding. These act as a bridge linking the rest of the surfactants, leading to a relatively lower flotation recovery and contact angle for the quartz. This study is beneficial for complementing the flotation theories and mechanisms of mixed cationic/anionic surfactants on minerals. (C) 2016 Elsevier B.V. All rights reserved.