Adsorption configuration of dodecylamine at gas–liquid interface and its relationship with foam stability: MD simulation and ToF-SIMS investigation

Abstract

Dodecylamine (DDA) as a collector was widely applied in flotation, but its high foam stability has also been proven in many laboratories or beneficiation plants. In this work, the adsorption configuration of DDA at the gas–liquid interface and its relationship with foam stability at different pH and concentration levels was investigated to gain insights into the performance and stability mechanism of DDA. A direct, reliable, and new way to investigate the gas–liquid interface information was introduced. Froth stability experiments, surface tension measurements, time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements assisted by principal component analysis (PCA), and molecular dynamics (MD) simulation were carried out. Results revealed that the foam stability of DDA was extremely high under strong acidic condition. It increased gradually and then decreased as the DDA concentration increased, and reached the maximum at the critical micelle concentration. The positive adsorption of DDA was directly observed and confirmed by ToF-SIMS. The primary factor affecting the foam stability of DDA at different pH levels was not the adsorption capacity of DDA at the gas–liquid interface (surface tension) but the interaction intensity between the head groups of DDA and water molecules. The dominant factors affecting the foam stability of DDA at different concentrations were the adsorption capacity of DDA at the gas–liquid interface (surface tension), the interaction intensity between the head groups and water molecules, and the arrangement configuration of DDA molecules at gas–liquid interface.