Mechanisms of amine–feldspar interaction in the absence and presence of alcohols studied by spectroscopic methods

Abstract

Abstract The adsorption of long-chain primary amines on feldspars at neutral pH 6–7 was investigated using Hallimond flotation, zeta-potential, FT-IR and XPS studies. Two-dimensional (2D) followed by three-dimensional (3D) precipitation mechanism of amine adsorption on quartz reported earlier (Langmuir 16 (2000) 8071) was further substantiated. The orientation and packing of dodecyl- and hexadecylammonium acetate and chloride adsorbed on albite in the different regions of the adsorption isotherm were determined. It was shown that these characteristics depend strongly on the substrate. The influence of long-chain alcohols on the adsorption of amines in mixed amine/alcohol on feldspars, i.e. albite (NaAlSi3O8) and microcline (KAlSi3O8), was also examined. Coadsorption of the counterion was not revealed, but the counterion was found to affect indirectly the adsorption at concentrations above the concentration of the bulk amine precipitation. It was proved spectroscopically that co-adsorption of long-chain alcohols along with amine cations leads to formation of a closed packed surface layer as compared to the case of adsorption of pure amine alone at the same concentration. The highest order and packing at the surface were observed when the alkyl chain length of mixed amine and alcohol were the same. The condition of same chain length of amines and alcohols adsorbing at the surface corresponded to maximum flotation recovery. The results also confirmed the synergistic enhancement of amine adsorption in the presence of alcohols. A mechanism of mixed long-chain amine and alcohol adsorption onto silicates (albite and quartz) consistent with the primary adsorption species of alkylammonium–water–alcohol complex, where deprotonation of ammonium groups in the adsorbed layer leading to 2D precipitation of molecular amine was illustrated.