The flotation of aluminosilicate polymorphic minerals with anionic and cationic collectors

Andalusite, sillimanite, and kyanite are three polymorphic minerals with the same formula of Al2SiO5 but different crystal structures. Despite their high economic values, selectively recovering them by flotation is a challenge. In this study, the flotation behavior of the three minerals with two types of widely used collectors, anionic sodium hexadecanesulfonate (SHS) and cationic octadecylamine (OA) were examined at acidic pH. It was found that the flotation behavior of the three polymorphic minerals was different under the same flotation condition. In the presence of collector OA, the order of the flotation recovery of the three minerals was kyanite > sillimanite > andalusite, and the recovery increased with slurry pH. However, in the presence of collector SHS, the trend of the flotation recovery of the three minerals was completely opposite. X-ray photoelectron spectroscopy (XPS) was applied to quantitatively measure the collector adsorption and the surface active sites. The interaction between collectors and minerals was also studied by zeta potential measurements and calculating the adsorption energy using molecular dynamics (MD) simulation. It was found that the adsorption of collector OA was through the interaction of amine cations with O atoms by electrostatic attraction and hydrogen bonding. The highest flotation recovery of kyanite among the three minerals was related to the closest packing arrangement of oxygen atoms which leads to the highest electronegativity and therefore the lowest adsorption energy of OA. In comparison, the adsorption of collector SHS was mainly through the chemical interaction of sulfonate anions with Al atoms. The adsorption energy of SHS on andalusite surface was the lowest, which resulted from the lowest electronegativity of andalusite surface.