The first use of a Gemini cationic surfactant. butane-alpha,omega-bis(dimethyl dodeculammonium bromide) (BDDA), as a collector for reverse flotation to separate illite, pyrophyllite and kaolinite from diaspore is reported in this study. Micro-flotation tests of the pure minerals are employed to detect the minerals' flotation behaviors with the Gemini and to comparatively investigate the collecting ability both with the dimeric surfactant and the corresponding monomeric. The results show that the Gemini surfactant demonstrates a stronger collecting power than the monomer. Moreover, with the Gemini, the floatability of kaolinite is better than that of illite and pyrophyllite in the entire pH range. When corn starch was used as a depressant, flotation separation of the artificial mixed-mineral samples and the bauxite ore were conducted by using BDDA as a collector at pH around 9-10. The Gemini presents a significant selectivity for illite, pyrophyllite and kaolinite against diaspore. Mass ratio of Al to Si of the concentrate was 9.72 for the bench-scale separation, and the recovery of Al was 81.25%. To understand mechanisms of the Gemini adsorption on the mineral surfaces, we employed FTIR spectra analysis, density functional theory (DFT) calculation, electrokinetic measurements and surfactant property studies as well. In addition, the role of corn starch in the selective depression of diaspore was also explained. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.