The effect of cationic groups on performance of 12-carbon chain collectors in flotation separation of diaspore from kaolinite, pyrophyllite and illite has been investigated by flotation tests and explained by density functional computations. The flotation test results indicated that the separation of diaspore from these aluminosilicate minerals was feasible at strong alkaline conditions by using cationic collectors, dodecylamine chloride (DDAC), dodecyl trimethyl ammonium chloride (DTAC) or dodecylguanidine sulfate (DDGS), respectively. In strong alkaline conditions, these three collectors showed excellent selectivity against diaspore, however, DDGS returned superior collecting ability for aluminosilicate minerals compared with DDAC and DTAC. By using the density functional theory (DFT), we calculated some properties such as the H and N atomic charges and cationic group charges which are related to the reactive behavior of 12-carbon chain collectors at B3LYP/6-31G (D) level. The results of calculations indicated that the efficiencies of these three cationic collectors depend on the investigated parameters, and DDGS is better than DDAC and DTAC as a collector agent. The theoretically obtained results are consistent with the flotation tests. (C) 2008 Elsevier Ltd. All rights reserved.