The number of double bonds effects on the flotation of low-grade poor manganese ores using hydroxamic acid was studied. Four types of hydroxamic acids, namely stearic hydroxamic acid (SHA), oleic hydroxamic acid (OHA), linoleate hydroxamic acid (LHA) and alpha-Linolenic hydroxamic acid (alpha LHA) were synthesized and tested to float manganese ores containing 10.7% Mn. In all of the collectors screened, the study showed that LHA is a particularly good collector and has an excellent selectivity in rhodochrosite flotation. The surface tension experiment indicates that the values of surface tension cannot always function as a reliable indicator of the effectiveness of flotation collectors. The results of zeta potential and Fourier transform infrared spectroscopy (FTIR) demonstrate that chemisorption accounts for the flotation mechanism. Besides, the formation of five-membered chelate ring of rhodochrosite with LHA was proposed. The scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) data indicate that the flotation separation using LHA is significantly efficient, and the adsorption of LHA onto rhodochrosite leads to the formation of hydrophobic agglomerates of rhodochrosite particles which enhance the floatability of rhodochrosite. (C) 2015 Elsevier Ltd. All rights reserved.