The use of biodegradable reagents such as hemicelluloses was shown to improve copper recovery from high clay ores, but, at the same time these reagents also depressed molybdenite. Hemicelluloses are heteropolysaccharides formed by monosaccharides such as xylose, glucose, arabinose, galactose, and mannose. Since these monosaccharides are the basic compounds of the structure of hemicelluloses, the objective of this work was to study the effect of D-xylose, D-mannose and D-glucose on the flotation behavior of molybdenite and propose mechanisms to explain the mineral/reagent interactions. The effect of a non-polar collector on molybdenite flotation in the presence of the tested monosaccharides was also evaluated with the aim of looking for solutions to reduce molybdenite depression. It was found that all the monosaccharides tested depress molybdenite flotation. The depressing effects of D-mannose and D-glucose are stronger than that of D-xylose. These results can be explained by the fact that D-glucose and D-mannose molecules have more carbon atoms and hydroxyl groups in their structure than D-xylose, thus more chances to interact with the metallic sites existing on molybdenite surfaces. The depressing effect of the tested monosaccharides increases with pH which is explained by the increase of the concentration of basic sites on molybdenite surfaces and by ionization of the hydroxyl groups of monosaccharide molecules. The addition of kerosene reduces the depressing effect of the tested monosaccharides. It can be postulated that when molybdenite faces are covered by kerosene, those acidic/basic metallic sites that explain the interactions between monosaccharides and molybdenite disappear and adsorption is attenuated. (C) 2020 Elsevier B.V. All rights reserved.