In this work cenospheres, zeolite, silica or mixtures of them were injected into amolten aluminumalloy using argon as a carrier gas in order tomeasure their efficiency as Mg removers. The Mg content of the molten alloy was measured during the injection period and the produced dross was weighted for each experiment. The physicochemical characterization and the use of the thermodynamic software FactSage version 6.2, allowed the determination of the reaction mechanism between the powders and the molten aluminum. Cenospheres demonstrated their capacity as Mg removers with an efficiency similar to silica but lower than that corresponding to zeolite and zeolite:silicamixtures. The use of a zeolite:silica mixture (65:35wt%) produced the best results, removing the magnesiumof the alloy from an initial content of 1wt% to a final content of 0.0072wt%