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In the present work, five different flotation frothers were tested in order to evaluate their performance in the flotation of two coal samples in terms of their effect on the entrainment of fine particles. The experimental program included the characterization of the investigated frothers by means of surface tension measurements, dynamic foamability index (DFI), critical coalescence concentration (CCC) and water recovery tests in aqueous solutions. The experiments also included both forward and reverse batch flotation tests in the presence of the tested reagents. The results indicate that, while there is a clear relationship between water recovery in a two-phase system and the fundamental properties of the frothers, expressed in terms of DFI, the trend observed in the batch flotation tests in the presence of coal for the same frothers is different. This indicates that characterization of flotation frothers in a two-phase experiment is not adequate since the water transport results obtained in the two-phase and three-phase experiments were different. The reverse flotation tests revealed that dodecyl trimethyl ammonium bromide (DTAB), which is used as a collector for mineral matter and as a frother, generates froths characterized by low water contents and high stability, which promote the entrainment of unwanted particles to the froth collection zone. It was also observed that when polyacrylamide (PAM) was used in addition to the coal depressant (dextrin) and DTAB, the selectivity of the process slightly improved. However, in the presence of PAM, the rates of transfer of water and solids to the froth also increased, which translated into a higher degree of entrainment of coal particles in the froth product. The selectivity of the coal reverse flotation process and the reagent consumption, at this point of the development of this technology, constitute a problem which remains unsolved. ii 1. INTRODUCTION