Physicochemical Problems of Mineral Processing, 41 (2007), 5-11 Fizykochemiczne Problemy Mineralurgii, 41 (2007), 5-11 Jan ZAWALA * , Jan. DRZYMALA ** , Kazimierz. MALYSA * NATURAL HYDROPHOBICITY AND FLOTATION OF FLUORITE Received March 15, 2007; reviewed; accepted May 15, 2007 The free ascending bubble–fluorite surface collision test showed that the three phase contact (TPC) was formed and time of the TPC formation was strongly affected by the roughness of the fluorite surface. The time of the TPC formation varied by an order of magnitude, from ca. 20 to 200ms, depending on the fluorite origin and surface roughness. The fact that the TPC was formed shows that fluorite can be considered as a naturally hydrophobic material. The contact angle formed by the bubble attached to fluorite plate was found to be 40 o in comparison to 10-25 o measured by flotometry and 55 o by sessile drop. Thus, the macroscopic contact angle of fluorite depends on the method of measurement as well as its origin and color since colorless fluorites float better. Hydrophobicity of fluorite and the time of the three phase contact formation influence its flotation. The best flotation is observed in Hallimond tubes while flotation is significantly reduced or absent in laboratory flotation machines. This is very likely a result of relatively long time of the TPC formation and/or low hydrophobicity of fluorite, which is not enough to withstand the detachment force during enhanced hydrodynamics of larger flotation devices. Key words: fluorite, contact angle, bubble-particle attachment, induction time, three phase contact, hydrophobicity, hydrophilicity INTRODUCTION Natural flotation of minerals frequently interferes with collectors flotation of useful components of ores. Such difficulties may occur during upgrading by flotation of ores containing chalcopyrite, talc, and graphite. It was mentioned by Barskij (1984) that also fluorite may cause problems due to its native flotation. Until sixties of the previous century fluorite was considered a hydrophilic mineral, that is material which forms in the water-air-fluorite system contact angle (θ) equal to zero. Gaudin an his coworkers (1957), in their classic paper on native floatability, did not include fluorite in the list of hydropbobic materials. As a result many researchers and technologists have been considering fluorite hydrophilic even today. * Institute of Catalysis and Surface Chemistry Polish Academy of Sciences, Cracow, Poland. ** Wroclaw University of Technology, Mining Engineering Department, Wroclaw, Poland.