Hydrophobicity of ZnS particles in the 150-212 mu m size fraction was examined using film flotation. It was revealed that hydrophobicity of studied ZnS particles was affected by slime coatings as well as prolonged conditioning in water. Conditioning in concentrated methanol solution resulted in increased hydrophobicity of ZnS particles, similar to the activation with CuSO4. Copper activation with CuSO4 is a common procedure to increase hydrophobicity of ZnS and to facilitate xanthate adsorption to form stable chemical compound. Conditioning ZnS with concentrated methanol was shown to have beneficial effect on the increase of hydrophobicty of ZnS particles. The atomic force microscopy (AFM) with tapping mode imaging technique, was used to examine ZnS surface before and after the methanol treatment. The nanobubbles were found on the ZnS surface after the methanol treatment and this led to an increased in hydrophobic force and an increase in the range of attraction between examined hydrophobic surfaces. The slime effects on hydrophobicity of ZnS surface were investigated using contact angle (captive bubble and sessile drop). The slime coatings before and after methanol treatment were observed with AFM. The methanol conditioning was shown to result in aggregation of slimes and eventually cleaning the surface of the mineral. (C) 2008 Elsevier Ltd. All rights reserved.