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Serpentine minerals, which have the generalized composition (Mg,Fe)3Si2O5(OH)4, can be easy to crush and grind due to their convoluted and bent layered structures. These serpentines can hinder the enrichment of some metallic minerals and dilute their concentrates by entrainment during flotation. The resulting high pulp viscosities, slime coatings, and high content of dissolved ions adversely affect the flotation recoveries of copper and nickel sulphides, and high levels of MgO entrained in the concentrates lead to heavy penalties from smelters. Since the quality of nickel flotation concentrate depends heavily on its MgO content (generally less than 6–7% for No.1 or 2 grade nickel concentrate according to the standard requirement from National Nonferrous Industry), reducing the entrainment of serpentine during flotation is becoming more and more pressing. Previous research has focused on the collectors and depressants that are commonly used in copper-nickel flotation, as well as their interaction mechanisms. The traditional collectors, like xanthate (Senior et al., 2005; Malysiak et al., 2002; Bozkurt et al., 1998), dithiophosphate (Wiese et al., 2006), or mixed/combined collectors (Glembotaskii, 1958; Lotter and Bradshaw, 2010; Wiese et al., 2008) are used to enhance the hydrophobicity of copper or nickel sulphides during flotation. Lu et al. (2011) indicated that potassium amyl xanthate is adsorbed on a mixture of pyrite and serpentine, but that adsorption is minimal on serpentine alone in alkaline pulp. Feng et al. (2012) found that the longer the hydrocarbon chain of xanthate, the lower the Ni grade and recovery, indicating that serpentine entrainment is influenced significantly by the type of collector. These collectors might not affect the natural floatability of serpentine directly, as indicated by Edwards et al. (1980). However, they may possibly influence the entrapment of serpentine indirectly by forming hydrophobic flocs of ultra-fine metal values. Also, slime coating is a common way for serpentines to be incorporated into metallic mineral concentrates. However, according to some researchers (Wellhame et al., 1992; Bulatovic, 1999; Chen et al., 1999), slime coatings can be reduced or removed from nickel mineral surfaces through strong and lengthy agitation. A possible additional mechanism for serpentine entrainment during the flotation of this type of ultra-fine ore, other than water recovery or slime coating, is indicated by some unsatisfactory results, coupled with high content of MgO in concentrates, even when using efficient depressants like carboxymethyl cellulose (CMC) and guar gum combined with high-intensity agitation (Wellhame et al., 1992; Senior et al., 1994; Senior and Thomas, 2005). The flocculation behaviour of ultra-fine Effects on entrainment of serpentines by hydrophobic flocs of ultra-fine copper-nickel sulphides during flotation