The interactions of serpentine with talc and implications for talc depression by carboxymethyl cellulose (CMC) have been investigated through flotation tests, sedimentation tests and zeta potential measurements. Talc is a hydrophobic mineral and CMC is effective for talc depression. At pH value 9, where flotation of nickel sulfide ores is routinely performed, the two magnesium silicate bearing (MgO) gangue minerals are oppositely charged and therefore attract through an electrostatic mechanism. Slime coatings of serpentine adhere to the surface of talc, reducing talc flotation recovery to some extent, but also causing problem to its depression by CMC as serpentine is a hydrophylic gangue mineral which cannot be depressed by CMC depressant. Pretreatment of serpentine with acid leaching results in a shift of the zero charge points, from pH value 10.2 to 6.8 and the leached serpentine is negatively charged at pH 9. The negatively charged serpentine does not interfere with the talc depression by CMC. Adsorption of sodium hexametaphosphate (SHMP) at the serpentine/solution interface also compensates the positive charge on the serpentine particle and its zeta potential is rendered negative. When the serpentine surface is negatively charged, a repulsive interaction energy generates and serpentine slimes drop off from the surface of talc, allowing talc to once again be depressed by CMC. (c) 2012 Elsevier Ltd. All rights reserved.