The hydrophilicity–hydrophobicity of minerals, which is associated with floatability, can be assessed by measuring the contact angles of the minerals. Larger contact angles indicate that a mineral is hydrophobic, and smaller contact angles indicate stronger hydrophilicity. As shown in Figs. 11a and b, the pH of the pulp was adjusted with NaOH and CaO, respectively, and the effects of sodium humate on the contact angles of pyrite and chalcopyrite were determined. The results indicated that the contact angle of pyrite decreased significantly after the addition of sodium humate,
suggesting that the adsorption of sodium humate on the surface of pyrite reduced the hydrophobicity and floatability of pyrite. Moreover, the combination of CaO and sodium humate resulted in the smallest contact angle (see curve 4).