As shown in Fig. 8, the pH of the pulp was adjusted with NaOH and CaO, and the effect of sodium humate on the zeta potential of pyrite was determined as a function of the pH. A comparison of curves 1 and 2 and of curves 3 and 4 indicated that the addition of sodium humate shifted the zeta potential of pyrite to more negative values, suggesting that the anion (A) was adsorbed to the surface of pyrite.