As shown in Fig. 4, the pH of the pulp was adjusted with NaOH or CaO in the presence of a constant concentration of sodium humate,and the recovery of chalcopyrite and pyrite was evaluated as a function of the pH. The results indicated that the pH of the pulp had a stronger effect on pyrite recovery than chalcopyrite recovery, Moreover, the depression of pyrite was enhanced when CaO was used to adjust the pH of the pulp, while the combination of CaO and sodium humate had little effect on the chalcopyrite recovery.