The results of the present study suggested that the depression of pyrite by sodium humate was more effective when the pH of the pulp was adjusted with lime (CaO), in comparison to adjustment with sodium hydroxide. Lime (CaO) has been shown to depress pyrite; thus, the mechanism of the effect of sodium humate and lime (CaO) on pyrite and chalcopyrite flotation was investigatet by analyzing the concentration of free calcium oxide (CaO) in the tailing pulp in the presence and absence of sodium humate. As shown in Fig. 7, in the presence of sodium humate, the Cu content of the concentrate increased sharply with an increase in the concentration of free calcium oxide (CaO) in the tailing pulp. Alternatively,
in the absence of sodium humate, the Cu content of the concentrate increased slowly with an increase in CaO. Thus, in
the absence of sodium humate, a higher CaO concentration is required to achieve a separation efficiency that is similar to that of sodium humate/CaO. For instance, in the presence of sodium humate, the content of Cu in the concentrate was 24.6%, and the concentration of free calcium oxide in the tailing pulp was 350 mg/L. However, in the absence of sodium humate, a free calcium oxide concentration of 1000 mg/L was required to achieve the same Cu content in the concentrate. Thus, the results indicated that sodium humate was an effective depressant for Cu–S separation in pulp with reduced alkalinity.