Fig. 10 illustrates the adsorption of xanthate on pyrite and chalcopyrite in the presence and absence of sodium humate. The results indicated that the adsorption of xanthate on pyrite decreased significantly as the concentration of sodium humate increased. Alternatively, the adsorption of xanthate on chalcopyrite remained relatively constant and was independent of the sodium humate concentration. In addition, when CaO was used to adjust the pH, the adsorption of xanthate on pyrite (curve 1) was signifi-cantly lower than when NaOH was used as a base (curve 2).