To study the effects of collector and hydrogen ion concentrations on the floatabllity of sulfide minerals, a series of flotation experiments were conducted in which flotation recoveries as a function of pH were measured by flotation tests in a laboratory flotator. The results of flotation tests using -100 +200 mesh size galena particles as a feed, MBT as a collector, and 4-methyl -2-pentanol as a frother, are given in Figure 5. As seen from Figure 5, the galena recovery is remarkable in neutral solutions and shows a maximum recovery of galena at the pH region from 6.0 to 9.0. In these tests, the flotation recovery increases with increasing the concentration of collector.
The data of Figure 6 Indicate the pH dependence on the flotation recovery of chalcopyrite with varying the concentration of MBT. From this figure, the flotation recovery curves with MBT clearly indicate the maximum recovery at pH region from 4.0 to 10.0. The flotation recovery of chalcopyrite with addition of MBT, 1.4 x 10 -5 mol/l is nearly similar to that obtained with addition of MBT, 9.7 x 10 -6 mol/l.
Flotation curves for pyrite in solution of various concentrations of MBT are shown in Figure 7. As seen from Figure 7, the pyrite recovery is remarkable in acid solutions and shows a maximum recovery at pH region from 3.0 to 5.0. It is recognized from the above results that galena and chalcopyrite can be recovered sufficiently by flotation using MBT as collector. Consequently, the recovery of galena and chalcopyrite in the flotation was as high as 80-95 % in the region of 5-9 pH.
Figure 8 gives the MBT adsorption on galena as a function of time. In these experiments, the addition of MBT was held at 16 mg/l and the pH value was at 5.6 or 6.2. In each case, the adsorption amount of MBT increases with increasing reaction time and attains to an equilibrium value within about 30 minutes reaction time.
Adsorption measurements for MBT on galena were conducted at 25°C at pH 5.4, 5.9, 6.4, 8.9 and 9.9. These pH values are final pH values. The adsorption isotherms give the adsorption density in mol/gram as a function of the equilibrium MBT concentration, and presented in Figure 9. The adsorption density varies linearly with the equilibrium MBT concentration. A replot of the above data in the form of adsorption density vs. pH at constant equilibrium concentration is given in Figure 10. All the curves exhibit a maximum near pH 7.0 corresponding to pKa of MBT.
The optimum pH condition for galena flotation is related to the pH dependence on the conditional solubility product of a complex formed between mineral constituent and MBT. The conditional solubility product of Pb-MBT as a function of pH were calculated. Figure 11 shows the pH dependence on the conditional solubility product of Pb-MBT. From Figure 11, the conditional solubility product depends markedly on the pH and Pb-MBT is extremely stable between pH 6 and 8. The conditional solubility product of lead with MBT gives a tendency in the adsorbability of galena as a function of pH.
Figure 12 shows the results obtained with chalcopyrite. Adsorption measurements were conducted at 25°C at pH 3.1, 4.4, 6.0, 7.8, and 9.9. As seen in this figure, there is a significant increase in adsorption density with the increase of the equilibrium MBT concentration, and the adsorption density increases with the decrease of pH value and becomes maximum at about pH 3.1.
The floatability of sulfide minerals, such as galena, chalcopyrite and pyrite were measured by using KEX and MBT, and then the effects of the collector ion concentrations and hydrogen ion concentrations on the floatability of these minerals were considered surface-chemically. The effects of the hydrogen ion concentration on the floatability of each mineral were established in the solution of various concentrations of the collector. The correlation between the floatability of the sulfide minerals and the adsorbability of MBT to the sulfide minerals was confirmed by the obtained results. The critical flotation curves of each mineral were determined, and coincided fairly well with the pH range where MBT ion or hydroxyl ion preferably reacts on the sulfide minerals. The competitive adsorption of collectors on sulfide mineral was recognized in the case of MBT-KEX combination.