Heterocoagulation of sulphide minerals

Interactions among sulphide minerals (sphalerite, galena and pyrite) and sphalerite and silica were studied using electrophoresis, an automated settling apparatus and, in the sphalerite/silica case, atomic force microscopy (AFM).;Significant changes in zeta-potential were observed in some cases as a result of contact (conditioning) with a second mineral. As a function of pH when sphalerite was conditioned with pyrite, the zeta-potential increased to ca. pH 9 and decreased above this pH. For sphalerite conditioned with galena, the zeta-potential decreased below pH 5, increased between pH 5 to 9 and decreased above pH 9. Galena conditioned with sphalerite and pyrite resulted in a decrease in zeta-potential below pH 5 and an increase above this pH. The results are interpreted on the basis of galvanic interactions. The mineral with the lower rest potential preferentially oxidizes and the ions released migrate and influence the zeta-potential. Measurements made in solutions of various suspected released ions generally supported the galvanic model. The zeta-potential results for mixed sulphide minerals were correlated with settling velocity. For the pyrite/galena, sphalerite/pyrite and sphalerite/galena systems, the pH of maximum settling rate corresponded to the zeta-potential of both minerals approaching zero. When the minerals were oppositely charged the conditions remained (relatively) dispersing. In the case of silica and sphalerite/silica at around pH 2 and 8.5 sphalerite homocoagulated and some silica was dispersed; from ca. pH 3 to 7, the system heterocoagulated; and above pH 9.5 the suspension was dispersed. This behavior did not correlate with the behaviour of the minerals alone. In the presence of calcium ions, from ca. pH 2 to 7, the sphalerite homocoagulated and the silica was dispersed while above pH 7 heterocoagulation was observed. This behavior did correlate more closely with that of minerals alone. The zeta-potential measurements provided only a partial interpretation: a force of attraction between sphalerite and silica appears to exist at moderately alkaline pH. An electrostatic origin to the attractive force due to the large difference in zeta-potential for sphalerite and silica is discussed.;The settling results for the sphalerite/silica system were Correlated with AFM measurements. For silica alone, the interaction was repulsive at pH 6.2 and 8.3. This behavior did correlate with the settling tests. In the presence of calcium ions, the interaction was repulsive at pH 6.1 and 9.6 and was attractive at pH 11.4. This behavior also correlated with the settling data. For the mixed system, the interaction was repulsive at pH 7.2, 8.4 and 10.6 and was attractive at pH 9.6. The behavior at pH 8.4 and 10.6 correlated with the settling tests but not at pH 7.2 and 9.6. The lack of correlation is discussed.