Surface forces between sphalerite and silica particles in aqueous solutions

Surface forces between a fractured sphalerite surface and a silica particle in supporting electrolyte solutions were measured using an atomic force microscope. Below pH 8, the long-range surface forces were found to be attractive, decreasing with increasing solution pH. The adhesion force varied from 18 mN/m at pH 4 to 7 mN/m at pH 8. At pH 10, an exponentially decayed repulsive force was measured and no adhesion was observed. The decay length was found to scale with the supporting electrolyte concentration. Although the repulsive force was reduced significantly when up to 0.5 mmol/1 calcium ions were added, the surfaces remained non-adhering at contact. In contrast, an attractive force profile was obtained when 0.5 mmol/1 cupric ions were added, accompanied by an adhesion force of 16 mN/m. In general, the measured force profile can be accounted for by considering classical van der Waals and electrical double-layer forces for constant surface charge density conditions. The measured force behavior correlates well with the observations in sphalerite-silica heterocoagulation tests.