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 mi croscope. Below pH 8, the long-range surface forces were found to be attrac tive, decreasing with increasing solution pH. The adhesion force varied fro m 18 mN/m at pH 4 to 7 mN/m at pH 8. At pH 10, an exponentially decayed rep ulsive force was measured and no adhesion was observed. The decay length wa s found to scale with the supporting electrolyte concentration. Although th e repulsive force was reduced significantly when up to 0.5 mmol/1 calcium i ons 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 measure d force profile can be accounted for by considering classical van der Waals and electrical double-layer forces for constant surface charge density con ditions. The measured force behavior correlates well with the observations in sphalerite-silica heterocoagulation tests.