Alkali halide flotation chemistry: A study of interaction forces at high ionic strengths by atomic force microscopy

The interfacial phenomena occurring in soluble salt flotation systems at high ionic strengths have been investigated by atomic force microscopy. Specifically, the role of surface charge in these flotation systems has been studied to further understand the heterocoagulation event occurring between oppositely charged collector colloids and alkali halide mineral particles which frequently accounts for the effective flotation of soluble salt minerals from their saturated brines.; Recently, nonequilibrium electrokinetic measurements using laser-Doppler electrophoresis were reported for alkali halides and the sign of their surface charge was thus determined. These surface charge results for alkali halides are generally as expected from simplified lattice ion hydration theory with some exceptions, specifically LiF, KCl, NaCl, KBr, RbBr, KI, and RbI. In this regard, ion-dipole interaction energies have been considered and the calculations indicate that the sign of the surface charge of alkali halides can be accurately predicted from an extended lattice ion hydration theory that involves the partial hydration of surface lattice ions. Further, it was found that oxygen defect states in the salt lattice can, in some cases, influence the surface charge of alkali halides.; Atomic force microscopy was used for the first time to determine the nature of the interparticle forces responsible for the heterocoagulation of oppositely charged particles at high ionic strengths. Results from these measurements indicate that while repulsive hydration forces exist between similarly charged hydrophilic particles, attractive forces exist between oppositely charged hydrophilic particles in high ionic strength solutions. These results suggest that surface charge plays an important role in influencing the nature of the interaction forces even at high ionic strengths. The experimentally measured forces were found to be in reasonable agreement with calculated interaction forces based on van Oss's concept of polar acid-base interactions.; The surface charge results coupled with the interaction forces at high ionic strengths between dissimilar surfaces suggest that the selective flotation of alkali halides is due to the adsorption of oppositely charged collector colloids thus establishing the previously proposed surface charge/collector colloid adsorption mechanism for alkali halide flotation systems.