The selective separation of alkali halide salts such as KCl from NaCl by flotation in saturated brines (ionic strength similar to 4 M) is of considerable industrial significance and has been studied. by flotation chemists for many decades. Electrokinetic information coupled with the stability and prevalence of certain collector colloids in these soluble salt flotation systems suggest that the selective flotation of alkali halide minerals is due to the adsorption of oppositely charged collector colloids by heterocoagulation. Recent contributions have revealed the nature of the interparticle forces responsible for heterocoagulation of oppositely charged particles at high ionic strengths and the reasons for the deviations of the surface charge of some alkali halides from theory. Because of the progress made in interparticle force measurements at high ionic strengths by atomic force microscopy (AFM), more information is now available and results from recent AFM measurements are reported. Also extension of the simplified lattice ion hydration theory by considering partial hydration of the surface state allows for the prediction of the sign of the surface charge of all alkali halides from first principles, Thus the interactions at high ionic strengths and the deviations of the surface charge of some alkali halides may be explained by structural forces as measured by AFM and the extended lattice ion hydration theory, respectively.