illustrative, the flotation process is used for purification of potassium chloride from sodium chloride and clay minerals. the crushed mineral is suspended in brine in the presence of fatty ammonium salts. because the ammonium group and k have very similar ionic radii (ca. 0.135, 0.143 nm respectively), the ammonium centers exchange for the surface potassium sites on the particles of kcl, but not on the nacl particles. the long alkyl chains then confer hydrophobicity, to the particles, which enable them to form foams.