Competitive flotation of Zn(II) and Cd(II) ions from dilute aqueous solutions (c(Mc) = 1 x 10(-5) M), by a series of lipophilic proton-ionizable lariat ethers varying ring sizes in the presence of nonylphenol(nonylethylene glycol) ether as the nonionic foaming agent is reported. The influence of the rings size variations from DB-13-C-4 through DB-16-C-5 to DB-19-C-6 on separation of zinc and cadmium ions is discussed. The influences of structural variation within the lariat ether, concentration of the macrocycle, and pH of the aqueous solution is presented. An effect of alkali metal cations, i.e. Li+, Na+ and K+, on Zn(II) and Cd(II) ion flotation removal is also reported. It was shown, that the removal of Zn2+ and Cd2+ increases with increase of pH value and decreases with alkali metal cations concentration increase in aqueous solutions. (c) 2005 Elsevier B.V. All rights reserved.