An aqueous solution of Tween 40 forms liquid and solid phases in the presence of various salts, depending on the Tween 40 concentration, the identity and concentration of the salt, and the solution acidity. The distribution of Zr(IV), U(VI), Fe(III), Pb(II) and some organic photometric reagents between the Tween 40 phase and aqueous phase containing salt was examined. The quantitative extraction, separation and determination of Zr(IV) or U(VI) in the presence of Pb(II) was achieved by controlling the solution acidity in the system. The extraction mechanism has been tentatively studied.