Adsorption behavior of fluorine-ions on thermotreated products of electrochemical machining of aluminum alloy AMG-6 treated at temperatures 100, 200, 400, and 600 0C has been examined. The analysis of the conditions determining equilibrium distribution of fluorine between the bulk solution and the solid surface has been done. All the samples have been shown to be good adsorbents for fluorine removing; AMG-200 appears to be the best one. Kinetic curves and adsorption isotherms have been constructed. It has been shown that the growth of the solution temperature leads to increase of adsorption capacity for all the samples, what can be evidence of chemical nature of the process under examination. The mechanism of fluorine fixation on the modified surface of aluminum oxyhydrates has been proposed: anion exchange of F- ions with surface OH- groups with formation of covalent bond and its further conversion into ionic one.