o-Arylazo-β-arylols (HA) were first time chosen as the extractants for lithium (Li^+) with the formation of chelating anion (LiA~2^-), which could be extracted into inactive solvents in the presence of a quaternary ammonium base (Q^+X^-). The mechanism of this chelation-ion association synergic extraction was discussed in detail. The dynamics data and the thermodynamics parameters and the structure of the extractable complexes were determined. It was shown that the new system exhibits excellent properities, especially the larger separation coefficient β~Li~/~Na than other systems hitherto issued.

Key words: EXTRACTION, AZO COMPOUNDS, EXTRACTION SYSTEM, LITHIUM, CHELATING AGENT, CHLOROBENZENE, QUATERNARY AMMONIUM SALTS