Abstract: The extraction behavior of trivalent rare-earth ions (except Sc, Pm) in hydrochloric acid solution using a n-octane solution containing his(2,4,4-trimethylpentyl) phosphinic acid(HBTMPP) was studied. The mean separation factor (β_z^z+1) for the system was found to be 3.24. The system showed an advantage of higher selectivity and easier stripping ever that With HEH/EHP. The extraction mechanism for Er(Ⅲ) and Tm(Ⅲ) ions has been investigated by the method,of solpe analysis.The equilibrium constants of the extraction have been calculated and the IR and ¹H NMR spectra of the Er (Ⅲ) complex have been discussed.

Key words: bis(trimethylpentyl) phosphinic acid, rare earth ions(Ⅲ), extraction