THE EXTRACTION OF CERIUM(III) AND LANTHANUM(III) FROM CHLORIDE SOLUTIONS WITH LIX-54

A study has been made of the extraction equilibrium of cerium(III) and lanthanum(III) from NaCl solution with dodecylphenyl-methyl-beta-dike tone (LIX 54)(1) in n-heptane. It was found that the extraction of bot h metals depends strongly on pH as well as on the extractant concentra tion and does not depend on chloride concentration. The extraction of lanthanum is independent of its concentration in the aqueous phase up to 0.05 M but the extraction of cerium diminishes markedly when its co ncentration exceeds 1.5 mM. Experimental results show that the predomi nant complexes extracted are CeR(3) and LaR(3) . 3HR. The extraction e quilibrium constants are: log K-ex = -15.67, for the CeR(3) complex, l og K-ex = -14.2, for the LaR(3) . 3HR complex, and log K-ex = -18.2 wh en the LaR(3) complex is assumed. The change in enthalpy associated wi th the extraction for lanthanides is about 7.3 kJ/mol. Cerium is bette r extracted with LIX 54 than lanthanum. During simultaneous extraction of the metals with 0.1 M LIX 54 the selectivity of their separation i s appreciable if the pH range is strongly limited.