SOLVENT-EXTRACTION KINETICS OF RARE-EARTH ELEMENTS

The kinetics of solid-liquid extraction of rare earth elements (RE) (L a, Ce, Sm, Dy and Yb) were studied with 1-(2-pyridylazo)-2-naphthol (P AN) at 60 degrees C using paraffin wax as a diluent. The rate of extra ction is first order with respect to metal ion and hydrogen ion in the aqueous phase and second order with respect to the extractant in the organic phase. The rate-determining step is the formation of an [RE(PA N)(2)](+) complex between RE(3+) and PAN in the aqueous phase. The rat e constant for the extraction was found to be about 10(11) l mol(-1) s (-1). The temperature dependence of extraction rate was determined and the activation parameters were calculated.