Solvent Extraction Studies of Rare Earths from Thiocyanate Medium with N,N,N′,N′-tetra(2-ethylhexyl) diglycolamide

The extraction behavior of rare earth (RE) elements from thiocyanate medium by N,N,N-',N-'-tetra(2-ethylhexyl) diglycolamide (TEHDGA), a neutral extractant, has been investigated and the optimum conditions for their separations were determined. Isodecyl alcohol was used as phase modifier and a concentration of 5%(v/v) was found sufficient to mitigate third phase formation under our experimental conditions. The extraction mechanism of RE with TEHDGA was established by analyzing distribution data with slope analysis technique and showed the formation of a neutral species, RE(SCN)(3).2TEHDGA, in the organic phase. The extraction of rare earth decreased with increase in temperature indicating exothermic nature and the enthalpy change (Delta H) obtained for Y(III) was -14.27 kJ/mol. Among various stripping agents studied, oxalic acid was found to be efficient in quantitative stripping of rare earths from TEHDGA. The extraction efficiency for all the rare earths by TEHDGA was also investigated. High separation factor of 6.4 for Er/Y pair at 0.03 M thiocyanate has indicated the feasibility of using TEHDGA as extractant to separate Y from heavy rare earths, in particular Er, from thiocyanate medium.