Abstract

Solvent extraction studies on Tb (III) from thiocyanate solutions were carried out using various extractants and
their mixtures in benzene. The systems involving 4,4,4-trifluoro-1-pheny-1,3-butadione (TPBD) as a synergist in
the extraction of terbium(III) using di-n-octyl sulphoxide (DOSO), Tri-n-octy1 phosphine oxide (TOPO),
triphenyl phosphine oxide (TPhPO), 2-thenoyltifluoroacetone (TTA) and their mixtures has been investigated in
benzene. At given extractant concentration (pH=3), the extraction of Tb (III) increases with thiocyanate
concentration. The slope of the plot log D (where D is distribution coefficient defined as the ratio of
concentration of metal in the organic phase to that present in the aqueous phase) against log [SCN-] is nearly 3
indicating the extraction of neutral species in to organic phase. Mixed species of the type Tb(TPBD)3.S and
Tb(TPBD)3.2S were obtained with mixtures of TPBD and DOSO/TOPO/TPhPO (where
S=DOSO/TOPO/TPhPO) may be responsible for the synergism , whereas species of the type Tb(TTA)2.SCN.2S
are obtained with mixtures of TTA and (DOSO/TOPO/TPhPO).