Effect of temperature on the selectivity of the extraction of lanthanides with dibutylphosphoric acid from thiocyanate solution

Extraction coefficients and separation factors of all lanthanides were determined in the system: dibutylphosphoric acid /HDBP/ - 3M NH₄NCS, in the temperature range of 15–50 °C. The values for the separation factors for such pairs as: Gd–Tb and Er–Tm, are higher than 4, those for the pair of Tb–Dy are higher than 3, and those for the La–Ce, Pm–Sm, Dy–Ho, Ho–Er and Tm–Yb pairs are higher than 2. The influence of temperature on the separation factors of light /La–Gd/ and heavy /Gd–Lu/ lanthanides is discussed and compared with that observed for the extraction from the nitric acid solutions. The results are also discussed in the light of the double-double effect and outer-, vs. inner-sphere complexation in the lanthanide series.