Lanthanide Separation Using Rate-Controlled Solvent Extraction

Solvent extractions of many of the lanthanide ions in both single ion and mixed ion environments have been carried out. These cations were first complexed with an aqueous complexing agent and were extracted with DEHPA (di-2 ethylhexylphosphoric acid) in an organic phase (kerosene). The experiments were designed to measure the rates of extraction in the hope that separation factors might be enhanced under non-equilibrium conditions. The complexing agents tried include ethylenediaminetetraacetic acid (EDTA), tetraethylenepentamine (tetraen), nitrilotriacetic acid (NTA), and diethylenetriamine (dien). These represent a hexadentate, pentadentate, tetradentate, and tridentate agent respectively. EDTA was determined to give the best results for non-equilibrium solvent extraction. Mixed ion solvent extraction results yielded separation factors with little to no improvements over equilibrium solvent extractions in most cases. The rate of extraction decreased uniformly across the series. After numerous repetitions, the sole exception is the Er/Yb system. In this system, the non-equilibrium extraction was markedly better