Experimental planning for industrial separation of pure lutetium

Electrolytic reduction of Yb³⁺ at a Hg cathode to the somewhat unstable Yb²⁺ was performed in various aqueous media in an attempt to separate Yb³⁺ from Lu³⁺ by forming relatively insoluble YbSO₄. The effects of the aqueous medium, current, and pH on the formation of Yb²⁺ and YbSO₄ were examined. The best experimental conditions for the reduction of Yb³⁺ to Yb²⁺ and the formation of YbSO₄ were found to be: 0.20-M Yb³⁺, 0.40-M H_{2SO4, and 0.50-M (NH4)2SO4 in the aqueous phase, a direct current of 0.20-A, and a pH of 4.0-5.4(±0.3). Under these conditions, approximately 90-95% of the Yb³⁺ in solution was removed as YbSO4. Several experiments were conducted to determine suitable conditions for countercurrent solvent extraction for the separation of Lu³⁺ from a mixed lanthanide ore. A mixer-settler type counter-current solvent extraction process was used. The effects of settling time between the aqueous and organic phases, chemical equilibrium time between the lanthanides and the extractant mono-(2-ethylhexyl)2-ethylhexyl-phosphonate (IQ-801) in kerosene, the load concentration of the aqueous phase, and the equilibrium acidity of the aqueous phase were studied. The experimental results indicated that an adequate settling time was approximately 30 sec, and a mixing time of 2 min was sufficient to reach chemical equilibrium. Furthermore, the aqueous load concentration of 0.15-M Ln³⁺ in 1.4- M to 2.2-M HCl along with an organic phase of 0.45-M IQ-801 in kerosene was satisfactory for limiting emulsion formation while properly utilizing the extractant. The optimum equilibrium acidity range in the aqueous phase was found to be 1.4-M to 1.9-M HCl using a titration method and 1.6-M to 2.2-M HCl using inductively coupled plasma/mass spectrometry for analysis.}