Abstract:

The hollow fiber dispersion liquid membrane technique was applied for the enrichment of rare earth using 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester(HEHEHP) as the extractant and HCl as the stripping agent. All experiments were conducted in the hollow fiber modules that were self-assembled with 20 microporous hydrophobic hollow fiber of polyvinylidene fluoride membrane(PVDF) lumens. The experiment parameters, e.g., HCl concentration, extractant concentration, initial pH in feed phase and rare earth ions concentration, and the volume ratio of the stripping dispersion phase to the feed solution, etc., were investigated. The stripping dispersion phase and the feed phase(50 mL each) were agitated continuously to provide a uniform concentration of metal ions and circulated by means of precise constant flow pumps through the shell side and lumen side of the module, respectively. A membrane pressure was applied in the lumen side to prevent the dispersion of the organic phase into the feed phase. The flow rates of both phases were maintained constant with the help of the constant-flow pump equipped with a precise flow controller. After the stable flows are achieved on both the shell side and the lumen side, aqueous samples are taken from the reservoir every ten minutes for analysis of concentrations of rare earth ions. The optimum extraction conditions of Yb³⁺ were obtained:the HCl concentration is 4.00 mol/L in the stripping dispersion phase, the concentration of HEHEHP is 0.25 mol/L, the volume ratio of the stripping dispersion phase to the feed solution is 10:40, the pH value in the feed phase is 2.80, and the initial concentration of Yb³⁺ is 0.025 mol/L. The optimum conditions obtained may contribute to the development of new methods for the extraction of heavy rare earth ions.

Key words: hollow fiber dispersion liquid membrane, rare earth, enrichment, ethylhexylphosphonic acid mono-(ethylhexyl) ester