The effective recovery of praseodymium from mixed rare earths via a hollow fiber supported liquid membrane and its mass transfer related

The recovery of praseodymium from mixed rare earths via a hollow fiber supported liquid membrane (HFSLM) was examined. Bis(2,4,4-trimethylpentyl) phosphinic acid – known as Cyanex 272 – was used as an extractant carrier. The stripping solution was hydrochloric acid solution. The experiments examined in functions of the concentrations of the carrier in liquid membrane, the (initial) pH's of initial feed solution within the acidic-pH range, the concentrations of hydrochloric acid, the flow rates of feed and stripping solution, and the operation mode of runs through the hollow fiber module. In addition, the influence of circulation of the stripping solution at various numbers of runs through the HFSLM on the outlet concentration of praseodymium ions in the stripping solution was observed.Mass transfer mechanism in the system was investigated. Extraction equilibrium constant (Kex), distribution ratio (D), permeability (P) and mass transfer coefficients were determined. The aqueous-phase mass-transfer coefficient (ki) and organic-phase mass-transfer coefficient (km) were reported to 0.0103 and 0.788 cm s−1, respectively, in which km is much higher than the ki. Thus it suggests the rate-controlling step is the diffusion of praseodymium ions through the film layer between the feed solution and the liquid membrane. Model prediction of the dimensionless concentrations and separation factors were also put on trial in this paper. The results showed promising agreement with the experimental data.

Figure optionsDownload as PowerPoint slideResearch highlights▶ Maximum percentage of praseodymium extraction at 91.7% from 10% (v/v) bis (2,4,4-trimethylpentyl) phosphinic acid as extractant carrier in multi cycle operation through single HFLSM module. ▶ Mass transfer mechanism of this system was investigated. ▶ The rate-controlling step of this system was the diffusion of praseodymium ions through the film layer between the feed solution and the liquid membrane. ▶ Model prediction of the dimensionless concentrations and separation factors showed promising agreement with the experimental data.