Abstract
Bis(2-ethylhexyl)phosphoric acid (HDEHP) is frequently used as an extractant in the separation and recovery of lanthanides by solvent extraction and extraction chromatography, where HDEHP (stationary phase) is fixed on an inert support and the mobile phase is an aqueous solution. Because the results of extraction chromatography strongly depend on the support material, in this study, we aim to prepare solid extractants (extraction chromatography materials) with different inorganic supports impregnated with HDEHP for the adsorption of Gd and Tb from HCl solutions, putting emphasis on the effect of the supports on the solid extractant behavior. Gd and Tb partition data were determined in HCl solutions from the prepared extraction chromatography materials using elution analysis. Solid extractants were characterized by X-Ray diffraction, electron microscopy, and infrared spectroscopy in order to determine their properties and to explain their extraction behavior. The characterization of the solid extractants showed a heterogeneous distribution of the HDEHP on the surfaces of the different supports studied. The irregular shape of the support particles produces discontinuous and heterogenous silanization and HDEHP coatings on the support surface, affecting the retention performance of the solid extractant and the chromatographic resolution.
Highlights
Extraction chromatography combines the selectivity of liquid–liquid extraction with the multistage character of chromatography
HDEHP (2-ethylhexyl) phosphoric acid) from Fluka Biochemika was used as an extractant agent and six powdered materials were used as supports: Kieselguhr, alumina, fluorite, and three volcanic rocks from Mexico: tezontle, chiluca, and cantera
The HCl concentrations used as the mobile phase in the determination of the extraction capacity from the prepared solid extractants were selected from the Gd and Tb distribution coefficients from the prepared solid extractants were selected from the Gd and Tb distribution coefficients determined by our group (Figure 1, in triangles) and by Horwitz and Bloomquist (Figure 1 in squares) determined by our group (Figure 1, in triangles) and by Horwitz and Bloomquist (Figure 1 in squares) with the commercial resin Ln spec resin from Eichrom
Summary
Extraction chromatography combines the selectivity of liquid–liquid extraction with the multistage character of chromatography. In this method, the stationary phase is an organic liquid (extractant) fixed on an inert support, and an aqueous solution is used as the mobile phase. Many extractions and re-extractions occur during the extraction chromatography process [1,2]. In most of the methods of synthesis of the materials for extraction chromatography, which is used to remove and recover metals from aqueous solutions, the support (inorganic materials or porous polymeric) is in contact with a solution of extractant in a suitable solvent. The solvent is evaporated, leaving the pores of the support material filled with the extractant. The extraction mechanism is considered to be similar to conventional solvent extraction [2,3]
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