Phosphoric acid lanthanides, effect

Di(2-ethylhexyl) phosphoric acid (HDEHP) is an extractant molecule used for An(III)/Ln(III) separation. Used in TALSPEAK-type processes in a mixture with TBP, or in the DIAMEX-SANEX process in a mixture with a malonamide (154-157), it has also been proposed, in a mixture with TBP, to remove strontium from PUREX acid waste solution in the Hanford B plant (158). Therefore, numerous studies have focussed on the radiolytic degradation of HDEHP and its effects on the extraction of Sr(II), lanthanides(III), and actinides(III) (10, 158-163). 

Tachimori, S., Kroos, B., Nakamura, H. 1978. Effect of radiolysis products of di-(2ethylhexyl)phosphoric acid upon the extraction of lanthanides. J. Radioanal. Chem. 43 53-63. 

Another possibility is to take advantage of the effect of various supporting electrolytes (in a wide sense) that act as luminescence enhancers, as discussed in sect. 3.3, such as phosphoric acid. This method has been investigated in details both for lanthanides and actinides... 

It should be remarked here, that the tetrad effect is really not a new one" (our italics), and can be traced back to Endres (48) who divided the whole of the lanthanide series into four subdivisions, very much similar to those in the modern tetrad series. The paper of Fidelis and Siekierski (46) prompted Rowlands (49) to review the regularities . He plotted some 21 plots for 15 ligands and observed that the regularity proposed was based on insufficient data and this leaves doubt as to its general validity . Although the phosphoric acid systems exhibit the regularity, the same correlation could not be obtained for several other ligands. 

Preconcentration by an acidic organophosphorus extractant is also effective, though the lanthanides are extracted from dilute acid solutions (10 -10 M) and stripped into acidic (>1M) solutions when HDEHP is employed as the extractant. A representative application of liquid-liquid extraction to rare-earth preconcentration is the 100 to 200-fold concentration of the rare earths in seawater prior to ICP/MS determination using a mixture of HDEHP and mono-(2-ethylhexyl)phosphoric acids (Shabani et al. 1990, Shabani and Masuda 1991). When the same extractant system was adsorbed on a Cig cartridge and used in an extraction chromatographic mode, the rare earths were concentrated 200-1000-fold (Shabani et al. 1992). 

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