Trivalent actinides extraction

In a polar solvent in which the dialkylphosphoric acid is primarily a monomer, trivalent actinide extraction has been described as (59) ... 

The dialkylphosphoric acid most commonly used and studied for trivalent actinide extraction is probably HDEHP. Even though this compound is not as strong an extractant as some other straight-chain analogs, it offers advantages such as low aqueous-phase solubility, less tendency to third-phase formation, and ready availability. 

Extensive investigations by Chmutova and co-workers of l-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) indicate that the synergistic enhancement for TBP and TOPO adducts (in benzene) of the trivalent actinides (extracted from nitric acid) increases in the order Am < Cm < Bk < Cf (Chmutova et al. 1973). On the other hand. 

Solvent extraction in the separation of rare earths and trivalent actinides. B. Weaver, Ion Exch. Solvent Extr., 1974, 6,190-277 (538). 

In an investigation of the extraction of trivalent actinides, An(III) from 0.01 M nitric acid solutions of various LiNOj concentrations into o-xylene containing the tertiary amine salt trilaurylmethylammonium nitrate, TLMA HNOj, Van Ooyen [29] found that the amine was monomeric only at very low concentrations (<0.1M in the organic phase) but at higher concentration formed both dimers and trimers. 

The many laboratories involved in this work allowed a large experimental program to be set up to test the behavior of these soft donor extractants in countercurrent separations. The trivalent actinide-lanthanide separation process was named SANEX and four chemical systems have been explored (Fig. 12.20) ... 

SANEX 3 used the 2,6-Z) -(5,6-dialkyl-1,2,4-triazine-3-yl)pyridine family of extraetants eontaining the propyl group, whieh are able to selectively extract trivalent actinides from Imoldm EINO3 [53,78]. The extractant was 0.04mol dm in a mixture of 70%/30% TPH/octanol. A flow sheet based on this solvent has been tried and is shown schematically in Fig. 12.21 the results are given in Table 12.13. The feed was an... 

Byers, P. 1998. Novel extraction reagents for the solvent extraction of lanthanides and trivalent actinides. Ph.D. Thesis. University of Reading. 

Modolo, G., Vijgen, H., Serrano-Purroy, D. et al. 2007. DIAMEX counter-current extraction process for recovery of trivalent actinides from simulated high active concentrate. Sep. Sci. Technol. 42 (3) 439-452. 

Jarvinen, G., Barrans, R., Schroeder, N. et al. 1994. Selective extraction of trivalent actinides from lanthanides with dithiophosphinic acids and tributylphosphate. American Chemical Society, San Diego, CA, March. LA-lJR-94-4350. 

Modolo, G., Odoj, R. 1998. Influence of the purity and irradiation stability of Cyanex 301 on the separation of trivalent actinides from lanthanides by solvent extraction. J. Radioanal. Nucl. Chem. 228 (1-2) 83-89. 

Recently, another class of neutral organophosphorus compounds, namely, N,N-dialkyl carbamoyl methyl phosphonate (CMP) (59) and its phosphine oxide analog (CMPO) have received attention due to their ability to extract even trivalent actinides from acidic solutions along with the hexa- and tetravalent actinide ions. These biden-tate phosphorus-based neutral extractants are reported to be stronger extractants as compared to TOPO (59-62). Pu(IV) and U(VI) are extracted as per the following extraction equilibria ... 

Yong-Jun, Z. Extraction of trivalent actinides with phosphine oxides, In Handbook on the Physics and Chemistry of Actinides, AJ. Freeman and C. Keller (Eds.), Elsevier Science, Amsterdam, North Holland (1985), p. 482. 

This review will exclusively deal with studies related to solvent-extraction processes (neither solid-phase precipitation nor ion-exchange chromatography) aiming at separating trivalent actinides from PUREX raffinates or spent-fuel dissolution... 

The SETFICS process (Solvent Extraction for Trivalent /-elements Intragroup Separation in CMPO-Complexant System) was initially proposed by research teams of the former Japan Nuclear Cycle Development Institute (JNC, today JAEA) to separate An(III) from PUREX raffinates. It uses a TRUEX solvent (composed of CMPO and TBP, respectively dissolved at 0.2 and 1.2 M in -dodecane) to coextract trivalent actinides and lanthanides, and a sodium nitrate concentrated solution (4 M NaN03) containing DTPA (0.05 M) to selectively strip the TPEs at pH 2 and keep the Ln(III) extracted by the TRUEX solvent (239). However, the DFs for heavy Ln(III) are rather poor. An optimized version of the SETFICS process has recently been proposed as an alternative process to extraction chromatography for the recovery of Am(III) and Cm(III) in the New Extraction System for TRU Recovery (NEXT) process. NEXT basically consists of a front-end crystallization of uranium, a simplified PUREX process using TBP for the recovery of U, Np, and Pu, and a back-end Am(III) + Cm(III) recovery step (240, 241). 

As in the SETFICS and TALSPEAK processes, the DIAMEX-SANEX/HDEHP process involves selectively back-extracting the trivalent actinides by a hydrophilic polyamino-carboxylate complexing agent, HEDTA, in a citric acid buffered solution (pH 3). However, the combination of HDEHP and DMDOHEMA at high acidity promotes the coextraction of some block transition metals, such as Pd(II), Fe(III), Zr(IV), and Mo(VI), which must be dealt with by specific stripping steps (as described on Figure 3.26) that increase the total volume of the output streams ... 

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