Reagents and methods that have been developed during the past 20 years for hydrometallurgical partitioning of actinides from different types of transuranium (TRU) wastes and dissolved fuels are reviewed. Emphasis is placed on the extraction performance of the fully-optimized reagents rather than on the structural iterations that were undertaken (and in some cases are still being conducted) to identify the optimum species. Particular attention is paid to separation processes that have been demonstrated in batch and counter-current solvent extraction, and batch and column mode extraction chromatography. The salient features of the various techniques and reagents for actinide recycle are compared. Sections of the review focus on neptunium behavior in hydrometallurgy and on characterization of those reagents best suited to the separation of trivalent actinides from fission product lanthanides. Selected flowsheets that have been reported for the separation and recovery of actinides from TRU wastes are presented.

Actinide partitioning—a review

A generic transurantc (TRU) element extraction/recovery process was developed based on the use of octyl(phenyl)-N,N-diiso-butylcarbamoylmetliylphosphine oxide, 0φD(iB)CMPO, dissolved in PUREX process solvent (tribntyl phosphate, TBP, in normal paraffluic hydrocarbon, NPH). The process (called TRUEX) is capable of reducing the TRU concentration by many orders of magnitude In waste solutions containing a wide range of nitric acid, salt, and fission product concentrations. A major feature of the process is that it is readily adaptable for waste processing in existing fuel reprocessing facilities.

THE TRUEX PROCESS - A PROCESS FOR THE EXTRACTION OF THE TKANSURANIC ELEMENTS EROM NITRIC AC In WASTES UTILIZING MODIFIED PUREX SOLVENT*

Actinide partitioning is a proposed strategy for effective mitigation of the long-term hazards associated with high-level waste (HLW). Octyl-(phenyl)–N,N-diisobutyl carbamoyl methyl phosphine oxide (CMPO) and diphenyl–N,N-diisobutyl carbamoyl methyl phosphine oxide (DφCMPO) are amongst the promising extractants extensively studied since the 1980s for actinide partitioning from wastes of different origin. During the last two decades, substituted malonamide extractants such as N,N'-dimethyl-N,N'-dibutyl tetradecyl malonamide (DMDBTDMA) and N,N'-dimethyl-N,N'-dioctyl hexylethoxy malonamide (DMDOHEMA) have emerged as viable green alternatives to phosphine oxides. During the last decade, diglycolamide-based extractants such as N,N,N′,N′-tetraoctyl diglycolamide (TODGA) and N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (TEHDGA) have received considerable attention due to overwhelmingly favourable extraction and stripping efficiencies of minor actinides from different types of transuranium (TRU) wastes. The focus o...

Aqueous Partitioning of Minor Actinides by Different Processes

A number of neutral extractants containing the P(0)(CH2)nC(0)N raolety were evaluated for their ability to extract Am from nitric acid and their selectivity for Am over Fe and selected fission products. Extractants containing alkoxy, alkyl, and aryl substltuents were evaluated. Tetrachloroethylene was used as a diluent. Fission products selected for study were Y, Zr, Mo, Tc, Ru, Rh, Pd, La, Ce, Pr, Nd, Sra, and Eu. The conclusions drawn were that the most efficient and selective Am extractant contains a single carbon bridging group, one or two phenyl groups attached to the phosphorus atom and l9obutyl groups attached to the amide nitrogen.

EXTRACTION OF Am FROM NITRIC ACID BY CARBAMOYL-PHOSPHORYL EXTRACTANTS: THE INFLUENCE OF SUBSTITUENTS ON THE SELECTIVITY OF Am OVER Fe AND SELECTED FISSION PRODUCTS

N,N,N  ′,N  ′-Tetraoctyl-3-oxapentanediamide (TODGA) in n-dodecane solvent was studied to clarify the characteristics of third phase formation in extraction of lanthanides(III) and to modify the solvent. The loading capacity of the solvent was found to be dependent not only on the aqueous acidity and the temperature but also on molecular size of alkane solvent and kinds of aqueous anions. The loading capacity of 0.1 M TODGA-n-dodecane was 0.008 M Nd(III) with an aqueous phase of 3 M HNO3. Addition of N,N,-dihexyloctanamide (DHOA) of more than 0.5 M to the solvent eliminated the third phase in the extraction of Nd(III). The modified solvent of 0.1 M or 0.2 M TODGA with 1 M DHOA exhibited a satisfactorily high metal loading and slightly lower extractability for Nd(III) and moderately higher extraction of HNO3 than neat TODGA.

MODIFICATION OF TODGA- n -DODECANE SOLVENT WITH A MONOAMIDE FOR HIGH LOADING OF LANTHANIDES(III) AND ACTINIDES(III)

The mixed solvent extractants, dibutyl N,N-diethylcarba-moylmethylenephosphanate (DBDECMT)-tributyl phosphate (TBP), using carbon tetrachloride diluent, were studied for extracting americium (III) and plutonium (IV) from 0.35 and 7M HNO3 at 25°C. Synergistic effects were observed in this system as was the case with preliminary results (described herein) using the dihexyl analogue DHDECMP and TBP.

Extraction Behavior of Americium and Plutonium with Mixed Solvent Extractants

Solid supported liquid membranes(SLM) are useful in transferring and concentrating americium and plutonium from nitrate solutions. Specifically, DHDECMP (d ihexyl-N, N-diethylcarbamoyImethylphosphonate) supported on Accurel or Celgard polypropylene hollow fibers assembled in modular form transfers >95% of the americium and >70% of the plutonium from high nitrate (6.9 M), low acid (0.1 M) feeds into 0.25 M oxalic acid stripping solution. Membranes supporting TBP (tri-n-butylphosphate) also transfer these metal ions. Maximum permeabilities were observed to be 1 × 10−3 cm sec−1, similar to the values for other systems. The feed:strip volume ratio shows an inverse relationship to the fraction of metal ion transferred. Cation exchangers may be used to concentrate americium from the strip solution.

Supported Extractant Membranes for Americium and Plutonium Recovery

(1981). Removal of Solubilized Solvent Extractants from Aqueous Waste Streams. Journal of Nuclear Science and Technology: Vol. 18, No. 7, pp. 561-562.

Removal of Solubilized Solvent Extractants from Aqueous Waste Streams

The bifunctional organophosphorus compound DHDECMP (dihexyl-N, N-diethylcarbamoylmethylphosphonate) is effective in the extraction of hydrolytic plutonium (IV) polymer from both 0.04 and 7.0M nitric acid. Stripping the polymer- is difficult, even with hydrofluoric acid. However, 1.0M sodium carbonate is a very effective stripping agent. The extracted complex contains one to two molecules of DHDECMP per plutonium ion and the plutonium (IV) maintains a polymeric structure.

Solvent extraction of plutonium(IV) polymer by dihexyl-N, N-diethyl-carbamoylmethylphosphonate (DHDECMP)

Microreticular and macroreticular anion exchange resins were compared for their capability of recovering plutonium from nitric acid waste streams. Plutonium breakthrough capacity and elution behavior of the resins were determined as a function of resin properties. Small-bead microreticular resins with a polystyrene matrix containing 4% divinylbenzene cross-linkage showed the best performance. Of the 20- to 50-mesh resins, the macroreticular resin, Amberlite IRA-938, gave the highest plutonium breakthrough capacity and eluted plutonium the fastest.

James D. Navratil

Papers

Extraction Behavior of Americium and Plutonium with Mixed Solvent Extractants

Supported Extractant Membranes for Americium and Plutonium Recovery

Removal of Solubilized Solvent Extractants from Aqueous Waste Streams

Solvent extraction of plutonium(IV) polymer by dihexyl-N, N-diethyl-carbamoylmethylphosphonate (DHDECMP)

Comparison of anion exchange resins for recovering plutonium from nitric acid waste