Lanthanide actinides, HDEHP extraction

In a modification of the TALSPEAK process known as the Reverse TALSPEAK process, trivalent actinides, and lanthanides together are extracted by 1 M HDEHP from the 0.1 M... 

Separation factors for trivalent lanthanide/actinide extraction by HDEHP/ toluene (Stary 1966) and HDEHP/kerosine (Sato 1989). 

A promising application of HDEHP extraction appears to lie in the partitioning of actinides from lanthanides. The TALSPEAK process (Trivalent Actinide Lanthanide Separation by Phosphorus Reagent Extraction from Aqueous Komplexes) involves extraction of Ln s with HDEHP from an aqueous solution of a complex (such as DTPA) which has a high affinity for and represses extraction of the middle and heavier lanthanons and actinide elements most of all . The separation factor between the An s, Am and Cm ", and the Ln s exceeds 100. 

A mixture of well-known extractants, di-(2-ethylhexyl)phosphoric acid (HDEHP) and CMPO, in n-paraffin was used for the study of combined extraction of different actinides (americium, plutonium, and uranium) and lanthanides (cerium and europium) and their separation from fission products (cesium, strontium, ruthenium, and zirconium).54 Combined extraction of MAs and lanthanides was studied together with group separation of MAs from lanthanides by selective stripping with a solution of diethylenetriaminepentaacetic acid (DTPA), formic acid, and hydrazine hydrate. This solution strips only MAs, leaving lanthanides in the organic phase. Subsequently, the lanthanides are stripped using a mixture of DTPA and sodium carbonate. 

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). 

An initial experiment involving the treatment of small irradiated Pu/Al targets for the production of americium 243 and curium 244 was carried out in France in 1968 (2). The chemical process was based essentially on the use of a system comparable to the Talspeak system. After plutonium extraction by a 0.08 M trilaurylammonium nitrate solution in dodecane containing 3 vol % 2-octanol, the actinides (americium, curium) were coextracted with a fraction of the lanthanides by a 0.25 M HDEHP -dodecane solvent from an aqueous solution previously neutralized by A1(N0 ) x(0H)x and adjusted to 0.04 M DTPA. The actinides were selectively stripped by placing the organic phase in contact with an aqueous solution of the composition 3 M LiN0 -0.05 M DTPA. While this experiment achieved the recovery of 150 mg of americium 243 and 15 mg of curium 244 with good yields, the process presented a drawback due to the slow extraction of Al(III) which saturates the HDEHP. This process was therefore abandoned. 

The acid dependency observed in practice hal been only approximately inverse third power. Impurities in Cleanex feed solutions often cause a departure from ideality (e.g., by common-ion effect or by consumption of some of the HDEHP), and we have not been able to control the extraction of the actinide elements solely by monitoring the aqueous-phase acidity. Fortunately, when processing transplutonium elements, the high specific activity of 21+I+Cm facilitates the detection of that isotope in both phases, thus permitting a rapid determination of the degree of extraction. The extraction coefficients of the trivalent actinides and lanthanides are all quite similar, so the 21+1+Cm serves as an excellent marker for all the extracted ions. 

Experimental studies were therefore directed to investigate the removal of actinides from both diluted (5000 l/t) and concentrated (about 500 l/t) HAW solutions. Three alternative processes have been selected for this purpose. They all rely upon actinide separation at low acidity conditions requiring a preliminary denitration step. Two of them (TBP and HDEHP processes) are based on solvent extraction techniques using as extractants a neutral (TBP) and an acidic (HDEHP) organophosphorus compound respectively. The third process (OXAL) applies as the first step the precipitation of actinides and lanthanides FP as oxalates. 

A procedure for the rapid separation of berkelium from other actinides, lanthanides, and fission products was developed in order to measure the decay properties of short-lived isotopes [54]. Bk and Ce were separated from other elements using solvent extraction with HDEHP followed by cation-exchange high-pressure liquid chromatography (HPLC) using a-hydroxyisobutyrate as the eluant. The elution curve, showing a clean separation of Bk from Ce, is shown in... 

---