Extraction HDEHP

The family of polyaminoacetic complexing agents, especially diethylene triaminopentaacetic acid (DTPA), helps to obtain this objective. Table V summarizes some separation factors obtained for systems all using DTPA in combination with the extractants HDEHP 03), TBP (2) and TLAHNO (2). 

The separation of transplutonium elements from the lanthanides constitutes the delicate phase of chemical treatment, owing to their comparable affinities for the usual extractants HDEHP, TBP and TLAHNO3. Among all the systems described in the literature and covered by a recently published critical compilation (JO), we selected those which appeared to be much suitable for adaptation to extraction chromatography the Talspeak process (7) and the... 

Table 2. Comparison of the extraction behavior of tracer einsteinium, fermium, and mendelevium after treatment with various reducing agents. The column-elution method of extraction chromatography was used with the extractant HDEHP adsorbed on a column bed of a fluoroplastic powder (20)...

A number of more recent reports have discussed applications, process experience, and modifications of TALSPEAK. Kosyakov and Yerin (1980) report that the Cm extraction from TALSPEAK-type aqueous solutions using HDEHP/decane solutions both extractant (HDEHP) and acid dependence are reduced to two, indicating the extraction of. a 1 1M-Iactate complex for the aliphatic diluent. Similar extractant dependencies were reported for Bk, Eu, and Ce. The extraction reaction is established as independent of [DTPA] (i.e., DTPA complexes are not extracted). 

The extent of extraction can be increased by a salting out effect. The selectivity of TBP is very poor compared with HDEHP and it is only useful for light rare-earth separation however, organic phase loadings or REO higher than 100 g/L can easily be achieved. There are a large number of TBP manufacturers in Japan, the United States, and Europe. 

Sediments Sample leached with HNO3/HF, filtered, purified by KL-HDEHP resin columns, solvent extracted, and electrodeposition a -Spectroscopy No data 95-99% Guogang et al. 1998... 

Lichen, moss Ashed, leached with HCI, Microthene-TNOA and KL-HDEHP column extractions, solvent extraction, electrodeposition a -Spectroscopy 0.9 fCi/g No data Jia et al. 1997... 

Several methods have been used to separate the lanthanides chemically solvent extraction, ion exchange chromatography, HPLC using Q-hydroxyisobutyric acid and, in limited cases, selective reduction of a particular metal cation.40-43 The use of di(2-ethylhexyl)orthophosphoric acid (HDEHP) for the separation of various rare-earth elements via solvent extraction has also been reported.44 16 This separation method is based on the strong tendency of Ln3+ ions to form complexes with various anions (i.e., Cl- or N03 ) and their wide range of affinities for com-plexation to dialkyl orthophosphoric acid. When the HDEHP is attached to a solid phase resin, the lanthanides can be selected with various concentrations of acid in order of size, with the smallest ion being the most highly retained. 

Lin [ 1 ] used coprecipitation with lead sulfate to separate 237-actinium from sea water samples. The 237-actinium was purified by extraction with HDEHP, and determined by alpha spectrometry via Si (Au) surface barrier detection. The method has a sensitivity of 10 3 pCig"1 of ashed sample. 

Dapex [Di-alkylphosphoric acid extraction] A process for the solvent extraction of uranium from sulfuric acid solutions using di-(2-ethylhexyl) phosphoric acid (HDEHP). The HDEHP is dissolved in kerosene containing 4 percent of tributyl phosphate. The uranium is stripped from the organic phase by aqueous sodium carbonate and precipitated as uranyl peroxide (yellow cake). The process was no longer in use in 1988. See also Amex. 

Liquid ion-exchangers have been discussed in the section on solvent extraction (p. 65). They can be used in column form by coating them on to a solid support such as cellulose powder or Kel-F (polytrifluorochloroethylene). Tris-n-octylamine (TNOA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) behave as strong-base and strong-acid exchangers for anions and cations respectively. 

Phosphates Florida H2SO4 leads to a phosphoric acid solution that contains 50-200 ppm of U Synergistic extraction of U(VI) by HDEHP-TOPO or extraction of U(1V) by diaUcylphosphoric acids mixtures Few % will vary with U price. The phosphate rocks are the second largest potential source of U after sea water... 

Various processes have been used for uranium extraction from phosphoric acid solution their main features are listed in Table 12.4. The HDEHP-TOPO process is increasingly preferred over others because of the stability of the extractant and the well-understood chemistry of the process. 

During development of the Truex process, various monofunctional organophosphorus reagents [e.g., TBP DBBP (dibutylbutylphosphonate) HDEHP (di-(2-ethylhexyl)phosphoric acid)] were considered for removal of alpha-emitters from HNO3 waste solutions. Two typical flow sheets for the use of HDEHP and TBP are shown in Fig. 12.14. Because of the poor performance of these two extractants, the processes were complicated. Distribution ratios... 

The use of HDEHP for extraction of actinides from waste solutions also has several drawbacks, including extraction of trivalent ions at a pH at which tetravalent ions such as Zr(IV) and Pu(IV) are hydrolyzed, and difficulties in stripping tetravalent and hexavalent actinides. All in all, monofunctional organophosphorus reagents are vastly inferior to their bifunctional counterparts for extracting Am(III) and other actinides from strong HNO3 media. 

As noted earlier (see section 12.3.1), the Amex process, which uses long-chain amines, is preferred over the Dapex process, which uses HDEHP, for solvent extraction of uranium from H2SO4 leach solutions. Because the surfactant properties of amine sulfates are conducive to formation of objectionable emulsions, the Amex process is very sensitive to the presence of solids in the H2SO4 leachate. For acceptable phase coalescence in the Amex process, feeds should contain no more than 20 ppm solids. The Dapex process can tolerate feeds containing as much as 100 ppm solids. 

Thus there is considerable incentive to find extractants that could tolerate higher quantities of solids in H2SO4 leach liquors. Stripping of uranium from the Amex process extractant and subsequent regeneration of the amine solvent also consume considerable quantities of acid and base. Recovery of uranium from H2SO4 solutions would be simplified if a convenient neutral extractant could be found. An extractant with better selectivity for vanadium and molybdenum than HDEHP and long-chain amines is also desirable. 

Diethyl fluorothiophosphate, 2 130 Di-2-ethyl hexyl phosphoric acid (HDEHP), in liquid-liquid extraction, 9 36, 38, 39, 40, 41, 59-63... 

However, a number of organophosphorus compounds are efficient extractants as they and their complexes are very soluble in organic solvents. The most important of these are monobasic diethylhexylphosphoric acid (HDEHP) and dibutylphosphoric acid (HDBP). The actinide MO + ions are very effectively extracted by these reagents as are the actinide (IV) ions. 

Figure 14 The extraction of UVI from H2S04 by HDEHP in kerosene.106 Curves are labelled by HDEHP concentration...

Figure 15 The effect of uranium concentration on uranium extraction from H2S04 by 0.1 M HDEHP in kerosene.106 The curves are labelled with U concentration (g dm-3)...

Figure 16 The extraction of uranyl nitrate (5gdm 3) from nitric acid by HDEHP in kerosene at 2(1 C.112 Curves are labelled with HDEHP concentration (M)...

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