Extraction bidentate

The selectivity of extractive separations of metal ions M" is commonly described by the separation factor (SF), defined as the ratio of the distribution ratios, [Eq. (4.3)], of the ions in the same system. In the case of two metal ions A" and Z" extracted from the same aqueous solution by an acidic bidentate extractant HE, with no synergist in the system, one obtains ... 

B). However, most selective stripping of Ans is undertaken by using complexants under conditions of low acidity or pH region where the bidentate extractants lose their affinity toward Lns. Therefore, other methods were contrived as alternatives. 

Recovery of actinides at the RFP with an organic phosphorous bidentate extractant has been proposed. A conceptual production flow sheet is shown in Figure 3. The bidentate reagent, dihexyl-N, N-diethylcarbamoylmethylenephosphonate (DHDECMP), is especially attractive since it can recover actinides from MSE residues containing aluminum. The cation exchange process is unable to effect actinide purification when aluminum is present. (DHDECMP extracts actinides and lanthanides, but does not extract common RFP contaminants, e.g., aluminum. No lanthanides are used in process streams at RFP.)... 

Bidentate phosphate compounds. The organophosphorus bidentate extractants are neutral species extractants that undergo no keto-enolization and have no exchangeable hydrogens (as is the case in extraction by the bidentate diketones). They contain either two P=0 groups or one P=0 and one C=0 group. The carbamoylmethyl-phosphonates (CMPs) and carbamoylphosphonates (CPs) are examples of the latter, while the tetraalkyldiphosphonates and tetraalkyl-diphosphinedioxides [or bis-(disubstituted phosphinyl)-alkanes] are examples of the former. 

Upon entry into the WTF, the HLLW is contacted (see Figure l) with the bidentate extractant dihexyl-N,N-diethylcarbamylmethylene phosphonate (CMP) which is diluted to 30 vol with di-isopropyl-benzene. Under high acid conditions (l3.,l ), this extractant will remove all trivalent and tetravalent actinides to some degree from the HLLW. Of the fission products, only Zr, Tc, Ru, Mo, Nb, Y, and Pd extract to any significant extent. These species can be controlled either by subsequent scrubbing of the organic phase or by adjusting extraction conditions so as to reject those fission products that exist as anions to the raffinate. 

Siddall investigated the ability of these compounds to extract Am(III), Ce(III), Pm(III), and HN03 from 0.1 to 12M HN03 solutions. His favorable results led him to suggest such bidentate extractants could be used to remove trivalent actinides from high-level TBP extraction process waste. This idea was later patented (5). Schulz demonstrated in 1973 that DHDECMP was an effective extractant for americium and plutonium from radioactive Hanford generated wastes (6). 

Two techniques appear to be useful for the bidentate extraction of actinides. The first is liquid-liquid solvent extraction, a method which has several advantages. Currently, however, the type of equipment needed (mixer-settlers, centrifugal contactors, etc.) is not available at RFP. We are better equipped to use a column technique. This can be done by sorbing the bidentate extractant on an inert solid support, loading ion exchange columns with the sorbent, and proceeding with column runs (extraction chromatography). 

Since TBP leaves Am(iii) behind in an addic raffinate, an effective extractant is needed to remove Am(iii) from such media. Siddall found that bidentate extractants have this desirable property [44]. Schulz [45] and Mclsaac [46] at the Hanford and Idaho Falls sites, respectively, have recently revived interest in plant-scale application of neutral bidentate organophosphorus extractants, particularly dihexyl-iV,iV-diethylcarbamoyl methylenephosphonate (DHDECMP) and dibutyl-iV,iV-diethylcarbamoyl methylenephosphonate (DBDECMP). The binding of actinide ions to DHDECMP has not been eluddated fully. Horwitz [335] states that in perchloric add the extractant is... 

The chain-growth catalyst is prepared by dissolving two moles of nickel chloride per mole of bidentate ligand (BDL) (diphenylphosphinobenzoic acid in 1,4-butanediol). The mixture is pressurized with ethylene to 8.8 MPa (87 atm) at 40°C. Boron hydride, probably in the form of sodium borohydride, is added at a molar ratio of two borohydrides per one atom of nickel. The nickel concentration is 0.001—0.005%. The 1,4-butanediol is used to solvent-extract the nickel catalyst after the reaction. 

The soft S2 donor sets presented by these bidentate ligands lead to very strong binding of heavy metals (Table 7) which are not stripped by sulfuric acid, ensuring that these deleterious elements do not transfer to the Zn electrolyte.196 However, co-extraction of copper is accompanied by reduction to Cu1 which has proved very difficult to strip to regenerate the reagent and will lead to poisoning of the extractant unless all traces of copper are removed from the feed solution. 

The reaction to form the palladium complex is similar to that reported for amine salts, although here, because a bidentate chelating ligand is used, no chlorine atoms are retained in the complex, and the system is easy to strip. Also, as both reactions involve initial ion pair extraction, fast kinetics are observed with 3-5 min contact time to reach equilibrium at ambient temperature. The extraction conditions can be easily adjusted in terms of acidity to suit any relative metal concentrations and, because the reagent is used in the protonated form, good selectivity over base metals, such as iron and copper,... 

Schulz, W. W. Navratil, J. D. Solvent extraction with neutral bidentate organic phosphorus reagents. In Recent Developments in Separation Science, Li, N. N. Ed. CRC Press Boca Raton, Florida, 1982 Vol. VII, pp. 31-72. Myaesoedov, B. F. Chmutova, M. K. New methods of transplutonium elements isolation, purification and separation. In Separation of f Elements, Nash, K. L. Choppin, G. R. Eds. Plenum Press New York, 1995 p. 11. 

DSM370 has patented platinum systems based upon tetrasulfonated bidentate water soluble ligand 29 (Table 2 x=4, m=0, n=0) as catalysts for the hydroformylation of a mixture 1-butene (45%) and 2-butene (22%) with 33% butane at 100°C and 80 bar CO/H2 in an aqueous/methanol (300/32), CF3SO3H acidic medium. The olefin conversion was 86% and the selectivity to the aldehydes 95% (n/i ratio of 2.8) together with small amounts of aldolcondensation products and acids. The products were isolated from the aqueous catalyst mixture leaving the reaction zone by extraction with ether and the aqueous phase recycled to the reactor. 

The action of H202 on acidic dichromate solutions gives an unstable blue species which can be extracted into ether (equation 128).2,518,1428 On the addition of pyridine the blue compound Crvl0(02)2py crystallizes. The molecules are distorted pentagonal pyramids with sideways-bonded peroxo groups (298) 1429 some workers with less refined data have reported rather different bond distances.1430 In water the blue species is considered to be CrO(62)2(OH2), in ether it is Cr0(02)20Et2, and amines such as aniline, bipy and phen can replace the pyridine. With bidentate bipy the coordination sphere becomes essentially a pentagonal bipyramid (299),... 

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