Neutral organophosphorus compounds

The chemistry of the extraction of UO + by mixtures of organophosphoric acids and neutral organophosphorus compounds has been the subject of many studies, and the available information has been widely discussed.75 118 127 131 134 There is no general agreement on the mechanism of the synergistic effect, although an addition process such as... 

In contrast to the chemistry of extraction of uranium(VI) by organophosphorus acids, that of uranium(IV) has not been widely studied. It is known,135 however, that the extraction of U4+ by mono(2-ethylhexyl)phosphoric acid (2-ethylhexyl dihydrogen phosphate), for example, exceeds that of U022+ by a factor of 105. This clearly provides the basis for the strong extraction of uranium(IV) from phosphoric acid solutions by extractants containing monoalkyl phosphates. The existence of a synergistic effect in the extraction of uranium(IV) by mixtures of mono(2-ethylhexyl)phosphoric acid and neutral organophosphorus compounds was also reported recently.136... 

Modolo, G., Odoj, R. 1999. Synergistic selective extraction of actinides(IH) over lanthanides from nitric acid using new aromatic diorganyldithiophosphinic acids and neutral organophosphorus compounds. Solvent Extr. Ion Exch. 17 (1) 33-53. 

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 ... 

Blake, C.A. Jr. Baes, C.F. Jr. Brown, K.B. Coleman, C.F. White, J.C. Solvent extraction of uranium and other metals by acidic and neutral organophosphorus compounds, In Peaceful Uses of Atomic Energy. Vol. 28, Basic Chemistry in Nuclear Energy, United Nations, Geneva (1958), pp. 289-298. 

Diphcnyl-/V,/V-di obutylcarbamoylmcthylphosphinc oxide (Ph2-CMPO, Figure 3.3), a bidentate neutral organophosphorus compound (BNOPC) derived from the TRUEX process, which proved to be efficient for the removal of actinides and REEs. 

FIGURE 3.6 Bidentate neutral organophosphorus compounds (BNOPCs) diphosphine dioxides. 

The extraction ability of neutral organophosphorus compounds closely related to the charge density of phosphoryl oxygen (qo) and phosphorus atom(qp). It was found that the distribution ratio of cerium enhanced as the qo and qp values was increased. Meanwhile a linear free energy relationship exists between the 2A.i values and the Kabachnik constant for substituents of phosphorus compounds. As estimated by least squares method, an empirical equation v° =-3.84+0.1682Ai was deduced... 

It is generally agreed that the extracted uranium species is U02(N03)2(TBP)2 in which, in contrast to the species extracted into ether, the extractant molecules are directly coordinated to the metal ion. The extraction of uranium(VI) by neutral organophosphorus compounds increases with the number of C—P bonds (as opposed to C—0—P bonds) and with the increased branching of the substituent alkyl groups, as would be expected from the effect of these changes on the electron-donor properties of the phosphoryl group. The extracted thorium(IV) complex has been formulated as Th(N03)4-2S and as Th(N03)4-3S,2 2 and its composition may depend to some extent on the conditions of extraction. The extraction of thorium (like that of... 

The alkyl phosphoric acids were first recognized as excellent actinide extractants because dibutyl phosphoric acid existed as an impurity in TBP (8). They extract well from unsalted solutions and from systems such as sulfate in which TBP is ineffective. Organo-phosphorus acids are thus suitable for uranium hydr metallurgical applications where ore is leached with sulfuric acid. The Dapex process is an example in which bis(2-ethylhexyl) phosphoric acid (HDEHP) is used alone or in synergistic combination with neutral organophosphorus compounds for uranium and vanadium recovery (9,10). 

Solvent Extraction of Transplutonium Elements from Acid Solutions by Polydentate Neutral Organophosphorus Compounds and from Alkaline Solutions by Quarternary Ammonium Bases and by Alkylpyrocatechols... 

The purpose of the present work consists in the investigation of polydentate neutral organophosphorus compounds as extractants for isolation and concentration of TPE from acid solutions and quaternary ammonium bases and alkylpyrocatechols for isolation and separation of TPE and rare earth elements from alkaline solutions. 

It is well-known that certain bidentate neutral organophosphorus compounds are far better extractants than their monodentate analogues (1, ). 

Bidentate neutral organophosphorus compounds were synthesized in the laboratory of organophosphorus compounds, USSR Academy of Sciences as described in ( -11), the tri- and tetradentate compounds as described in (11). The reagents were dissolved in chloroform or cTTchloroethane. 

In liquid-liquid extraction by solvation, the solvent itself takes part in complexation of the metal ion. This is brought about by donation of electrons by the donor atom present in the solvent molecule to the coordination sphere of the metal ion. Such an association of the solvent molecules with the metal ion results in the formation of a solvated complex that is extractable in the solvent. Thus, for example, octanol, Cg H17-OH, extracts Co2+ in the presence of perchlorate ion as [Co (C8 H17-OH)] (C104)2. Extraction by solvation generally employs oxygenated solvents such as alcohols, ethers or ketones or neutral organophosphorus compounds. These solvents stand the competition from water for solvation of the metal ion successfully because of the higher availability of electrons from their donor atoms. 

As extractants of polyvalent metal ions from acidic solutions, these reagents have one additional limitation they are also moderately efficient extractants for mineral acids. As the neutral organophosphorus compound extracts the free acid, the free-extractant concentration in the counter-phase is reduced, and metal-ion extraction efficiency suffers. To overcome this limitation, considerable effort has been expended in recent years to evaluate the ability of carbamoylphosphonates (CPs,(RO)2 PO(CO)N(R )2), carbamoylmethyl phosphonates (CMPs (RO)2POCH2(CO)N(R )2), and carbamoylmethylphosphine oxides (CMPOs, R2POCH2(CO)N(R )2) to extract lanthanide and actinide metal ions. These extractants are referred to collectively as bifunctional extractants. The first report of these ligands were made by Siddall (1963,1964). 

MINERAL ACIDS EXTRACTION BY SOLID POLYMERIC EXTRACTANTS TVEX CONTAINING NEUTRAL ORGANOPHOSPHORUS COMPOUNDS (TBP, DIOMP)... 

---