Extractants third phase

As metal extraction into a diluent—extractant solution proceeds, there is sometimes a tendency for formation of two organic phases in equiHbrium with the aqueous phase. A third phase is highly undesirable and its formation can be prevented by adding to the organic phase a few percent of a modifier which is typically a higher alcohol or tri- -butyl phosphate (TBP) (7). 

For extraction of uranium from sulfate leach Hquors, alkyl phosphoric acids, alkyl phosphates, and secondary and tertiary alkyl amines are used in an inert diluent such as kerosene. The formation of a third phase is suppressed by addition of modifiers such as long-chain alcohols or neutral phosphate esters. Such compounds also increase the solubihty of the amine salt in the diluent and improve phase separation. 

The introduction of a third phase - the membrane phase - between the two conventional phases (i.e., the aqueous and the organic phases) helps in overcoming many of the problems of solvent extraction. The membrane phase is a thin film, immiscible with the aque-... 

The majority of the alkaloids we are searching for will convert to salts in the first extraction phase. The second and third extraction phases take place over a longer period of time. This will ensure that we will be able to extract as many alkaloids as possible from our material. The third phase can be reduced to 1-2 days but will not produce the best yields. Remember, these measurements are all crude estimates. 

The formation of a third phase during the extraction of a metal by solvent (extractant and diluent) cannot be tolerated in liquid-liquid extraction processes for obvious reasons. Elimination of a third phase is usually accomplished by the addition of a modifier to the solvent, or by increasing the temperature of the system. 

The amount of modifier required to prevent third phase formation can be determined in the following way. The aqueous and solvent phases are first contacted, and once the three phases have separated, the lower aqueous phase is drawn off and discarded. The modifier to be considered is then added from a burette in small increments to the two organic phases, and the mixture shaken after each addition. The amount of modifier required to produce a single organic phase is then used to calculate the amount required to be added to the solvent. Generally, about 2-5 vol% of modifier is needed, but more may be necessary if high concentrations of extractant are used in the solvent. Any effects of modifiers on the kinetics and equilibria of metal extraction and stripping can be determined by shakeout tests. 

The formulation of the three phases must be such that the liquid membrane extracts the solute from one of the phases and the third phase strips it from the membrane. Thus extraction and stripping take place in the same contactor, and the stripping phase is where the solute is accumulated, instead of the organic phase as in the case of conventional solvent extraction. This allows for a middle phase of small volume that, being thin, behaves like a membrane. 

The Modifiers. Additional chemicals are sometimes added to solvents to prevent a third phase formation. In the past, long chain alcohols or tri-n-butyl phosphate (TBP) have been used. Certain modifiers enhance the rate of extraction and the final equilibirum position. It is known for example, that tributylphosphate acts synerglstically with dialkyIphosphoric acids. 

Typically, a PK study is composed of three phases, namely the in-life phase, bioanalysis, and data analysis. The in-life phase includes administering the compound to animals or humans and collecting samples from an appropriate matrix of interest such as blood or urine at predetermined time intervals for bioanalysis. The bioanalytical phase involves analysis of a drug and/or its metabohte(s) concentration in blood, plasma, serum, or urine. This analysis typically involves sample extraction and detection of analytes via LC-MS/MS. The third phase is data analysis using noncompartmental or compartmental PK computational methods. 

Elucidation of the phenomenon of TPF by studies of extraction mechanism and structure of metal complexes in the liquid phase and the mesoscopic features of the third-phases formed. Finally, the method of eliminating TPF is to be pursued. 

Chiarizia, R. 2006. Mechanism and energetics of third phase formation in TBP solvent extraction of metal salts. IPNS Progress Report 2001-2006. In Celebration of the 25th Anniversary of IPNS. ANL-06/54. Argonne National Laboratory. 

Rao, P.R.V., Kolarik, Z. 1996. Areview of third phase formation in extraction of actinides by neutral organophosphorus extractants. Solvent Extr. Ion Exch. 14 (6) 955-993. 

Chiarizia, R., Thiyagarajan, P., Jensen, M.P. et al. 2003. Third phase formation in TBP solvent extraction systems as a result of interaction between reverse micelles. In Leaching and Solution Purification, Vol. 1. Proc. Hydrometallurgy 2003 5th Int. Conf. in Honor of Prof. I. Ritchie. Young, C. A. et al. Eds. The Minerals, Metals and Materials Society, Warrendale, PA, pp. 917-928. 

Chiarizia, R., Jensen, M.P., Rickert, P.G. et al. 2004. Extraction of zirconium nitrate by TBP in n-octanc Influence of cation type on third phase formation according to the sticky spheres model. Langmuir 20 (25) 10798-10808. 

Chiarizia, R., Briand, A. 2007. Third phase formation in the extraction of inorganic acids by TBP in n-octane. Solvent Extr. Ion Exch. 25 (3) 351-371. 

Berthon, L., Martinet, L., Testard, F., Madic, C., Zemb, T. 2007. Solvent penetration and sterical stabilization of reverse aggregates based on the DIAMEX process extracting molecules Consequences for the third phase formation. Solvent Extr. Ion Exch. 25 (5) 545-576. 

Erlinger, C.V. 1998. Towards a physical interpretation of third phase formation in liquid-liquid extraction. Application to the DIAMEX process for the treatment of high radioactive nuclear wastes. Thesis. University Paris XI, Paris. 

Lefrancois, L., Belnet, F., Noel, D., Tondre, C. 1999. An attempt to theoretically predict third-phase formation in the dimethyldibutyltetradecylmalonamide (DMDBTDMA)/ dodecane/water/nitric acid extraction system. Sep. Sci. Technol. 34 (5) 755-770. 

The term Third-Phase Formation in solvent extraction refers to a phenomenon in which the organic phase splits into two phases (126). One of the two phases is diluent rich, whereas the other is rich in extractant and also contains the metal solvate. Third-... 

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