Equilibrium extraction system

A countercurrent multistage extraction system is shown below, which is to be modelled as a cascade of equilibrium stages. 

EQMULTI - Continuous Equilibrium Multistage Extraction System... 

Temperature can have a considerable effect on both the extraction and stripping properties of a solvent extraction system relative to equilibrium, kinetics, and metal separations [5] (see Chapters 3-5). Therefore, it is advisable to investigate these effects, especially when the solvent tends to be viscous or high loadings of metal are to be obtained in the solvent (Fig. 7.5). 

A simplified equilibrium extraction model (Fig. 6) was presented by Dordick and colleagues [188] to explain the resolution behavior of glycoproteins in affinity based reverse micellar extraction and separation (ARMES). Their system for the study includes soybean peroxidase (SBP, MW 37 KDa, pi 4.1) and aj-acid glycoprotein (AGP, MW 43 KDa, pi 3.7) as glycoprotein solutes, concanavalin A (ConA) as the affinity ligand in AOT/isooctane RMs. The separation factor (a) for the separation of SBP from AGP can be given by... 

Conversely, it was shown that the composition of the polar core depends only on the polar heads of the malonamide and on the initial salt concentration in the aqueous phase in equilibrium. The extraction efficiencies of HN03 and H20 are independent of the diluent and extractant chain lengths (34). Diluent-extractant interactions and variations in the amphiphilic balance of the extractant thus do not influence the extraction equilibrium of HN03 and H20. Here again, this conclusion is consistent with published results for other extractant systems. 

Because of interference from the radioactive decay of other nuclides (which are typically formed with much higher yields), extraction systems with relatively high decontamination factors from actinides, Bi, and Po must be chosen, and the transactinide activity can only be measured in the selectively extracting organic phase. For this reason, measurement of distribution coefficients is somewhat difficult. By comparing the Rf or Db detection rate under a certain set of chemical conditions to the rate observed under chemical control conditions known to give near 100% yield, distribution coefficients between about 0.2 and 5 can be determined. If the control experiments are performed nearly concurrently, many systematic errors, such as gas-jet efficiency and experimenter technique, are cancelled out. Additionally, extraction systems which come to equilibrium in the 5-10 second phase contact time must be chosen. 

Calculations of multicomponent liquid-liquid equilibrium are needed in the design of liquid (solvent) extraction systems. Since these operations take place considerably below the bubble point, it is not necessary to consider the equilibrium-vapor phase. The equations to be solved are ... 

In these complicated extraction systems containing the polymeric and/or hydroxo species, one would expect the solvent used as a diluent to exert a considerable effect on the extraction equilibrium. In the extraction of gallium (III) with decanoic acid it has been found that the less polar the solvent, the more polymerized the extracted species (150). More recently, the solvent effect on the extraction (156) and dimerization (151, 153) of copper(II) decanoate has been interpreted according to regular solution theory (141,142). 

As stated earlier the polymeric species are often involved in the extraction of metal carboxylates. Therefore, the extraction equilibrium is sometimes more complicated than in the chelate extraction system. As is evident from the following treatment, it is advantageous and often indispensable to study the total metal concentration in the organic phase [Eq. (8)] instead of the conventionally utilized distribution ratio of the metal [Eq. (7)]. 

One would expect the organic phase of other amine extraction systems in which more than one metal anion can be formed to exhibit similar equilibria. It is fortunate that in this system not only is the solvent not present in the coordination sphere of either complex but also the equilibrium constant between the two is of an order of magnitude which allows concentration of both to be measured readily by spectrophoto-metric methods. This allows the effect of the dielectric constant of the solvent on the ratio of the species to be studied easily without the perturbing effect of specific interactions caused by differences in the tendency of the solvents to enter the coordination sphere. 

Calculations of the relations between the input and output amounts and compositions and the number of extraction stages are based on material balances and equilibrium relations. Knowledge of efficiencies and capacities of the equipment then is applied to find its actual size and configuration. Since extraction processes usually are performed under adiabatic and isothermal conditions, in this respect the design problem is simpler than for thermal separations where enthalpy balances also are involved. On the other hand, the design is complicated by the fact that extraction is feasible only of nonideal liquid mixtures. Consequently, the activity coefficient behaviors of two liquid phases must be taken into account or direct equilibrium data must be available. In countercurrent extraction, critical physical properties such as interfacial tension and viscosities can change dramatically through the extraction system. The variation in physical properties must be evaluated carefully. 

After an extraction system has been left for enough long time, equilibrium between the phases is reached and mass transfer from the donor to the acceptor has stopped. This is the natural end point for the extraction in many cases. In the majority of... 

In many cases, synergists are added to HTTA extraction systems to enhance the separation of actinide ions. One example is the addition of the crown ethers (CE) dibenzo-18-crown-6, dicyclo-hexyl-18-crown-6, dibenzyl 24-crown-8, and benzyl-15-crown-5. These crown ethers have been shown to synergistically enhance extraction into benzene and the increase follows Eu > 1102 " > Th". The extraction equilibrium for crown ether/HTTA systems for the separation of Th is shown in Equation (23). The binding of the crown ether in the extracted complex seems to be a function of crown ether basicity and steric effects2 ... 

In particular, when a solvent extraction system of uranyl nitrate, aqueous nitric acid, and tri-n-butyl phosphate (TBP) in a hydrocarbon diluent was irradiated with a CO2 laser, a change was observed in the equilibrium distribution of uranyl nitrate between the phases (14). When the solution was irradiated at 944 cm 1, close to the uranyl asymmetric stretching frequency, the effect was observed. When a nonresonant frequency was used or the energy was absorbed in the solvent, no effect was observed. Little heating could be expected, and, in any case, heating effects should have been in the opposite direction from that observed. 

Solvent Extraction Relationships. In a solvent extraction system, the two phases are immiscible, but under proper conditions phase-transfer of one or more species can occur across the organic/aqueous interface. Expansion of the interface by gentle agitation of the vessel containing the two phases allows phase equilibrium to be attained quickly, usually in 1 to 2 minutes. In such an extraction system, the distribution of a metal, M, between the two phases at equilibrium is described by a distribution coefficient, Dj, where [M] represents the concentration of the metal. 

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