Synergistic extraction kinetics

From the fundamental knowledge concerning the interfacial complexation mechanism obtained from the kinetic studies on chelate extraction, ion-association extraction, and synergistic extraction, one can design the interfacial catalysis. The main strategy is to raise the concentration of the reactant or intermediate at the interface. 

A combination of known extractants can increase the net extraction both in degree and kinetics through synergistic extraction. This subject also is poorly explored, though it is of considerable importance to industrial solvent extraction processes. 

This chapter will review the recent developments of ILs in REEs separation, with a special emphasis on Bif-ILEs and IL-functionalized separation materials from our group. Besides the preparation of Bif-ILEs, we will discuss the extraction mechanisms and kinetics of Bif-ILEs, and the synergistic extraction from Bif-ILEs thus reveals highly efficient and environmentally friendly potential in REEs separation. In order to provide a supplement to liquid-liquid extraction, various IL-functionalized materials, demonstrating improved extraction efficiency toward REEs, are also commended. 

These equations do not provide complete definition of the reactions that may be of significance in particular solvent extraction systems. For example, HTTA can exist as a keto, an enol, and a keto-hydrate species. The metal combines with the enol form, which usually is the dominant one in organic solvents (e.g., K = [HTTA]en i/[HTTA]]jet = 6 in wet benzene). The kinetics of the keto -> enol reaction are not fast although it seems to be catalyzed by the presence of a reagent such as TBP or TOPO. Such reagents react with the enol form in drier solvents but cannot compete with water in wetter ones. HTTA TBP and TBP H2O species also are present in these synergistic systems. However, if extraction into only one solvent (e.g., benzene) is considered, these effects are constant and need not be considered in a simple analysis. 

The dynamic self-assembly processes of such supramolecular systems undergoing continous reversible exchange between different self-organized entities in solution may in principle be connected to kinetically controled sol-gel process in order to extract and select an amplified supramolecular device under a specific set of experimental conditions. Such dynamic marriage between supramolecular self-assembly and in sol-gel polymerization processes which synergistically might communicate leads to constitutionnal hybrid materials. ... 

Dynamic self-assembly of supramolecular systems prepared under thermodynamic control may in principle be connected to a kinetically controlled sol-gel process in order to extract and select the interpenetrated hybrid networks. Such dynamic convergence between supramolecular self-assembly and inorganic sol— gel processes, which synergistically communicate, leads to higher self-organized hybrid materials with increased micrometric scales. 

In the case of separation of Ni ions, 8-hydroxyquinoline and the industrial extractant Kelex 100 were used in water/SDS/butanol or pentanol/dodecane microemulsions. The kinetic and mechanistic formalisms in the extraction process were worked out by Tondre and coworkers [144,147]. To understand the coupled transport, crown ether or Kelex 100 were used by Derouiche and Tondre [143]. In several instances of metal ion transport, synergistic effects were observed the results were explained on the basis of carrier diffusion in the stagnant layers. 

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