Metal ions transfer

In practice, thermodynamic data are obtained from the metal-ion transfer reactions ... 

Fig. 4-16. Energy levels of metal ion and electron in an ionic electrode of metal ion transfer 4Cjn i = sublimation energy of solid metal /m" = ionization energy of gaseous metal atoms > >s = outer potential of electrolyte solution E s electrode potential (absolute electrode potential).

For a metal electrode at which a metal ion transfer reaction Mf = Mfi, is in equilibrium, as shown in Fig. 4-19, the metal ion level aM (M/s/v) in the electrode equals the hydrated metal ion level aM-(s/v) in the aqueous solution and the energy for the metal ion transfer across the electrode/solution interface equals zero (ciii-(M ) = 0). As shown in Fig. 4-20, then, we obtain Eqn. 4-22 ... 

The electrode potential, i, in the equilibrium of metal ion transfer is thus derived from Eqns. 4-14 and 4-23 to obtain Eqn. 4-24 ... 

Fig, 4-19. Ionic electrode in equilibrium of metal ion transfer M = metal ion to transfer Pm" = electrochemical potential of metal ions. 

Fig. 4-20. Reaction cycle and energy levels of metal ion and electron in equilibrium of metal ion transfer. = equilibrium electrode poten-...

It, thus, follows that the electrode potential in equilibrium of metal ion transfer is given by the free enthalpy for the formation of a solid metal from both hydrated metal ions and standard gaseous electrons as shown in Eqn. 4—25 ... 

Fermi level to or hypothetical Fermi level of the metal ion transfer equilibrium i.e. the Fermi level of hypothetical electrons equivalent to the metal ion level in the ion transfer equilibrium. 

Fig. 6-6. Electrochemical cell composed of an electrode of metal ion transfer and a normal hydrogen electrode = metal ion in metal-...

In electrochemistry, the chemical potential of hydrated ions has been determined from the equilibrium potential of ion transfer reactions referred to the normal hydrogen electrode. For the reaction of metal ion transfer (metal dissolution-deposition reaction) of Eqns. 6-16 and 6-17, the standard equilibriiun potential Sive in terms of the standard chemical potential, li, by Eqn. 

Similarly, for metal ion transfer reactions, the cathodic and anodic reactions are expressed by Eqn. 7-3 and Eqn. 7-4, respectively ... 

From the flow of electric charge it follows that the cathodic transfer of metal ions requires the electrode to accept electrons from an external cell circuit, and that the anodic transfer of metal ions requires the electrode to donate electrons to an external cell circuit. No electron transfer, however, takes place across the electrode interface this is the reason why no electrons are involves in the metal ion transfer reactions in Eqns. 7-3 and 7-4. 

Fig. 9-3. Polarization curves estimated for a simple electrode reaction of metallic ion transfer i = reaction current to - exchange reaction current in reaction equilibrium = symmetric factor (0 < 3 < 1).

For some metals the transfer of metallic ions involves a reaction intermediate of an adsorbed metallic ion complex which is coordinated with anionic ligands hence, the overall reaction occurs in a series of two elementaiy steps rather than one. Such a multistep transfer of ions can result, in the course of metallic ion transfer, from the reduction of the activation energy for ion transfer due to the formation of adsorbed intermediates. We examine a transfer reaction of divalent metallic ions via an adsorbed complex ion according to the steps in Eqn. 9-13 ... 

Thus, in the stationary state, the rate of anodic transfer of metal ions across the metal/film interface equals the rate of anodic transfer of metal ions across the film/solution interface this rate of metal ion transfer represents the dissolution rate of the passive film. The thickness of the passive film at constant potential remains generally constant with time in the stationary state of dissolution, although the thickness of the film depends on the electrode potential and also on the dissolution current of the passive film. 

The E/Z stereoselection can be rationalized by assuming metal-centered pericyclic chairlike transition states 1 13,10 , 12 and 13. In this model proton transfer and metal ion transfer are assumed to occur simultaneously. When R is a bulky group, the nonbonded steric interaction between this group and the methyl group becomes strong and the Z-enolate will be the predominating isomer under kinetic control. 

The effect of halide, cyanate, cyanide, and thiocyanate ions on the partitioning of Hg in [BMIM][PF6]/aqueous systems (Figure 3.3-2) has been studied [8]. The results indicate that the metal ion transfer to the IL phase depends on the relative hydrophobicity of the metal complex. Hg-I complexes have the highest formation constants, decreasing to those of Hg-F [42]. Results from pseudohalides, however, suggest a more complex partitioning mechanism, since Hg-CN complexes have even higher formation constants [42], but display the lowest distribution ratios. 

Luo et al.90 have described yet another approach to reducing the impact of ion exchange in metal ion extraction by neutral extractants in ILs, one which relies on modifying neither the structure of the IL nor the properties of the extractant. Instead, a sacrificial species that transfers in preference to the IL cation upon metal ion extraction (thereby reducing loss of the IL) is added to the IL phase. Ideally, the sacrificial species should exhibit no affinity for the extractant (in order not to interfere with extraction of the metal ion of interest) and be more hydrophilic than the IL cation (in order to favor its loss to the aqueous phase upon metal ion transfer). Tests with sodium tetraphenylborate indicate that its addition to a solution of a calix-crown ether in [C4mim+][Tf2N ] reduces the loss of the IL induced by cesium extraction by nearly one-quarter with no adverse effect on the efficiency of cesium extraction. 

It is apparent from the foregoing discussion that both ILs and supercritical carbon dioxide do indeed offer promise as alternative solvents in the reprocessing of spent nuclear fuel and the treatment of nuclear wastes. It is equally apparent, however, that considerable additional work lies ahead before this promise can be fully realized. Of particular importance in this context is the need for an improved understanding of the fundamental aspects of metal ion transfer into ILs, for a thorough evaluation of the desirability of extractant functionalization of ILs, and for the development of new methods for both the recovery of extracted ions (e.g., uranium) and the recycling of extractants in supercritical C02-based systems. Only after such issues have been addressed might these unique solvents reasonably be expected to provide the basis of improved approaches to An or FP separations. 

Dietz, M. L. Fundamental aspects of metal ion transfer into ionic liquids Implications for the design of ionic liquid-based solvent extraction systems. In Proceedings of the DAE-BRNS Biennial Symposium on Emerging Trends in Separation Science and Technology, SESTEC, Delhi, India, 2008, pp. 5-11. 

The rate of metal ion transfer from the oxide electrode to the electrolyte can be enhanced by complexing substances in the solution which can adsorb at active sites and weaken the M-0 bonds. However, it is known that certain organic complexing ions can slow down the rate of dissolution by adsorbing and blocking active sites at the surface [37],... 

Based on the wealth of both in vivo and in vitro biochemical experiments described in Section II, A, a diffusion-driven or bucket brigade mechanism of metal ion transfer between MXCXXC-motifs on the copper chaperone proteins and their target domains was predicted (Pufahl et al.. 

This quantity is independent of the surface profile and directly connected to the exchange frequencies oidep tink or diss,kink od can be considered as a system property giving a key to the kinetics of the metal ion transfer reaction. The local exchange current density as defined by eq. (2.23) is an imaginary quantity assuming a surface fully covered by kink sites. 

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