Cation exchange, outer-sphere

Illustrate solution, cation exchange, and outer- and inner-sphere species around a soil particle. 

Metal ions are adsorbed onto chelating resins from aqueous solution by a mechanism similar to that shown above for cation-exchange resins (equation 92). However, the exchange of metal cations in solution with protons on the resin does not involve dehydration of the metal ion for cation-exchange resins, but for chelating resins it does, and the metal cation is bound in the resin phase by a combination of outer-sphere ionic and inner-sphere covalent forces ... 

Similar results have been found for the electron exchange between [Fe(CN)6]3 and [Fe(CN)e]4. In that case, the acceleratory effects are found to vary with the nature of the cation in the order Cs+ > Rb+ > K+ NH4+ > Na+ > Fi+, in accord with the size and solvation effects discussed earlier. For +2 ions, the order of effect on the rate is Sr2+ > Ca2+ > Mg2+, which is also in accord with the softness of these species. Exchange in these outer sphere cases is believed to involve the formation of bridged species containing cations that are probably only partially solvated. 

Interaction 1 denotes electrostatic forces between humic substances (negatively charged) and metal ions (positively charged). It is a relatively weak interaction (outer-sphere complex) and the cation can be readily exchanged by other weakly bonding cations,... 

Complex formation of lanthanides is a rapid process. This is very obvious from the high rates for water exchange in lanthanide ions. Thus rapid motion of molecules of water in and around the lanthanide ion can be envisaged. Most of the time the relative positions with respect to one another and the cation are the same. The complexes have dynamic structures. Inner sphere complexation will certainly affect the water molecules in the outer spheres. Both dissociative and associative pathways of complex formation in aqueous media for lanthanides are possible. 

Rapid exchange reactions between Mn04 and Mn04- have been studied, and cation effects were interpreted in terms of an outer-sphere bridged activated complex. 

During the exchange in the interlayer space, the cations keep their hydrate shell this process is called outer-sphere complexation. It is directed by electrostatic forces that, the greater the charge and smaller the size of the hydrated cation, the more favorable is the ion exchange. 

The negative layer charge is mostly neutralized by the hydrated cations in the interlayer space. These cations are bonded to the internal surfaces by electrostatic forces, and they are exchangeable with other cations. The interaction strength between the hydrated cation and the layers (the internal surface) increases when the charge of the cation increases, and the hydrated ionic radius decreases. Cations with hydrate shell can be considered as outer-sphere complexes. Cation exchange is the determining interfacial process of the internal surfaces of montmorillonite. 

Inner-sphere complexes are relatively stable in comparison to outer-sphere complexes under equivalent solution conditions (i.e. pH, ionic strength), and in a competitive situation will tend to displace less stable adsorbates. This is a fundamental property of coordination reactions, and explains the observed trends in metal uptake preference observed in lichen studies (Puckett et al., 1973). Metal sorption results previously attributed to ion exchange reactions are more precisely described as resulting from competitive surface complexation reactions involving multiple cation types. Strictly speaking, each metal adsorption reaction can be described using a discrete mass law relation, such as... 

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