Metal ions water complexes

It is evident from Table 6.3" that the most impressive rate enhancements are due to metal ion-water complex catalysis 100- and 14000-fold rate acceleration due to Zn +-H20 complex and Cu +-H20 complex, respectively. Catalytic effects due to Zn ll or 13 and Cn +12 or 13 complexes are - 1.6- to 5-fold and 10-fold, respectively. Similarly, the catalytic effects due to Zn +-10 or 11 and Cu +-10 or 11 complexes are 2-fold and 5-fold, respectively, which could be easily explained in terms of merely nsual concentration and medium effects of the micromicellar reaction environment. 

The principle of solvent extraction in refining is as follows when a dilute aqueous metal solution is contacted with a suitable extractant, often an amine or oxime, dissolved in a water-immiscible organic solvent, the metal ion is complexed by the extractant and becomes preferentially soluble in the organic phase. The organic and aqueous phases are then separated. By adding another aqueous component, the metal ions can be stripped back into the aqueous phase and hence recovered. Upon the identification of suitable extractants, and using a multistage process, solvent extraction can be used to extract individual metals from a mixture. 

The metal ion-water exchange process must be important in areas other than those of simple metal complex formation. For example, the discharge of nickel ion at a mercury cathode is probably controlled, not by diffusion, but by rearrangement of the water coordination shell. The estimated rates and heat of activation for this agree with the idea that this, in turn, is related to the water exchange process (66). Then too, the dimerization rate of metal hydroxy species may be controlled by water exchange. The reaction... 

An example of the conflict between stabilization from the Jahn-Teller effect and chelate geometrical requirements is found in the ethylenediamme complexes of Cu2+. Most divalent transition metal ions form complexes with elhylencdiaminc (en) by stepwise replacement of water ... 

At that time, passing samples of water through a filter with 45 pm diameter pores was sufficient to properly separate the two phases. Later, following the development of electrochemical analytical methods, it was possible to identify different forms that metals assumed in a dissolved state—free metal ions and complex ion forms. 

But it was not to be. Try as we might, the difference in scattering lengths between the 6Li and 7Li isotopes was too small to permit us to measure the lithium ion distribution in the swollen state. We had to content ourselves with the results for the crystalline phase, where the behavior of the lithium ions is different from that of the larger alkali metal cations [27], Potassium and cesium ions bind directly to vermiculite clay surfaces rather than hydrating fully. Because only lithium-substituted vermiculites of the alkali metal series will swell macroscopically when soaked in water, it seems that interlayer cations must form fully hydrated ion-water complexes if the particles are to expand colloidally. This conclusion has since been supported... 

It is assumed that the best catalytic effect can be achieved if the pA a or pA), value of the interphase material is close to 7 [71]. Some weak ion-exchange groups such as tertiary amines, phosphoric acid, carboxylic acids, or pyridine show the required dissociation constant or p ta-values. Certain heavy metal ion complexes, such as chromium(lll)- or iron(Ill)-complexes, provide the required catalytic water dissociation effect. In principle, there are many more suitable metal ions available. The metal ions or complexes are immobilized by either including an insoluble salt in the casting solution of the interface layer between the ion permeable layers or by converting a soluble form by a follow-up treatment [45]. An additional requirement for the catalytic material is to be effective and stable for a long period. It must also remain in the interphase, where it is the most active, for the anticipated lifetime of the membrane. 

Chaufer, B. and Deratini, A., Removal of metal ions by complexation ultrafiltration using water soluble macromolecules Perspective of application to waste water treatment, Nucl. Chem. Waste Manag. 8, 175, 1988. 

---