Sodium ionic exchanger

Sposito, G., K. M. Holtzclaw, L. Charlet, C. Jouany, and A. L. Page. 1983. Sodium-calcium and sodium-magnesium exchange on Wyoming bentonite in perchlorite and chloride background ionic media. Soil Sci. Soc. Am. J. 47 51-56. 

Typical of sodium-containing glasses such as ZBLAN or BIG-Na, another way to increase the refractive index is to substitute Li+ for Na+ ions, despite the lower polarizability of lithium ions because of their small size. Actually, Li+ ions are so small that they induce a local collapse of the glassy network resulting in an increase of the densification and of the refractive index [10,24,25]. This property is utilized for the elaboration of fluoride glass planar waveguides by ionic exchange, as described in Sec. 5.3. 

Energy for transport by pumps may be derived from ATP hydrolysis or from the ionic gradients of another ion. This is the case of the sodium/calcium exchanger, which uses the electrical energy stored in the sodium gradient across the plasma membrane to transport calcium out of the cell while harnessing the energy from concerted sodium influx (Komuro et al, 1992). 

The bulk and surface compositions of tungstates and molybdates can be modified through ionic exchange process, such as those used to obtain transition metal molybdate from sodium molybdate [5]. In this topic, as a specific example of preparation and uses of modified tungstates and molybdates, will be presented the preparation of Eu(III) compounds for optical purposes. 

Fig. 2. Distribution coefficient of calcium on untreated Wyoming montmorillonite as a function of solution-phase ionic-strength fraction of sodium (molal basis) at three total ionic strengths, pH = 5.0, sodium-calcium exchange.

A number of factors have been suspected in calcium transport ionic exchange, a calcium sensitive ATPase, a calcium binding protein, vitamin D, parathormone, cortisone. Calcium uptake is depressed by sodium and enhanced if one-third of the sodium is replaced by mannitol. It appears that sodium is not required for calcium uptake or transepithelial transfer. The intestinal brush border contains a calcium-sensitive magnesium dependent ATPase. In contrast to the K, Na" ATPase, the enzyme is not inhibited by ouabain. Vitamin D induces its appearance. The exact role of the ATPase remains unresolved. 

Other redox systems were also proposed in the past, such as the zinc/alkaline sodium ferricyanide [NajFeCCN) H2O] couple, and initial development work was performed. However, none of these efforts proved successful, mainly because of difficulties resulting from the efficacy and resistance of the ionic exchange membranes, until the development of the vanadium redox battery, by the University of New South Wales, Australia, in the late 1980s. Almost concurrently with this, development work started on VRBs at Sumitomo Electric Industries (SEI) of Osaka, Japan. Starting in the mid-1990s, VRB development has also been conducted at Mitsubishi Chemical s Kashima-Kita facility, although at a lower level of effort than at SEI. 

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