Counter-current ion-exchange

The principle used for the counter-current ion-exchange isotope separation by electromigration in a column is the balancing of the hydraulic flow of the ions X, the isotopes of which are to be separated, by the opposite flow of ions Y in an electric field. The X ions should be the more strongly sorbed on the ion exchanger and the Y ions should be the more mobile ones in the field. A sharp boimdary between the two kinds of ions is attained at some place in the column and is maintained there by the balancing of the flows. The steady passage of electric current is equivalent to movement of the sorbed band of X (which is actually... 

A number of other continuous counter-current ion-exchange contactors have been developed s-based, for instance, upon mixer-settlers, Archimedean screws, etc., but these are hkely to involve too high a degree of attrition of the resin or the frequent occurrence of blockages, to be satisfactory in a production plant. 

Comparison with solvent extraction. Although a substantial effort has been devoted to the development of satisfactory continuous counter-current ion-exchange processes for metal extraction, it is debatable whether any of... 

Increasing the number of ion-exchange sites by the use of counter-current (counterflow) regeneration... 

A design feature of an ion exchange plant whereby service flow and regenerant flow are in the same direction. The opposite of counter-current (counterflow). 

Continuous ion-exchange separation technology, which adopts counter-current processing in a rotating turntable, is currently making an impact and 70% of the world s lysine manufacture units use this technology. 

In the United States and most parts of the world, iodine is obtained com-merciaUy from brine wells. Many subsurface brines have iodine concentrations in the range of 10 to 100 mg/L. Various extraction processes are known including (i) precipitation with silver nitrate, (ii) oxidation with chlorine, and (hi) ion exchange. In the chlorine oxidation process, natural subsurface brine first is acidified with sulfuric acid and then treated with chlorine. Chlorine hberates iodine from the brine solution. Iodine is blown out into a counter-current stream of air. It is dissolved in a solution of hydriodic acid and sulfu-... 

Modolo, G., Asp, H., Vijgen, H., Malmbeck, R., Magnusson, D., Sorel, C. 2008. Demonstration of a TODGA-based continuous counter-current extraction process for the partitioning of actinides from a simulated PUREX raffinate, Part II Centrifugal contactor runs. Solvent Extraction and Ion Exchange 26(1) 62-76. 

In columns with a fixed bed, ion-exchanger capacity is not completely used since the process is performed up to breakthrough, that is until the appearance of the substance injected into the column in the outlet of the column. So a considerable part of ion-exchange capacity which is within the zone of the sorption front is not used. The counter-current process is carried out so that completely exhausted ion exchanger is in equilibrium with the injected solution when it leaves the column. In this case the capacity is fully used. 

When a direct current passes through an ion exchange membrane immersed in electrolyte solution, counter-ions are transported through the membrane, accompanied by water molecules, which is the electro-osmotic water. Because the liquid in a membrane pore has the same charge as the counter-ion, the liquid moves in... 

Permselectivity of counter-ions through the ion exchange membrane depends on the fixed ion concentration of the membrane (Chapter 2.3). Many attempts have been made to increase the fixed ion concentration of the membrane to increase the ion exchange capacity and to decrease the water content of the membrane, namely, to increase the fixed ion concentration without increasing the electrical resistance of the membrane. Figure 4.8 shows an example of the relationship between current efficiency to produce sodium hydroxide and the fixed ion concentration of the membrane for the electrolysis of sodium chloride solution.17 It is apparent that the current efficiency increases with increasing fixed ion concentration of the membrane. 

For a diluted feed or brine solution an ion-exchange membrane in general is more or less strictly semipermeable, i.e. the membrane is permeable to counter ions only. When, however, the ion concentration in the feed solution is of the same order as that of the fixed charges in the membrane co-ions may also enter the membrane and its selectivity will then be decreased, with the consequence that the current efficiency decreased, too. 

About the same time a novel liquid-liquid or solid-liquid counter-current contacting system was being developed by W. H. Morris (30, 31) at ROF Pembrey who proposed its use for the manufacture of TNT as one of a number of applications (including the manufacture of antibodies and other solvent-extraction applications and ion exchange).cThe equipment... 

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