Process ion exchange

Ion-exchange processes are basically chemical reactions between ions in solution and ions in an insoluble solid phase. The techniques used in ion exchange so closely resemble those used in adsorption that for the majority of engineering purposes ion exchange can be considered as a special case of adsorption. 

In ion exchange certain ions are removed by the ion-exchange solid. Since electroneutrality must be maintained, the solid releases replacement ions to the solution. The first ion-exchange materials were natural-occurring porous sands called zeolites and are cation exchangers. Positively charged ions in solution such as diffuse into the pores of the solid and exchange with the Na ions in the mineral. 

Most present-day ion-exchange solids are synthetic resins or polymers. Certain synthetic polymeric resins contain sulfonic, carboxylic, or phenolic groups. These anionic groups can exchange cations. 

Here the R represents the solid resin. The Na in the solid resin can be exchanged with H or other cations. 

Similar synthetic resins containing amine groups can be used to exchange anions and OH in solution. 

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For very small quantities, ion exchange processes may be utilised (p. 55) even with water-soluble neutral substances. 

For the more advanced student, we have extended the section on Quantitative Semi-micro Analysis, and we have included a section dealing with Special Techniques in Separation and Purification, namely Adsorption Chromatography, Paper Chromatography, and Ion- Exchange Processes. 

One ion-exchange process, which was used for several years by Quebec Lithium Corp., is based on the reaction of P-spodumene with an aqueous sodium carbonate solution in an autoclave at 190—250°C (21). A slurry of lithium carbonate and ore residue results, and is cooled and treated with carbon dioxide to solubilize the lithium carbonate as the bicarbonate. The ore residue is separated by filtration. The filtrate is heated to drive off carbon dioxide resulting in the precipitation of the normal carbonate. 

Ammonium Ion Removal. A fixed-bed molecular-sieve ion-exchange process has been commercialized for the removal of ammonium ions from secondary wastewater treatment effluents. This application takes advantage of the superior selectivity of molecular-sieve ion exchangers for ammonium ions. The first plants employed clinoptilolite as a potentially low cost material because of its availability in natural deposits. The bed is regenerated with a lime-salt solution that can be reused after the ammonia is removed by pH adjustment and air stripping. The ammonia is subsequentiy removed from the air stream by acid scmbbing. 

Silica Polymei Metal Ion Interactions in Solution. The reaction of metal ions with polymeric sihcate species in solution may be viewed as an ion-exchange process. Consequently, it might be expected that sihcate species acting as ligands would exhibit a range of reactivities toward cations in solution (59). Sihca gel forms complexes with multivalent metal ions in a manner that indicates a correlation between the ligand properties of the surface Si-OH groups and metal ion hydrolysis (60,61). For Cu +, Fe +, Cd +, and Pb +,... 

FIG. 16"44 Multicomponent ion-exchange process for chromate recovery from plating rinse water. Adaptedfrom Rhom Haas with peimission.)... 

FIG. 16-63 Asahi countercurrent ion-exchange process. [Gilwood, Chem. Eng., 74(26), 86 (1967) copyiight 1967 hy McGraw-Hill, Inc., New York. Exceipted with special peimission of McGi aw-Hill.]... 

A. Dyer, M.J. Hudson and P.A. Williams (Eds), Ion Exchange Processes Advances and Applications, Royal Society of Chemistry, London, 1993. ISBN 0851864457. 

Deionized water Water that goes through an ion exchange process in which all positive and negative ions are removed. 

As the re-introduction of mixtures of cinchona alkaloids for use in medicine has given rise to some discussion, a list of the principal papers on this subject is given. Several of these provide analyses of locally produced totaquina. Applezweig and Ronzone have described an ion exchange process for the preparation of totaquina. 

Russell, C., M.S. Thesis, Desalination of Bicarbonate Brine Waters Experimental Findings Leading to an Ion Exchange Process Design New Mexico Tech, Socorro, NM, 1994. 

All ion-exchange processes produce wastewater from backwash, regeneration and rinse. The proportion of waste depends on the concentration of hardness or to TDS being removed, and can be as high as 15 per cent of the product flow. Any pretreatment has to take this additional flow into account. 

The discussion so far has been limited to the behaviour of polymer films after immersion in potassium chloride solutions for only a short time. When varnish films were immersed in potassium chloride solutions for a month or more a steady fall in resistance took place. Further experiments indicated that the effect was reversible and dependent on both the pH of the solution and the concentration of potassium chloride. It was concluded that an ion exchange process was operative . 

If Eqs. (28) and (32) are inserted into Eq. (30) the mixed potential of the ion-selective membrane for an ion exchange process of only monovalent ions of the same sign is obtained ... 

Ion exchange equilibria. The ion exchange process, involving the replacement of the exchangeable ions Ar of the resin by ions of like charge Bs from a solution, may be written ... 

Investigations in aqueous systems have established many of the fundamental principles of ion exchange as well as providing useful applications. The scope of the ion exchange process has, however, been extended by the use of both organic and mixed aqueous-organic solvent systems.32,33... 

If the preference for hydrogen ion exchange shown by lime-soda glasses can be reduced, then other cations will become involved in the ion exchange process and the possibility of an electrode responsive to metallic ions such as sodium and potassium exists. The required effect can be achieved by the introduction of aluminium oxide into the glass, and as shown in Table 15.2, this approach has led to new glass electrodes of great importance to the analyst. 

Occasionally, separation, e.g. by solvent extraction or by an ion exchange process, may be necessary to remove an interfering element such separations are most frequently necessary when dealing with flame emission spectroscopy. 

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