Amphoteric ions

Zwistigkeit, /. difference, dispute, discord. Zwitter, m. hermaphrodite hybrid bastard mongrel (Petrog.) zwitter. -ion, n. hybrid ion, amphoteric ion. 

Matsushita, T. (1996) Sulfate and chlorate removal in brine by amphoteric ion-exchange resin. In Soda Chlorine, Vol. 47, pp. 234-242. Japan Soda Industry Association. 

Another ion-exchange system has recently been developed by Nippon Rensui [8]. The Nippon Rensui system employs an amphoteric ion-exchange resin called Diaion DSR01 which can be eluted with water. In the DSR01 system, the resin takes up the sodium chloride and rejects the sodium sulphate. Purified NaCl is then recovered from the resin by water elution. This seems like a difficult approach since it is necessary to take-up huge amounts of NaCl on the resin in order to separate out a relatively small amount of sulphate impurity. Excessive dilution of the purified brine may also be an issue with this process. 

The Eco-Tec BDS (brine de-sulphurisation system) process uses a very different type of amphoteric ion-exchange resin. Unlike the DSR01 process, the BDS resin takes up the dilute sodium sulphate impurity and the concentrated, purified NaCl passes through the bed and is collected as product. The sodium sulphate impurity is then eluted from the resin with water. There is a fundamental advantage with this approach in that the amount of salt which must be adsorbed by the resin is lower by a factor of about 30 times. This reduces appreciably the amount of resin required and the associated equipment and cost. Typical BDS results are shown in Table 24.1. 

As with other hydrous metal oxides, such as alumina and zirconia, tin oxide is an amphoteric ion exchanger that exhibits cation exchange properties at basic pH. Hydrous tin oxide, however, appears to be particularly favored by virtue of its high Sr(ll) distribution coefficient (Kd Sr-bound/Sr-free) and high separation factor, Kd[Sr(ll)/Rb(l)], over a broad pH range (Table II Figure 1). 

Soluble, amphoteric ion exchange resins have been prepared by reaction of pyridinecarb-oxylic acids, especially 2-pyridinecarboxylic acid (215), with chloromethylated poly(styrene) (192 Scheme 104) (76IZV33). Resin (216) exhibited pronounced selectivity for Cu2+ and Ni2+ ions, and also, at pH 1.65, for the U022 ion. 

The sorption isotherm of NaCl in an amphoteric ion exchange resin containing... 

This specific property of o- and p- nitroaniline may be explained by assuming the structure of an amphoteric ion ... 

Dybczynski, R., Samczynski, Z. The use of amphoteric ion exchange resin for the selective separation of cadmium from other radioelements present in neutron irradiated biological materials. J. Radioanal. Nucl. Chem. 150, 143-153 (1991)... 

With its determination carried out at constant ionic strength the pH, value, so obtained, provides an assessment of the acidity of the amphoteric ion exchanger. This pH, relatable to the average value of pKj and pK2 with Eq. (16), is very close to the value of the isoelectric point 0 )- Paries [105] has pointed out that the relationship between the lEP of a solid surface and the valency-effective ionic radii, when corrected for crystal field effects, coordination, hydration, and other factors, is quite good. He also has indicated that the broad probable lEP range characteristic of a cation oxidation state may be selected from the data in Table 2 as shown below. It is known that the lEP for amphoteric oxides is affected by the presence of impurities, crystallinity and the chemical species under investigation. 

The oxides of metals, such as Ti, Zr, Ce(IV) and Th exhibit amphoteric ion-exchange behavior (Fig. 3). The decrease in acid strength of their oxides, Ti > Zr > Ce > Th, is paralleled by the decrease in the effective crystal ionic radii of these metals. The pH, of the oxides follows the opposite pattern, Ti < Zr < Ce < Th. It has been believed until recently that silica gel shows no anion-exchange character, even in acid solution, but anion... 

Ion-exchange membranes are classified according their function as follows cation exchange membrane, anion exchange membrane, amphoteric ion exchange membrane, bipolar ion exchange membrane, and mosaic ion exchange membrane. 

Write chemical equations that show how the hydrogen carbonate ion, HCO3, acts as an amphoteric ion. 

Figure 3.15 Transport number of hydrogen ions relative to sodium ions (PNaH) and current efficiency of cations to the composition of an amphoteric ion exchange membrane. (O, ) quarternized membranes (N-methyl pyridinium and sulfonic acid groups) (A, A) tertiary amino groups membrane (pyridinium hydrochloride and sulfonic acid groups) (, A) PNa 11 (O, A) current efficiency (%). Electrodialysis was carried out at a current density of 20 mA cm 2 using a mixed solution of 0.25 N sodium chloride and 0.25 N hydrochloric acid for 60 min at 25.0 °C.

Recently, membranes prepared by a layer-by-layer method have been actively studied. For example, a cationic polyelectrolyte can be adsorbed on a fiat plate as a monolayer and then an anionic polyelectrolyte layer added to it. The same procedure can be repeated, thus forming an ultrathin, multi-layer, amphoteric ion exchange membrane.107 The multi-layers have been formed on a porous membrane in studies on separation membranes108 and, further, such membranes have been studied as new functional materials for sensors, devices for photoelectronics,109 etc. 

Attempts to concentrate acetic acid by thermo-osmosis have employed various anion exchange membranes acetic acid is concentrated by 1.5 times in concentrated steam on the hot side using diethylaminated polystyrene membrane groups.213 Sodium chloride solution is concentrated to the hot side using an amphoteric ion exchange membrane.214... 

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