ion exchange

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ion exchange

the process in which ions are exchanged between a solution and an insoluble solid, usually a resin. It is used to soften water, to separate radioactive isotopes, and to purify certain industrial chemicals

Ion Exchange


the exchange of ions in electrolytic solutions (homogeneous ion exchange). When dilute electrolytic solutions, such as NaCl and KNO3, are mixed, Na+, K+, NO3, and Cl ions are present in the mixture. The state of equilibrium for this case is expressed by the equation NaCl + KNO3 ⇄ NaNO3 + KCl (double-exchange reaction). If one of the substances produced during the interaction is less dissociated than the others, the equilibrium shifts toward the formation of the poorly dissociated substance. The equilibrium also shifts toward the formation of a volatile or poorly soluble product (if it is precipitated from the particular phase) according to the reactions

H2SO4 + 2KCN ⇄ K2SO4 + 2HCN ↑

NaCl + AgNO3 ⇄ NaNO3 + AgCl↓ I

The crystallization of a salt (ion combination), which has lower solubility, is the first process to take place upon evaporation of an equilibrium solution. The selectivity of crystallization may also be caused by the addition of organic solvents, such as alcohol, acetone, or dioxane.

During heterogeneous ion exchange (ion-exchange sorption), exchange takes place between ions that are in solution and those that are on the surface of the solid phase (the ion exchanger). When an ion exchanger saturated with one ion (such as H+) comes into contact with a solution containing other ions (for example, Na+ and Ca2+), ion exchange occurs between the ion exchanger and the solution: the concentration of Na+ and Ca2+ in the solution is reduced, and an equivalent quantity of H+ ions appears.

Heterogeneous ion exchange takes place during sorption of certain minerals (aluminosilicates, metallic hydroxides, and zeolites) from electrolytic solutions in the cells and membranes of living organisms and in synthetic ion-exchange sorbents. This type of ion exchange is widely used for the desalinization of water used to feed high-pressure steam boilers, as well as in hydrometallurgy and the chemical and pharmaceutical industries.


ion exchange

[′ī‚än iks‚chānj]
(physical chemistry)
A chemical reaction in which mobile hydrated ions of a solid are exchanged, equivalent for equivalent, for ions of like charge in solution; the solid has an open, fishnetlike structure, and the mobile ions neutralize the charged, or potentially charged, groups attached to the solid matrix; the solid matrix is termed the ion exchanger.
References in periodicals archive ?
Perfluorosulfonic acid polymers (PFSA) and perfluorocarboxylic acid polymers (PFCA) are typical fluorinated functional polymers that have been used to prepare ion exchange membranes, which serve as the barrier membrane to separate the anode and cathode compartments of electrolytic cells in the production of alkali metal hydroxide and chlorine [6-9].
To obtain the optimum performance of the electrolytic cell, PFSA and PFCA were combined to prepare two-layer ion exchange membranes.
Ion exchange membrane chromatography media have proved to be valuable purification tools, and the new Membrane [EX technology can reduce bottlenecks, and costs, while improving throughputs in downstream processing of antisense oligonucleotides.
Figure 1 demonstrates the difference in pore structures for binding between packed columns and ion exchange membranes.
The ion exchange membranes separate diluate chambers containing the solution from which ions are removed and concentrate compartments, into which the ions are transported.
By selection of special membrane types involving monopermselective ion exchange membranes and a modified arrangement of anionic and cationic ion exchange membranes orthophosphite anions are removed from the diluate (= electroless nickel bath), at a much higher rate than the hypophosphite anions.
The projects will respectively explore the development of novel low-density graphene-based foams for various engineering applications, inkjet-printed graphene micro-sensors for energy and defense applications, and graphene-enabled ion exchange membranes for desalination.
Arulanandan and Smith (8) studied the dielectric permittivity and conductivity of unspecified ion exchange membranes in the range of [10.