# Ion exchanger

Resin -Ionenaustauscherkartusche
Ion exchange column

Ion exchangers or ion exchangers are materials with which dissolved ions can be replaced by other ions of the same charge (i.e. positive or negative); an ion exchange takes place. Ion exchangers come on the market as columns filled with an ion exchange material or as membranes and the solution to be treated flows through them. The ions to be exchanged are bound to the ion exchange material, which in turn releases an equivalent amount of charge from previously bound ions into the solution.

For example, a cation exchanger can exchange calcium cations that are dissolved in normal tap water for sodium cations that are bound to the ion exchanger. Such cation ion exchangers are also used in dishwashers . In them, water that is free of calcium cations is prepared for washing processes, which would otherwise lead to the formation of white limescale deposits (limescale stains) on the dishes during drying and the deposition of scale on heating elements and in the machine's pipes (limescale). When this cation exchanger is exhausted and completely saturated with calcium cations, it must be regenerated. This happens by displacing the bound calcium cations by offering a solution of sodium chloride (table salt) that is as highly concentrated as possible . This process is called the regeneration of an exchanger.

Cation ion exchangers are particularly important for the cation exchange capacity in the soil . They ensure that cations remain available for the plants and are not washed out by the rain. For the remediation of contaminated waters and soils, special cation exchangers can be produced which are able to remove specific heavy metal cations from water and soils in a very targeted manner .

## history

People used the principle of ion exchangers long before the chemical background was understood.

In the Second Book of Moses, to the ion exchange process is implicitly the oldest mention: It is on the transfer of bitter in potable water drawn by the insertion of old tree trunks - rotted cellulose is a good exchanger for magnesium - ions :

“So they came to Mara; but they could not drink the water from Mara because it was very bitter. Hence the name of the place Mara. Then the people murmured against Moses, saying, What should we drink? He cried out to the Lord, and the Lord showed him a stick; he threw it into the water and it became sweet. "

- Ex 15,23-25  LUT

The first ion exchangers specifically used in technology were aluminosilicates , which can reversibly absorb or release alkaline earth and alkali ions from a solution. Natural exchangers of this type are e.g. B. in certain volcanic deposits. The first artificial aluminosilicates were developed under the name Permutit at the beginning of the 20th century and used to soften water.

Further developments were weakly acidic ion exchangers based on special carbon and weakly basic ion exchangers based on phenolic resins . All of these older types of exchange were mechanically broken granulates, sieved according to certain grain sizes. With the development of phenolic resins, spherical polymers could later be obtained directly. With strongly basic ion exchangers it became possible to remove silicates from the raw water. Today's exchangers are mainly based on modified polystyrenes and polyacrylic acids .

## functionality

The principle of ion exchange is based on the fact that ions are bound more strongly to the ion exchanger, the higher their charge, and with the same charge, the larger their ionic radius . For example, Na + in the ion exchanger is displaced by Ca 2+ , but also Ca 2+ by Al 3+ . The stronger binding ion displaces the weaker binding ion from the binding sites of the ion exchange material. It must therefore be ensured that the undesired ion that is to be removed from the solution is bound more strongly than the ion that is bound to the ion exchanger. Other important influencing factors are: the pH value of the solution in connection with the type and number of binding sites of the ion exchange material and also the respective substance concentration .

The following list for divalent metal ions shows how strongly the ion radius influences the selectivity of an ion exchange resin. The values ​​are valid for a solution with a pH value of 4.0 and calcium as a basis with 1.0 for K M / Ca and a weakly acidic cation exchange resin with a polyacrylic structure:

Metal ion K M / approx Metal ion K M / approx Metal ion K M / approx
Hg 2+ 2800 Ni 2+ 57 Fe 2+ 4.0
Cu 2+ 2300 Zn 2+ 17th Mn 2+ 1.2
Pb 2+ 1200 Cd 2+ 15th Ca 2+ 1.0

In addition to the selectivity, absorbed ions can also be displaced by the ion exchange material by increasing a substance concentration. The latter is carried out during a regeneration. The reactions are given below using the example of sodium ions, which are present as common salt (NaCl) in an aqueous solution. A strongly acidic cation exchange resin is used for absorption (= loading / operation) and detachment (= regeneration). The regenerant is hydrochloric acid.

${\ displaystyle \ mathrm {R-SO_ {3} H + Na ^ {+} + Cl ^ {-} + H_ {2} O \ \ rightleftharpoons \ R-SO_ {3} Na + H_ {3} O ^ { +} + Cl ^ {-}}}$
${\ displaystyle \ mathrm {R-SO_ {3} ^ {\, -}}}$: Basic structure of a cation exchanger, such as B. sulfonated polystyrene

When loaded, the reaction runs from left to right. If the concentration of the H 3 O + ion in the right part of the equation is increased, the reaction shifts to the left again and the exchanger is converted back into the acid form, it is regenerated. When the exchanger at loading / regeneration operation and in the same direction from the fluid to be desalinated and the regeneration solution flows through, one speaks of a direct-current exchanger in a direction opposite the direction of flow of a counter flow exchanger . The concentration of the regenerant is usually 3–10% HCl.

In the example given, a dilute hydrochloric acid is formed during loading in the draining water. Due to a counter- ion effect, depending on the salt concentration in the raw water and the loading status of the ion exchange resin, sodium slip occurs during loading. A small amount of sodium is therefore still present in the pure water running off after the exchanger. This can reach values ​​of 1 mg Na + / l and higher , especially with a direct current exchanger . With a countercurrent exchanger , they are ≤ 0.1 mg Na + / l.

## Types of ion exchangers

Depending on which type of ions are exchanged, a distinction is made between cation exchangers and anion exchangers. In the case of a cation exchanger, the active group is an anionic group, such as, for example, sulfonic acid groups , or carboxy groups with a dissociable cation. A distinction is made between weakly acidic cation exchangers (carboxy groups) and strongly acidic ones with sulfonic acid groups.

In anion exchangers , strongly basic types contain quaternary ammonium groups as active groups that can exchange their counterion. Type I and type II anion exchangers are generally used. The distinction between types I and II relates to the properties for thermal resistance and exchange capacity. A type I anion exchanger is thermally more stable, but has a lower exchange capacity than a type II exchanger. The active exchange group of the type I exchanger is a trimethyl-ammonium group (-N + (CH 3 ) 3 ). In type II at least one of the three methyl groups has been replaced by a hydroxyethyl group (-CH 2 -CH 2 -OH).

Weakly basic exchangers contain amino groups to which the anions of free acids are attached. The acid anions are bound reversibly. With alkalis , the free amino groups are re-formed during regeneration. Depending on the type of amino group - primary (–NH 2 ), secondary (–NHR) or tertiary amino group (–NR 2 ) - the basicity of the exchangers is weak to medium basic.

Amphoteric exchangers can exchange anions and cations at the same time. Cation exchangers exchange dissolved cations (positively charged ions) for other cations that are part of the exchange material. Cation exchange materials are themselves salts, whereby the cations (in the equation below: Z + ) can easily go into solution, i.e. are mobile (mobile). The polymeric and water-insoluble anions (in the equation below: Q m− ) of the cation exchange material are stationary , i.e. immobile. As a general equation for the process of the exchange of monovalent cations (Ka + ) from a dissolved salt (Ka + + An - ) by the ion exchanger [(Z + ) n Q m− ] one can write:

${\ displaystyle x \ {\ text {Ka}} ^ {+} + x \ {\ text {An}} ^ {-} + [({\ text {Z}} ^ {+}) _ {n} { \ text {Q}} ^ {m -}] \ longrightarrow x \ {\ text {Z}} ^ {+} + x \ {\ text {An}} ^ {-} + [({\ text {Z} } ^ {+}) _ {nx} ({\ text {Ka}} ^ {+}) _ {x} {\ text {Q}} ^ {m-}]}$

Anion exchangers exchange anions (negatively charged ions) of a dissolved salt for other anions. The stationary cations of the ion exchanger are polymeric, while the anions of the anion exchanger are mobile .

Examples of ion exchange materials:

## Technical ion exchange columns

While columns made of glass or plastic filled with replacement resins are used in the laboratory, in technical systems the columns are designed as containers. These containers are mainly made of steel with an inner hard rubber lining. Drainage systems or nozzle bases for the inlet and / or outlet of the treated liquid and the regeneration solutions are built into the container. Depending on the version of the exchanger or its function, the following types are used:

The first four types of exchangers are filled with either cation or anion exchange resins. Accordingly, weakly and strongly acidic or weakly and strongly basic ion exchange resins are used. At least two exchangers are required for desalination so that cations and anions can be removed. The remaining three types work with cation and anion exchange resins. Desalination is possible here in a container.

A typical demineralization system contains an exchanger for cations, an exchanger for anions and, if deionized water with a residual conductivity of <1.0 µS / cm is to be produced, a mixed-bed exchanger. This combination is also known as a desalination line. A trickle tank is often arranged between the cation and anion exchangers for CO 2 removal . The latter reduces the free carbonic acid formed from the carbonate hardness to <10 mg / l. This is more economical than removal using anion exchangers.

Two roads are required for continuous pure water production. One road is in operation and the second road is being regenerated or is on hold. The normal operating time of a road before regeneration is more than 6 hours. If the system is designed for less than 4 hours, it is called a short-cycle system .

In addition to the systems listed above, which all work as batch systems, there are also systems in technology that work continuously. Various processes have been developed for this type of desalination plant, but these are rarely used in practice. More on this under continuous ion exchange systems .

### Resin ion exchanger

Synthetic resin ion exchangers can differ in the structure of their polymer / polycondensate frameworks: One speaks of gel resins or macroporous resins. The first exchangers of this type were developed by Robert Grießbach in the Wolfen paint factory (then part of IG Farben ) in the 1930s and marketed under the trade name Wofatit ( Wo lfener Fa rbenfabrik Permu tit replacement). The production of Wofatit in Wolfen was continued and further developed in the GDR. By 1988, 95 different types of wofatite had been put into production, including cation exchangers and anion exchangers. Current trade names are Lewatit ( Lanxess ), Dowex (Dow Chemicals), Amberlite (Rohm and Haas), Treverlite (CHEMRA) and Resinex (Jacobi Carbons). The resin exchangers are a means of treating different types of water and aqueous solutions.

If organic ion exchangers are used for the treatment of drinking and industrial water or in the food industry, special quality requirements must be met. Due to the manufacturing process, new exchangers can release monomers into the treated liquid during the initial operating time . The permissible slip of organic components is limited by law. In Germany, the limit value for the release of TOC (organic carbon) may amount to a maximum of 2.5 mg per m 2 of contact surface and day if the contact attempt is repeated twice for 72 hours .

Below is a table with the general characteristics given by the manufacturers for the various types of ion exchange resins. The data listed are the characteristics of a strongly acidic cation exchange resin and the regenerants hydrochloric acid (HCl) and sulfuric acid (H 2 SO 4 ):

unit Data
Resin type Polystyrene resin, gel resin, functional group: sulfonic acid
Grain shape mm Spheres, 0.3-1.2
Temperature range  ° C to 120
pH range no limit
Bulk weight g / l 800–900 (wet resin)
Usable volume capacity (NVK) val CaO / l Max. 1.85 ( max. 1.4 ) °
Total volume capacity val / l 2.2 (wet resin)
min. Layer height resin bed mm 600 ( 900 ) °
Regeneration agent expenditure g 100% HCl / l up to 200 ( up to 90 ) °
Concentration of regenerant % HCl 4-6 ( 8-10 ) °
Regeneration agent expenditure g 100% H 2 SO 4 / l up to 250 ( 50-120 ) °
Concentration of regenerant % H 2 SO 4 1.5-6 ( 1.5-10 ) °
Washing water requirement l / l 4-7 ( 2-3.5 ) °
spec. Load operation l / h l 4–40 ( up to 180 ) °°
Backwash m / h 7–15 ( normally not required ) °
Pressure loss each m + m / h 0.15-0.2 mWC at 20 ° C
Delivery form, normal loaded with sodium
Swelling Na → H form % 5-10

° in front of brackets = for direct current, in brackets = for countercurrent

°° in front of brackets for water desalination, in brackets for condensate desalination

Gel resins, for example, absorb humic acids from organically contaminated water with humic substances , which cannot be removed when the ion exchanger is regenerated; they lead to what is known as fouling of the ion exchangers.

Anion exchange resins in particular are affected by fouling and become amphoteric when such compounds are absorbed , since the anion exchange resins then carry base and acid groups. When the exchanger is regenerated with sodium hydroxide solution, sodium ions are now also bound. Overall, the fouling reduces the performance of the exchangers by blocking active base groups, increases the washing water requirement when washing out the regeneration liquor, and worsens the quality of the pure water due to higher sodium slip. After various operating cycles, the ion exchange resins become largely inactive and must be replaced. With the development of macroporous ion exchange resins, the removal of organic substances has been improved.

So-called scavenger exchangers can be connected upstream for the ion exchange of surface water such as bog water and black water with a high concentration of organic substances . The only task of the scavenger exchangers is to intercept disruptive humic substances. In systems with multi-chamber exchangers, one chamber can also be designed as a scavenger stage. The properties can be controlled within wide limits by means of suitable formulations and conditions during production, so that it is possible to produce exchangers which are selective for certain ions (e.g. Lewatit Mk51 for borate).

### regeneration

The regeneration of ion exchangers is based on the fact that the ion exchange is an equilibrium reaction. In fact, the desired forward and undesired reverse reactions also take place simultaneously during operation. When using the ion exchanger, however, the forward reaction predominates . The reverse reaction is promoted during regeneration by adding an excess of "weaker" ions, because many weaker ions displace the "stronger" ions preferred by the exchanger. (See also: Principle of the smallest compulsion )

The regeneration is carried out in cocurrent or countercurrent, which relates to the direction of flow of the liquids during operation (also called loading) and regeneration. With direct current, the ion exchanger flows through in the same direction both during operation and during regeneration. In the case of countercurrent, the regeneration is opposite to the loading. Various processes are used for regeneration. The most important processes are cocurrent, countercurrent, compound and progressive regeneration. They have various advantages and disadvantages in terms of chemical consumption and regeneration effect. Depending on the different ion exchange resins, the following regeneration chemicals are usually used:

• For cation exchangers: dilute sulfuric acid or hydrochloric acid, as well as aqueous saline solution.
• For anion exchangers: aqueous ammonia solution, dilute sodium hydroxide solution and sodium carbonate or aqueous saline solution

Processes have also been developed to regenerate exchangers with the aid of electrical current, in which the exchanger (especially for mixed bed exchangers) is filled between two exchanger membranes (KAT and AAT) and voltage is applied. The ions migrate in the field and are bound by the anolyte (acid) and the catholyte (lye) and thereby separated. The membranes prevent the electrolytes from diffusing back to the exchanger. If they are not electrolytically regenerated, mixed-bed exchangers must be separated into columns by flushing from below (the AAT settles at the top).

In the 1970s, it was investigated whether, instead of chemicals, differences in temperature were sufficient for ion exchange and regeneration. Ion exchange resins have been developed which absorb cat and anions from a salt solution at room temperature and release them again when heated to H + and OH - ions. The equation for these reactions is:

${\ displaystyle \ mathrm {R_ {a} ^ {+} OH ^ {-} + R_ {c} ^ {-} H ^ {+} + Na ^ {+} + Cl ^ {-} \ rightleftharpoons R_ {a } ^ {+} Cl ^ {-} + R_ {c} ^ {-} Na ^ {+} + H_ {2} O}}$
Anion resin in OH form + cation resin in H form react with Na + Cl ions to form cation resin in sodium and anion resin in chloride form + water

At 20 ° C the reaction runs from left to right. When heated to 80 ° C, the absorbed ions are released again, the reaction is reversed and the resins are converted into the regenerated form. In the case of mild brackish water, more than 80% desalination can be achieved. The first pilot plants were successfully tested as Sirotherm Process in the USA. However, due to the increase in energy costs, this process has so far not been able to establish itself economically in practice.

Ion exchange resins blocked by the absorption of impurities and thereby largely inactive - for example cation exchangers with protein compounds or anion exchangers with humic acids - can be treated with warm alkaline saline solution. As a result, these contaminants can often be at least partially removed again. Normal regeneration is also required after such a special treatment.

## Applications

Ion exchangers are very often used for softening , salinization , partial desalination or full desalination of water or aqueous solutions.

A process for drinking water treatment in which carbon dioxide (CO 2 ) is used as a regenerant is the "Carix process" developed around 1980. This is now used more often both for partial desalination and to reduce the sulfate or nitrate content in drinking water.

Powdered ion exchangers are used for the removal of minor impurities such as dyes, traces of metal, toxic organic chlorine compounds, etc. from aqueous solutions or non-aqueous liquids e.g. B. used by precoat filtration .

Ion exchangers with fine grain size and in greater layer heights are used for the chromatographic separation of organic compounds. One example is the separation of glucose and fructose from the mixtures that result from the fermentation of corn starch to invert sugar.

Ion exchange resins are also used in chemistry as catalysts for various syntheses. This use is also carried out in part in non-aqueous solutions.

Other important applications for ion exchangers are:

• Production of demineralized water : often also called deionized water or incorrectly called distilled water (water that has been purified by distillation ). With the help of cation and anion exchangers, unwanted salts are removed from the water. In science and technology is therefore also referred to as demineralized water , deionized water or demineralized water ( v oll e ntsalzt).
• Electronics industry : Extremely clean deionized water, also known as ultrapure water , is required for the production of electronic components - especially in chip production. For the production of ultrapure water, deionized water with a conductivity <0.08 µS / cm is additionally filtered through a candle filter, pore size ≤ 1 micron, and treated with UV light to kill germs.
• Cleaning of sugar juice solutions : Cation and anion exchangers are also used for cleaning sugar juices during the production of sugar (sucrose), glucose or fructose concentrates. This removes salts, proteins and dyes from the raw solutions and improves the purity of the end products. Furthermore, the function of the ferments used in the production of glucose or fructose from corn starch is improved. The sugar yield can be improved by salting the remaining molasses from beet sugar. If the raw sugar beet juice is already desalinated, it can be processed directly into white sugar by evaporation in a vacuum without any molasses. Other substances contained in the beet can also be extracted from the regeneration wastewater.
• Brewing water : The brewing water used in the production of beer must not have a high content of carbonate hardness. Furthermore, the magnesium and calcium salts should be present in a certain ratio. Natural waters often do not meet these requirements. Brewing water is therefore partially decarbonised using weakly acidic cation exchangers. The exchanger is regenerated with hydrochloric or sulfuric acid.
• Uranium extraction: In addition to the recovery of especially + 2-valent metal ions from wastewater, the ion exchange process is specifically used for uranium production in uranium extraction from ore. The ore is digested using alkaline carbonate. The uranium can be concentrated from the resulting solution with weakly acidic cation exchangers or with strongly basic anion exchangers. The uranium is then precipitated from the regenerates as an oxide, also known as yellow cake .
• In dishwashers : ion exchangers are used here to protect the machine from Ca 2+ and Mg 2+ ions, which can lead to scale ( colloquially : calcification ). These ions are replaced by Na + ions and not, as with other exchangers, by "acid" H + ions, as these would attack the metal in the dishwasher. A built-in ion exchanger is loaded with Ca 2+ and Mg 2+ ions after a while . There is a special regeneration salt that has to be refilled regularly for the regeneration required.
Household water filters
• In water filters : these “filters” usually not only contain an ion exchanger to decalcify the water and thus prevent limescale deposits in kettles, but also mostly activated carbon filters to remove odor and taste impairing substances.
• In detergents : the ion exchanger should also reduce the calcium carbonate content of the water in detergents in order to prevent the formation of lime soaps . This means that less detergent is required. Zeolite A , for example, is an important ion exchanger in detergents .
• Purification of wastewater : One example is the purification of the wastewater that is left behind after electroplating , i.e. during the production of metal coatings. This wastewater contains heavy metal ions that would poison the biological treatment stage in sewage treatment plants. The retained metal ions (e.g. silver) can then be recycled.
• Purification and recovery of phenols from wastewater : Chemical wastewater must be pre-cleaned if it contains higher phenols , bisphenols and p-nitrophenol . Without separation of these ingredients, the biological purification stage in a sewage treatment plant would be severely hindered or largely blocked. Such contaminated wastewater can be pre-cleaned with special macroporous anion exchangers. The phenols can also be recovered at higher levels.
• In the pharmaceutical industry , ion exchange resins are used for concentration, cleaning, such as removing salts and organic impurities, and decolorization. The type of ion exchanger used depends on the desired and required reactions. Weakly basic exchangers are mainly used for the purification of amino acids and the separation of antibiotics with carboxylic acid groups. Antibiotics with basic groups, on the other hand, are treated with weakly acidic exchangers. The latter type of exchanger is also used, for example, for the production of vitamin B12. Strongly basic exchangers are used especially for decolorization. Strongly acidic exchangers enable the separation and isolation of alkaloids.
• In medicine : for example, for the release of active ingredients by absorbing protons (H + ions) or metal ions in the body into the ion exchanger and releasing the active ingredient contained in the ion exchanger. Another application is the treatment of hyperkalemia by removing K + ions from the body and replacing them with Na + ions. In the therapy of hypercholesterolemia , anion exchangers are used (as so-called ion exchange resins ) to bind negatively charged bile acids in the intestine and, in exchange, release citric acid, for example. This inhibits the enterohepatic circulation of bile acids, the liver has to produce more bile acids from cholesterol and the LDL cholesterol level in the blood drops by up to 20%. Positive side effects are an increase in the beneficial effect of HDL cholesterol by 3–8% and the increase in the density of the LDL receptors, which leads to an increased extraction of the LDL from the blood. Constipation (constipation), nausea and a reduced absorption of fat-soluble vitamins A, D, E, K can be disadvantageous. In Germany, cholestyramine is used, albeit rarely for this indication .
• Hydroponics : In classic German hydroponics with expanded clay substrate (not to be confused with hydroponic systems ), long-termresin-based fertilizer pelletsare usually placedin the waterstorage tank . They supply the plants with minerals through ion exchange.
• Separation of the rare earth metals : The ion exchange method has been used with great success in the previously extremely cumbersome and difficult separation of the various rare earth metals . In the nuclear research their benefits proven in separating the plutonium from the uranium and the nuclear fission products. The rare earth metal promethium and some transuranic elements could be detected and isolated for the first time through ion exchange .
• In the aquarium hobby: For sensitive fish, molluscs or crustaceans to remove unwanted ions (e.g. copper ions). Also for removing nitrite NO 2 - and nitrate NO 3 - ( nitrate filter ) in freshwater aquariums if bacterial-biological filters cannot be implemented.

## Ion exchange membrane

An ion exchange membrane (also known as ion exchange membrane ) is a thin film (thickness: 20-100 micrometers) that can only be passed by ions with a certain charge sign. “Anion exchange membranes” are permeable to electrically negatively charged particles (anions), while “cation exchange membranes” only allow electrically positive charged particles (cations) through.

Ion exchange membranes serve as charge-selective filters, with the help of which cations or anions can be specifically removed from solutions. Such membranes are used in electrodialysis for the enrichment of salt solutions or for the separation of salts and are used for the production of acids and bases from salt solutions.

Technical ion exchange membranes (e.g. Amberplex) consist of water-swollen polymer networks to which electrically charged chemical groups (e.g. COO - , SO 3 - , PO 4 - , NR 4 + ) are fixed via covalent bonds . The overall charge on the membrane is balanced by mobile counterions that are dissolved in the aqueous phase. These mobile counterions can be exchanged for other mobile ions with the same charge as soon as the membrane is brought into contact with a salt solution. As a result, all ions with the same charge sign as the mobile counterions can pass through this membrane, while oppositely charged ions - with the same charge sign as the fixed ions (functional group) of the membrane network (polymer matrix) - are rejected. This mechanism is known as "Donnan's exclusion" (after Frederick George Donnan ) and means that ion exchange membranes can be used as charge-selective filters.

The selectivity , S +/-, of an ion exchange membrane is defined as the ratio of the concentrations of cations to anions in the membrane. This size decreases with increasing salt concentration, i. H. The membranes become ineffective in concentrated salt solutions (salt concentration> 10–15 mol / L). The calculation of the cation / anion selectivity is extremely difficult because S +/- depends simultaneously on the ion activity and the osmotic pressure within the membrane.

## swell

1. Charges in surface layers
2. ^ Rohm and Haas Co .; In: amber-hi-lites. No. 162, Fall 1979, p. 2.
3. G. Kühne and F. Martinola; In: Ion exchangers - their resistance to chemical and physical agents ; VGB Kraftwerkstechnik, 57, issue 3, March 1977, p. 176.
4. ^ Bayer AG; In: ion exchanger. 1999, K + W art and advertising printing, Bad Oeynhausen, p. 10.
5. Gerhard Schwachula, Hans Reuter: The development of synthetic resin ion exchangers from Wolfen - The first 50 years. In: eyewitness reports. Volume III: Chemical Industry. (Monograph Vol. 19). Society of German Chemists, Frankfurt 2000, ISBN 3-924763-88-7 .
6. Federal Health Gazette 28, No. 12-1985; For: Health assessment of plastics in the context of the Food and Commodities Act ( Memento of the original from April 13, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 654 kB), section 1.3.13.3.1.2.
7. Data are mainly based on the manufacturer's product data sheets for the types Lewatit S 100 and Amberlite IR 120.
8. Calvin Calmon, Harris Gold: New directions in ion exchange. In: Environmental Science & Technology. October 1976, Volume 10, No. 10, pp. 980-984.
9. Klaus Hagen, Wolfgang Hoell: The Carix process - a technology that has been tried and tested for many years. 2009, special number GWF Wasser Abwasser, pp. W44 to W48, .
10. Evan H. Crook, Roger P. McDonnel, James t. Mc.Nulty: Removal and Recovery of Phenols from Industriel Waste Effluents. In: Ind. Eng. Chem., Prod. Res. Dev., 1975, Vol. 14, No. 2 pp. 113-118.
11. Hubert Schneemann, Lloyd Young, Mary Anne Koda-Kimble: Applied drug therapy: Clinical-pharmaceutical care in ... Springer DE, 2001, ISBN 3-642-56505-0 , p. 216 ( limited preview in Google Book search).

## literature

• Gerd Krüger: Ion exchangers - an overview. In: Chemiker-Zeitung . 79 (21), (1955), pp. 733-737; Chemist Newspaper. 79 (22), (1955), pp. 768-772; Chemist Newspaper. 79 (23), (1955), pp. 804-806,
• Friedrich Martinola: Ion exchangers and adsorbers - versatile tools for the chemical industry . In: Chemical Engineer Technology. 51 (7) (1979), pp. 728-736, .
• AF Holleman , E. Wiberg : Textbook of Inorganic Chemistry . 37-39 Edition. Walter de Gruyter, Berlin 1956, p. 330.
• Babcock Handbook: Water. 1962.
• Rohm and Haas Comp .: amber-hi-lites. No. 127 March 1972, No. 132 Jan. 1973, No. 142 Sept. 1974, No. 160 Winter 1978-79, No. 174 Spring 1984.
• Product brochures from the manufacturers of ion exchange resins, e.g. B. Lanxess for Lewatit, Rohm and Haas for Amberlite etc.