Ion exchange is the process of exchange of solid matrix ions ( ionite ) with water ions.

Ion exchange is one of the main methods of water purification from ionic pollution, deep water desalination. The presence of a variety of ion-exchange materials makes it possible to solve the problems of water purification of various chemical compositions with high efficiency. This is the only method that makes it possible to selectively extract some components from a solution, for example, hardness salts, heavy metals.

Ionites - solid insoluble substances containing functional (ionogenic) groups capable of ionization in solutions and exchange of ions with electrolytes. During the ionization of functional groups, two types of ions arise: some are rigidly fixed on the frame (matrix) R of the ion exchanger, others are of the opposite sign (counterions), capable of passing into solution in exchange for an equivalent amount of other ions of the same sign from the solution.

Ionites are divided according to the properties of ionogenic groups into four main types:

• ampholytes;
• selective ion exchangers.

By the nature of the matrix, they are divided into:

• inorganic ion exchangers;
• organic ionites.

Cation exchangers- ion exchangers with anions or anion-exchange groups fixed on the matrix, exchanging cations with the external environment.

If the cation exchanger was in the hydrogen H + - form, then all the cations in the water are extracted. The purified solution is acidic.

When a solution containing a mixture of cations such as Na, Ca, Mg, Fe (natural water) moves through the cation exchanger, sorption fronts of each cation form in its layer and their non-simultaneous breakthrough into the filtrate occurs. Purification is completed when the main extractable or controlled ion appears in the filtrate.

anion exchangers- ion exchangers with cations or cation-exchange groups fixed on the matrix, exchanging anions with the external environment.

If the anion exchanger is in the hydroxyl OH - form, then, as a rule, a solution after contact with the cation exchanger in the H + - form, which has an acidic reaction, is supplied for purification from anions.

In this case, all anions present in the solution are extracted. The purified solution is neutral.

When a solution containing a mixture of anions, such as Cl, SO 4 , PO 4 , NO 3, is passed through the anion exchanger, sorption fronts of each ion are formed in its layer and their breakthrough into the filtrate does not begin at the same time. Water purification ends when an extractable ion appears in the filtrate.

Ampholytes contain fixed cation-exchange and anion-exchange groups, and under certain conditions act either as a cation exchanger or an anion exchanger. Used for processing technological solutions.

Selective ion exchangers contain specially selected ionogenic groups that have a high affinity for one or a group of ions. They can be used to purify water from certain ions, such as boron, heavy metals or radionuclides.

The main characteristics of ion exchangers are:

• exchange capacity;
• selectivity;
• mechanical strength;
• osmotic stability;
• chemical stability;
• temperature stability;
• granulometric (fractional) composition.

exchange capacity

The following values ​​are used for the quantitative characterization of the ion-exchange and sorption properties of ion exchangers: total, dynamic and working exchange capacity.

Full exchange capacity(POE) is determined by the number of functional groups capable of ion exchange per unit mass of air-dry or swollen ion exchanger and is expressed in mg-eq/g or mg-eq/l. It is a constant value, which is indicated in the passport of the ion exchanger, and does not depend on the concentration or nature of the exchanged ion. POE can change (decrease) due to thermal, chemical or radiation exposure. Under real operating conditions, POE decreases with time due to aging of the ion exchanger matrix, irreversible absorption of poison ions (organics, iron, etc.), which block functional groups.

The equilibrium (static) exchange capacity depends on the concentration of ions in water, pH, and the ratio of the volumes of the ion exchanger and the solution during measurements. It is necessary for carrying out calculations of technological processes.

Dynamic exchange capacity (DOE) the most important indicator in water treatment processes. Under real conditions of repeated use of the ion exchanger in the sorption-regeneration cycle, the exchange capacity is not fully used, but only partially. The degree of use is determined by the method of regeneration and consumption of the regenerating agent, the contact time of the ion exchanger with water and with the regenerating agent, salt concentration, pH, design and hydrodynamics of the apparatus used. The figure shows that stop the water purification processut at a certain concentration of the limiting ion, as a rule, long before the complete saturation of the ion exchanger. The number of ions absorbed in this case, corresponding to the area of ​​\u200b\u200bthe rectangle A, related to the volume of the ion exchanger, will be DOE. The number of absorbed ions corresponding to full saturation when the breakthrough is 1, corresponding to the sum of the DOE and the area of ​​the shaded figure above the S-shaped curve, is called the total dynamic exchange capacity (PDEC). In typical water treatment processes, DOE usually does not exceed 0.4–0.7 PFU.

Selectivity. Selectivity is understood as the ability to selectively sorb ions from solutions of complex composition. Selectivity is determined by the type of ionogenic groups, the number of cross-links of the ion exchanger matrix, the pore size, and the composition of the solution. For most ion exchangers, the selectivity is low, but special samples have been developed that have a high ability to extract certain ions.

Mechanical strength shows the ability of the ion exchanger to withstand mechanical stress. Ionites are tested for abrasion in special mills or by the weight of a load that destroys a certain number of particles. All polymerization ion exchangers have high strength. In polycondensation, it is significantly lower. Increasing the degree of crosslinking of the polymer increases its strength, but worsens the ion exchange rate.

Osmotic stability. The greatest destruction of ion exchanger particles occurs when the characteristics of the medium in which they are located change. Since all ionites are structured gels, their volume depends on the salt content, pH of the medium, and the ionic form of the ionite. When these characteristics change, the grain volume changes. Due to the osmotic effect, the grain volume in concentrated solutions is less than in dilute ones. However, this change does not occur simultaneously, but as the concentrations of the "new" solution equalize over the grain volume. Therefore, the outer layer contracts or expands faster than the core of the particle; large internal stresses arise and the upper layer is chipped or the entire grain is split. This phenomenon is called "osmotic shock". Each ion exchanger is capable of withstanding a certain number of cycles of such changes in the characteristics of the medium. This is called its osmotic strength or stability. The largest change in volume occurs in weakly acidic cation exchangers. The presence of macropores in the structure of ionite grains increases its working surface, accelerates overswelling and makes it possible to "breathe" individual layers. Therefore, strongly acidic cation exchangers of a macroporous structure are the most osmotically stable, while weakly acidic cation exchangers are the least osmotically stable. Osmotic stability is defined as the number of whole grains, related to their total initial number, after repeated (150 times) treatment of a sample of the ion exchanger alternately in an acid and alkali solution with intermediate washing with demineralized water.

Chemical stability. All ion exchangers have a certain resistance to solutions of acids, alkalis and oxidizers. All polymerization ion exchangers have a greater chemical resistance than polycondensation ones. Cation resins are more stable than anion resins. Among anion exchangers, weakly basic ones are more resistant to acids, alkalis, and oxidizing agents than strongly basic ones.

Temperature stability cation exchangers are higher than anion exchangers. Weakly acidic cation exchangers are efficient at temperatures up to 130 °C, strongly acid type KU-2-8 - up to 100–120 °C, and most anion exchangers - no higher than 60, maximum 80 °C. In this case, as a rule, H- or
OH-forms of ion exchangers are less stable than salt ones.

Fractional composition. Synthetic ion exchangers of the polymerization type are produced in the form of spherical particles with a size ranging from 0.3 to 2.0 mm. Polycondensation ion exchangers are produced in the form of crushed particles of irregular shape with a size of 0.4–2.0 mm. Standard polymerization type ion exchangers have a size of 0.3 to 1.2 mm. The average size of polymerization ion exchangers is from 0.5 to 0.7 mm (Fig.). The coefficient of heterogeneity is not more than 1.9. This ensures acceptable hydraulic resistance of the layer. For processes when ion exchangers were used in a fluidized bed, in the USSR they were produced in the form of 2 classes by size: class A with a size of 0.6–2.0 mm and class B with a size of 0.3–1.2 mm.

Abroad, using special technologies, ion exchangers of the monospheric type Purofine, Amberjet, Marat h on are produced, having particles with a very small size spread: 0.35 ± 0.05; 0.5 ± 0.05; 0.6 ± 0.05 (Fig.). Such ion exchangers have a higher exchange capacity, osmotic and mechanical stability. Layers of monospheric ion exchangers have a lower hydraulic resistance, mixed layers of such cation exchange resin and anion exchange resin are much better separated.

Rice. Particle size distribution curves for standard ( 1 ) and monospheric ( 2 ) ion exchangers ( a) and photographs of such ion exchangers ( b)

A significant number of processes occurring in nature and carried out in practice are ion-exchange processes. Ion exchange underlies the migration of elements in soils and organisms of animals and plants. In industry, it is used for the separation and production of substances, water desalination, wastewater treatment, concentration of solutions, etc. Ion exchange can occur both in a homogeneous solution and in a heterogeneous system. In this case, under ion exchange understand the heterogeneous process by which an exchange takes place between ions in solution and in a solid phase called ion exchanger or ion exchanger. The ion exchanger sorbs ions from the solution and in return gives the ions that are part of its structure into the solution.

3.5.1. Classification and physico-chemical properties of ion exchangers

Ion exchange sorbents, ion exchangers are polyelectrolytes that are composed of matrices- immobile groups of atoms or molecules (high-molecular chains) with active ionogenic groups atoms that provide its ion exchange capacity. Ionic groups, in turn, consist of immobile ions bound to the matrix by chemical interaction forces, and an equivalent number of mobile ions with the opposite charge - counterions. Counterions are able to move under the action of a concentration gradient and can be exchanged for ions from a solution with the same charge. In the system ion exchanger - electrolyte solution, along with the distribution of exchanging ions, there is also a redistribution between these phases of the solvent molecules. Together with the solvent, a certain amount of coions(ions of the same name in charge with fixed ones). Since the electrical neutrality of the system is preserved, together with the coions, an additional amount of counterions, equivalent to them, passes into the ion exchanger.

Depending on which ions are mobile, ion exchangers are divided into cation exchangers and anion exchangers.

Cation exchangers contain immobile anions and exchange cations, they are characterized by acidic properties - a mobile hydrogen or metal ion. For example, cation exchanger R / SO 3 - H + (here R is a structural base with a fixed functional group SO 3 - and counterion H +). According to the type of cations contained in the cation exchanger, it is called H-cation exchanger, if all its mobile cations are represented only by hydrogen, or Na-cation exchanger, Ca-cation exchanger, etc. They are denoted RH, RNa, R 2 Ca, where R is the frame with the fixed part of the active group of the cation exchanger. Cation exchangers with fixed functional groups -SO 3 -, -PO 3 2-, -COO -, -AsO 3 2-, etc. are widely used.

anion exchangers contain immobile cations and exchange anions, they are characterized by the main properties - a mobile hydroxide ion or an ion of an acid residue. For example, the anion exchanger R / N (CH 3) 3 + OH -, with the functional group -N (CH 3) 3 + and the counterion OH -. The anion exchanger can be in different forms, as well as the cation exchanger: OH-anion exchanger or ROH, SO 4 - anion exchanger or RSO 4, where R is a frame with a fixed part of the active group of the anion exchanger. The most commonly used anion exchangers with fixed groups - +, - +, NH 3 +, NH +, etc.

Depending on the degree of dissociation of the active group of the cation exchanger, and accordingly on the ability to ion exchange, cation exchangers are divided into strongly acidic and weakly acidic. So, the active group -SO 3 H is completely dissociated, therefore, ion exchange is possible in a wide pH range, cation exchangers containing sulfo groups are classified as strongly acidic. Medium strength cation exchangers include resins with phosphoric acid groups. Moreover, for dibasic groups capable of stepwise dissociation, only one of the groups has the properties of an acid of medium strength, the second behaves like a weak acid. Since this group practically does not dissociate in a strongly acidic medium, it is therefore expedient to use these ion exchangers in slightly acidic or alkaline media, at pH4. Weakly acidic cation exchangers contain carboxyl groups, which are little dissociated even in weakly acidic solutions, their operating range at pH5. There are also bifunctional cation exchangers containing both sulfo groups and carboxyl groups or sulfo and phenolic groups. These resins work in strongly acidic solutions, and at high alkalinity they sharply increase their capacity.

Similarly to cation exchangers, anion exchangers are divided into high basic and low basic. Highly basic anion exchangers contain well-dissociated quaternary ammonium or pyridine bases as active groups. Such anionites are capable of exchanging anions not only in acidic, but also in alkaline solutions. Medium and low basic anion resins contain primary, secondary and tertiary amino groups, which are weak bases, their operating range at pH89.

Amphoteric ion exchangers are also used - ampholytes, which include functional groups with properties of both acids and bases, for example, groups of organic acids in combination with amino groups. Some ion exchangers, in addition to ion-exchange properties, have complexing or redox properties. For example, ion exchangers containing ionogenic amino groups give complexes with heavy metals, the formation of which occurs simultaneously with ion exchange. Ion exchange can be accompanied by complexation in the liquid phase, by adjusting its pH value, which allows the separation of ions. Electron-ion exchangers are used in hydrometallurgy for the oxidation or reduction of ions in solutions with their simultaneous sorption from dilute solutions.

The process of desorption of an ion absorbed on an ion exchanger is called elution, while the ion exchanger is regenerated and it is transferred to its initial form. As a result of the elution of the absorbed ions, provided that the ion exchanger is sufficiently "loaded", eluates are obtained with an ion concentration 100 times higher than in the initial solutions.

Some natural materials have ion-exchange properties: zeolites, wood, cellulose, sulfonated coal, peat, etc., however, they are almost never used for practical purposes, since they do not have a sufficiently high exchange capacity, stability in the treated media. The most widely used organic ion exchangers are synthetic ion-exchange resins, which are solid high-molecular polymer compounds, which contain functional groups capable of electrolytic dissociation, therefore they are called polyelectrolytes. They are synthesized by polycondensation and polymerization of monomers containing the necessary ionic groups, or by adding ionic groups to individual units of a previously synthesized polymer. Polymer groups are chemically bonded to each other, cross-linked into a framework, that is, into a spatial three-dimensional network called a matrix, with the help of a substance interacting with them - a watercress agent. Divinylbenzene is often used as a crosslinker. By adjusting the amount of divinylbenzene, it is possible to change the size of the resin cells, which makes it possible to obtain ion exchangers that selectively absorb any cation or anion due to the "sieve effect", ions larger than the cell size are not absorbed by the resin. To increase the cell size, reagents with larger molecules than those of vinylbenzene are used, for example, dimethacrylates of ethylene glycols and biphenols. Due to the use of telogens, substances that prevent the formation of long linear chains, an increased permeability of ion exchangers is achieved. In places where the chains are broken, pores appear, due to this, the ion exchangers acquire a more mobile frame and swell more upon contact with an aqueous solution. Carbon tetrachloride, alkylbenzenes, alcohols, etc. are used as telogens. The resins obtained in this way have gel structure or microporous. For getting macroporous ionites in the reaction mixture add organic solvents, which are higher hydrocarbons, such as isooctane, alcohols. The solvent is captured by the polymerizing mass, and after the formation of the framework is completed, it is distilled off, leaving large pores in the polymer. Thus, according to the structure, ion exchangers are divided into macroporous and gel ones.

Macroporous ion exchangers have better kinetic exchange characteristics compared to gel ones, since they have a developed specific surface of 20-130 m 2 /g (unlike gel ones, which have a surface of 5 m 2 /g) and large pores - 20-100 nm, which facilitates the heterogeneous exchange of ions that takes place on the surface of the pores. The exchange rate significantly depends on the porosity of the grains, although it usually does not affect their exchange capacity. The larger the volume and grain size, the faster the internal diffusion.

Gel ion-exchange resins consist of homogeneous grains, which in dry form do not have pores and are impermeable to ions and molecules. They become permeable after swelling in water or aqueous solutions.

Swelling of ion exchangers

swelling called the process of gradual increase in the volume of the ion exchanger placed in a liquid solvent, due to the penetration of solvent molecules deep into the hydrocarbon frame. The more the ion exchanger swells, the faster the exchange of ions takes place. Swelling characterized weight swelling- the amount of absorbed water per 1 g of dry ion exchanger or swelling ratio- the ratio of the specific volumes of swollen ion exchanger and dry. Often, the volume of the resin in the process of swelling can increase by 10-15 times. The swelling of a high-molecular resin is the greater, the lower the degree of cross-linking of its constituent units, that is, the less rigid its macromolecular network. Most standard ion exchangers contain 6-10% divinylbenzene in copolymers (sometimes 20%). When using long-chain agents instead of divinylbenzene for cross-linking, well-permeable macroreticulated ion exchangers are obtained, on which ion exchange occurs at a high rate. In addition to the structure of the matrix, the swelling of the ion exchanger is affected by the presence of hydrophilic functional groups in it: the ion exchanger swells the more, the more hydrophilic groups there are. In addition, ion exchangers containing singly charged counterions swell more strongly, in contrast to two- and three-charged counterions. In concentrated solutions, swelling occurs to a lesser extent than in dilute ones. Most inorganic ion exchangers do not swell at all or almost, although they absorb water.

Ion exchanger capacity

The ion-exchange capacity of sorbents is characterized by their exchange capacity, depending on the number of functional ionogenic groups per unit mass or volume of the ion exchanger. It is expressed in milliequivalents per 1 g of dry ion exchanger or in equivalents per 1 m 3 of ion exchanger and for most industrial ion exchangers is in the range of 2-10 meq / g. Full exchange capacity(POE) - the maximum number of ions that can be absorbed by the ion exchanger when it is saturated. This is a constant value for a given ion exchanger, which can be determined both in static and dynamic conditions.

Under static conditions, in contact with a certain volume of electrolyte solution, determine full static exchange capacity(PSOE), and equilibrium static exchange capacity(PCOE), which varies depending on the factors affecting the equilibrium (solution volume, composition, concentration, etc.). Equilibrium ion exchanger - solution corresponds to the equality of their chemical potentials.

Under dynamic conditions, with continuous filtration of the solution through a certain amount of ion exchanger, determine dynamic exchange capacity- the number of ions absorbed by the ion exchanger before the breakthrough of sorbed ions (DOE), full dynamic exchange capacity until the complete development of the ion exchanger (PDOE). The breakthrough capacity (working capacity) is determined not only by the properties of the ion exchanger, but also depends on the composition of the initial solution, the rate of its passage through the ion exchanger layer, the height (length) of the ion exchanger layer, the degree of its regeneration and the size of the grains.

The operating capacity is determined from the output curve fig. 3.5.1

S 1 - working exchange capacity, S 1 +S 2 - full dynamic exchange capacity.

When elution is carried out under dynamic conditions, the elution curve has the form of the curve shown in fig. 3.5.2

Typically, the DEC is greater than 50% of the PDOE for strongly acidic and strongly basic ion exchangers and 80% for weakly acidic and weakly basic ion exchangers. The capacity of strongly acidic and strongly basic ion exchangers remains practically unchanged in a wide range of pH solutions. The capacity of weakly acidic and weakly basic ion exchangers largely depends on pH.

The degree of use of the exchange capacity of the ion exchanger depends on the size and shape of the grains. Usually the grain sizes are in the range of 0.5-1 mm. The shape of the grains depends on the method of preparation of the ion exchanger. They may be spherical or irregular in shape. Spherical grains are preferable - they provide better hydrodynamic conditions and high process speed. Ion exchangers with cylindrical grains, fibrous and others are also used. The finer the grains, the better the exchange capacity of the ion exchanger is used, but at the same time, depending on the equipment used, either the hydraulic resistance of the sorbent layer increases or the carryover of small grains of the ion exchanger by the solution. Carryover can be avoided by using ion exchangers containing a ferromagnetic additive. This allows you to keep the fine-grained material in suspension in the zone - the magnetic field through which the solution moves.

Ion exchangers must have mechanical strength and chemical resistance, that is, they must not be destroyed as a result of swelling and operation in aqueous solutions. In addition, they should be easily regenerated, thereby retaining their active properties for a long time and working without a change for several years.

Definition of dynamic exchange capacity

and full dynamic exchange capacity of the cation exchanger

The ability of ion exchangers for ion exchange is characterized by exchange capacity, i.e. the number of functional groups involved in the exchange, which is expressed in equivalent units and refers to a unit of the number of ion exchangers. Exchange capacity can be determined both in static and dynamic conditions, so there are concepts of static exchange capacity and dynamic exchange capacity.

Objective: to determine the exchange capacity of the cation exchanger in dynamic conditions (DOE and PDOE).

DOE (dynamic exchange capacity) - the exchange capacity of the ion exchanger, determined by the appearance of a given ion in the solution flowing from the column (by "breakthrough") (mg-eq / dm 3).

PDOE (full dynamic exchange capacity) - is determined by the complete cessation of the extraction of a given ion from a solution, i.e. at the moment of equalization of the concentration of the absorbed ion in the solution and the filtrate when the solution is passed through a column with an ion exchanger (mg-eq / dm 3).

The essence of the dynamic method for determining the exchange capacity lies in the fact that a solution of a saturating ion is continuously passed through a compacted layer of an ion exchanger located in a column until a sorption equilibrium is established between the initial solution and the sorbent. As the solution passes through the column, a sorption layer is formed in it; in its upper part, the ion exchanger is completely saturated, then the sorption front moves down the column. When the front reaches the end of the column, the saturating ion "leaks" into the filtrate.

From the moment of formation of a saturated layer, sorption proceeds under the regime of parallel transfer of the sorption front. Further transmission of the initial solution leads to the fact that complete saturation is achieved throughout the entire thickness of the sorbent, i.e. balance comes. From this time on, the concentration of the filtrate becomes equal to the concentration of the initial solution.

In this work, a copper ion (copper sulfate) is used as a saturating ion. In this case, the ion exchange reaction in the column:

CuSO 4 + 2HR \u003d CuR 2 + H 2 SO 4

The “leakage” of the copper ion into the filtrate is determined using a qualitative reaction for Cu 2+ with an ammonia solution. In this case, the reaction proceeds:

2CuSO 4 + 2NH 4 OH \u003d ↓ (CuOH) 2 SO 4 + (NH 4) 2 SO 4

(

bright blue complex

Reagents and equipment

Copper sulfate, 0.05N solution.

Potassium iodide KJ, 20% solution.

Sodium thiosulfate Na 2 S 2 O 3,

0.05n solution.

Starch, 1% solution.

Sulfuric acid, 2n solution

Cation exchange resin KU-2.

Glass chromatographic column with a tap 20 cm long, 1 - 1.5 cm in diameter.

Support chemical with paws.

Measuring cylinder for 25 ml - 10 pcs.

Conical flask for titration 250 ml - 2 pcs

Titration burette 25 ml.

Pipettes for 2, 5 and 10 ml

Analysis progress

The column is filled with a pre-prepared cation exchanger, strictly observing the requirements of uniform and dense packing. The column is fixed in a tripod strictly vertically. By turning the tap, the required flow rate is set (3 ... 4 ml / min). During the analysis, it is necessary to ensure that there is always a layer of liquid above the cation exchanger layer and that air bubbles do not form in the column and the cation exchanger does not float.

1. Determination of the volume of the solution passed through the ion exchanger until the moment of breakthrough

A solution of copper sulfate is continuously passed through the column, collecting the filtrate flowing from the column into a beaker. Periodically, a few drops of the filtrate are taken into a drop plate and a qualitative reaction is carried out for the presence of copper ions. The appearance of a bright blue color indicates a “leakage” of copper ions into the filtrate. Using a graduated cylinder, measure the volume of the filtrate collected before the "breakthrough" of copper ions and record it (V breakthrough).

2. Determination of the volume of the solution passed through the ion exchanger

until the leveling of concentrations

After the onset of the "breakthrough", the copper sulfate solution is continued to flow, but the filtrate flowing from the column is collected in graduated cylinders in portions of 25 ml. In each portion of the filtrate determine the content of copper ions by iodometric titration.

For this, an aliquot of the filtrate (10 ml) is taken, transferred to a titration flask, 4 ml of a 2N sulfuric acid solution and 10 ml of a 20% potassium iodide solution are added. Titrate with 0.05 N sodium thiosulfate solution until the solution becomes light yellow, then add 3-4 drops of starch and continue titration until the blue solution becomes colorless. (If the solution after adding potassium iodide has a light yellow color, then starch is added immediately).

The passage of a solution of copper sulfate through the column is stopped after the content of the copper ion in the filtrate is equal to its concentration in the original solution. Record the volume of the solution passed through the column until the concentrations equalize (Vfull).

At the end of the experiment, the cation exchanger is regenerated by passing 150 ml of a 5% hydrochloric acid solution through the column. The completeness of regeneration is checked by a qualitative reaction to copper ions (in the absence of blue coloration of the filtrate sample, when ammonia is added to it, the regeneration is considered complete). After passing the regeneration solution, the column is washed with distilled water until the filtrate is neutral (check by adding methyl orange or bromthymol blue).

Computing

1. The calculation of the concentration of copper ions in the filtrate is carried out according to the formula:

Mg-eq / dm 3

2. Based on the results of the analysis, an output chromatogram is built (a graph in the coordinates: C - f (V solution)), plotting the volume of the filtrate on the abscissa axis (in milliliters), and on the ordinate axis - the concentration of copper ions in portions of the filtrate (in mg-eq / dm 3).

3. DOE and PDOE are calculated using the formulas:

,

where: C is the concentration of ions (cations for the cation exchanger, anions for the anion exchanger) in the passed solution, mg-eq / dm 3; V slip - the amount of water passed through the filter before the breakthrough of the absorbed ion, dm 3; V total - the amount of water passed through the filter until the concentrations are equalized, dm 3; V of the ion exchanger is the volume of the ion exchanger, dm 3.

The volume of the ionite is calculated by the formula:

,

where: r – column radius, dm; h is the height of the ion exchanger layer, dm.

Defense Questions:

What is the basis of ion exchange? What are ionites?

What ion exchangers are called macroporous, gel, isoporous?

What exchange groups do cation and anion exchangers contain in their structure?

What are nuclear grade ion exchange resins?

Give a description of the quality indicators of ion exchangers (granulometric composition, mechanical strength, chemical resistance, osmotic stability, thermal stability, swelling).

Why do ion-exchange properties of ion exchangers worsen at high temperatures? With the formation of what substances does the destruction of the cation exchanger KU-2-8 and the anion exchanger AV-17-8 occur at high temperatures?

The sorption capacity of ion exchangers is characterized by the distribution coefficient K. What is it?

What is POE of ion exchangers?

Define DOE. In what units is DOE expressed? How is the DOE of an ion exchanger calculated?

Define PDO. In what units is the PFU expressed? How is the PCOE of an ion exchanger calculated?

What exchange capacity is taken equal to the working exchange capacity and why?

What factors affect the exchange capacity of an ion exchanger?

What is the regeneration of cation exchangers and anion exchangers?

Why should there always be a liquid layer above the ion exchanger layer in the column?

Give the calculation for the preparation of a 0.05 N solution of copper sulfate.

Write the reaction that takes place in the column between the cation exchanger and the solution passed through it.

When does the “leakage” of ions into the filtrate occur? How is the “leakage” of copper ions into the filtrate checked? Write a reaction.

Until what point is the copper sulfate solution passed through the column after the onset of the "breakthrough"? What characterizes this moment?

What method determines the copper content in the filtrate? Write the equations of the occurring reactions using the ion-electron balance method. Name the titrant, indicator. What is the role of 2N sulfuric acid? How does the indicator work? Why is starch added at the end of a titration?

How is the cation exchanger regenerated after the experiment? Give the calculation for the preparation of the regeneration solution.

exchange capacity

The following values ​​are used for the quantitative characterization of the ion-exchange and sorption properties of ion exchangers: total, dynamic and working exchange capacity.

Full exchange capacity(POE) is determined by the number of functional groups capable of ion exchange per unit mass of air-dry or swollen ion exchanger and is expressed in mg-eq/g or mg-eq/l. It is a constant value, which is indicated in the passport of the ion exchanger, and does not depend on the concentration or nature of the exchanged ion. POE can change (decrease) due to thermal, chemical or radiation exposure. Under real operating conditions, POE decreases with time due to aging of the ion exchanger matrix, irreversible absorption of poison ions (organics, iron, etc.), which block functional groups.

The equilibrium (static) exchange capacity depends on the concentration of ions in water, pH, and the ratio of the volumes of the ion exchanger and the solution during measurements. It is necessary for carrying out calculations of technological processes.

Dynamic exchange capacity(DOE) - the most important indicator in the processes of water treatment. Under real conditions of repeated use of the ion exchanger in the sorption-regeneration cycle, the exchange capacity is not fully used, but only partially.

The degree of use is determined by the method of regeneration and the consumption of the regenerating agent, the contact time of the ion exchanger with water and with the regenerating agent, salt concentration, pH, design and hydrodynamics of the apparatus used. The figure shows that the water purification process is stopped at a certain concentration of the limiting ion, as a rule, long before the complete saturation of the ion exchanger. The number of ions absorbed in this case, corresponding to the area of ​​\u200b\u200bthe rectangle A, related to the volume of the ion exchanger, will be DOE.

The number of absorbed ions corresponding to full saturation when the breakthrough is 1, corresponding to the sum of the DOE and the area of ​​the shaded figure above the S-shaped curve, is called the total dynamic exchange capacity (PDEC). In typical water treatment processes, DOE usually does not exceed 0.4-0.7 PFU.

Rice. one

experimental part

Reagents and solutions: MgCl2*6H2O salts in distilled water in a volumetric flask with a capacity of 250 cm3

A solution of 1 calcium nitrate (0.02 M) was prepared by dissolving a sample (1.18 g) of Ca(NO3)2 4H20 salt. After dissolving the sample, the solution was diluted in distilled water in a volumetric flask with a capacity of 250 cm3.

Calcium nitrate solution 2 (О.1М) was prepared by dissolving a sample (5.09 g) of Ca(NO3)2 4Н20 salt. After dissolving the sample, the solution was diluted in distilled water in a volumetric flask with a capacity of 250 cm3.

The initial solution of the complexone III prepared from fixanal. Standardization was carried out for magnesium sulfate.

Buffer solutions were prepared from NH4Cl “analytical grade.” and NH4OH.

The residual concentration of Mg 2+ ions was determined complexometrically with the indicator eriochrome black T.

The residual concentration of Ca 2+ ions was determined complexometrically with the indicator murexide.

The sorbed concentration was found by the difference between the initial and residual.

The zeolite-containing rock of the Atyashevsky manifestation was used as a sorbent.

Sorbent preparation.

CSP Atyashevsky manifestation was crushed, sieved, collected fractions of granules with a size of 1 - 2 - 3 mm and dried in an oven.

Ion exchange capacity in static mode. To 20 cm3 of a solution containing Ca 2+ ions, in another case Mg 2+, with a known concentration and

5.0 g of sorbent was added at a certain pH value, shaken for a specified time, and the solid phase was separated by filtration. AT

The selectivity of chelatometric titration with respect to calcium can be increased by carrying out the determination in a strongly alkaline medium (magnesium filtrate determined the residual concentration of Ca 2+ ions, in another case Mg 2+. The sorbed concentration was found by the difference between the initial and residual.

The metal-chromic indicator is murexide.

EDTA, 0.05M solution; ammonia buffer mixture pH=9; NaOH, 2M solution; indicators - eriochrome black T and murexide - solid (mixture with NaCl in a ratio of 1: 100).

Method of determination

1. A sample of the analyzed solution was transferred into a titration flask, 10 cm 3 of an ammonia buffer mixture (pH 9), 25 cm 3 of distilled water were added, 30–40 mg of eriochrome black T were added at the tip of a spatula, and the system was weighed until the indicator was completely dissolved. The solution acquired a wine-red color. Titration with EDTA solution was carried out drop by drop from a burette with continuous stirring until the color changed to clearly blue.

2. A sample of the analyzed solution was transferred to a titration flask, 5 cm 3 of a 2M NaOH solution, 30 cm 3 of distilled water, and 30 mg of murexide at the tip of a spatula were added. The solution turned red. Titration was carried out with an EDTA solution until the color changed to violet.

Calculation of statistical terms with respect to calcium and magnesium ions.

Determination of the exchange capacity for magnesium

To 20 cm 3 of a solution of magnesium chloride with a molar concentration equivalent of 0.02 mol/l was added 5.0 g of sorbent, previously dried at 105 0 C for 1 hour and shaken for a specified time (0.5 hour). Otherwise, 1 hour and so on. After time, the solution was filtered. 5 cm 3 of the filtrate were taken for analysis and the residual concentration of Mg 2+ ions was determined by the complexometric method.

2. To 20 cm3 of a solution of calcium chloride with a molar concentration equivalent of 0.l mol/l was added 5.0 g of the sorbent preliminarily dried at 1050C for 1 hour and shaken for the specified time (0.5 hour). Otherwise, 1 hour and so on. After time, the solution was filtered. We took 5 cm3 of the filtrate for analysis and determined the residual concentration of Ca2+ ions by the complexometric method.

Effect of contact time of CSP and CaCl2 * 4H2O solution on the exchange capacity of CSP under static conditions.

(С(Са2+)ref = 0.1 mol/L; mcsp = 5.0 g.)

With an increase in the contact time of the phases, an increase in the equilibrium concentration is observed. And after 3 hours, a dynamic mobile equilibrium is established.

Thank you in advance for your response.

C100E is a gel type strong acid cation exchange resin with high exchange capacity, chemical and physical stability and excellent performance. C100E effectively retains suspended particles, and also, in acidic (H +) form, removes iron and manganese ions.

The high exchange capacity makes it possible to obtain water with a total hardness of the order of 0.05 meq/l, and the excellent ion exchange kinetics make it possible to achieve high flow rates. When using C100E, the slippage of ions that cause water hardness under normal operating conditions, as a rule, does not exceed 1% of the total hardness of the source water. In this case, the exchange capacity of the resin practically does not change, provided that the proportion of monovalent ions does not exceed 25%.

C100E is insoluble in acid and alkali solutions and in all common organic solvents. The presence of residual oxidizing agents (such as free chlorine or hypochlorite ions) in the water can reduce the mechanical strength of the cation exchange resin particles. C100E is thermally stable up to a temperature of 150°C, however, at high temperatures, the exchange capacity of the cation exchange resin in the acid (H+) form decreases.

Specifications

A BRIEF DESCRIPTION OF
free space above download - 50%
grain size 0.6mm up to 90%
Bulk weight 820gr/l
Water content (humidity) 42-48%
Total capacity up to 2 g eq/l
operating temperature from 4 - 120 0 C
water pH 0 - 14
transition of Na ions to H - 8%
layer height from 0.8 - 2m
service speed from 5 - 40m/h
specific speed of service 20oz/hour
backwash speed at 20 C from 10 - 12m/h
volume of water for backwashing with a new load 20oz
backwash water volume 4oz
volume of water for slow washing of salt 4oz
salt consumption during regeneration per 1 liter of load - 150g
residual hardness - 0.5mg equiv/l
specific pressure loss in kPa m 2 loading height - 1
pressure loss of 11mbar at 4°C per 1m loading height
regeneration speed - 5m/h
speed when washing salt with water - 5m/h

APPLICATION CONDITIONS
lack of oxidized iron (Fe 3+) in water
lack of dissolved oxygen in water
lack of organic matter in water
the absence of any oxidizing agents in the water
after sodium - softening, the total alkalinity and dry residue will increase.
strong oxidizing agents such as nitric acid can cause violent reactions
suspended solids in source water up to 8 mg/l
color of source water up to 30 0 С
turbidity of source water up to 6 mg/l
total hardness of source water up to 15 mg equiv/l

Below are the methods for calculating the exchange capacity and other parameters of the cation exchanger.

The working exchange capacity of the cationite E f g÷eq / m3, can be expressed by the following formula:

E f \u003d Q x W; Ep = ep x Vk.

The volume of the cationite loaded into the filter in the swollen state is expressed by the formula:

The formula for determining the working exchange capacity of the cation exchanger ep, g÷eq / m 3:

ep \u003d Q x W / S x h;

where W is the hardness of the source water, g÷eq/m3; Q - the amount of softened water, m 2; S is the area of ​​the cationite filter, m 2 ; h is the height of the cationite layer, m.

Denoting the speed of movement of water in the cation exchanger as v k , the amount of softened water Q can be found using the following formula:

Q \u003d v k x S x Tk \u003d ep x S x h / W;

from which it is possible to calculate the duration of the operation of the cationite filter Tk:

Tk = ep x h/v k x W.

It is also possible to calculate the exchange capacity of the cation exchanger using correlating graphs.

Based on approximate practical data, your filter will be able to clean no more than 1500 liters. water. For more accurate calculations, you need to know the amount (volume) of resin in your filter and the working exchange capacity of your resin (for cation exchange resins, the working capacity varies from 600 to 1500 meq/l). Knowing these data, you can easily calculate the exact amount of softened water according to your formulas.