LU87168A1 - PROCESS FOR OBTAINING DISSOLVED SALTS AND ACIDS USING ION-EXCHANGING RESINS - Google Patents

Description

L-3221

‘Ί A" 7 A & û GRAND-DUCHÉ DE LUXEMBOURG

Patent N ° R /.............. LJ? ° * ____ ·

^ Minister I EPA EPO-EPO

of ...... IBIZS ....... 19.8.8 --------------- 'of the Economized and Class is Moyemj ^ f "1 ^

Title issued .......................... SM Property Service Int, _Z_J EgÆ? LUXEMBOURG υ c ü0 1300

Patent Application for InvÂttrïn ^ ------------------------------------------- ---------------------------------------------------------- - (1) I. Application

Industrial ..... Quiinica del Nalon S.A., Avenida de Galicia 31, 33005 Oviedo, (2)

Spain and Empresa Nacional de Fertilizantes S .A., Prim. 12, 28004 J ^^ id,

Spanish, represented by Mr. Jean Waxweiler, 55 rue des Bruyères 7 ..........

Hovrald, aged ”in quality '" ................

.................................................. .................................................. .................................................. ................. — ................................ ................................... * ----- · --- V 3) deposit) this eighteenth of March one thousand nine hundred and eighty-eight _________________________ (4).

at ............. hours, at the Ministry of the Economy and the Middle Classes, in Luxembourg: 1. the present request for the obtaining of a patent of invention concerning:

Er.Q. céd.é ...... d. '. Oh..tent.ion ..... de._sel.s ....... et ..... diacides ... ... dissolved by means of ^ (s)

Usinas ...... â £ hang £ n.SÊS ..._ .. d.liQn.s .. «...................... .....................: ___________________________________________________________ 2. the description in French language is -................. ....................................... of the invention in triplicate; 3. ........................ 2 ....................... .................... drawing plates, in triplicate; · 4. receipt of the fees paid to the Registration Office in Luxembourg, on .18 · 03 * 1988 _______________.

5. the delegation of power, dated from Madrid ___________________ on ______ Q „7“ Q3 “1988___________.

6. the successor document (authorization); declare (s) assuming responsibility for this declaration, that the inventor (s) is (are): (6)

Manuel ...... Olivo ...... Gonzalez, Pedro Masaveu 1, 33007 Oviedo, Spain_______

Manuel Bravo, Avenida de Burgos 27, 28036 Madrid, Spain__________ claims (s) for the above patent application the priority of one (s) application (s) of (7) ............ .......... ferevet -------------------------------- filed in (8 ) -Spain ------------------------- (9) ... 18 ...... March ..... l9B2________________________________________________________________________________________________ under N ° (10) 87 Q.0 .7.6.9 ________________________________________________________________________________________________________ in the name of (11) Industrial Quimica del Nalon SA and Empresa Nacional de Fertilizanta S .A "elects (elect) domicile for him and, if designated, for its representative, in Luxembourg________________________________ 55 rue des Bruyères, Howald ___________ ^) request) the grant of a patent for the subject described and represented in the abovementioned appendices, with postponement of this grant to _________ / _________ Q .__________________________________ _____________________________month. (13)

The Boneless / Agent: ___________________-------------------------------------------- --- (14) Π. Deposit Minutes

The above application for a patent for invention has been filed with the Ministry of the Economy and the Middle Classes, Service de la Propriété InteIleetu $ aà Tïïxembourg, dated: 18.03.1988 / V * '“f $% \ $ * / ¾¾¾¾1 \ * e \ Pr. the Minister for the Economy and the Middle Classes, at hours d £ · '\ i | \ $ \ $ The head of the service at intellectual property, \ -Vf / / / N. S ~) / Il A 68007_ '// \] _ EXPLANATIONS RELATING TO THE DEPOSIT FORM.

Π N * 4 (1) if applicable "Request for certificate of addition to the main patent, on main patent application No ............ of ...... ...... ”- (2) enter the surname, first name, profession, U aj / address of the applicant, when the latter is an individual or the company name, legal form, address of the head office, when the applicant is a legal person- (3) enter XJ ÏJJL 1 the name "first name, address of professional representative, industrial property attorney, with special powers, if applicable;" represented by ....... ..... acting as agent ”~! - (4) date of birth in full - (5) title of the invention - (6) write the names, first names. inventors' addresses or the indication "(see) separate designation (will follow)", when the

J

CLAIM OF PRIORITY

Filing of the patent application in Spain of March 18, 1987 UNDER number 8700769

DESCRIPTIVE MEMORY FILED IN SUPPORT OF A PATENT INVENTION APPLICATION IN THE GRAND DUCHY OF LUXEMBOURG

by; Industrial Quimica del Nalon S.A. + Empresa Nacional de Ferti Avenida de Galicia 31 lizantes S.A.

33005 Oviedo Prim 12

Spain 28004 Madrid

Spain for; Process for obtaining salts and dissolved acids by means of ion exchange resins.

♦ I

-1- λ

PROCESS FOR OBTAINING SALTS AND D1 ACIDS DISSOLVED BY ION-EXCHANGING RESINS

‘The process according to the present invention relates to the use of ion exchange resins, of a cationic nature, to carry out ion exchanges between saline and acid solutions and to obtain solutions of other 5 products.

The ion exchange resin is a copolymer of styrene and divinylbenzene sulfonate, of macroporous structure, which is in the solid form of spheres with an approximate diameter of 0.6 mm. Different manufactures of this type of resins are available on the world market.

Such resins resist osmotic changes created by contact with solutions of different concentrations, without undergoing a physical change altering their shape. They can pass from the acid form to the saline form and vice versa, an indefinite number of times, while maintaining their structure and resistance with respect to the oxidizing or reducing action of any solutions.

20

Cationic ion exchange resins are sulfonic acids and behave like a strong acid. In contact with a solution of a salt, an acid / salt balance is established which can be represented according to the reversible equation:

RH + KA = RK + HA

wherein (RH) is the acidic resin; (RK) is the saline resin; (K) is the cation of the salt in 3o solution; (a) is the anion of the salt in solution, and (H) is the hydrogen ion or a cation distinct from the cation (K).

An ion exchange resin is said to charge when it changes to the salt form and to regenerate when it changes to the acid form.

0 -2-

When an acidic ion exchange reBine is arranged as a sufficiently tall column in a suitable container, and a solution of a salt such as potassium chloride (KC1) flows slowly, from bottom to bottom above, through the stationary resin, ion exchanges take place between the resin and the solution which tend to establish a physicochemical equilibrium at each point of the column. As a result of the ion exchange, the solution becomes more acidic as it advances, through resin 10 which transforms all the salt into acid, and the resin is charged with the corresponding cation. There is thus established in the column a salt concentration gradient descending from the top into an area in which only a resin in acid form is present, and a solution of the acid 15 corresponding to the salt introduced, and at the end, only the charged resin and a saline solution remain.

The ion exchange zone which is established advances in the column, progresses upwards, as the salt solution is supplied by the lower part, so that the resin takes charge in the presence saline solution and generates a solution of the acid corresponding to the salt which is extracted from the top.

The concentration of the anion corresponding to the salt that is. fed, remains practically constant over the entire column with small variations due to distinct degrees. of solvation of the resin in acidic and saline environments.

The height of the ion exchange zone in the column depends on the affinity of the resin for the cation of the salt with respect to the hydrogen ion. This affinity is greater in value, if the cation has large volumes and valences. 1 if you reverse the direction of circulation of the solution which • immerses the resin by feeding the acid solution through the upper part of the column and extracting it from below - 3 - • cele-ei, the area ion exchange moves down in the same direction as the solution and the resin regenerates in reversible form. In this case, the amplitude of the ion exchange zone is distinct as a function of the different affinity of the resin for the H + and K + cations.

In agreement with the behavior described, if on a regenerated cationic resin, arranged in the form of a column of sufficient height, a saline solution passes in the ascending direction 10 and at a suitable speed: - the resin is gradually loaded in the ascending direction at l inside the column; the ion exchange zone represents a defined volume of resin inside the column, this depending on the type of cations to be exchanged between the resin and the solution; - the ion exchange zone moves inside the column in the same direction as the solution, and - above the ion exchange zone there occurs a solution of the acid corresponding to the salt which is introduced.

The amount of acid produced keeps the stoichiometry with the charged resin. The macroporous ion exchange resins currently available have ► exchange capacities close to two equivalents per liter.

If the direction of circulation of the solutions inside the column is reversed, by introducing an acid solution through the top of the column and by extracting the saline solution through the bottom of the ion exchange zone. gradually moves downward as the resin regenerates, and an amount of saline is produced which keeps the stoichiometry with the regenerated resin.

-4-

As stated above, the subject of the invention is a process for obtaining salts and acids in solution, based on ion exchange with ion exchange resins in separate stages, which gives rise to to the advantages mentioned 5 in the following paragraphs.

The method of the invention allows production units capable of a high degree of automation to be produced. It also allows independent regulation of the process steps. It allows the ion exchange process to be carried out at a temperature close to room temperature while requiring minimal energy; one can operate at higher temperatures with the only limitation of not * damaging the resin under the conditions specific to each case.

The use, in the process according to the invention, of macroporous ion exchange resins, based on copolymers of styrene and of divinylbenzene sulfonate, highly resistant to osmotic shocks, makes it possible to operate with concentrated solutions without altering the structure of the resin • with the advantage that it entails in obtaining crystallized products. This type of resin is very resistant to disintegration, so that it can withstand a large number of cycles without undergoing significant deterioration. , 25 The small proportion of fines which inevitably occurs in the use of the resin, separates normally during the washing operations thereof,

The ion exchange resin is preferably a cationic resin formed by a copolymer of styrene and divinylbenzene sulfonate in the form of spheres of 0.6 mm in average diameter, although this process can also be used. other types of resins including. anionic resins, having a similar shape and resistant under the physicochemical conditions of the process,

Basically, the method consists in carrying out the charging and regeneration of the resin in two separate stages and in different columns, and for its description, reference is made to the appended drawings in which:

FIG. 1 is a schematic representation of an example of organization of the device and elements involved in the method of the invention in a first embodiment, and 10

Figure 2 is a schematic representation similar to the first, of a second embodiment.

In a first column, the resin is loaded with a salt in solution, at the same time as a solution of the acid corresponding to the salt is generated. In the appended figures, this column is designated by the reference (10).

This column (10), as shown schematically, is a cylindrical container arranged vertically. At its upper and lower ends are provided valves for isolating and transferring the resin. Near the lower end and laterally there is a tube (11) for supplying saline solution, and in the vicinity of the upper end there is another tube (12) for extraction. of the acid (or saline) solution that is generated in the process. Tubular distributors connected internally make it possible to obtain a uniform flow of the solutions which circulate through the resin over the entire section of the column. The distributors are provided to allow the passage of. liquids and retain the resin, and then, the movement of the resin in the column.

The dimensions in diameter and height of the column (10) 35 can vary within wide limits, depending on the expected production capacity.

-6- * For the sake of clarity, the description of the process for the resin loading step will be made using a potassium chloride solution as saline solution. Potassium chloride (KOI) is prepared in a 3N solution at room temperature (20 ° C) and is free from solid impurities in solution which can disturb the operation or damage the resin.

In the first step of the process which is the subject of the invention, the filling column (10) is first filled with an ion exchange resin, in acid form, and by immersing the latter t in hydrochloric acid in solution. 3N contained in a container (13). Once the column (10) is filled, the resin transit valves are closed and the 3N potassium chloride solution is fed through the lower tube (11) of the column and the solution is extracted. hydrochloric acid from above (12).

The process of feeding the saline solution is regulated, by equivalence, considering that there is a volume of resin contained in the column per hour when operating with the 3N potassium chloride solution. The condition which * · defines the degree of supply of salt solution is the obtaining of a short and well differentiated, ion exchange zone, inside the column, above which only the resin in acid form and the acid solution corresponding to the salt that is supplied coexist; and below which coexist the charged resin (RK) and the salt solution which is supplied. Such conditions vary, among other parameters, depending on the concentration of the salt, the physicochemical affinity of the salt cation (K +) for the resin, in relation to the possibility of substitution of (H +) and the curve particle size of the resin. 1

As the salt solution is fed, the ion exchange zone moves from the base of the column upwards, generating an amount of hydrochloric acid in solution equivalent to that of the resin which charge.

-7- »When the ion exchange zone arrives near the upper tube (12), through which the hydrochloric acid solution is extracted, the salt supply is stopped. In this way, all of the resin located in the column is loaded in form (RK) below the ion exchange zone.

Once the resin contained in the column (10) is loaded in the form (RK), the inlet and outlet valves 10 of the solutions are closed, and the volume of regenerated resin corresponding to a cycle is circulated. This volume of regenerated resin arrives in a container (13), placed above the column (10) and connected by means of a valve.

The resin is immersed in the acid solution from the process, which enters through the pipe (17) as explained below. Through the valve at the bottom of the • column a form-filled resin (RK) is extracted.

During this operation, the ion exchange zone which initially was in the vicinity of the upper tube (12), descends as the resin circulates until> reaching the level of the lower tube (11) At this time, the circulation of the resin in the column is stopped by the corresponding valves. The volume of circulating resin is kept constant during each cycle to facilitate the operation.

Then the opening of the solution inlet and outlet valves occurs again, and the salt solution is fed until the ion exchange zone is located near the upper tube (12 ) of the column.

In this embodiment, during the first step of the process and subsequent repetitive cycles, the regenerated resin of acid form (RH) is transformed into charged resin of saline form (RK), and the saline solution which is supplied becomes transforms the corresponding acid into solution.

-8-

The total quantity of salt in solution supplied in each cycle is the quantity necessary to charge the quantity of resin which circulates, plus the quantity of salt which leaves the column accompanying the resin in each cycle. For its part, the amount of acid in the form of solution which moves in each cycle, is the stoichiometric amount equivalent to the amount of resin which is loaded, plus the amount of acid which enters the column to immerse the resin at each cycle.

10 To ensure that the ion exchange zone moves in the column at each cycle between the established limits, and in order to guarantee that in the column, the acid solution will not be contaminated with the salt and the charged resin (RK ) or with the resin (RH), ion detectors are installed in the vicinity of said limits. Data from these detectors is used to adjust the amount of salt solution fed to each cycle.

The first step of the process according to the invention is valid, not only for transforming a salt into the corresponding acid, but also serves to transform a salt into another salt of the same anion. In this case, the resin which is supplied to the column (10) at each cycle must be charged with the cation 25 corresponding to the salt which it is desired to obtain. Thus, if the resin is loaded with sodium, in the form of (RNa), and a solution of potassium chloride (KC1) is fed into the column, a solution of sodium chloride (NaCl) and a resin loaded with potassium (RK). In this case, the concentration limit of the solutions involved is determined by the solubility of the least soluble salt.

In the process according to the invention, the resin and the solutions always flow against the current. In the example shown, the resin flows downwards and the solutions upwards, inside the column (10), but these directions can be reversed. To establish the direction of circulation, we use the criterion according to which the least dense solution must be in the upper part of the zone to avoid disturbances of the • ion exchange zone by convection currents pr ο voiced by the difference in densities.

5

The resin loaded in the form (RK) which leaves the column (10) • at each cycle, is sprayed with the salt solution used to load it. Before transferring this resin into a second column (20), to carry out the second step 10 of the process, it is necessary to properly separate the anion of this salt from the resin, to avoid saline contamination in the products to be obtained. For example, in FIG. 1, the resin accompanying the saline solution which is extracted from the column (10) is transferred into a container (14) in the form of a vertical column. This container is equipped with a double bottom in the form of a sieve which retains the resin and lets the liquids through. First, p the salt solution is extracted through the pipe (15), and is washed with water which enters through the pipe (16) to remove the salt. The diluted salt solution is extracted through the pipe (15) and can be used to dissolve more salt, and be reused once the concentration is adjusted.

The resin after washing and drying is extracted from the container (14) and is available for use in the second step of the process. For this, it is transferred to a container (23) and a salt solution carries it into the column ( 20) by the pipe (27). 1 2 3 4 5 6

The second step of the process according to the invention consists of an ion exchange 2 between the resin charged during the first 3 step of the process, and an acid or a salt in solution with a 4 anlon and a cation different from those used in the first 5 step, The ion exchange process takes place in the column (20) of construction and shape similar to those of the first column (10).

-10-

The operating mechanism of this second stage is similar to that of the first, but backwards. The volume of resin corresponding to each cycle and coming from the first step is introduced into the column (20), sprinkled with a solution of the salt obtained in the same way. At the same time as the resin loaded in form (RK) is introduced through the lower part of the column, the same volume of regenerated resin is extracted from the upper part. During each cycle, the established ion exchange zone moves from the lower part of the column, to the upper part.

With the ion exchange zone at the top of the column (20), and the transfer valves closed, the acid solution is fed to the acid by the upper tube (21) at the same time as the corresponding salt solution via lower tubing (22). The acid solution supplied regenerates the volume of resin introduced into the column (20) in one cycle. Thus, the ion exchange zone moves towards the lower part of the column where it is before the introduction of the resin, and an amount of salt is generated equivalent to the volume of regenerated resin.

The molar concentration of the acid which is supplied corresponds approximately to the concentration of the salt which is obtained, and is limited by the saturation concentration of the most insoluble component at the operating temperature.

If a solution of a salt is used to regenerate the resin, the exchange mechanism occurs in a similar way and this time the resin is obtained in acid form (rh) corresponding to the salt,

The circulation of the resin and the solution in each cycle 35 can be synchronized during the two stages of the process.

-11-

The regenerated resin which leaves the column (20) at each cycle is sprayed with the acid or salt solution used for its regeneration "Before transferring this resin to the first column (10) to carry out the first step of the process and • 5 close the resin cycle, it is necessary to properly separate the spray solution. For this, the resin and the spray solution are transferred to a container (24) in the form of a column similar in shape to that of the container (14) described above. Then the solution is recycled through the pipe (25), and the resin is washed with water which enters through the pipe (16) to properly remove the anion from the solution.

The washed and drained resin is transported in the 1S container (13) in acid or salt solution obtained in the column (10) which penetrates through the pipe (17) which makes it available to pass to the first step of the process. ,. In a second embodiment of the process according to the invention, it is possible to separate the salt solution from the resin by displacement with the solution of another salt obtained in the second step of the process. The operating diagram of this second embodiment is shown in FIG. 2.

25

The resin loaded in the form (RK) which leaves each cycle of a first column (100) is transferred into a container (130) in the form of a column, with characteristics and shape similar to those of the column (100). Next, a volume of dissolved salt obtained in a second column (200) in the second stage of the process, equal to the volume of salt solution introduced with 30 g, is fed into this container (130) through the lower tube (140). the resin previously in the column (100). Simultaneously, the corresponding volume of saline solution which enters with the resin is extracted through the upper tube (CL50) from the container (130).

-12-

Between the salt solutions in the container (130) a saline mixing zone is established, in which the two anions have inverted degrees of concentration, and above which the supplied solution coexists with solution 5 in the resin . The resin does not undergo transformations in this phase, # Said zone of saline mixingCours with each cycle from one end to another of the container (130) within * 10 limits established so that it is not extracted with extracted extracts. At the start of the resin transfer, the saline mixing zone is located in the upper part of the container (130), which is always kept full of resins immersed in the saline solutions. During the circulation phase, the resin leaving (130) enters through a valve into the column (200).

In the second step of the process, there is also the separation of the solution from the resin by displacement with another solution. In this case, the operation is carried out in a container (230), the shape and operation of which are similar to those of (130) previously described. In each cycle, the corresponding resin which leaves the column (200) is introduced. into a container (230) from the lower part, at the same time as an equal volume comes out from the upper part thereof. The displacement of the solution which enters the container with the resin, is carried out at each cycle by the upper tube (250) and 'against the current with the resin, an equivalent quantity of acid solution (or salt) is supplied. produced in column (100) in the first step of the process. The mechanism for moving the solution is similar to that which occurs in the container (130), 1

The resin which leaves the container (230) at each cycle is received in a container (300) for its transfer to another container (310) for supplying the column (100). In this embodiment of the process of the invention, the movement -13- of the resin corresponding to each cycle is synchronized between all the elements or equipment, and the resin is directed towards the container (310), 5 On FIG. 2 , the numerical references (tubing, valve pipes, etc.) have been omitted, the function of which follows from the explanation and the similarity between the steps and »arrows represented.

10 EXAMPLE 1

A production unit, defined to obtain potassium nitrate (KN03) and hydrochloric acid (HCl), from potassium chloride (KC1) and nitric acid (HN03), 15 with an approximate capacity of 5,000 Tons of potassium nitrate per year, has the following characteristics: - dimension of the columns: diameter 1.2 m; height 5 m.

- volume of resin moving during each cycle: 1 m3.

, 20 number of cycles per hour: 3, - approximate quantity of ion exchange resin in the circuit: 15 m3, € In the first step of the process, the resin is charged with potassium ions (RK) by means of a 3 N potassium chloride (KCl) solution, and hydrochloric acid in solution at a concentration of 2.8 N is obtained simultaneously. In the second step of the process, the resin regenerates in its acid form (RH) with a solution of nitric acid of 3ô concentration 3 N, and potassium nitrate (KN03) in solution is obtained, the concentration of which is approximately 3 N.

35 -14- EXAMPLE 2

In the same production unit, potassium nitrate (KN03) in solution can be obtained from sodium nitrate (NaNQ3). The resin regenerates in the second step with a solution of sodium nitrate (NaN03) of concentration 3 N. In the first step, the resin is charged with a solution of potassium chloride (KC1) of concentration 3 N, and one obtains simultaneously a solution of sodium chloride (NaCl), concentration 3 N.

EXAMPLE 3 In the same production unit, monopotassium phosphate in solution can also be obtained from a solution of monocalcium phosphate. For this, the resin is loaded in the first step with a potassium chloride solution (KC1) of 3 N concentration, and at the same time, a calcium chloride solution (CaCl2) is obtained. In the second step the process, the resin regenerates with a monocalcium phosphate solution and a monopotassium phosphate solution (KH2PO4) is obtained. 1 2 3 4 5 6 7 8 9 10 11 2 EXAMPLE 4 3 • 4

In the same production unit, phosphoric acid in solution can also be obtained from a solution of 6 monocalcium phosphate. For this, the resin is loaded in 7 the first -é.tape with a solution of phosphate 8 monocalcique Caô ^ PO ^, and one obtains simultaneously 9 phosphoric acid (H3PO4) in solution. In the second step, the resin regenerates with hydrochloric acid (HCl) in solution. ’-15-

The preceding examples show that the process according to the invention lends itself to an infinity of combinations for obtaining soluble salts and acids of industrial and commercial interest from other available salts and acids.

5 "

Claims (9)

1. Process for obtaining salts and acids in solution from other salts and acids, available by ion exchange facilitated by ion exchange resins, characterized in that the loading steps 5 and for regenerating the resin in separate containers in the form of columns. 2, A method according to claim 1, characterized in that the first step of the method consists in charging the ion exchange resin 10 with the cation corresponding to the salt which it is desired to obtain in the second column, by causing the circulation through the resin of a solution of a salt whose anion corresponds to that of the salt which it is desired to obtain, and in that the second step of the process consists of 15. regenerating in the second column the resin loaded in the first step by circulation through the resin, * of a solution of a salt or acid whose anion corresponds to • that of the salt or acid which it is desired to obtain, and whose cation corresponds to that of the salt obtained in the first column. 20 3. Method according to one of claims 1 or 2, characterized in that the solutions which circulate through the two columns for loading or regenerating the resin are supplied by one end of the column in an amount sufficient to displace the ion exchange zone towards the other end of the column, without leaving said column. 4, Method according to one of the preceding claims, characterized in that once the resin is charged with the corresponding cation in the first column, it is transferred to the second column for its regeneration and in that a fols As the resin is regenerated in the second column, it is transferred to the first column to be loaded, the resin being maintained in a closed cycle and working in a cyclic manner. "-17-" 5. Method according to any one of the preceding claims, characterized in that, before transferring the resin from one column to another, it is separated from the solution which immerses it, in a container allowing washing with 5 water or displacement with the solution 'fed the column where it will be transferred. 6. Method according to any one of the preceding claims, characterized in that the quantity of resin extracted from each column during each cycle is equivalent and sufficient to cause the displacement of the ion exchange zone from one end to the other. 'other of the column, without leaving said column. 7. Method according to any one of the preceding claims, characterized in that, inside the two columns corresponding to the two stages of the process, the ion exchange resin and the solution of the products (salts and acids) which are involved in the process, circulate, alternately against the current and cyclically, moving, at each half-cycle, the ion exchange zone from one end to the other of the column; and in that the resin is transferred from one column to another in a closed circuit by transporting the cation of the salt which it is desired to obtain at each stage of the process; and in that the intervening salt and acid solutions are kept separate in the two process steps. 8. Method according to any one of the preceding claims, characterized in that the solutions are fed into the columns during the two stages, so as to. that their quantity be adjusted to maintain well differentiated the three zones of physicochemical equilibrium which are established in each column, namely the zone of charged resin and of charge solution, the zone qr of ion exchange with the resin, and the regenerated resin zone and the corresponding solution,, ”• * -18- 9. Method according to any one of the preceding claims, characterized in that the columns are of cylindrical shape, the relationship between their diameter and their height preferably being from one to five. 5>