WO1990011829A1 - Process for the elimination of undesirable substances in a liquid without modification of its characteristic composition and device for implementing said process - Google Patents

Abstract

Process and medium for treating liquids, particularly aqueous liquids, with a view to eliminating undesirable substances in particular, such as manganese and uranium and radium ions, by percolation of the liquid on said means, which is a compound resulting fro m the insertion of amorphous manganese oxides into the network of a strong resin, an anion exchanger, with a self-reducing property, thus reducing the permanganate ion (MnO4?) for which it has a great affinity.

Description

PROCESS FOR REMOVING UNDESIRABLE SUBSTANCES FROM A LIQUID WITHOUT MODIFYING ITS CHARACTERISTIC COMPOSITION AND DEVICE FOR IMPLEMENTING SAME.

The subject of the invention is a method for eliminating undesirable substances from a liquid without modifying its characteristic composition and a device for its use. The elimination of undesirable substances in industrial or food liquids has been carried out for a long time and in multiple forms by using either techniques proceeding by ion exchanges, whether they are cation exchangers and / or anion exchangers, either by techniques using chelation, or by adsorption or finally by co-precipitation-adsorption resulting in the formation of subsequently decanted flocs. If these different techniques are usually satisfactory for applications such as the purification of industrial effluents and drinking water, their application to liquids whose characteristic compositions are desired, for example liquids for industrial use or mineral waters, spring water or various food liquids such as milk or sugary juices poses problems which, to date, have not been resolved.

Indeed, if one carries out a treatment of elimination of undesirable substances in a liquid using an ion exchanger implementing a natural or synthetic med, the ion exchange does not intervene exclusively on the substances to be eliminated, so that the characteristic composition of the treated liquid is not conserved, see for example, M. GASCOYNE: "A highl selective method for removing natural radioactivity fro drinking water", & PROC. , ANNU. CONF. - CAN. NUCL. so

1986, 7TH, 105-8. Similarly, if the treatment is carried out by the techniques of co-precipitation-adsorption, by flocculation, the reagents introduced into the liquid lead to physico-chemical modifications of the treated liquid, which are also unacceptable. As a result, the known methods and devices are unsuitable for the treatment of liquids such as natural mineral waters, the physico-chemical characteristics of which, in particular with regard to the particular mineralization or the characteristic composition, must not be altered during the treatment carried out for elimination unwanted substances.

If, in addition, it is desired that the elimination of the undesirable substances be carried out under conditions allowing its industrial application, that is to say at a sufficiently low cost and with sufficiently high flow rates, it is then understood that, to date, it has not been possible to satisfactorily resolve all of the problems mentioned above using known techniques.

It is, precisely, an object of the invention to provide a solution to these problems and, in particular, to provide a method for the removal of undesirable substances from liquids, in particular aqueous liquids, which can be applied. used on an industrial scale, that is to say for the rapid and efficient treatment of large liquid flow rates.

It is also an object of the invention to provide such a process which is well suited to the conditions imposed by public health standards, on the one hand with regard to drinking water and, on the other hand , as regards environmental protection when the treated water is waste water, such as mine water, or contaminated water, for example made radioactive.

It is, again, an object of the invention to provide such a process which, when used for the treatment of drinking water, does not involve any modification of the physico-chemical and mineral characteristics major of it and, thus, can be applied to natural mineral waters.

Finally, it is an object of the invention to provide a device for implementing the method, in particular a medium which is both sufficiently simple to use, of high efficiency and of a cost allowing its industrial exploitation.

A method according to the invention, for the elimination of undesirable substances such as uranium, radium, and manganese ions in a liquid, in particular a food liquid, without modification of its characteristic composition and by treatment of said liquid with a medium on which it is percolated, is characterized in that said medium is a compound for inserting amorphous manganese oxides into the network of a strong anion exchange resin with self-reducing property, reducing the ion permanganate (MuO ^) for which it has a great affinity.

When the reducing power of the amines of the anion exchange resin with significant self-reducing property is sufficient to reduce the potassium permanganate, (Mn0 ₄ K), the use of this resin allows, without other reagent, to obtain 'an insertion compound in which the manganese oxides - and this term is here used on purpose not to be limited to a particular stoechio etric formula -, are present in amorphous form and diffuse in the meshes of the unaltered network of resin.

Given that the medium as defined above has a very strong affinity for sulphates, the invention provides complementarily, according to another of its characteristics, to first carry out a sulphidation step prior to the operation of actual treatment of the liquid to be treated by percolation on said medium, when said liquid contains ions sulfate in its characteristic composition which one does not want to modify.

In a preferred embodiment of the process, the sulfation step is a potassium bisulfate treatment.

The medium according to the invention for the implementation of the process, then consists of a compound for the insertion of amorphous and diffuse manganese oxides in the network of a strong anion exchange resin, with great affinity for 1 ' ion permanganate (MnO ^), and the reducing power of the amines is sufficient to reduce the permanganate in said macromolecular network of the resin.

In a preferred embodiment, the medium results from the treatment of a strong anion exchange resin, of food quality, with self-reducing property and having a great affinity for the permanganate ion, with a solution of (Mnθ) for the formation of manganese oxides, part of which is precipitated in the network of the resin and the free fraction of which is eliminated by successive flotation-decantation operations and washing with distilled water, then elimination of the ammonium ions and residual amines by treatment with acetic acid followed by washing with distilled water until a very slightly acidic pH of approximately 6 is obtained.

The media thus obtained is a stable, neutral product, which does not react with the medium to be treated and which, in particular when the latter is potable water, does not give it a bad odor or a particular taste. When, in addition, the liquid to be treated is natural mineral water, the use of the medium which has just been defined leads under suitable conditions to decontamination with uranium, radium, manganese, iron, barium and strontium ions , without modification of the other physico-chemical characteristics of the water, in particular its pH, its conductivity and its composition in major mineral salts.

Other characteristics and advantages of the invention will appear from the following description of preferred embodiments thereof. I - Media preparation

The method according to the invention, for the elimination of undesirable substances in a liquid, in particular radioactive elements such as uranium and radium ions, but also manganese, firstly involves the production of a fixing medium for these elements.

In accordance with the invention, the medium consists of a compound for the insertion of amorphous and diffuse manganese oxides into the network of a strong anion exchange resin with self-reducing property, having a great affinity for 1 ion (Mnθ), this ion being reduced to manganese oxides in contact and within the macromolecular polymer constituting the resin.

In view of the fact that the resin must, moreover, be suitable for the treatment of food products, such as drinking water, milk, sugary juices, etc., and present, in addition, characteristics which allow it to use in an industrial process (for example spherical particle size to avoid clogging of the columns) various media which will be described below have been manufactured from commercially available resins after description of a comparison example. 1. Example of comparison outside the invention The anion exchange resin used is that sold under the name DOWEX 1 X 8 by the company DOW CHEMICAL CORPORATION.

It is an anion exchanger whose strong basic exchanger groups (quaternary ammonium) are fixed on a matrix of polystyrene type. After treating the resin with sodium hydroxide at the rate of 2 eq / l and then washing with distilled water, the resin is equilibrated with a solution of MnO ₄ K at 2 g / 1. The solution is then treated with hydrogen peroxide at 110 vol., At a rate of 120 ml per gram of resin and this operation is followed by washing with distilled water until a pH of approximately 8 is obtained. and removing particles of Mn oxides not included in the resin network.

To evaluate the power of elimination of uranium and radium ions by the media thus produced, the radioactivity α is measured and, more precisely, the decontamination factor α expressed in% and which represents the percentage of the initial radioactive activity α eliminated from the treated liquid, i.e. fixed by the test medium. The liquid to be treated, consisting of natural mineral water, feeds "per ascendum" a column comprising the media arranged in stages in the column. First, there is a significant change in the pH of the water and unpleasant odors of ammonium. It can also be seen that the elimination yields of radium and uranium are of the order of 60 to 80%, respectively, and since the resin is not of the food type, the use of a medium such as defined above for the implementation of a process for eliminating undesirable substances in a liquid food, such as milk, drinking water or the like is totally inappropriate.

Given, moreover, that the reduction treatment with hydrogen peroxide is a "violent" treatment which significantly alters the particle size, geometry and macromolecular network of the resin, thus making it unsuitable for industrial use, the The Applicant has been led, after numerous attempts, to consider finding another solution to the problems posed. To do this, the Applicant has first chosen new anion exchange resins and, in particular such resins with self-reducing properties, the reducing power of which is sufficient to reduce potassium permanganate, as explained below.

2. Example of realization

A media according to the invention is prepared from a resin known under the name of IMAC HP 441, sold by the company ROHM & HAAS and which is a strong anion exchanger, of the gel type, strongly basic, with functional groups trimethylamine known for its use in the denitration of water intended for food. Its density relative to water at 20 "C is close to 0.5 (wrung out resin hydrated at about 46%) and the macromolecule which constitutes it is obtained by polymerization of styrene and divinylbenzene, then chloromethylation treatment and reaction of a ination.

The resin is first treated with a potassium permanganate solution at 50 g / 1 which reacts with the resin to form manganese oxides, part of which is precipitated in the network of the resin and the free fraction of which is eliminated by a succession of flotation, decantation and washing operations with distilled water. Following this treatment, the ammonium ions and the residual amines are eliminated by a treatment with acetic acid at 1% (V / V) and washing with distilled water until a pH of approximately 6.

The media thus prepared is in the form of shiny black beads with a diameter of between 0.3 and 1.2 mm.

-Its density (product drained on a cellulose filter) is approximately: 0.928

-its water loss on drying at 180 ° C in 24 hours: 48.4% - its loss on calcination at 800 "C in 1 hour: 72.8%.

It has a total adsorption capacity for Mn ²⁺ of: 0.20 eq / kg. The media is then subjected to the following tests to determine its effectiveness. Test A

It is carried out at 20 ° C. on natural mineral water doped with uranium at 5 mg / 1, by stirring 1 g of medium in 200 ml of water, for six hours.

The decontamination factor measured for uranium is 99%.

The characteristics of natural mineral water before and after treatment are given in Table I below.

TABLE I

Water Before treatment After treatment pH 7.52 7.52

^po_ 0,0 0,0 Ca 253 253Conductivity 1.52 μS x cm 1.52 μS x cm C Cll ^"" 72 mg / 1 72 mg / 1

^in. 0.0 0.0 0.0 Ca 253 253

Mg 95 95 M Mnn 0.54 0.00

NH. 0.0 0.0 Test B

It repeats the procedure set out above for test A, and for a stirring time of 6 h. The decontamination factor for uranium is the same as that reported above, namely 99% and the characteristics of the treated mineral water are those of Table II. TABLE II

Water Before treatment After treatment pH 6.54 6.54

Conductivity 1.85 μS x cm 1.85 μS x cm

ca 251 251Cl ^" 70 mg / 1 70 mg / 1 n / a ₄ " 47.8 35

ca 251 251

Mg 98 98

MMnn 0.50 0.06

NH „ ⁺ 0.0 0.0 Test C

The natural mineral water treated is, in this test, water doped at 4.54 Bq / 1 in ² Ra. The procedure being the same as that of the tests

A and B above, we see that the decontamination factor for radium is 66% after 3 h of stirring and 90.5% after 15 h of stirring.

It thus appears that the media according to the invention, whose maximum retention capacity for uranium in natural mineral water is of the order of 35 mg / g at 20 ^β C, allows a decontamination of 99.98 % for uranium for a contact of the order of 1.30 h and, as regards radium, a decontamination of 90.5% for a contact of 15 h or 66% for a contact of 3 h.

It is also noted that the medium according to the invention does not modify the pH and the conductivity of the treated water, does not impart to it either a bad smell or a bad taste. The tests reported above having shown the effectiveness of the medium according to the invention, the safety of an installation intended to use it is then determined by a non-salting-out test. For the latter, the medium which has fixed uranium is stirred in the natural mineral water used in test B, but without doping.

No uranium salting out is observed and the results obtained after 12 h stirring are reported in Table III below.

TABLE III Before treatment After treatment S0 ₄ "47.8 mg / 1 40 mg / 1 Mn 0.50 0.03

Sr 1.08 0.086

The test also shows that manganese is retained by the media with a retention factor of 94% for a contact of 12 h, on the one hand, and, on the other hand, that the impact on the sulfate ion is substantially negligible, the retention factor for this ion being of the order of 16.3% for a contact time of water and the media of 12 h.

The test also shows that the strontium is fixed by the medium with a retention factor of 92%, which makes the medium according to the invention particularly suitable for the treatment of decontamination of liquids accidentally or not contaminated by radioactive isotopes. of this element. The effectiveness of the medium is also determined, more particularly with respect to the manganous ion in the following tests.

Tests D

They are carried out on a laboratory pilot comprising a percolation column of 8 cm in diameter in which the media is added in a bed 17 cm in height whose volume V _L is equal to 0.854 1.

The tests made it possible to determine the influence:. percolation rate physico-chemistry and the manganese content of raw water. Dl Influence of the percolation flow

The results obtained for the flow rates of 15 V / V _d / h are reported in Tables A and B, respectively. It emerges from their examination that the corresponding manganese decontamination factors are 80% and 100%, without any alteration in the physico-chemical characteristics of the treated water. D.2. Influence of physico-chemistry and Mn content

The results obtained are shown in the tables

C, D, E, F, G. They show that the manganese decontamination factors are satisfactory.

TABLE A

Influence of the flow rate on manganese decontamination Results obtained for a flow rate of 15 V / V _d ^ / h

Vol. Of water 10 15 20 25 30 37 45

© harvested * Water parameters <Treated water> initial p (Ω.cm 20 ° C) 1824 2564 2173 2040 1960 1886 1883 1870 1851 pH 6.9 6.77 6.76 6.79 6.81 6.60 6.70 6.70 6.70

TAC (me / l) 5 3.4 4.1 4.2 4.4 4.5 4.8 4.8 4.75

TH (° f) 14.8 8.6 10.6 10.8 11.8 14 13.8 13.8 14

S04 ~ (mg / 1) 13, 6 22 17 15, 7 14 13, 4 13, 5 13, 5 13, 6

Cl- (mg / l) 44 12, 4 28 32 38 40 43 42 43

Na + (mg / l) 83 69 79 78 81 81 81 83 82

K + (mg / 1) 8 1.5 4 6 6.6 5.5 6.5 7.7 7.8

Mn (mg / 1) 0.15 <0.03>

* Expressed in number of bed volumes, V / V _L TABLE B

Influence of flow rate on manganese decontamination Results obtained for a flow rate of 160 V / Vτ / h

* Expressed in number of bed volumes, v / v _L

TABLEAU C

TABLE C

Influence of pH on manganese decontamination Results obtained for raw water at pH 5.68 and at flow rate = 136 V / V _d / h

* Expressed in number of bed volumes, V / V _L

TABLEAU D

TABLE D

Influence of pH on manganese decontamination Results obtained for raw water at pH 6.27 and at flow rate = 160 V / V _d / h

* Exprimé en nombre de volume de lit, V/V_L

* Expressed in number of bed volumes, V / V _L

TABLEAU E

TABLE E

Influence of pH on decontamination in Mn Results obtained for raw water at pH 6.5 and at flow rate = 160 V / V _d / h

* Expressed in number of bed volumes, v / v _L

TABLEAU F

TABLE F

Influence of pH on decontamination in Mn Results obtained for raw water at pH 6.5 and at flow rate = 136 V / V _d / h

* Expressed in number of bed volumes, V / V _L

TABLEAU G

TABLE G

Influence of the Mn concentration of raw water on its Mn decontamination

Parameters Percolated water volume

Initial water Treated water L

Flow rate (V / V _d / H) 12 p (ohms.cm 20 ° C) 2930 3001 3030 pH 7.22 7.09 7.15

Mn (mg / 1) 4.5 0.015 0.015

FDMn (%) 99.6 99.6

Flow rate (V / V-J- / H) 12 p (ohms.cm 20 ° C) 3030 3133 3120

PH 7.30 7.32 7.32

Mn (mg / 1) 2.5 0.01 0.01

FDMn (%) 99.6 99.6

Flow rate (V / V --- / H) 12 p (ohms.cm 20 ° C) 3130 3130 3130

PH 7.08 7.05 7.10

Mn (mg / 1) 1.2 0.01 0.01

FDMn (%) 99.5 99.5

Flow rate (V / V _d / H) 1 20 p (ohms.cm 20 ° C) 3330 3330 3330 pH 7.30 7.33 7.30

Mn (mg / 1) 1 0.02 0.02

FDMn (%) 98 98

* expressed in number of bed volumes V / V _L II - The demineralization process Since the medium as defined above has a strong affinity for sulphates, the invention provides for preliminary conditioning of sulphation of the medium, before percolation of the liquid to be treated, when said liquid contains sulphate ions in its characteristic composition which one does not want to modify.

In a preferred embodiment, ensuring good stability and standardization of the media, this sulfation conditioning is carried out using a potassium bisulfate solution (KHS0 ₄ ) until a balance is obtained with the liquid to be treated.

The media thus conditioned can be used in columns for the treatment by percolation of the liquid, such as water, from which it is desired to remove undesirable substances without modification of the characteristics of composition of said liquid.

Thus, by the process of the invention, the possibility of treating large flow rates of liquid is obtained, whether it is edible water such as natural mineral water, dewatering water or water contaminated, for example ^* made radioactive, this list having, of course, no limiting nature since the invention finds application for the treatment of other liquids, in particular but not exclusively aqueous, such as milk, sugary drinks , juices, etc.

Claims

1. Method for treating a liquid, especially an aqueous liquid, with a view to eliminating undesirable substances such as manganese, uranium and radium ions, by percolation of the liquid on a medium, characterized in that said medium is a compound d insertion of amorphous manganese oxides into the network of a strong anion exchange resin with self-reducing property, reducing the permanganate ion (Mn0 ₄ ) for which it has great affinity. 2. Method according to claim 1, characterized in that the resin is chosen from the group of those whose reducing power of the amines is sufficient to reduce the permanganate. 3. Method according to one of the preceding claims, characterized in that the resin is chosen from food resins with spherical particle size having 1 * order of the following affinities for the sulfate, nitrate, chloride and carbonate anions: HCO ₃ <Cl ^" < N0 ₃ <S0 ₄ T 4. Method according to any one of the preceding claims, characterized in that before the treatment of the liquid from which it is desired to remove the undesirable substances, a step of sulfation of the medium is carried out. 5. Method according to claim 4, caracté¬ ized in that the sulfation step is carried out with potassium bisulfate. 6. Method according to any one of the preceding claims, characterized in that it is carried out by percolation of the liquid to be treated on at least one column enclosing the medium. 7. Media for implementing the method according to any one of claims 1 to 6, characterized in that it is constituted by a compound for inserting oxides of amorphous and diffuse manganese in the network of a strong anion exchange resin, with great affinity for the permanganate ion (Mn0 ₄ ), and whose reducing power of the amines is sufficient to reduce the permanganate in the maσromolecular network of said resin. 8. Media according to claim 7, characterized in that it results from the treatment of an anion exchange resin, strong- food grade, self-reducing property and having a great affinity for the permanganate ion by a solution of (Mn0 ₄ ) for the formation of amorphous manganese oxides, part of which is precipitated in the network of the resin and the free fraction of which is eliminated by successive flotation-settling operations and washing with distilled water and then elimination ammonium ions and residual amines by treatment with acetic acid followed by washing with distilled water until a very slightly acidic pH of approximately 6 is obtained. 9. Media according to one of claims 7 or 8, characterized in that the resin is of the type marketed under the name of IMAC HP 441 by the company ROHM & HAAS.