RU2361819C1 - Water demineralisation method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: proposed method involves ionising water in cation- and anion-exchange filters, regeneration of filters and electrochemical treatment of waste regenerant solution after regeneration of anion-exchange filters in the middle chamber of a three-chamber electrolysis unit with ion-exchange membranes at current density 400-800 A/m². The alkali and acid formed in the cathode and anode chambers are used for regenerating ion-exchange filters.

EFFECT: simplification of water demineralisation process, reduced concentration of sulphates and chlorides in waste regenerant solution with possibility of its repeated use.

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Description

The present invention relates to the field of producing demineralized water by passing it through ion-exchange cation exchange and anion exchange filters.

A known method of treating water by ion exchange by passing it through 3 sequentially located ion-exchange filters: the 1st filter is loaded with strongly acidic cation exchanger; The 2nd filter is loaded with weakly basic anion exchange resin, which is located in the upper part of the filter, and strongly acidic cation exchange resin; 3rd loaded with strongly basic anion exchange resin. To regenerate the anion exchange resin, a NaOH solution is used, which is first passed through the 3rd filter, and then through the anion exchange resin loaded in the 2nd filter. The cation exchange resin is regenerated with a HCl solution, and this solution is first passed through the 1st filter and then through the cation exchange resin contained in the 2nd filter (Patent 53-3350 Japan, MKI B01J 1/09. Water treatment by ion exchange. / Ichikawa Hajime ( Japan) .- No. 47-23 013; filed March 6, 72).

The disadvantages of this method include the formation of wastewater obtained during the regeneration of ion-exchange filters and containing significant amounts of chlorides and sulfates of alkali and alkaline earth metals.

A known method of purifying water and aqueous solutions by two-stage ion treatment and regeneration of spent ion exchanger with parallel and countercurrent movement of the treated water and regeneration solution, the parallel current being carried out in the first stage, and countercurrent in the second processing stage (A.S. 460712 USSR, MKI C02B 1/16. Method for the purification of water and aqueous solutions. / F. N. Belan, A. P. Mamet, D. L. Tsyrulnikov (USSR). - No. 1695223; claimed 16.09.71).

The disadvantages of this method include the formation of wastewater obtained during the regeneration of ion-exchange filters and containing sufficiently large amounts of chlorides and sulfates of alkali and alkaline earth metals.

Closest to the claimed, i.e. The prototype is a method of desalting water, which includes ionizing water in cation exchange and anion exchange filters, regenerating filters, treating the spent regeneration solution with the withdrawal of excess regenerant into the non-liquid phase, separating the regenerant from the spent regeneration solution, dissolving the regenerant in water and reusing it. Impurities in ionized water are exchanged for readily soluble substances, characterized by their suitability for regeneration of both cationic and anionic filters and the ability to be removed from water into a non-liquid phase, for example, ammonium hydroxide, ionized water is treated to remove substances dissolved in it into a non-liquid phase, and they are separated from water, dissolved in water and used to regenerate ion-exchange filters (Patent 2036160 Russia, MKI C02F 1/42. Method for desalting water. / K.K. Bekbulatov, V.N. Suvorov, I.V. Bekbulatova, Yu.V. Gasselbach, A.G.N Abiullin, V.A. Mikhailov, I.A. Zakirov, A.S. Sapozhnikov, N.I. Varlamov (Russia). Scientific and Technical Cooperative Search. - No. 5002010/26; claimed on 08.29.91).

The main disadvantages of the prototype include the use of the reagent necessary to remove excess regenerating material into the non-liquid phase, separating the obtained sludge from wastewater and dissolving this sludge in water for reuse, which complicates the process of water desalination. In addition, only excess of the regenerating substance is extracted from the wastewater, and the chlorides and sulfates of alkali and alkaline earth metals formed during the regeneration process are often contained in wastewater in amounts exceeding the maximum permissible concentrations.

The present invention solves the technical problem of simplifying the process of desalination of water and purification of wastewater generated during the regeneration of ion-exchange filters from chlorides and sulfates with the simultaneous production of alkali and acid, which can be used in the process of regeneration of ion-exchange filters.

The essence of the invention lies in the fact that in the known method for producing demineralized water by passing it through cation exchange and anion exchange filters and regenerating ion-exchange filters with alkali and acid solutions, according to the invention, the waste water generated during the regeneration of anion-exchange filters is subjected to electrochemical treatment in the middle chamber of a three-chamber electrolyzer with ion-exchange membranes at a current density of 400 ... 800 A / m ² , and the alkali and acid formed in the cathode and anode chambers are used for regeneration and ion-exchange filters.

A typical ion-exchange water desalination plant includes two groups of ion-exchange filters, of which the first serves to extract cations from water, and the second group of filters serves to remove anions from water. The regeneration of cation exchange filters is carried out with acid solutions (usually 2-4% solution of H ₂ SO ₄ ). This produces wastewater containing mainly sulfates of alkali and alkaline earth metals. The regeneration of anion exchange filters is carried out with alkaline reagents (as a rule, 2-4% NaOH solutions). The resulting wastewater mainly contains sulfate and sodium chloride.

Example 1

Table 1 shows the maximum salt content in the wastewater generated during the regeneration of ion-exchange filters of the water treatment plant of the Sterlitamak TPP.

Table 1 Filter type Concentration, g / l Na ₂ SO ₄ CaSO ₄ MgSO ₄ K ₂ SO ₄ NaCl H ₂ SO ₄ NaOH Cation exchanger 37.1 0.8 0.4 0.2 - 12.8 - Anionite 32,5 - - - 4.9 - 15.7

From the results shown in table 1, it is seen that the wastewater generated at the stage of regeneration of cation exchange filters mainly contains sodium sulfate and sulfuric acid. At the same time, this wastewater contains up to 0.8 g / l of calcium sulfate and up to 0.4 g / l of magnesium sulfate. The wastewater generated during the regeneration stage of anion exchange filters contains sodium sulfate, sodium chloride and sodium hydroxide.

During the electrochemical treatment of wastewater generated during the regeneration of cation exchange filters due to the presence of calcium and magnesium salts in them, the surface of the cathode is covered with a precipitate of hydroxides of these metals, which makes the process of electrochemical treatment of such a drain impossible. In contrast, the waste water after regeneration of anion exchange filters contains sodium sulfates and chlorides and sodium hydroxide. During the electrochemical treatment of such a drain in a three-chamber membrane electrolyzer, solutions of acid and alkali are concentrated in the anode and cathode chambers, respectively.

The method of desalting water is as follows. Wastewater obtained during the regeneration of anion exchange filters and containing sodium sulfate, sodium chloride and sodium hydroxide is placed in the middle chamber 2 of a three-chamber electrolyzer (see drawing). In the cathode chamber 1, separated by a cation exchange membrane K, is placed 0.1 N. sodium hydroxide solution. In the anode chamber 3, separated by an anion exchange membrane A, is placed 0.1 N. sulfuric acid solution. In the electric field produced in the electrolytic cell by applying a voltage to the electrodes on the transfer of the cations Na ⁺ from the middle chamber by a cation exchange membrane into the cathode compartment of the cell and the anions Cl ^-, SO ^2- _4, OH ^- through the anion exchange membrane into the anode chamber of the cell. In the cathode chamber, water decomposes with the release of gaseous hydrogen and the formation of OH anions ^-

2Н ₂ O + 2е → Н ₂ + 2ОН ^- .

As a result of this, sodium hydroxide is concentrated in the cathode chamber. Chlorine and hydroxyl ions decompose in the anode chamber

2Сl ^- -2е → Cl ₂

2OH ^- -2e → O ₂ + 2H ⁺ .

This leads to concentration in the anode chamber of sulfuric acid.

Example 2

Waste water is pumped through the middle chamber of a three-chamber electrolyzer, obtained during the regeneration of anion exchange filters of the water treatment plant of the Sterlitamak TPP and containing 19.8 g / l sodium sulfate, 1.8 g / l sodium chloride and 15.7 g / l sodium hydroxide. In the cathode and anode chambers of the electrolyzer, 150 ml of 0.1 N are poured. a solution of sodium hydroxide and sulfuric acid, respectively. The process of electrochemical treatment of runoff is carried out at room temperature for 6 hours at various current loads. The results of the experiments are presented in table 2.

table 2 Current strength, A Current density, A / m ² Concentration NaOH, g / l Concentration H ₂ SO ₄ , g / l Current output,% The cost of electricity, kW · h / kg 5 400 88.6 20.3 70.8 9,4 7.5 600 124.2 37.9 71.2 11.3 10 800 134.7 45.1 68.7 13.7 12.5 1000 153.4 62.9 65,2 15.0 fifteen 1200 169.9 69.0 64.7 15.8

From the data presented in table 2, it can be seen that sodium hydroxide and sulfuric acid formed in the cathode and anode chambers of the electrolyzer can be used to regenerate ion-exchange filters. An increase in current density leads to an increase in the concentration of acid and alkali, a decrease in current efficiency, and an increase in energy consumption for the process. At current densities above 800 A / m ² , a significant heating of the solutions in the electrolyzer occurs, therefore, an increase in current density above 800 A / m ^{2 is} not desirable.

Using the proposed method of desalination of water in comparison with the existing has the following advantages:

a) electrochemical wastewater treatment of anion exchange filters leads to a decrease in the concentration of sulfates and chlorides in wastewater without the use of reagent treatment;

b) alkali and acid solutions obtained by electrochemical treatment of wastewater of anion exchange filters are suitable for their use in the process of regeneration of ion exchange filters.

Claims (1)

A method for desalting water, including ionizing water in cation exchange and anion exchange filters, regenerating filters, treating spent regeneration solution, characterized in that the spent regeneration solution after regeneration of anion exchange filters is subjected to electrochemical treatment in the middle chamber of a three-chamber electrolyzer with ion-exchange membranes at a current density of 400-800 A / m ² , and the alkali and acid formed in the cathode and anode chambers are used to regenerate ion-exchange filters.

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