RU1838248C - Method of purifying water - Google Patents

Description

The invention relates to water purification technology and can be used independently for producing soft deionized water, as well as for preparing water in desalination plants using electrodialyne, reverse osmosis or ion exchange technology.

The purpose of the invention is to reduce the content of hardness salts in purified water, to completely remove hydrocarbonate ions from it, and to eliminate the consumption of acid reagents.

In FIG. 1 shows a diagram of an implementation of the proposed method; Figure 2 is a flow direction diagram in electrodialyzers.

The circuit includes an electrocoagulator 1, a clarifier 2, a tank for clarifying water 3, a pump 4, a filter 5, electrodialyzers 6 and 7, a degasser vessel 8. The electrodialyzer 6 consists of alternating bipolar 9, anion exchange 11 and cation exchange 10 membranes. In electrodialyzers 6 and 7, the cation exchange sides of the bipolar membranes 9 face the cathode 12 and form acid chambers 13 with the adjacent anion exchange 11 and cation exchange 10 membranes. The anion exchange sides of the bipolar membranes 9 face the anode 14 and form 10 alkaline with adjacent cation exchange membranes 10 chambers 15. The cation exchange 10 and anion exchange 11 membranes in the electrodialyzer 7 form desalination chambers 16. In the electrodialyzer 6, a unit of alternating membranes 9 and 10 can be repeated five times. In the electrodialyzer 7, a unit of alternating membranes 9. 11 and 10 can be repeated n times.

The source water is passed through an electrocoagulator 1, where when passing along: P

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a constant electric current at the anode, iron hydroxide is formed. Enriched with coagulant - iron hydroxide - water is alkalinized with alkali from the electrodialyzer 7 before entering the lower part of clarifier 2. The solid phase, consisting of hydroxides of iron, calcium, magnesium, and also calcium carbonate, remains in the lower part of clarifier 2, and passed through clarified water is discharged into the tank 3. From the tank 3, the liquid 4 is pumped to the filter 5, where the solid phase is separated. The filtrate is separated into two streams. One of them is fed sequentially to the alkaline chambers 15 of the electrodialyzers 6 and 7 and returned to the clarifier 2. The other stream is sent to the acid chambers 13 of the electrodialyzer 6. Under the influence of a constant electric current in the electrodialyzer, alkali metal ions are transferred from acidic chambers 13 through cation exchange membranes 10 into alkaline chambers 15. Bipolar membranes 9 generate hydrogen ions into acid chambers 13, and hydroxyl ions into alkaline chambers 15. In the acid chambers 13 of the electrodialyzer 6, water is obtained having a pH of 6.5-7.5. This water is divided into two streams in a ratio of 1: (5-10). and served respectively in acid 13 and desalting 16 chambers of the electrodialyzer 7.

Under the influence of a constant electric current in the electrodialyzer 7, the salt concentration in the desalination chambers 16 formed by the anion exchange 11 and cation exchange 10 membranes decreases. In the acid chambers 13, ions are concentrated.

In alkaline chambers 15, cations are concentrated. Due to the fact that the acid chambers 13 of the electrodialyzer 7 are anion concentration chambers and a 10-20% solution is passed through them with respect to desalination chambers 16, the concentration of anions increases 5-10 times, and the pH value in chambers 13 decreases to values of 2.5 - 2.8.

Water flows from chambers 13 and 16 are combined and sent to a degasser 8, thus obtaining a pH value of pre-prepared water of 4.3, at which the complete decomposition of bicarbonate ions occurs according to the reaction equation:

HCO3 + H + -9 H20 + CO2 f Example, Processed water with a total hardness of 4.6 mEq / l, pH 7.35 and a concentration of bicarbonates of 6.5 mEq / l is supplied at a rate of 60 l / h installation.

Electrocoagulator 1 has six iron electrodes with an area of 1.8 dm2 each. The distance between the electrodes is 5 mm.

Clarifier 2 has a volume of 100 l, a mirror area of 100 dm. The filter is made of porous titanium, the average pore diameter is 5-10 microns, the total density of the filtering surface is 20 dm2.

Electrodialyzer 6 has 41 MK-40 cation exchange membranes 10 and 40 Mapi & i M-1 bipolar membranes 9, which form forty acid 13 and forty alkaline 15 chambers. The electric current density on the electrodialyzer 6 is 0.7 - 1.0 A / dm2. Electrodialyzer 7 has 31 cation exchange membranes 10 grade MK-40, 30 bipolar membranes grade MB-1 and 30 anion exchange membranes 11 grade MA-40, which form thirty desalination chambers 16, thirty acid chambers 13 and thirty alkaline chambers 15. Electric current density on the electrodialyzer 7 is 0.1-1.5 A / dm2. Cathodes

12 are made of stainless steel grade X18H10T. Anodes 14 are made of titanium coated with ruthenium oxide.

Table 1 shows the dependence of the total hardness of clarified water on the pH in the clarifier.

As can be seen from Table 1, in the pH range of Ј 10.5, the maximum possible purification of water (hardness is 0.2 - 0.1 mEq / L.

Table 2 presents indicators characterizing the quality of the source and purified water, depending on the parameters of the treatment method.

As can be seen from table 2, with the ratio of the flows of purified water through acid

13 and the desalting 16 chambers of the electrodialyzer 7 equal to 1: (5-10) (Examples 4 and 5), it is possible to reduce the hardness in the water to be purified to the level of 0.05 mg-Sq / L and completely remove hydrocarbonate ions from it. With the ratio of the same water flows 1: (12 - 20) (Example 6-8), intense heating of the water in the acid chambers 13 is observed, which leads to the exit of the electrodialyzer 7 from the Straw, as serial ion-exchange membranes of the MK-40, MA-40 type and MB-1 operate at t 35 ° C. When the ratio of n water outflows is less than 1: 5, it is not possible to completely eliminate the content of bicarbonate ions in the treated water.

In addition, as can be seen from the table, the optimal range of current density at which the goal is achieved is 0.3-1.0 A / dm2 (examples 11-14 and 20-22). At current densities x greater than

0.1 A / dm2 (example 15-16 and 23-24) observed the intense heating of water in acid chambers 13 to 35 ° C, which leads to the failure of the electrodialyzer 7.

Table 3 presents the results of the TQB experiment on water purification by the proposed method in comparison with the known one.

As can be seen from Table 3, the proposed method, in comparison with the known one, allows halving the concentration of hardness salts (0.05 mEq / L and 0.1 mEq / L, respectively) and completely eliminates the content of bicarbonate ions in the treated water.

Thus, clarification of water at pH 10.5, electrodialysis using two electrodialyzers, one of which consists of alternating bipolar and cation-exchange membranes, and the second of alternating bipolar, anion-exchange and cation-exchange membranes, water supply from the alkaline chambers of the first electrodialyzer to the alkaline chambers of the second electrodialyzer and the alkali return to clarification, separation of the water flow from the acid chambers of the first electrodialyzer in a ratio of 1: (5 - 10) and its supply, respectively, to acid and the second electrodialysis desalting chamber, and conducting the process

electrodialysis at a current density of 0.3 - 1.0 A / dm makes it possible to reduce the content of hardness salts in the water to be purified, to completely remove hydrocarbonate ions from it and to eliminate the consumption of acid reagents.

Formula and method of water purification, including electrocoagulation, clarification, filtering, electrodialysis with bipolar membranes, characterized in that the clarification is carried out at pH 5-10.5 and electrodialysis is carried out in two series-connected electrodialyzers, one of which contains alternating bipolar and cation-exchange membranes, and the other bipolar, anion-exchange and cation-exchange membranes, water from the alkaline chambers of the first electrodialyzer is supplied to the alkaline chambers of the second electrodialyzer and sent to branching, and the water from the acid chambers of the first electrodialyzer is divided into two streams in a ratio of 1: 5–10 and supplied respectively to the acid and desalination chambers of the second electrodialyzer, followed by the combination of streams, while the electrodialysis process is carried out at a current density of 0.3 - 1.0 A / dm3.

Table 1

The dependence of the total hardness of clarified water on the pH in the clarifier

Communication of the main parameters of the water treatment method

table 2

 Table3

The characteristics of the purified water by the proposed method in comparison with the known

(prototype)

Continuation of the table. 2

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