JP4866448B2 - Method and apparatus for treating waste liquid containing inorganic salt - Google Patents

Description

  The present invention relates to a method and an apparatus for treating an inorganic salt-containing waste liquid for treating an inorganic salt-containing waste liquid such as factory effluent and leachate.

  As a method for treating a waste liquid containing an inorganic salt, a method for recovering acid and alkali from the waste liquid using a bipolar electrodialyzer is known. Examples of the acid include hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid. Examples of the alkali include caustic soda and caustic potash. When these anions or cations are mixed and dissolved in the inorganic salt-containing waste liquid, the acid and alkali recovered by the bipolar membrane become an acid and alkali mixed according to the respective ion balance. Moreover, in electrodialysis using a bipolar membrane, as disclosed in Patent Document 1, polyvalent cations such as calcium and magnesium contained in the solution are precipitated in the cation exchange membrane to cause membrane destruction. It has been conventionally known that this may occur.

Japanese Patent No. 3151042

  The inorganic salt-containing waste liquid often contains various anions or cations. When the acid and alkali are recovered by the bipolar membrane, the mixed acid and alkali become mixed. When reusing the mixed acid and alkali, for example, hydrochloric acid, nitric acid, hydrofluoric acid, etc. are mixed into the recovered acid such as sulfuric acid to form a highly corrosive acid. From the standpoint of maintaining corrosion resistance, the equipment material cost and running cost There was also a problem that became high. Further, as a condition for reuse, it has often been required to recover the target main component acid and alkali as much as possible.

  For removal of polyvalent cations contained in inorganic salt-containing waste liquid, a method using a chelate resin is known, but when this is applied to waste liquid treatment, polyvalent cations contained in large quantities in the waste liquid. As a result, the load of the chelate resin becomes excessive, and there is a problem that the facilities become excessive.

  Then, this invention aims at provision of the processing method and apparatus of an inorganic salt containing waste liquid which can fully remove the impurity contained in an inorganic salt containing waste liquid, and can collect | recover high quality acid and alkali at low cost. .

  The object of the present invention is to provide an inorganic salt-containing waste liquid comprising an impurity removing step for removing impurities from a waste liquid containing an inorganic salt, and a recovery step for separating and recovering an acid solution and an alkaline solution from the waste liquid after removing the impurities. In the treatment method, the impurity removing step includes a salt separation step for crystallizing and separating an inorganic salt contained in a waste liquid, a dissolving step for producing a solution of the separated inorganic salt, and a polyvalent amount contained in the inorganic salt solution. And a polyvalent cation removing step for removing cations, wherein the recovery step is achieved by a method for treating an inorganic salt-containing waste liquid in which bipolar electrodialysis is performed on the solution after the removal of the polyvalent cation.

  The method for treating a waste liquid containing inorganic salt preferably further comprises a concentration step of concentrating the filtrate produced in the salt separation step, and the salt separation step crystallizes the inorganic salt remaining in the filtrate after concentration. It is preferable to include the step of separating. Furthermore, it is preferable that the concentration step includes a step of concentrating the diluted salt solution from which the acid solution and the alkali solution are separated in the recovery step.

  Further, the object of the present invention is an inorganic device comprising an impurity removing device for removing impurities from a waste liquid containing inorganic salts, and a bipolar electrodialysis device for separating and recovering an acid solution and an alkaline solution from the waste liquid after removing the impurities. An apparatus for treating a salt-containing waste liquid, the impurity removing apparatus comprising: a crystallizer for precipitating an inorganic salt contained in the waste liquid; a salt separator for separating the precipitated inorganic salt from the filtrate; and the separated inorganic salt This is achieved by an inorganic salt-containing waste liquid treatment apparatus comprising a dissolution tank for producing a solution of the above and a polyvalent cation removing device for removing the polyvalent cation contained in the inorganic salt solution.

  ADVANTAGE OF THE INVENTION According to this invention, the processing method and apparatus of an inorganic salt containing waste liquid which can fully remove the impurity contained in an inorganic salt containing waste liquid and can collect | recover high quality acid and alkali at low cost can be provided. .

It is a schematic block diagram which shows the processing apparatus of the inorganic salt containing waste liquid which concerns on one Embodiment of this invention.

  Hereinafter, actual forms of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing an inorganic salt-containing waste liquid treatment apparatus according to an embodiment of the present invention. This processing apparatus 1 includes an impurity removing apparatus 10 that removes impurities from waste liquid containing inorganic salts, and a bipolar electrodialysis apparatus 20 that separates and recovers an acid solution and an alkaline solution from the waste liquid after removing impurities. .

  The impurity removing device 10 includes a pretreatment device 11 that includes a filter for capturing suspended substances (SS components) contained in the waste liquid and performs operations such as neutralization and filtration, and the waste liquid that has passed through the pretreatment device 11. Crystallizer 12 for crystallizing and depositing inorganic salt crystals, salt separator 13 for separating the precipitated inorganic salt from the filtrate, dissolution tank 14 for producing a solution of the separated inorganic salt, inorganic salt A polyvalent cation removing device 19 for removing polyvalent cations contained in the solution and a concentrating device 15 for concentrating the filtrate produced by the salt separation device 13 are provided. The filtrate concentrated by the concentrating device 15 is The crystallization apparatus 12 is supplied again.

  In the present embodiment, the crystallization apparatus 12 uses a cooling crystallization apparatus that cools the supplied waste liquid with a cooling crystallization can to precipitate crystals of the target inorganic salt. Any crystallization method may be used, and for example, an evaporation crystallization apparatus, a recrystallization apparatus, or the like can be used.

  The salt separation device 13 is configured to centrifuge crystals from a slurry of waste liquid on which inorganic salts are deposited. Inorganic salt crystals are supplied to the dissolution tank 14. The dissolution tank 14 dissolves the supplied inorganic salt crystals in water so as to obtain a desired concentration, generates an inorganic salt solution, and supplies the solution to the bipolar electrodialysis apparatus 20.

  On the other hand, the filtrate from which the inorganic salt has been separated by the salt separation device 13 is supplied to the concentration device 15. As the concentrating device 15, a known one can be used, and the inorganic salt slightly contained in the filtrate is concentrated. As the concentrating device 15, for example, a known evaporating and concentrating device that sprays the filtrate under reduced pressure on the surfaces of a plurality of heat transfer tubes through which the heating fluid passes can be used. Moreover, as the concentrating device 15, an electrodialyzer, a reverse osmosis membrane device, or a combination thereof can be used. The filtrate after being concentrated by the concentrating device 15 is supplied again to the crystallizing device 12, but since impurities are contained, a part thereof is discharged as a blow liquid. This discharge ratio can be set to a desired value by adjusting the valve opening.

  The polyvalent cation removing apparatus 19 is an apparatus that removes impurities of divalent or higher polyvalent cations (typically calcium ions and magnesium ions), and specifically, a column packed with a chelate resin. The structure which can flow aqueous solution can be illustrated. As the chelating resin, those capable of selectively capturing the target polyvalent cation can be used, and examples thereof include iminodiacetic acid type and aminophosphoric acid type. Other examples of the polyvalent cation removing device 19 include those that add a chelating agent and those that use an ion exchange resin.

  The bipolar electrodialysis apparatus 20 can use a known configuration such as a three-chamber cell system in which a plurality of cells each having a cation exchange membrane, a bipolar membrane and an anion exchange membrane are laminated between an anode and a cathode. A solution of an inorganic salt is introduced into a desalting chamber formed by a cation exchange membrane and an anion exchange membrane. Water is introduced into the alkali chamber formed by the cation exchange membrane and the bipolar membrane, and the acid chamber formed by the bipolar membrane and the anion exchange membrane, respectively. Each is collected. The diluted salt solution after desalting in the desalting chamber is supplied to the concentrating device 15.

  Next, the processing method using the processing apparatus 1 of the inorganic salt containing waste liquid provided with said structure is demonstrated. The treatment apparatus 1 of the present embodiment removes waste liquids such as industrial wastewater and leachate containing a strong acid such as hydrochloric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid and an inorganic salt of alkali metal or alkaline earth metal such as potassium or sodium. In the following, the treatment of waste liquid containing sodium sulfate (bow glass) as an inorganic salt will be described as an example.

  The waste liquid supplied to the impurity removing device 10 is introduced into the crystallizer 12 after the suspended matter (SS component) is removed when passing through the pretreatment device 11. In the crystallizer 12, by utilizing the fact that the saturation solubility and the temperature dependence of solubility differ depending on the salt, only crystals of the target salt are precipitated. In the present embodiment, the fact that the temperature dependence of the solubility of sodium chloride is smaller than that of hydrous bow glass is utilized. That is, only water-containing bow glass is precipitated by cooling to a temperature equal to or higher than the precipitation temperature of sodium chloride at the supply concentration and lower than the precipitation temperature of water-containing bow glass. Other trace impurities can be dissolved on the solution side to increase the crystal purity. In this manner, crystals of sodium sulfate are precipitated, and the waste liquid becomes a slurry, and this waste liquid is solid-liquid separated in the salt separation device 13.

  The sodium sulfate crystals separated by the salt separation device 13 are dissolved in pure water in the dissolution tank 14 to form a solution and supplied to the polyvalent cation removal device 19. The polyvalent cation removing device 19 can remove polyvalent cations such as calcium ions and magnesium ions that could not be removed by the crystallizer 12 and the salt separator 13. An adverse effect on the ion exchange membrane can be prevented. On the other hand, since the aqueous solution after most of the impurities are removed by the crystallizer 12 and the salt separator 13 is introduced into the polyvalent cation removing device 19, the processing load on the polyvalent cation removing device 19 is increased. Therefore, the removal efficiency of polyvalent cations can be maintained well for a long period of time without frequent backwashing.

  The solution supplied from the polyvalent cation removing device 19 to the bipolar electrodialysis device 20 passes through the crystallization device 12, the salt separation device 13, and the polyvalent cation removing device 19, so that the purity of the dissolved salt is increased. Therefore, the produced acid solution and alkali solution (that is, sulfuric acid solution and caustic soda solution) can be of high quality, and valuable acid and alkali having a sufficiently high concentration can be recovered. In addition, since the impurities such as chlorine ions, nitrate ions, and fluorine ions contained in the solution are sufficiently reduced, the problem of material corrosion can be suppressed, and the initial cost and running cost of the recovery equipment can be greatly improved. Therefore, the merit of collecting acid and alkali is increased. The acid solution and alkali solution to be recovered may be further concentrated to a desired concentration to facilitate reuse.

  On the other hand, the filtrate produced by the salt separation device 13 is supplied to the concentration device 15 and concentrated, and then supplied to the crystallizer 12 again. Thereby, since the sodium sulfate slightly remaining in the filtrate is concentrated and recrystallized in a state where it is easily precipitated, the recovery rate of the acid solution and the alkali solution in the bipolar electrodialysis apparatus 20 can be increased. In addition, the condensed water and demineralized water produced | generated by the concentration apparatus 15 are recoverable instead of the pure water used in the dissolution tank 14. FIG.

  By repeatedly concentrating the filtrate with the concentrating device 15, impurities are concentrated together with sodium sulfate (hydrous bow glass), so that the impurities are easily mixed into the crystalline salt produced by the salt separating device 13, and the acid / alkali to be recovered The quality of the product may be reduced. In such a case, while continuously supplying the waste liquid to the crystallizer 12, a part of the concentrated liquid generated by the concentrator 15 is continuously discharged to the outside as a blow liquid. An increase in the impurity concentration of the concentrated liquid supplied to the analyzing apparatus 12 can be suppressed. As the amount of blown liquid discharged increases, the recovery rate decreases while the quality of the recovered acid / alkali increases, so the amount of blown liquid discharged can be adjusted appropriately by monitoring the impurity concentration in the filtrate. It is preferable to adjust.

  Most of the solution of sodium sulfate supplied to the bipolar electrodialysis apparatus 20 is recovered as an acid solution and an alkali solution when passing through the desalting chamber, but the sodium sulfate is also contained in the liquid discharged from the desalting chamber. Is slightly included. This dilute salt solution is supplied to the concentration device 15 together with the filtrate produced by the salt separation device 13 and concentrated, so that sodium sulfate can be precipitated again by the salt separation device 13, and the acid and alkali can be recovered. The rate can be further increased.

DESCRIPTION OF SYMBOLS 1 Treatment apparatus 10 Pretreatment apparatus 11 Filter apparatus 12 Crystallization apparatus 13 Salt separation apparatus 14 Dissolution tank 15 Concentration apparatus 19 Multivalent cation removal apparatus 20 Bipolar electrodialysis apparatus

Claims (4)

An impurity removal step of removing impurities from the waste liquid containing the inorganic salt;
A method for treating an inorganic salt-containing waste liquid comprising a recovery step of separating and recovering an acid solution and an alkali solution from the waste liquid after removing impurities,
The impurity removal step includes a salt separation step for crystallizing and separating the inorganic salt contained in the waste liquid, a dissolution step for producing a solution of the separated inorganic salt, and a polyvalent cation contained in the inorganic salt solution. A cation removal step,
The said collection | recovery step is a processing method of the inorganic salt containing waste liquid which performs bipolar electrodialysis with respect to the solution after a polyvalent cation removal. A concentration step of concentrating the filtrate produced in the salt separation step;
The method for treating an inorganic salt-containing waste liquid according to claim 1, wherein the salt separation step includes a step of crystallizing and separating the inorganic salt remaining in the filtrate after concentration. The method for treating an inorganic salt-containing waste liquid according to claim 2, wherein the concentration step includes a step of concentrating the diluted salt solution from which the acid solution and the alkali solution are separated in the recovery step. An apparatus for treating an inorganic salt-containing waste liquid comprising an impurity removing apparatus for removing impurities from a waste liquid containing an inorganic salt, and a bipolar electrodialysis apparatus for separating and recovering an acid solution and an alkaline solution from the waste liquid after removing the impurities. ,
The impurity removing device includes a crystallizing device for precipitating an inorganic salt contained in a waste liquid, a salt separating device for separating the precipitated inorganic salt from a filtrate, a dissolution tank for producing a solution of the separated inorganic salt, and an inorganic An inorganic salt-containing waste liquid treatment apparatus comprising: a polyvalent cation removing apparatus that removes polyvalent cations contained in a salt solution.

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