JP4781374B2 - 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 various inorganic salts such as sodium sulfate (bow glass) and sodium chloride, a method for recovering acid and alkali from the waste liquid using an electrodialyzer has been conventionally known. For example, Patent Document 1 discloses that a alkaline waste liquid of sulfate is dealkalized and then supplied to an ion exchange membrane electrodialyzer to suppress deterioration of the anion exchange membrane of the electrodialyzer. ing.
Japanese Patent No. 3015486

  However, in the treatment method disclosed in Patent Document 1, since the pretreatment for supplying the waste liquid to the electrodialyzer is performed by dealkalization using an ion exchange membrane electrodialyzer, the ions used in the pretreatment are used. There was a problem that deterioration of the exchange membrane was inevitable.

  In addition, hydrochloric acid, nitric acid, hydrofluoric acid, etc. are mixed in the recovered sulfuric acid due to impurities that are difficult to remove by conventional pretreatment such as chlorine ion, nitrate ion, hydrofluoric acid ion, etc., and it tends to be highly corrosive acid. There is also a problem that the material cost and running cost of the equipment increase from the viewpoint of maintaining the corrosion resistance.

  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 comprising an impurity removing step for removing impurities from a waste liquid containing an inorganic salt, and a recovery step for separating and recovering the pretreated waste liquid into an acid solution and an alkaline solution by electrodialysis. A method for treating a contained waste liquid, wherein the impurity removing step includes a salt separation step for crystallizing and separating an inorganic salt contained in the waste liquid, and a dissolution step for producing a solution of the separated inorganic salt, and the recovery step Is achieved by an inorganic salt-containing waste liquid treatment method in which electrodialysis is performed on the solution produced in the dissolution step.

  The method for treating an inorganic salt-containing waste liquid preferably further comprises a concentration step for evaporating and concentrating the filtrate produced in the salt separation step, and the salt separation step crystallizes the inorganic salt remaining in the filtrate after concentration. Preferably, the step of analyzing and separating is included. Furthermore, the concentration step preferably includes a step of evaporating and concentrating the diluted salt solution from which the acid solution and the alkali solution have been separated in the recovery step.

  Further, the object of the present invention is to provide an impurity removing device for removing impurities from waste liquid containing inorganic salt, and an electrodialyzer for separating and recovering the pretreated waste liquid into acid solution and alkaline solution by electrodialysis. An apparatus for treating an inorganic salt-containing waste liquid, wherein the impurity removing apparatus is separated from a crystallizer that precipitates an inorganic salt contained in the waste liquid, and a salt separator that separates the deposited inorganic salt from a filtrate. A dissolution tank for producing a solution of the inorganic salt; and a concentrating device for evaporating and concentrating the filtrate produced by the salt separation device, and the filtrate obtained after the concentration produced by the concentrating device is supplied to the crystallization device. This is achieved by an inorganic salt-containing waste liquid treatment apparatus configured to supply.

  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. .

  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. The treatment apparatus 1 includes an impurity removal apparatus 10 that removes impurities from a waste liquid containing an inorganic salt, and an electrodialysis apparatus 20 that separates and collects the pretreated waste liquid into an acid solution and an alkaline solution by electrodialysis. ing.

  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 crystallizes the waste liquid that has passed through the pretreatment device. A crystallizer 12 that precipitates inorganic salt crystals, a salt separator 13 that separates the deposited inorganic salt from the filtrate, a dissolution tank 14 that produces a solution of the separated inorganic salt, and a salt separator And a concentrating device 15 for evaporating and concentrating the filtrate produced in 13, and the filtrate concentrated by the concentrating device 15 is configured to be supplied to the crystallizer 12 again.

  In this 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 to a desired concentration to generate an inorganic salt solution, and supplies the solution to the 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 evaporating and concentrating device for spraying and evaporating the filtrate under reduced pressure on the surfaces of a plurality of heat transfer tubes through which the heating fluid passes can be used, and is slightly contained in the filtrate. Concentrate the inorganic salt. The concentrated filtrate is supplied again to the crystallizer 12, but since impurities are contained, a part of the filtrate is discharged as a blow liquid. This discharge ratio can be set to a desired value by adjusting the valve opening.

  The electrodialysis apparatus 20 uses a known apparatus such as a three-chamber cell type bipolar membrane electrodialysis apparatus 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. Inorganic salt solution is introduced into the desalting chamber formed by the cation exchange membrane and the 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 operation of the inorganic salt-containing waste liquid treatment apparatus 1 having the above-described configuration will be described.
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 electrodialysis device 20. Since the purity of the dissolved salt is increased by passing through the crystallizer 12 and the salt separator 13, this solution is a high-quality acid solution and alkali solution (that is, sulfuric acid solution and caustic soda solution). Valuable acid and alkali whose concentration is sufficiently increased 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.

  On the other hand, the filtrate produced by the salt separation device 13 is supplied to the concentration device 15 and evaporated and concentrated, and then supplied to the crystallizer 12 again. Thereby, since the sodium sulfate slightly remaining in the filtrate is concentrated and crystallized again in a state where it is easily precipitated, the recovery rate of the acid solution and the alkali solution in the electrodialyzer 20 can be increased. The steam generated by the concentrator 15 can be recovered as condensed water.

  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 sodium sulfate solution supplied to the electrodialyzer 20 is recovered as an acid solution and an alkaline solution when passing through the desalting chamber, but sodium sulfate is also contained in the liquid discharged from the desalting chamber. 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 evaporated to concentrate, so that sodium sulfate can be precipitated again by the salt separation device 13, and the acid and alkali The recovery rate can be further increased.

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.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Treatment apparatus 10 Impurity removal apparatus 11 Pretreatment apparatus 12 Crystallization apparatus 13 Salt separation apparatus 14 Dissolution tank 15 Concentration apparatus 20 Electrodialysis apparatus

Claims (4)

An inorganic salt-containing waste liquid treatment method comprising an impurity removal step for removing impurities from a waste liquid containing an inorganic salt, and a recovery step for separating and recovering the pretreated waste liquid into an acid solution and an alkaline solution by electrodialysis. And
The impurity removal step comprises a salt separation step for crystallizing and separating inorganic salts contained in the waste liquid, and a dissolution step for producing a solution of the separated inorganic salts,
In the recovery step, the inorganic salt-containing waste liquid is treated by electrodialysis on the solution generated in the dissolution step. A concentration step of evaporating and 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 evaporating and concentrating the diluted salt solution from which the acid solution and the alkali solution have been 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 an electrodialysis apparatus for separating and recovering the pretreated waste liquid into an acid solution and an alkaline solution by electrodialysis. There,
The impurity removing device includes a crystallization device for precipitating inorganic salt contained in a waste liquid, a salt separation device for separating the precipitated inorganic salt from the filtrate, a dissolution tank for producing a solution of the separated inorganic salt, And a concentration device that evaporates and concentrates the filtrate produced by the salt separation device, and is configured to supply the filtrate after concentration produced by the concentration device to the crystallizer. Processing equipment.

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