JP2015199050A - Method of removing metal ion in saturated salt water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of removing metal ions in saturated salt water which identifies an optimal regeneration method for a method of removing metal ions by bringing saturated salt water containing impurity metal ions into contact with a chelate type ion exchange fiber so as to enable production of ultrahigh-purity saturated salt water.SOLUTION: A method of removing metal ions in saturated salt water includes a metal ion removal step of supplying saturated salt water containing impurity metal ions from the upper part toward the lower part of a tower packed with a chelate type ion exchange fiber to make the metal ions adsorbed on the chelate type ion exchange fiber, an elution regeneration step of supplying an acid aqueous solution from the lower part toward the upper part of the tower to elute the metal ions adsorbed on the chelate type ion exchange fiber and thereby converting the chelate type ion exchange fiber to the H type for regeneration and an activation step of supplying a caustic soda aqueous solution from the upper part toward the lower part of the tower to convert the chelate type ion exchange fiber converted to the H type to the Na type.

Description

  The present invention relates to a method for removing metal ions in saturated salt water, and more specifically, as a chelating agent that adsorbs trace metals, a chelate ion exchange fiber is used instead of a chelate resin. As an activation process to convert the chelate ion exchange fiber converted to Na into a Na type, metal ions in saturated salt water that enable the production of ultra-high purity saturated salt water by adopting a method different from the case of chelate resin It is related with the removal method.

  At present, the electrolytic soda industry uses salt as a raw material and produces caustic soda, chlorine, and hydrogen using an electrolytic process. Electrolysis methods include ion exchange membrane method, diaphragm method, and mercury method, but all of them currently use ion exchange membrane method. In the ion exchange membrane method, first, a salt as a raw material is made saturated brine in a dissolution tank, and then impurities are removed in a purification tank and sent to an electrolytic cell. Salt water is injected into the anode chamber of the electrolytic cell and dilute caustic soda is injected into the cathode chamber.

  By the way, an ion exchange membrane is used in the electrolytic cell. However, if metal ions are present in the electrolytic cell, a metal hydroxide is deposited on the membrane surface, causing a decrease in current efficiency and a physical breakdown of the membrane. There is a fear. Therefore, a chelate resin tower is installed at the rear stage of the purification tank to remove metal ions leaked in a small amount in the purification tank (Patent Document 1).

  The chelate resin is a resin having a functional group capable of forming a chelate bond with a metal ion, and is a typical chelating agent known for a long time. In general, a chelate resin that is used while being packed in a tower and has adsorbed metal ions in a metal ion removal step is reused after being treated in a regeneration treatment step. The regeneration treatment step elutes the metal ions adsorbed on the chelate resin by the aqueous acid solution, converts the chelate ion exchange fiber into H type and regenerates, and converts the chelate resin converted to H type into Na type. And an activation process.

  Recently, there has been proposed a method for removing metal ions, characterized in that saturated salt water containing impurity metal ions is brought into contact with a chelate ion exchange fiber (Patent Document 2).

  The reaction rate with the chelate resin is limited because the diffusion rate until the target ion reaches the functional group introduced into the particulate resin matrix is limited. The chelate type ion exchange fiber is advantageous in terms of reaction rate than the chelate resin because the exchange group is exposed on the surface, and therefore, the chelate type ion exchange fiber can be used instead of the chelate resin conventionally packed in the chelate resin tower. When removing trace amounts of metal ions by filling ion exchange fibers, there is an advantage that the amount of chelate ion exchange fibers can be reduced, the throughput can be improved, and the processing apparatus can be downsized. .

  Regeneration of the chelate ion exchange fiber can be performed in the same manner as in the case of the chelate resin, but no specific method has been proposed yet.

JP 2007-262443 A JP 2013-34940 A

  The object of the present invention is to find an optimum regeneration method in a method for removing metal ions in which saturated salt water containing impurity metal ions is brought into contact with a chelate ion exchange fiber, and enables the production of ultra-high purity saturated salt water. It is providing the removal method of the metal ion in salt water.

  That is, the gist of the present invention is that metal ions that adsorb metal ions to the chelate ion exchange fiber by supplying saturated salt water containing impurity metal ions from the upper part to the lower part of the column packed with the chelate ion exchange fiber. A removal step, an elution regeneration step in which an aqueous acid solution is supplied from the bottom to the top of the column to elute the metal ions adsorbed on the chelate ion exchange fiber and to convert and regenerate the chelate ion exchange fiber to H type, An aqueous solution of caustic soda from the upper part of the tower to the lower part of the tower to convert the chelate ion-exchange fibers converted to H-type into Na-type. It exists in the removal method.

  According to the present invention, for example, it is possible to produce ultra-high purity saturated brine whose total metal (Ca, Mg, Sr) ion concentration is reduced to 5 ppb or less.

  Hereinafter, the present invention will be described in detail.

  First, the saturated brine targeted by the present invention will be described. The method for removing metal ions according to the present invention can be used, for example, in the adjustment step of saturated brine (brine) in the sodium chloride electrolysis method described in JP-A-2007-262443.

  Saturated salt water is generally prepared by dissolving raw salt (sun salt or rock salt) and adding sodium hydroxide and sodium carbonate to make it alkaline, thereby almost crystallizing hardness impurities such as calcium and magnesium. After that, the slurry containing the generated crystals is sent to a continuous refining tank (forced settling tank) to almost settle and separate the crystals, and the overflow liquid is treated with a filter such as a sand filter or a microfilter to obtain a suspension. Is finally removed, and finally the filtrate is treated with a chelate resin treatment step to remove ionic calcium and the like. The method for removing metal ions according to the present invention can be used in place of the chelate resin treatment step.

  Next, the chelate ion exchange fiber used in the present invention will be described. The chelate ion exchange fiber is obtained by binding a chelate functional group to the surface of a resin fiber or a nonwoven fabric processed from the resin fiber. Examples of the resin fiber include polyolefin (polyethylene, polypropylene, etc.), nylon, polytetrafluoroethylene, and the like. Of course, it may be a copolymer. Examples of the chelate functional group include iminodiacetic acid group and N-methyl-glucamine group.

  In general, chelating functional groups are bonded to the surface of the resin fiber by applying a method using radiation graft polymerization technology (“Grafting recipe for graft polymerization” (Shinichi Saito, Takanobu Sango, Maruzen Co., Ltd.) (Issued February 15, 2008) In other words, after introducing a polymerizable monomer onto the surface of the resin fiber by a radiation graft polymerization method, a chelate-forming group is introduced into the side chain of the obtained graft polymer.

  As the polymerizable monomer (polymerizable monomer having a functional group) to be introduced onto the surface of the resin fiber by the radiation graft polymerization method, a polymerizable monomer having an epoxy group is particularly preferably used. Specific examples of the polymerizable monomer having an epoxy group include glycidyl methacrylate and glycidyl acrylate. Depending on the intended use and function of the adsorbent material, a polymerizable monomer having a hydrophilic group, for example, hydroxyethyl methacrylate, vinyl pyrrolidone, dimethyl acrylamide, ethylene glycol dimethacrylate, etc. may be used in combination. I can do it.

  The radiation graft polymerization method can be performed according to a known method. As the ionizing radiation, ultraviolet rays, electron beams, X-rays, α rays, β rays, γ rays and the like can be used. In addition, as a radiation irradiation method, (1) a simultaneous irradiation method of irradiating radiation in the coexistence of a substrate and a polymerizable monomer, and (2) a substrate after irradiating only the substrate in advance Any of the pre-irradiation methods in which a polymerizable monomer is brought into contact is possible. The pre-irradiation method is preferably used because side reactions other than graft polymerization hardly occur. Irradiation conditions are appropriately selected from the viewpoint of physical and chemical performance of the adsorbing material. The ratio (graft ratio) of the polymerizable monomer introduced onto the surface of the resin fiber by the radiation graft polymerization method can be arbitrarily selected. The graft ratio is usually 30 to 200%, preferably 60 to 100%. Examples of the chelate-forming group introduced into the side chain of the graft polymer include an iminodiacetic acid group and an N-methylglucamine group as described above.

  The method for removing metal ions in saturated brine according to the present invention includes a metal ion removal step, an elution regeneration step, and an activation step. Usually, a drug extrusion step is provided between the elution regeneration step and the activation step and after the activation step. Hereinafter, each step will be described.

The metal ion removal step is a step of supplying saturated salt water containing impurity metal ions from the top to the bottom of the tower packed with chelate ion exchange fibers to adsorb the metal ions to the chelate ion exchange fibers, Basically, it can be carried out in the same manner as in the conventional method using a chelate resin. The packed amount per 1 mL of the tower is usually 0.2 to 0.5 g, preferably 0.3 to 0.4 g, as a dried chelate ion exchange fiber. The superficial velocity (SV) at the time of passing the saturated salt water containing metal ions is usually 10 to 200 hr ⁻¹ , and the passing temperature is usually 50 to 85 ° C. When the temperature is lower than 50 ° C., a phenomenon in which the salt water saturation concentration is lowered to cause the salt to precipitate is not preferable, and it is not preferable from the viewpoint of the current efficiency of the subsequent electrolytic cell. When it exceeds 85 degreeC, a problem may arise in the heat resistance of a chelate type ion exchange fiber.

  The end of the saturated salt water flow can be determined by the breakthrough phenomenon (impurity leak) of the chelate ion exchange fiber. The determination of such an impurity leak is made by measuring metal ions in saturated brine at the outlet side of the tower.

The elution regeneration step is a step of supplying an acid aqueous solution from the lower part to the upper part of the tower to elute the metal ions adsorbed on the chelate ion exchange fiber and converting and regenerating the chelate ion exchange fiber to H type, Basically, it can be carried out in the same manner as in the conventional method using a chelate resin. A hydrochloric acid aqueous solution is used as the acid aqueous solution. The concentration of the hydrochloric acid aqueous solution is usually 0.1 to 10% by weight. Preferably it is 3 to 6% by weight. As the type of acid, an aqueous sulfuric acid solution can also be used in the elution step, but it is not preferable because it causes trouble in the subsequent treatment process. The superficial velocity (SV) when passing the acid aqueous solution is usually ¹ to 10 hr ⁻¹ , preferably SV 3 to 6 hr ⁻¹ . The liquid passing temperature is usually not normal but normal temperature. The end point of the passing of the acid aqueous solution is performed by measuring the metal ions in the acid aqueous solution on the outlet side of the tower in the same manner as described above.

  The drug extrusion process is a process for removing the drug used in the elution regeneration process from the tower, and can be basically performed in the same manner as in the conventional method using a chelate resin. In the case of a drug extrusion step between the elution regeneration step and the activation step, it is usually performed by supplying pure water that has been subjected to ion exchange treatment from the lower part to the upper part of the column. In the case of the drug extrusion step after the activation step, it is usually performed by supplying pure water that has been subjected to ion exchange treatment from the upper part to the lower part of the tower. The end of the flow of pure water is performed by measuring the liquid quality on the outlet side of the tower in the same manner as described above.

  The activation step is a step of supplying the aqueous solution of caustic soda from the upper part to the lower part of the tower to convert the chelate type ion exchange fiber converted to H type into Na type. This process is completely different from the conventional method using a chelate resin in terms of the direction in which the aqueous sodium hydroxide solution is passed.

  That is, since the chelate resin has a structure in which a functional group is introduced into the particulate resin matrix (for example, 297 to 1200 μm), the swelling and shrinkage of the chelate resin when converted to the Na type is severe. In many cases, the degree is increased by 1.5 to 2 times or more on a volume basis when the functional group terminal is converted from H-type to Na-type. This swelling pressure causes damage to the tower and deformation or pulverization of the chelate resin itself. Therefore, in the conventional method using a chelate resin, it is necessary to take measures to reduce the swelling pressure of the volume change of the resin, and in a mode opposite to that in the present invention, i.e., an aqueous caustic soda solution from the bottom to the top of the tower. It is necessary to avoid swelling and shrinkage by feeding and semi-fluidizing the chelate resin. In the first place, in the flow of saturated saline after flowing the flow direction of the aqueous solution of caustic soda used in the activation process from the upper part to the lower part of the tower, the swelling pressure of the chelate resin causes Since the differential pressure becomes very high, normal downward flow cannot be performed.

  By the way, when supplying caustic soda aqueous solution by an upward flow, there exist the following disadvantages. That is, although caustic soda contains a small amount of ppb order but contains ionic species such as Ca, Mg, and Sr that must be removed with a chelate resin, the lower part of the tower is contaminated with the above metal ions. Is done. Therefore, it is not possible to produce ultrapure saturated brine required from the viewpoint of protecting the ion exchange membrane in the electrolytic cell.

  On the other hand, the chelate ion exchange fiber used in the present invention has a very small fiber diameter, for example, about 40 μm, and has a diameter of 1/5 to 1/30 compared to the chelate resin. A large amount of functional groups are contained on the fiber surface, and the proportion affected by swelling and shrinkage due to the change of the functional group ends is extremely small. Therefore, it becomes possible to supply the caustic soda aqueous solution from the upper part to the lower part of the tower, and the above-mentioned metal ions are not adsorbed to the lower part of the tower, so that ultra-high purity saturated brine can be produced. Also, the differential pressure during liquid passage can be kept low compared to chelate resins.

The concentration of the caustic soda aqueous solution is usually 1 to 10% by weight, preferably 4 to 6% by weight. The superficial velocity (SV) at the time of passing the aqueous caustic soda solution is usually ¹ to 10 hr ⁻¹ , preferably SV 3 to 6 hr ⁻¹ . The liquid passing temperature is usually not normal but normal temperature. The end of the flow of the aqueous caustic soda solution is performed by measuring the liquid quality on the outlet side of the tower in the same manner as described above.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded. In the following examples, the following drugs and chelate ion exchange fibers were used.

(1) Saturated brine:
According to the method described in Example 1 of Japanese Patent Application Laid-Open No. 2007-262443, the raw salt is dissolved in ion-exchanged pure water so that the sodium chloride concentration is 300 g / L, and a saturated salt water 400 having a pH of 6.0 is obtained. Adjusted liters. The hardness component concentration in the obtained saturated brine was Ca: 4.14 ppm, Mg: 0.33 ppm, and Sr: 1.69 ppm.

(2) Chemicals used for regeneration treatment (hydrochloric acid aqueous solution and caustic soda aqueous solution):
(A) Reagent-grade 35% by weight hydrochloric acid was prepared by diluting to 4% by weight with pure water subjected to ion exchange treatment. The analysis results of metal ions by ICP-AES are as shown in Table 1. The unit of numerical values in the table is μg / L.
(B) A reagent-grade solid caustic soda was dissolved in ion-exchanged pure water to a concentration of 5% by weight. The analysis results of metal ions by ICP-AES are as shown in Table 1. The unit of numerical values in the table is μg / L.

(3) Chelate ion exchange fiber:
It manufactured according to the method of Example 1 of Unexamined-Japanese-Patent No. 2013-34940.

  First, the surface of a commercially available nylon (Ny) fiber was irradiated with a 200 kGy electron beam in a nitrogen atmosphere, and then immersed in a 10% by weight glycidyl methacrylate methanol solution at 40 ° C. for 10 minutes to give a graft chain to the Ny fiber. The graft ratio defined by the following formula (1) was 78%.

[Equation 1]
Graft rate [(w / w)%] = 100 × (weight of graft chain imparted) / (base material weight)
Formula (1)

  Next, the above graft polymerized fiber was immersed in a 0.4 M iminodiacetic acid solution (dioxane: water = 4: 6) at 80 ° C. for 12 hours. 1.2 moles of iminodiacetic acid groups per kilogram were introduced into the resulting chelate fiber. It was converted into Na type and used.

Example 1:
A tower (with an inner diameter of 15 mmφ and a height of 1000 mmH) with a jacket is packed with the chelate ion exchange fiber at a height of 800 mmH (0.3 g per 1 mL of the tower), and metal ions are removed under the conditions shown in Table 2 below. The process, the elution regeneration process, the drug extrusion process, the activation process, and the drug extrusion process were repeated. The liquid passing temperature in the metal ion removing step was 60 ° C., and the liquid passing temperatures in all other steps were room temperature. The total metal (Ca, Mg, Sr) ion concentration in the saturated brine on the outlet side of the tower after 2 hours of passing through the metal ion removal step in the second cycle was 2.82 μg / L.

Reference example 1:
In Example 1, it carried out similarly to Example 1 except having made the liquid passing direction of the activation process and the subsequent extrusion process upward. When the total metal (Ca, Mg, Sr) ion concentration in the saturated brine on the outlet side of the tower 2 hours after passing through the metal ion removal step in the second cycle was measured, it was 14.72 μg / L.

Claims (1)

  A metal ion removal step of supplying saturated salt water containing impurity metal ions from the top to the bottom of the tower packed with chelate ion exchange fibers to adsorb metal ions to the chelate ion exchange fibers, and from the bottom of the tower An elution regeneration process in which an aqueous acid solution is supplied to the upper part to elute the metal ions adsorbed on the chelate ion exchange fiber, and the chelate ion exchange fiber is converted into an H form, and from the upper part to the lower part of the tower. A method for removing metal ions in saturated salt water, comprising an activation step of converting a chelate ion exchange fiber converted to H-type by supplying an aqueous caustic soda solution into Na-type.