Method for recovering phosphorus and method for producing phosphorus recovery material

Abstract

This invention provides a method for efficiently recovering phosphorus using a Mg-Al layered double hydroxide. [Solution] According to one aspect of the present invention, a method for recovering phosphorus contained in wastewater is provided, comprising: a preparation step of preparing a Mg-Al layered double hydroxide having carbonate ions or hydroxide ions as interlayer anions; an exchange step of contacting the Mg-Al layered double hydroxide prepared in the preparation step with a gas containing hydrogen chloride to obtain a Mg-Al layered double hydroxide in which the interlayer anions have been replaced with chloride ions; and a recovery step of contacting the Mg-Al layered double hydroxide obtained in the exchange step with wastewater to replace the interlayer anions with phosphate ions contained in the wastewater and recover the phosphorus contained in the wastewater.

Description

[Technical Field]

[0001] This invention relates to a method for recovering phosphorus and a method for producing phosphorus recovery material. [Background technology]

[0002] Currently, the depletion of phosphorus resources is predicted for the future, and phosphorus recovery technology from wastewater is needed. While conventional phosphorus recovery methods include crystallization recovery as magnesium ammonium phosphate (MAP) or hydroxyapatite (HAP), these methods have not become widespread due to the large size of the equipment and the complexity of operation and management. Furthermore, phosphorus discharge standards have been established as a measure against eutrophication in enclosed water bodies such as lakes and bays. Conventional methods for removing phosphorus from wastewater include coagulation and sedimentation, which precipitate phosphate as aluminum or iron salts, and biological dephosphorization. However, these methods require large treatment tanks to ensure the necessary retention time for coagulation or biological dephosphorization, resulting in large equipment. Additionally, the generation of large amounts of coagulated sludge and excess sludge of biological origin is problematic. In light of these circumstances, treatment methods utilizing phosphorus adsorbents that selectively adsorb phosphorus are highly anticipated.

[0003] Since phosphorus generally exists as anions in wastewater, methods for removing phosphorus from wastewater using layered double hydroxides (hereinafter sometimes referred to as LDH (Layered Double Hydroxide)) as anion exchangers have been proposed. Specifically, Patent Document 1 describes a method for treating phosphorus-containing wastewater using a composite metal hydroxide having a predetermined structure. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-57695 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Conventional technologies have shown that phosphorus can be adsorbed with LDH, and that the phosphorus-adsorbed LDH can be regenerated with an aqueous solution of alkali metals, and that Mg-Al-based LDH containing chloride ions is particularly efficient at adsorbing phosphorus. However, phosphorus recovery using Mg-Al-based LDH containing chloride ions remains difficult to commercialize. One reason for this difficulty in commercialization is that obtaining Mg-Al-based LDH containing chloride ions is not industrially feasible.

[0006] In view of the above circumstances, the present invention aims to provide a method for recovering phosphorus that can efficiently recover phosphorus using a Mg-Al layered double hydroxide. [Means for solving the problem]

[0007] According to one aspect of the present invention, a method for recovering phosphorus contained in wastewater is provided, comprising: a preparation step of preparing a Mg-Al layered double hydroxide having carbonate ions or hydroxide ions as interlayer anions; an exchange step of contacting the Mg-Al layered double hydroxide prepared in the preparation step with a gas containing hydrogen chloride to obtain a Mg-Al layered double hydroxide in which the interlayer anions have been exchanged for chloride ions; and a recovery step of contacting the Mg-Al layered double hydroxide obtained in the exchange step with wastewater to exchange the interlayer anions for phosphate ions contained in the wastewater and recover the phosphorus contained in the wastewater.

[0008] According to the above embodiment, a method for recovering phosphorus efficiently using a Mg-Al layered double hydroxide is provided.

[0009] Furthermore, they may be provided in the following embodiments.

[0010] (1) A method for recovering phosphorus contained in wastewater, comprising: a preparation step of preparing a Mg-Al layered double hydroxide having carbonate ions or hydroxide ions as interlayer anions; an exchange step of contacting the Mg-Al layered double hydroxide prepared in the preparation step with a gas containing hydrogen chloride to obtain a Mg-Al layered double hydroxide in which the interlayer anions have been replaced with chloride ions; and a recovery step of contacting the Mg-Al layered double hydroxide obtained in the exchange step with the wastewater to replace the interlayer anions with phosphate ions contained in the wastewater and recover the phosphorus contained in the wastewater.

[0011] (2) A method for recovering phosphorus as described in (1) above, further comprising a detachment step of detaching the phosphate ions present as interlayer anions by contacting the Mg-Al layered double hydroxide after the recovery step with a solution having an anion different from the phosphate ion.

[0012] (3) A method for recovering phosphorus according to (1) or (2) above, wherein the preparation step involves preparing granules containing the Mg-Al layered double hydroxide and a binder.

[0013] (4) A method for recovering phosphorus according to any one of (1) to (3) above, wherein in the exchange step, the gas at 40 to 200°C is brought into contact with the Mg-Al layered double hydroxide.

[0014] (5) A method for recovering phosphorus according to any one of (1) to (4) above, wherein the concentration of hydrogen chloride in the gas during the exchange step is in the range of 50 to 500 ppm.

[0015] (6) A method for recovering phosphorus according to any one of (1) to (5) above, wherein the recovery step is performed by passing the wastewater through the Mg-Al layered double hydroxide filled in the first container.

[0016] (7) In the method for recovering phosphorus according to (6) above, after the recovery step, a solution having an anion different from phosphate ions is passed through the first container to further include a detachment step of detaching the phosphate ions present as the interlayer anion, the method for recovering phosphorus.

[0017] (8) In the method for recovering phosphorus according to (7) above, the solution is a solution stored in a second container, and in the detachment step, the solution passed through the first container is circulated to the second container, the method for recovering phosphorus.

[0018] (9) A method for producing a phosphorus recovery material, comprising a preparation step of preparing an Mg-Al-based layered double hydroxide having carbonate ions or hydroxide ions as an interlayer anion, and an exchange step of obtaining a phosphorus recovery material in which the interlayer anion is exchanged with chloride ions by bringing a gas containing hydrogen chloride into contact with the Mg-Al-based layered double hydroxide prepared in the preparation step, the method for producing a phosphorus recovery material. Of course, this is not the limit.

Brief Description of Drawings

[0019] [Figure 1] It is a schematic diagram showing the overall outline of the phosphorus recovery system of the present embodiment. [Figure 2] It is a graph showing the change over time of the phosphorus concentration. [Figure 3] It is a graph showing the breakthrough curve of phosphorus by column water flow.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described. Note that various characteristic matters shown in the embodiments below can be combined with each other. In addition, "~" in this specification represents from above to below unless otherwise specified.

[0021] [Method for Recovering Phosphorus] That is, the method for recovering phosphorus in the present embodiment is as follows. A method for recovering phosphorus contained in wastewater, A preparation step to prepare a Mg-Al layered double hydroxide having carbonate ions or hydroxide ions as interlayer anions, An exchange step is performed to obtain an Mg-Al layered double hydroxide in which the interlayer anions are replaced with chloride ions by contacting the Mg-Al layered double hydroxide prepared in the above preparation step with a gas containing hydrogen chloride, A recovery step is performed in which the Mg-Al layered double hydroxide obtained in the exchange step is brought into contact with the wastewater, thereby exchanging the interlayer anions for phosphate ions contained in the wastewater and recovering the phosphorus contained in the wastewater. A method for recovering phosphorus, which includes [the necessary components]. The following describes the various steps that may be included in the phosphorus recovery method of this embodiment.

[0022] (preparation process) First, in the phosphorus recovery method of this embodiment, a predetermined Mg-Al layered double hydroxide is prepared as a preparation step. Here, the Mg-Al layered double hydroxide prepared in the preparation step contains carbonate ions (CO3) as interlayer anions. 2- ) or hydroxide ion (OH - ) has.

[0023] Here, we will describe Mg-Al layered double hydroxides. In "layered double hydroxides (LDHs)," the multiple layers may be bonded together by weak van der Waals forces, in which case anions may be interposed between the layers. These interposed anions can undergo exchange reactions. In other words, the Mg-Al layered double hydroxide used in this embodiment can also undergo anion exchange reactions. The Mg-Al layered double hydroxide used in this embodiment can be represented by the following chemical formula (1).

[0024] [Mg 1-x 2+ Al x 3+ (OH)2][A x / n n- ·mH2O] ···(1)

[0025] In the chemical formula (1), 0.20 ≤ x ≤ 0.33, and A n- is an n-valent anion. Here, m represents the proportion of water molecules present between the layers, and usually, it is in the range of 0.4 to 0.6.

[0026] That is, in the preparation step, as the interlayer anion, a Mg-Al-based layered double hydroxide having carbonate ions or hydroxide ions is prepared. In the above chemical formula (1), this Mg-Al-based layered double hydroxide corresponds to a compound in which A n- is carbonate ions or hydroxide ions. Since Mg-Al-based layered double hydroxides having these anions are highly available, they are suitably used in the phosphorus recovery method of the present embodiment. Taking a Mg-Al-based layered double hydroxide having carbonate ions as the interlayer anion as an example, this compound is composed of a host layer having a positively charged octahedral layer formed by substituting a part of Mg in divalent metal Mg(OH)2 with Al, a trivalent metal 2+ and a guest layer having interlayer carbonate ions and interlayer water that compensate for the positive charge, and is widely industrially used as a stabilizer for polyvinyl chloride, for example. 3+

[0027] The preparation step of the present embodiment may be carried out by preparing the above-described Mg-Al-based layered double hydroxide compound itself (typically a powdery compound), or may be carried out by preparing a granulated product containing the Mg-Al-based layered double hydroxide and a binder.

[0028] The method used to obtain the granules (granulation method) is not particularly limited, but known methods that can obtain pellet-shaped or spherical granules can be employed. Typical methods include: tumbling granulation using drum-type granulators, dish-type granulators, etc.; mixing and stirring granulation using flexomics, vertical granulators, etc.; extrusion granulation using screw-type extruders, roll-type extruders, blade-type extruders, self-forming extruders, etc.; and compression granulation using tablet-type granulators, briquette-type granulators, etc. Of these, extrusion granulation is preferred when forming pellets, and tumbling granulation or mixing and stirring granulation is preferred when forming spherical granules.

[0029] Furthermore, the particle size (size) of the resulting granules can be appropriately set in consideration of other steps in the phosphorus recovery method of this embodiment, but as an example, the particle size of the granules is preferably in the range of 0.3 to 5.0 mm. By setting the particle size to this range, the gas containing hydrogen chloride can be passed through with a small pressure loss in the conversion step described later, making it easier to stabilize the process.

[0030] Furthermore, the binder may be made from various materials capable of dispersing and granulating Mg-Al layered double hydroxides. In other words, the granulated material can be prepared using various organic polymers or inorganic compounds such as ceramics as binders.

[0031] In this embodiment, it is preferable to use sodium metasilicate or water glass as a binder. That is, when sodium metasilicate or water glass is dissolved in water to obtain an aqueous solution, and this is used to obtain granules, the silicate ions react with magnesium and aluminum, which are constituent elements of Mg-Al layered double hydroxides, and solidification proceeds, making it easy to obtain tough granules. Other organic polymers that can be used to obtain granules include acrylic resins, fluororesins, hydrocarbon resins, epoxy resins, and urethane resins, but the invention is not limited to these, and various materials that are effective in constructing a phosphorus recovery process can be selected.

[0032] (Replacement process) After preparing the specified Mg-Al layered double hydroxide as described above, as an exchange step, the Mg-Al layered double hydroxide is brought into contact with a gas containing hydrogen chloride, thereby converting the interlayer anions into chloride ions (Cl - A Mg-Al layered double hydroxide is obtained by replacing it with ).

[0033] The inventors investigated and found the following points regarding the exchange of interlayer anions for chloride ions in the Mg-Al layered double hydroxide prepared in the preparation step. Specifically, they found that by contacting the Mg-Al layered double hydroxide with hydrogen chloride gas in the exchange step, the anion exchange reaction can be efficiently carried out, and by subjecting the resulting Mg-Al layered double hydroxide to the subsequent recovery step, a highly efficient phosphorus recovery process can be constructed. In other words, the phosphorus recovery method of this embodiment is unparalleled in the prior art in that it achieves highly efficient phosphorus recovery while using readily available raw materials as starting materials.

[0034] In the exchange process, there are no particular restrictions on the method of contacting the Mg-Al layered double hydroxide with a gas containing hydrogen chloride. One example is a method in which the Mg-Al layered double hydroxide is packed into a container equipped with a mechanism for circulating gas through it, and the gas containing hydrogen chloride is circulated through the container. The container equipped with a mechanism for circulating gas can be set as appropriate. For example, a container with a gas inlet and outlet, and equipped with a wire mesh, expanded metal, perforated plate, slit plate, etc. on the gas outlet side to prevent the Mg-Al layered double hydroxide (or granules) from flowing out of the gas outlet, can be used. This generally corresponds to a container packed with adsorbent material called a column or adsorption tower used in a general adsorption process. There are no particular restrictions on the material of the container (material of the gas contact surface), but it is preferable to use a metal material from the viewpoint of strength and heat resistance, and stainless steel from the viewpoint of corrosion resistance.

[0035] Furthermore, the temperature at which the Mg-Al layered double hydroxide is brought into contact with a gas containing hydrogen chloride during the exchange process can be set as appropriate. One example of a gas contact temperature in this exchange process is to bring the Mg-Al layered double hydroxide into contact with a gas at 40 to 200°C.

[0036] In other words, the gas used in the exchange process may contain hydrogen chloride along with nitrogen, air, etc., but care must be taken if the gas contains moisture. Hydrogen chloride gas readily dissolves in liquid water to form hydrochloric acid, which corrodes metals such as iron. To prevent corrosion due to hydrochloric acid formation, it is desirable to set the gas containing hydrogen chloride to a temperature above a specified level and to maintain it above the acid dew point where hydrochloric acid does not form. From this perspective, heating the gas used in the exchange process is effective in preventing corrosion. The gas temperature may be set to 40°C or higher, 50°C or higher, or 60°C or higher, depending on the amount of moisture present in the gas. The upper limit of the gas temperature can be set appropriately, taking into consideration energy efficiency, and may be set to 200°C or lower, 190°C or lower, or 180°C or lower.

[0037] In the exchange process, the concentration of hydrogen chloride in the gas when contacting the Mg-Al layered double hydroxide with a hydrogen chloride-containing gas can be set as appropriate, but one example is a concentration of 50 to 500 ppm. That is, by setting it to 50 ppm or higher, an efficient conversion reaction can be carried out, and by setting it to 500 ppm or lower, the risk of corrosion of the container can be reduced. Incidentally, waste incineration exhaust gas usually contains about 100 to 300 ppm of hydrogen chloride, so it is also effective to use such waste incineration exhaust gas in the exchange reaction. Of course, by using a container with extremely high corrosion resistance, it is also possible to carry out the exchange process using gas containing hydrogen chloride at concentrations higher than those mentioned above.

[0038] (Recovery process) In the recovery process, the Mg-Al layered double hydroxide obtained in the exchange process is brought into contact with wastewater to exchange the interlayer anions for phosphate ions contained in the wastewater, thereby recovering the phosphorus contained in the wastewater. In other words, the Mg-Al layered double hydroxide obtained in the exchange process has chloride ions as interlayer anions, but these chloride ions as interlayer anions are exchanged for phosphate ions (PO4). 3- By replacing it with ), phosphorus contained in the wastewater is recovered.

[0039] Such a recovery process can be carried out by appropriately selecting a method from among those that can bring Mg-Al layered double hydroxides into contact with wastewater. As an example, the process for recovering phosphorus will be explained with reference to Figure 1.

[0040] Figure 1 is a schematic diagram showing the overall overview of the phosphorus recovery system of this embodiment. The phosphorus recovery system 100 shown in Figure 1 comprises a first container 1 and a second container 2, with the first container 1 filled with a phosphorus recovery material 3. The second container 2 is configured to store a solution used in the detachment process described later. The phosphorus recovery system 100 is also provided with a pipe P11 that can allow wastewater Dr containing phosphorus (phosphate ions) to flow into the first container 1, and a pipe P12 that recovers the wastewater Dr that has flowed out of the first container 1. Furthermore, the phosphorus recovery system 100 is also provided with a pipe P21 that can allow the solution stored in the second container 2 to flow into the first container 1, and a pipe P22 that sends the solution that has flowed out of the first container 1 to the second container 2.

[0041] In other words, in the example of the phosphorus recovery system 100 shown in Figure 1, the Mg-Al layered double hydroxide obtained in the conversion process can be filled into the first container 1 as the phosphorus recovery material 3. Furthermore, by introducing wastewater Dr containing phosphate ions from the piping P11 into the first container 1, the wastewater can be brought into contact with the Mg-Al layered double hydroxide contained in the phosphorus recovery material 3 filled in the first container 1.

[0042] The wastewater used in the recovery process can be set as appropriate and may be either industrial wastewater or domestic wastewater. The concentration of phosphate ions in the wastewater can also be set as appropriate, and the volume of the phosphorus recovery material 3 and the contact rate with the Mg-Al layered double hydroxide can be adjusted accordingly.

[0043] As an example, the recovery process of this embodiment may be carried out as follows.

[0044] In other words, the recovery process of this embodiment may be carried out by filling an adsorption container (first container 1) with phosphorus recovery material 3 and passing wastewater at a volume 1 to 20 times the filling volume of phosphorus recovery material 3 per hour through the adsorption container (first container 1). The adsorption container referred to here may have the same structure as the container used in the conversion process, and only needs to be able to be filled with phosphorus recovery material 3 and through which water containing phosphorus (wastewater containing phosphate ions) can be passed. Generally, when an adsorbent or recovery material is filled into an adsorption container called a column and a fluid containing the substance to be adsorbed is passed through it, the flow rate can be expressed in terms of space velocity (SV). SV means how many times the filling volume (bed volume (BV)) of the adsorbent (phosphorus recovery material 3) is equivalent to the amount of fluid that is passed through per unit time, and is used when the contact time between the adsorbent (phosphorus recovery material 3) and the fluid affects the adsorption performance. The recovery of phosphate ions is affected by the contact time with the adsorbent (phosphorus recovery material 3), and SV is 1h -1 By doing so, an appropriate amount of wastewater can be treated, and SV is 20h -1 By doing the following, a certain level of phosphorus recovery efficiency can be ensured.

[0045] The phosphorus recovery method of this embodiment may further include the following detachment steps.

[0046] (Disengagement process) The detachment step in this embodiment is a step in which the phosphate ions present as interlayer anions are detached by contacting the Mg-Al layered double hydroxide after the recovery step with a solution having an anion different from the phosphate ion.

[0047] In other words, the Mg-Al layered double hydroxide after the recovery process is completed has phosphate ions as interlayer anions. By replacing these phosphate ions with other anions, phosphorus can be recovered, and the Mg-Al layered double hydroxide can be subjected to the recovery process again.

[0048] The solution that can be used in this detachment process contains anions other than phosphate ions, and the type of anion can be set as appropriate. Examples of anions here include hydroxide ions, carbonate ions, nitrate ions, bicarbonate ions, sulfate ions, sulfonate ions, trifluoromethanesulfonate ions, etc. On the other hand, from the viewpoint of performing the detachment process while keeping the cost of the solution down, it is preferable that the solution included in the detachment process contains hydroxide ions. That is, a solution (aqueous solution) of sodium hydroxide or potassium hydroxide may be used as the solution in the detachment process. On the other hand, the anion included in the solution used in the detachment process may be carbonate ions. That is, a solution of sodium carbonate or potassium carbonate may be used as the solution in the detachment process. When a solution containing these hydroxide ions or carbonate ions is used as the solution in the detachment process, the interlayer anions of the Mg-Al layered double hydroxide can be converted to hydroxide ions or carbonate ions. That is, at the stage when the detachment process is completed, it is converted to the Mg-Al layered double hydroxide that should be prepared in the preparation process, making it easier to perform the aforementioned conversion process again. From another perspective, the Mg-Al layered double hydroxide after the recovery process can be kept in the same container (first container 1), and the detachment process (which also serves as the preparation process) and the conversion process can be carried out sequentially. In other words, although not shown in the diagram, the first container 1 may be equipped with gas piping that can introduce a gas containing hydrogen chloride.

[0049] The concentration of the solution used in the detachment process can be appropriately set depending on the process being constructed. For example, when using an aqueous sodium hydroxide solution in the detachment process, its concentration may be in the range of 0.1 to 2 mol / L. While aqueous sodium hydroxide is sometimes used for anion desorption of anion exchangers, using a higher concentration of aqueous sodium hydroxide allows for more efficient detachment of phosphate ions from Mg-Al layered double hydroxides. On the other hand, if the concentration of the aqueous sodium hydroxide solution is too high, there is a risk of aluminum from the Mg-Al layered double hydroxide leaching out. From this perspective, it is preferable to adopt the above-mentioned concentration. The solution used in the detachment process is typically an aqueous solution, but it may also contain water-soluble organic solvents such as alcohol.

[0050] Such a detachment process is achieved by contacting the Mg-Al layered double hydroxide after the recovery process with a solution having an anion different from the phosphate ion, but this contact method can be set as appropriate. As an example, the phosphorus recovery system 100 shown in Figure 1 is described as follows.

[0051] In other words, the detachment step may involve passing a solution having an anion different from the phosphate ion through the first container 1 after the recovery step to detach the phosphate ion present as an interlayer anion. In the example shown in Figure 1, the solution is stored in the second container 2 and supplied to the phosphorus recovery material 3 in the first container 1 via piping P21. In the detachment step of this embodiment, the solution after contact with the Mg-Al layered double hydroxide may be recovered by various methods, but in the example shown in Figure 1, the solution that has passed through the first container 1 is circulated to the second container 2. Generally, in order to bring an adsorbent into contact with a solution and reach desorption equilibrium, a considerable amount of liquid flow and flow time may be required, but as shown in Figure 1, by circulating the solution used in the detachment step, it is possible to reach desorption equilibrium for the Mg-Al layered double hydroxide without requiring an excessive amount of solution. Although not limited to this, if a second container 2 as shown in Figure 1 is prepared and the solution is circulated through it, the phosphorus recovery material 3 can reach desorption equilibrium in a short time of about 2 hours, and a solution containing phosphate ions can be efficiently obtained.

[0052] Furthermore, the following method for producing phosphorus recovery material is also disclosed as an embodiment of the present invention.

[0053] [Method for manufacturing phosphorus recovery material] A method for manufacturing phosphorus recovery material, A preparation step to prepare a Mg-Al layered double hydroxide having carbonate ions or hydroxide ions as interlayer anions, An exchange step is performed to obtain a phosphorus recovery material by contacting the Mg-Al layered double hydroxide prepared in the above preparation step with a gas containing hydrogen chloride, thereby exchanging the interlayer anions for chloride ions. A method for manufacturing phosphorus recovery material, comprising the following:

[0054] In other words, the method for manufacturing the phosphorus recovery material of this embodiment is for manufacturing the phosphorus recovery material 3 shown in Figure 1 above. This phosphorus recovery material 3 can be manufactured by performing the preparation step and conversion step shown in the section on [Phosphorus Recovery Method]. Details will not be described here as it would be repetitive, but the preparation step and conversion step included in this manufacturing method can employ various configurations as shown in the above-mentioned section on [Phosphorus Recovery Method]. Furthermore, the manufactured phosphorus recovery material is typically used in various phosphorus recovery processes, and the phosphorus recovery material itself can be the subject of commercial transactions. [Examples]

[0055] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples. In the following examples, "Type X" for Mg-Al layered double hydroxides (Mg-Al LDH) refers to the anion species contained between the layers of the Mg-Al layered double hydroxide.

[0056] <Comparative Example Sample 1> 200g of powdered CO3-type Mg-Al LDH (Kyoward 1000, manufactured by Kyowa Chemical Industry Co., Ltd.) and 30g of perlite (from Mikata, Hyogo Prefecture) were mixed and stirred in a granulator (VG-01, manufactured by Powrec) at a rotation speed of 400 rpm. 220g of a 12% by weight sodium metasilicate aqueous solution, which served as a binder, was slowly added, and the particles were grown in a snowball-like manner by tumbling granulation. The resulting coarse granules were further processed in a wet extruder (Multigran MG-55, manufactured by Dalton) with a 2.5mm diameter die to produce granulated pellets. The resulting granulated pellets were dried at 105°C for 3 hours to obtain LDH granules with a particle size of 2.0-3.0mm. These LDH granules were designated as Comparative Example 1. Comparative Example 1 can be described as a CO3-type Mg-Al LDH granule because it was produced by granulating CO3-type Mg-Al LDH.

[0057] <Comparative Example Sample 2> In the same manner as in Comparative Example 1, powdered CO3-type Mg-Al LDH was granulated to obtain LDH granules. To convert the CO3-type Mg-Al LDH to Cl-type Mg-Al LDH, the obtained LDH granules were immersed in a 1 mol / L NaCl aqueous solution for 24 hours. At this time, the liquid-to-solid ratio with the NaCl aqueous solution was 10 mL / g. After immersion in the NaCl aqueous solution, the NaCl aqueous solution was removed by filtration with 5A filter paper, and the LDH granules were washed with pure water. The washed LDH granules were dried at 105°C for 3 hours, and this was designated as Comparative Example 2. Comparative Example 2 is expected to be Cl-type Mg-Al LDH granules because it was treated with an NaCl aqueous solution after granulation of CO3-type Mg-Al LDH.

[0058] <Example Sample 1> A granulated LDH product was obtained by granulating powdered CO3-type Mg-Al LDH in the same manner as in Comparative Example Sample 1. To convert the CO3-type Mg-Al LDH to Cl-type Mg-Al LDH, 60 g of the granulated LDH product was packed into a column with an inner diameter of 57 mm and a length of 250 mm, and gas with an HCl concentration of 180 ppm (air balance) heated to 150°C was passed through at an empty column velocity of 0.4 m / s. The HCl concentration at the column outlet was continuously measured using an FT-IR gas analyzer (GASMET DX-4000). The gas flow was stopped when the outlet HCl concentration reached 80% of the inlet concentration. The time required for the outlet HCl concentration to reach 80% of the inlet concentration was 8.5 hours. This granulated LDH product through which the HCl-containing gas was passed was designated as Example Sample 1. Since Sample 1 of Example was treated with a gas containing HCl after granulation of CO3-type Mg-Al-based LDH, it is expected to be a Cl-type Mg-Al-based LDH granule product.

[0059] <Example Sample 2> A granulated LDH product was obtained by granulating powdered CO3-type Mg-Al LDH in the same manner as in Comparative Example Sample 1. To convert the CO3-type Mg-Al LDH to OH-type Mg-Al LDH, the obtained LDH granules were immersed in a 1 mol / L NaOH aqueous solution for 24 hours. At this time, the liquid-to-solid ratio with the NaOH aqueous solution was 10 mL / g. After immersion in the NaOH aqueous solution, the NaOH aqueous solution was removed by filtration with 5A filter paper, and the LDH granules were washed with pure water. The washed LDH granules were dried at 105°C for 3 hours. It is expected that the CO3-type Mg-Al LDH contained in the LDH granules was converted to OH-type Mg-Al LDH upon contact with the NaOH aqueous solution. 60 g of this LDH granule was packed into a column with an inner diameter of 57 mm and a length of 250 mm, and gas with an HCl concentration of 300 ppm (air balance) heated to 150°C was passed through at an empty column velocity of 0.4 m / s. The HCl concentration at the column outlet was continuously measured using an FT-IR gas analyzer (GASMET DX-4000). Gas flow was stopped when the outlet HCl concentration reached 50% of the inlet concentration. The time required for the outlet HCl concentration to reach 50% of the inlet concentration was 4.6 hours. The LDH granules that were passed through this HCl-containing gas were designated as Example Sample 2. Example Sample 2 is expected to be a Cl-type Mg-Al LDH granule, as it was obtained by granulating CO3-type Mg-Al LDH, contacting it with an aqueous NaOH solution to obtain OH-type Mg-Al LDH, and then treating it with a gas containing HCl.

[0060] <Analysis of Cl content in Comparative Samples 1 and 2 and Example Samples 1 and 2> The obtained samples were ground in a mortar. 0.5 g of each ground sample was mixed with 100 ml of 2 mol / L nitric acid and stirred for 1 hour to dissolve the samples. The solution was filtered through 5C filter paper to remove the residue, and the filtrate was diluted 50 times with pure water. Cl ions were analyzed using an ion chromatograph (Dionex ICS-2100). Table 1 shows the results of calculating the Cl content per unit weight of adsorbent from the weight of the sample used for dissolution, the Cl ion concentration of the dilution water, and the dilution ratio. The Cl content was 0.36 mg / g for Comparative Example Sample 1, 12.8 mg / g for Comparative Example Sample 2, 109 mg / g for Example Sample 1, and 99 mg / g for Example Sample 2. Since the LDH content of the LDH granules is 78%, when the amount of Cl adsorbed is converted to the ion exchange equivalent per LDH, comparative example sample 1 is 0.013 meq / g-LDH, comparative example sample 2 is 0.462 meq / g-LDH, example sample 1 is 3.92 meq / g-LDH, and example sample 2 is 3.58 meq / g-LDH.

[0061] The stoichiometric ion exchange capacity of the CO3-type Mg-Al LDH used in this study, calculated from its molecular weight, was 3.94 meq / g-LDH. Therefore, it can be said that Example Sample 1 and Example Sample 2 were almost stoichiometric Cl-type Mg-Al LDH. On the other hand, Comparative Example Sample 2 only had 12% of its stoichiometric ion exchange capacity exchanged between interlayer ions. Even after immersion in an aqueous NaCl solution overnight, most of the interlayer ions remained CO3 ions, indicating that almost no ion exchange occurred with Cl ions. From these results, it is clear that contact between HCl gas and CO3-type Mg-Al LDH or OH-type Mg-Al LDH can effectively exchange the interlayer ions of CO3-type Mg-Al LDH or OH-type Mg-Al LDH with Cl ions.

[0062] [Table 1]

[0063] Next, the following evaluations were performed using the samples prepared as described above.

[0064] <Phosphate adsorption by batch testing> 10 g of the prepared sample was placed in a beaker, and 1000 mL of simulated wastewater with a phosphorus concentration of 100 mg / L was added to the beaker containing the adsorbent sample. The simulated wastewater was prepared by dissolving disodium hydrogen phosphate dihydrate (manufactured by Kishida Chemical Co., Ltd.), a special-grade reagent, in pure water. The simulated wastewater was stirred, and 5 mL was sampled at predetermined intervals. The sample was filtered through a 0.45 μm filter, and phosphate ions were analyzed using an ion chromatograph (Dionex ICS-2100). Sampling times were 1, 3, 7, and 24 hours, and the procedure was performed for Comparative Example 1, Comparative Example 2, and Example 1, respectively.

[0065] Figure 2 is a graph showing the change in phosphorus concentration over time. The phosphorus concentration was calculated as phosphate phosphorus (PO4-P) from the analysis of phosphate ions. As can be seen from Figure 2, although the phosphorus concentration in the simulated wastewater decreased over time for all samples, the decrease was small in Comparative Example Sample 1 and Comparative Example Sample 2. Looking at the phosphorus concentration after 24 hours, Comparative Example Sample 1 was 65.5 mg / L and Comparative Example Sample 2 was 65.1 mg / L, and in both cases the phosphorus adsorption rate was less than 50%. On the other hand, looking at Example Sample 1, the phosphorus concentration decreased to 26.3 mg / L after 1 hour, to 5.9 mg / L after 3 hours, and to less than the limit of quantification of 0.2 mg / L after 24 hours, indicating that the phosphorus in the simulated wastewater was almost completely adsorbed. Since Example Sample 1 is almost stoichiometric Cl-type Mg-Al LDH, it is thought that its phosphorus adsorption rate was higher than that of Comparative Example Sample 1, which is CO3-type Mg-Al LDH, and Comparative Example Sample 2, which is only partially Cl-type Mg-Al LDH.

[0066] <Phosphorus recovery by column testing> 25 g (50 mL) of sample 1 was prepared and packed into a glass column with an inner diameter of 31 mm. Then, SV5h -1 A simulated wastewater volume of 160 BV (8 L) was passed through at a flow rate of 4.2 mL / min. The simulated wastewater was prepared by dissolving special grade disodium hydrogen phosphate dihydrate in pure water to achieve a phosphorus concentration of 200 mg / L, similar to the batch test. Note that BV (bed volume) refers to the packed volume of the adsorbent (phosphorus recovery material), and here 1 BV = 50 mL.

[0067] The column outlet water was sampled every 2.5 BV from the start of water flow up to 10 BV, and every 10 BV from 10 BV to 160 BV. The phosphate ions were analyzed by ion chromatography, and the phosphorus concentration was determined as phosphate phosphorus (PO4-P) from the analysis of phosphate ions.

[0068] Figure 3 is a graph showing the breakthrough curve of phosphorus due to water flow through the column. As can be seen from Figure 3, the phosphorus concentration at the column outlet increases with the amount of water flowed through, and complete breakthrough occurs when approximately 100 BV of water is passed through, indicating that phosphorus has reached adsorption equilibrium.

[0069] After passing 160 BV sample water through the column, the packed sample was washed by passing 100 mL of pure water through it. After washing, 80 mL of 1 mol / L NaOH aqueous solution was stored in an Erlenmeyer flask as a regeneration solution. The column inlet and outlet were connected to the Erlenmeyer flask (the regeneration solution reservoir) with a tube, and the regeneration solution was circulated between the column and the Erlenmeyer flask at 10 mL / min for 2 hours. After circulation, the entire regeneration solution was drained, and the phosphorus concentration of the regeneration solution was determined in the same manner as above. The pH of the regeneration solution was also measured using a pH meter (Horiba D-75). Next, to wash away residual alkali and recover further phosphorus, 80 mL of pure water was circulated as a regeneration solution for 2 hours, and the phosphorus concentration and pH of the regeneration solution were determined in the same manner. This regeneration process using pure water circulation was repeated a total of three times.

[0070] Table 2 shows the phosphorus concentration and pH of the regenerated solution. As can be seen from Table 2, the phosphorus concentration of the regenerated solution circulated with NaOH reached 1411 mg / L, approximately seven times the concentration of the simulated wastewater, demonstrating the successful concentration of phosphorus recovery. Furthermore, the regenerated solution after the first circulation with pure water also achieved a phosphorus concentration of 462 mg / L, more than twice the concentration of the simulated wastewater. The reason why phosphorus could be concentrated and recovered with pure water is thought to be the effect of residual OH ions in the column after NaOH circulation, which then re-exchanged with PO4 ions remaining between the layers of the Mg-Al LDH. As evidence of this, the pH of the regenerated solution circulated with pure water was higher, not just the solution circulated with NaOH.

[0071] [Table 2]

[0072] The results above support the idea that efficient phosphorus recovery is possible when using Sample 1. Although Sample 2 also undergoes conversion to OH-type Mg-Al LDH, the resulting sample contains chloride ions equivalent to those in Sample 1. Therefore, it is expected that high-efficiency phosphorus recovery can be achieved using Sample 2, similar to Sample 1. [Explanation of Symbols]

[0073] 1: 1st container 2 :Second container 3: Phosphorus recovery material 100: Phosphorus recovery system P11, P12, P21, P22: Piping

Claims

1. A method for recovering phosphorus contained in wastewater, A preparation step to prepare an Mg-Al layered double hydroxide having carbonate ions or hydroxide ions as interlayer anions, An exchange step is performed to obtain an Mg-Al layered double hydroxide in which the interlayer anions are replaced with chloride ions by contacting the Mg-Al layered double hydroxide prepared in the above preparation step with a gas containing hydrogen chloride, A recovery step is performed in which the Mg-Al layered double hydroxide obtained in the exchange step is brought into contact with the wastewater, thereby exchanging the interlayer anions for phosphate ions contained in the wastewater and recovering the phosphorus contained in the wastewater. A method for recovering phosphorus, which includes [the necessary components].

2. In the phosphorus recovery method described in claim 1, A method for recovering phosphorus, further comprising a detachment step of contacting the Mg-Al layered double hydroxide after the recovery step with a solution having an anion different from the phosphate ion, thereby detaching the phosphate ion present as an interlayer anion.

3. In the phosphorus recovery method described in claim 1, A method for recovering phosphorus, wherein the preparation step involves preparing granules containing the Mg-Al layered double hydroxide and a binder.

4. In the phosphorus recovery method described in claim 1, A method for recovering phosphorus, wherein the exchange step involves contacting the Mg-Al layered double hydroxide with the gas at 40 to 200°C.

5. In the phosphorus recovery method described in claim 1, A method for recovering phosphorus, wherein the concentration of hydrogen chloride in the gas during the exchange step is in the range of 50 to 500 ppm.

6. In the phosphorus recovery method described in claim 1, The recovery step is performed by passing the wastewater through the Mg-Al layered double hydroxide filled in the first container, in a method for recovering phosphorus.

7. In the phosphorus recovery method according to claim 6, A method for recovering phosphorus, further comprising a detachment step after the recovery step, in which a solution having an anion different from the phosphate ion is passed through the first container to detach the phosphate ion present as an interlayer anion.

8. In the phosphorus recovery method according to claim 7, The aforementioned solution is the solution stored in the second container. A method for recovering phosphorus, wherein the detachment step involves circulating the solution passed through the first container to the second container.

9. A method for manufacturing phosphorus recovery material, A preparation step to prepare an Mg-Al layered double hydroxide having carbonate ions or hydroxide ions as interlayer anions, An exchange step is performed to obtain a phosphorus recovery material by contacting the Mg-Al layered double hydroxide prepared in the above preparation step with a gas containing hydrogen chloride, thereby replacing the interlayer anions with chloride ions. A method for manufacturing phosphorus recovery material, comprising the following:

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