Method for regenerating silica adsorbent

Abstract

To provide a method for recycling a used silica remover, that is, cerium hydroxide having silica adsorbed thereon, so that it can be used again for silica removal.SOLUTION: The present invention discloses a cerium hydroxide recycling method that detaches silica by the process of bringing cerium hydroxide having silica adsorbed thereon into contact with an aqueous solution of 9 or more in pH, an aqueous solution of 1 or less in pH, or aqueous sodium chloride solution.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for desorbing silica adsorbed on cerium hydroxide. [Background technology]

[0002] The adhesion and accumulation of scale (limescale) is a problem in water circulation systems such as the chilled water systems and cooling water systems of air conditioning equipment, boiler water supply systems, plant cooling water systems, hot spring facilities, etc. If scale adheres and accumulates on piping, it can clog the circulation system, and if it adheres and accumulates on the electric heating surfaces of a heat exchanger, it can cause a decrease in heat exchange efficiency. One of the main causes of scale is silica (silicon dioxide) ions in water, and there is a demand for efficient removal of these ions (Patent Document 1, etc.). Conventionally, methods for removing silica from a solution include ion exchange resins, reverse osmosis membranes, coagulation sedimentation, electrodialysis (EDI), and electrolysis.

[0003] When removing silica using ion exchange resin, it is usually not efficient because the silica adsorption capacity of ion exchange resin is small. Also, when the ion exchange resin becomes saturated with silica, silica leakage occurs. Therefore, when the silica concentration in the target solution is high, the ion exchange resin needs to be replaced more frequently. In addition, when removing silica using a reverse osmosis membrane, it is difficult to increase the concentration ratio in order to prevent silica fouling. Therefore, when the silica concentration in the target solution is high, the ratio of the treated water obtained to the raw water becomes small, which is not efficient. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2009-541036 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors conducted research and found that cerium hydroxide selectively adsorbs silicate ions in a solution and does not easily adsorb other ions, and came up with the idea that cerium hydroxide can be used as a silica adsorbent. In other words, a technology has been provided for efficiently removing silica from a solution by adsorbing silicate ions to cerium hydroxide.

[0006] In order to continuously carry out the silica removal technique in a water circulation system, it is necessary to replace the silica-adsorbed cerium hydroxide with cerium hydroxide without silica adsorbed. However, it is not preferable to discard the silica adsorbent after use, and it is preferable to reuse the silica adsorbent from the viewpoints of environment and cost. In view of such circumstances, an object of the present invention is to provide a technique for regenerating a used silica removing agent, i.e., potassium hydroxide having silica adsorbed thereon, so that it can be reused for removing silica. [Means for solving the problem]

[0007] As a result of extensive research to solve the above problems, the inventors discovered that under specific pH conditions or in the presence of ions, silica (silicate ions) does not adsorb to cerium hydroxide, and that silica (silicate ions) that had been adsorbed to cerium hydroxide is released, thereby completing the present invention. That is, one aspect of the present invention is a method for producing the silica-adsorbed cerium hydroxide, comprising the step of contacting the silica-adsorbed cerium hydroxide with an aqueous solution having a pH of 9 or more, an aqueous solution having a pH of 1 or less, or an aqueous solution of sodium chloride. This is a way to remove the sexual desire. In this embodiment, the aqueous solution having a pH of 9 or more is preferably an aqueous sodium hydroxide solution. In this embodiment, the aqueous solution having a pH of 1 or less is preferably an aqueous hydrochloric acid solution. In this embodiment, preferably, the cerium hydroxide is immobilized on a substrate. Another aspect of the invention is a method for regenerating cerium hydroxide comprising desorbing silica by the method of the previous aspect. In addition, the pH values ​​in this specification are those at 25°C. Effect of the Invention

[0008] According to the present invention, it is possible to desorb silica from cerium hydroxide to which silica (silicate ions) has been adsorbed. Since cerium hydroxide can adsorb silica (silicate ions) in a solution and function as a silica adsorbent, desorbing silica from a used silica adsorbent, i.e., from cerium hydroxide to which silica has been adsorbed, regenerates the silica adsorbent and enables its semi-permanent reuse. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing an embodiment in which the silica removing material (cerium hydroxide) of the present invention is used in an air conditioning system. The silica removing material may be installed at any position in the air conditioning system, not limited to the position shown in the figure. [Diagram 2] FIG. 2 is a diagram showing an embodiment in which the silica removing material (cerium hydroxide) of the present invention is used for pretreatment of an ion exchange resin. [Diagram 3] FIG. 2 is a diagram showing an embodiment in which the silica removal material (cerium hydroxide) of the present invention is used in pretreatment of a reverse osmosis membrane. [Figure 4] FIG. 1 is a diagram showing an embodiment in which the silica removal material (cerium hydroxide) of the present invention is used for treating boiler water, hot spring water, geothermal power generation water, etc. [Diagram 5] 1 is a graph showing the silica concentration remaining in tap water after adsorption treatment in a reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments of the present invention are merely examples of the present invention, and the technical scope of the present invention is not limited to the following embodiments.

[0011] <1> Cerium hydroxide Cerium hydroxide (Ce(OH)4) has the property of adsorbing silica and is an effective ingredient in silica adsorbents. Cerium hydroxide is usually available in the form of a powder, with particle sizes ranging from about 0.05 μm to 100 μm, and a cumulative median diameter of preferably 0.5 μm to 20 μm. Generally, the content of cerium hydroxide in the silica adsorbent is not particularly limited and can be adjusted arbitrarily within the range of 0.001 to 99.9% by weight. The purity of the cerium hydroxide used for silica adsorption is preferably 85% by weight or more, and more preferably 90% by weight or more.

[0012] Cerium hydroxide adsorbs silica in the form of silicate ions in a solution, usually an aqueous solution. Here, "adsorption" is not limited, but usually means adsorbing 2 mg or more of silica per 1 g of cerium hydroxide. Cerium hydroxide does not easily adsorb other ions such as sodium ions and magnesium ions, specifically, the amount of adsorption is less than 0.001 mg per 1 g of cerium hydroxide. Cerium hydroxide does slightly adsorb calcium ions, but the adsorption capacity decreases and almost disappears if the adsorption and desorption are repeated. That is, cerium hydroxide can selectively adsorb silica and remove it from solution. .

[0013] When cerium hydroxide is used as a silica adsorbent, other components may be included in the adsorbent as long as the silica adsorption effect is not impaired. Examples of other components include adsorbents of other components such as activated carbon and diatomaceous earth, binders for forming the adsorbent, antibacterial agents, etc. Examples of binders include inorganic binders such as silica sol and alumina sol, and polymer resins with high hydrophobicity and low reactivity. Examples of polymer resins with high hydrophobicity and low reactivity include polyolefin, nylon, polyethylene terephthalate, polyvinyl chloride, and polyvinylidene chloride.

[0014] <2> Silica adsorption filter material and its manufacturing method When cerium hydroxide is used as a silica adsorbent, it can be included in the silica adsorbent filter medium in a form immobilized on a substrate. Since cerium hydroxide is usually distributed in the form of a powder, when it is immobilized on a substrate, it becomes easy to handle, to remove silica, and to reuse the cerium hydroxide. The shape of the filter material is not particularly limited, but from the viewpoint of the efficiency of the method for removing silica from a solution and the method for desorbing silica from cerium hydroxide described below, the filter material is usually in a shape suitable for passing a solution and for installation in a flow path. Examples of such forms include column packings and filters that can increase the contact area with the silica-containing solution and the solution that desorbs silica, and these are preferred from the viewpoint of the efficiency of the adsorption and desorption reactions.

[0015] More specifically, examples of the method include immobilizing cerium hydroxide on a substrate and filling a container such as a column, and filling a pocket formed by multiple sheets of nonwoven fabric with cerium hydroxide to form a filter structure.

[0016] The cerium hydroxide may be immobilized on the substrate by covalent or non-covalent bonding. For example, the substrate may be a polymer or inorganic material that can be processed into an adsorption filter material, a chromatography carrier, a filter paper, a membrane, a filter, a hollow fiber, a fiber, a nanofiber, etc., which are already known as substrates. More specifically, the substrate may be a polysaccharide such as cellulose, agarose, starch, amylose, dextran, pullulan, glucomannan, etc.; a synthetic polymer such as polyacrylic acid or its derivatives, polyvinyl alcohol, nylon, polysulfone, polyacrylnitrile, polyethylene, polypropylene, polystyrene, etc.; an inorganic material such as glass, porous glass, silica gel, hydroxyapatite, etc.; a porous piece having pores such as activated carbon or zeolite; an inorganic binder such as silica sol or alumina sol; etc. In addition, the substrate may be one type of substrate, or two or more types of substrates may be used in combination.

[0017] The shape of the substrate is preferably a porous body from the viewpoint of contact with and passage of a silica-containing solution or a desorption solution, and more preferably includes filter paper, a membrane, a filter, a hollow fiber, a fiber, a nanofiber, a granular shape, a powder shape, and the like. The specific surface area of ​​the substrate is 100 to 300 m from the viewpoint of contact with and passage of the silica-containing solution. 2 It is preferred that the molecular weight is / g.

[0018] By immobilizing cerium hydroxide on these substrates, a silica adsorption filter medium can be produced. The immobilization of cerium hydroxide on the substrate can be carried out by any method. For example, there is a method in which cerium hydroxide is precipitated on a substrate by adding an oxidizing agent to an aqueous cerium solution. Another method is to mix cerium hydroxide powder with a binder, etc., and solidify it into granular pellets. In this case, the specific surface area of ​​the pellets is set to 100 to 300 m from the viewpoint of contact with and passage of a solution containing silica and a solution that releases silica. 2 The pellet shape is not particularly limited and may be spherical, discoid, crushed, or the like. Also, cerium hydroxide can be immobilized on filter paper, membranes, filters, hollow fibers, fibers, nanofibers, etc. by impregnating them with a cerium hydroxide solution for an appropriate period of time.

[0019] <3> Silica Removal Equipment The adsorption filter material of the present invention can be equipped in a silica removal device. This device can be preferably used to carry out the silica removal method described later. In addition, it can be repeatedly used by carrying out the method of desorbing silica of the present invention described later. In addition to the silica adsorption filter medium, the device usually includes a flow path for a solution, etc. The flow paths include, for example, a flow path for passing a solution (raw water) containing silica, a flow path for passing a treatment liquid from which silica has been removed, a flow path for passing a solution that will release silica (described later), a flow path for passing a solution (waste liquid) containing silica released from cerium hydroxide, etc. The mode of use of the device is not particularly limited as long as it is applied to anything that requires the removal of silica from a solution. Examples of the device include devices installed in water circulation systems such as cold water systems and cooling water systems of air conditioning equipment, boiler water supply systems, cooling water systems of plants, cooling water for molds, reverse osmosis membranes, ion exchange equipment, and hot spring equipment.

[0020] <4> How to Remove Silica By carrying out a step of contacting a silica-containing solution with the cerium hydroxide contained in the silica adsorbent or silica-adsorbing filter medium described above, silica can be removed from the solution. The solution is usually an aqueous solution, and the silica is usually contained as silicate ions.

[0021] The pH of the silica-containing solution is preferably from 4 to 9, more preferably from 6 to 7.5. Furthermore, the temperature of the silica-containing solution when the step of contacting the silica-containing solution with the silica adsorbent or silica-adsorbing filter medium is carried out is not particularly limited, and the step can be carried out at any temperature.

[0022] In the step of contacting the silica-containing solution with the silica adsorbent or silica adsorbent filter medium, in order to carry out this step efficiently, it is also preferable to circulate the silica-containing solution in the vicinity of the adsorbent or adsorbent filter medium of the present invention.

[0023] <5> Method for desorbing silica By carrying out a step of contacting the cerium hydroxide adsorbed by the silica with a desorption solution, the silica can be desorbed from the cerium hydroxide. Such a desorption solution is an aqueous solution having a pH of 9 or more, an aqueous solution having a pH of 1 or less, or an aqueous sodium chloride solution.

[0024] The aqueous solution having a pH of 9 or more is, but is not limited to, an aqueous solution of sodium hydroxide. The concentration of the aqueous solution of sodium hydroxide is preferably 0.1% by weight or more, more preferably 1% by weight or more, and even more preferably 4% by weight or more. Also, the concentration is preferably 48% by weight or less, more preferably 24% by weight or less, and even more preferably 10% by weight or less.

[0025] The aqueous solution having a pH of 1 or less is not particularly limited, but is an aqueous solution of hydrochloric acid. The concentration of the aqueous solution of hydrochloric acid is preferably 0.1% by weight or more, more preferably 1% by weight or more, and even more preferably 2% by weight or more. Also, the concentration is preferably 35% by weight or less, more preferably 10% by weight or less, and even more preferably 5% by weight or less.

[0026] The aqueous sodium chloride solution preferably has a concentration of 1% by weight or more, more preferably 10% by weight or more, and even more preferably a saturated concentration (about 26% by weight).

[0027] The desorption solution preferably contains a high concentration of cations, more preferably metal ions, further preferably alkali metal ions, and particularly preferably sodium ions. Such a concentration is, for example, 0.01 M or more.

[0028] These desorption solutions can desorb silica (silicic acid ions) adsorbed to cerium hydroxide due to the presence of a strong acid, a strong base, or a high concentration of cations. Usually, the "desorption" of silica means, but is not particularly limited to, liberating preferably 80% by weight or more, more preferably 85% by weight or more, and even more preferably 90% by weight or more of the silica adsorbed to cerium hydroxide. Therefore, the present method can be preferably applied to a method for regenerating cerium hydroxide, and the regenerated cerium hydroxide can be used again for silica adsorption.

[0029] The cerium hydroxide can be contacted with the desorption solution by, for example, immersing the cerium hydroxide in the desorption solution, passing the desorption solution through the cerium hydroxide, or circulating the desorption solution in the vicinity of the above-mentioned adsorption filter material containing cerium hydroxide. In addition, in a preferred embodiment, the silica removal step of adsorbing silica to cerium hydroxide and the step of desorbing silica from the cerium hydroxide to which the silica has been adsorbed are incorporated into a silica removal apparatus as described above. This allows the silica adsorbent to be regenerated and used repeatedly, thereby enabling the silica removal process to be carried out continuously and efficiently.

[0030] Furthermore, the temperature of the desorption solution when the step of contacting cerium hydroxide with the desorption solution is carried out is not particularly limited, and the step can be carried out at any temperature. The time for which the cerium hydroxide is contacted with the desorption solution is not particularly limited, but is preferably 1 minute or more, more preferably 1 hour or more, and even more preferably 12 hours or more.

[0031] <6> Use of silica removal by adsorption and regeneration of adsorbent by desorption Several application forms of the present invention will be described below, but the present invention is not limited to these.

[0032] The method for desorbing silica of the present invention, together with the above-mentioned method for removing silica, can be preferably applied to water flowing through a flow path, thereby making it possible to prevent the formation of silica scale in the flow path, and the process can be repeated. Here, the flow path is not particularly limited, but usually refers to piping through which water flows in a water circulation system such as a cold water system or cooling water system of an air conditioning system, a water supply system of a boiler, a cooling water system of a plant, a hot spring facility, etc. Furthermore, devices, equipment, parts, etc. that come into contact with water in a water circulation system may also be included in the flow path. Here, prevention of silica scale formation includes not only no silica scale formation at all, but also a reduction in the amount of silica scale and a delay in its formation compared to the case where silica removal is not performed.

[0033] Figure 1 shows the use of silica removal in air conditioning piping systems. Air conditioning facilities include a chilled water system, which is a water circulation system that circulates between the chiller and the air conditioner (AHU, FCU, etc.) to carry cold energy, and a cooling water system, which is a water circulation system that circulates between the chiller installed in the machine room inside the building and the cooling tower installed outdoors, and there is a high demand for silica removal. As shown in Figure 1, silica may be removed directly from the make-up water, or a part of the system may be branched off to remove silica. When the silica adsorption filter medium is porous, a flow path branched off from the system may be arranged for the silica removal filter medium, which may function as a device for removing dust from the solution. The cerium hydroxide with silica adsorbed thereon can be brought into contact with an aqueous sodium chloride solution, a strong acid, or a strong base in a separate system to release the silica, and then the silica can be returned to the flow path of the silica removal system. It is possible. A similar usage pattern can be adopted in the production cooling water system.

[0034] Figure 2 shows a form of use as a pretreatment for ion exchange resin. If the ion exchange resin becomes saturated with silica, silica leakage will occur. Therefore, it is preferable to remove silica from the aqueous solution before applying it to the ion exchange resin. This can extend the life of the ion exchange resin. The cerium hydroxide with silica adsorbed thereto can be brought into contact with an aqueous sodium chloride solution, a strong acid, or a strong base in a separate flow path to release the silica, and the silica can be returned to the flow path of the silica removal system.

[0035] Figure 3 shows a use form as a pretreatment for reverse osmosis membranes (RO membranes). In reverse osmosis membranes, silica may precipitate during concentration, causing clogging. To prevent clogging, it is necessary to operate the system at a low concentration ratio, which requires a large amount of concentrated water to be discharged, resulting in inefficiency. For this reason, it is preferable to remove silica from the aqueous solution before applying it to the reverse osmosis membrane. This makes it difficult for the membrane to become clogged, and the concentration ratio can be increased, improving treatment efficiency. The silica removal device containing cerium hydroxide may be installed in the concentration system, in addition to the location shown in the figure. The cerium hydroxide that has adsorbed silica can be brought into contact with an aqueous sodium chloride solution, a strong acid, or a strong base in a separate system to release the silica, and can be fed back to the flow path of the silica removal system.

[0036] Figure 4 shows how it can be used in the flow paths of boiler water, hot spring water, geothermal power generation water, etc. Before the raw water is circulated to each device, silica is removed by adsorption onto cerium hydroxide, which can prevent the formation of silica scale in pipes, etc. The cerium hydroxide with silica adsorbed can be brought into contact with a sodium chloride aqueous solution, a strong acid, or a strong base in a separate system to release the silica, and the silica can be returned to the flow path of the silica removal system.

[0037] In addition, the method for desorbing silica of the present invention, together with the above-mentioned method for removing silica, can be preferably applied to equipment having a water tank or a flow path, such as a humidifier or an iron. In this case, it is also preferable to use it together with an adsorbent such as zeolite that can adsorb calcium, and by adsorbing and removing silica and calcium, the generation of scale can be prevented, and the process can be repeated. EXAMPLES

[0038] EXAMPLES In the following, examples are shown to specifically explain the present invention, but these examples are merely examples of the present invention and the present invention is not limited to these examples.

[0039] <Reference Example> Silica adsorption with cerium hydroxide 1 g of sample was added to 100 mL of tap water (collected in Nagaoka City, Niigata Prefecture, pH 6) and shaken in a water bath at 25°C for 24 hours. 2 / g), iron hydroxide III powder (average particle size 1 μm, specific surface area 50 m 2 / g) , or activated alumina fibre (diameter 4mm, specific surface area 150m 2 / g, or 6mm specific surface area 150m 2 / g) was used. The residual silica concentration in the treated tap water was measured using an ICP emission spectrometer (ICPS-7510; Shimadzu Corporation).

[0040] The results are shown in Figure 5. An 85% reduction in silica was observed in tap water with added cerium hydroxide.

[0041] Example: Desorption of silica from cerium hydroxide Example 1 Cerium hydroxide powder (average particle size 50 μm, specific surface area 80 m) was added to 1 L of tap water (collected in Nagaoka City, Niigata Prefecture, pH 6). 2 0.1g (dry weight) of cerium hydroxide powder was added and immersed at 25°C for 48 hours. The residual silica concentration in the tap water after immersion was 10mg / L. The cerium hydroxide powder after immersion was collected and added to a 5% by weight aqueous hydrochloric acid solution, a 4% by weight aqueous sodium hydroxide solution, or a saturated aqueous sodium chloride solution, and immersed at 25°C for 48 hours. The cerium hydroxide powder after immersion was collected and washed 5 times for 1 minute with ultrapure water. 0.1g (dry weight) of the washed cerium hydroxide powder was added to 1L of new tap water, and immersed at 25°C for 48 hours. The residual silica concentration in the tap water after immersion was 10mg / L. The silica concentration in the aqueous solution was measured using an ICP emission spectrometer (ICPS-7510; manufactured by Shimadzu Corporation).

[0042] Comparative Example 1 0.1 g of cerium hydroxide powder was added to 1 L of tap water and soaked at 25°C for 48 hours. The residual silica concentration in the tap water after soaking was 10 mg / L. The cerium hydroxide powder after soaking was collected and added to 1 L of fresh tap water and soaked at 25°C for 48 hours. The residual silica concentration in the tap water after soaking was 16.9 mg / L.

[0043] Example 2 0.1 g of cerium hydroxide powder was added to 1 L of tap water and soaked at 25°C for 48 hours. The residual silica concentration in the tap water after soaking was 10 mg / L. The cerium hydroxide powder was collected after soaking and soaked in a 5 wt% hydrochloric acid solution, a 4 wt% sodium hydroxide solution, and a saturated sodium chloride solution. A negative correlation was observed between the amount of silica released and the time required for release.

Claims

1. A method for desorbing said silica, comprising the step of contacting cerium hydroxide having silica adsorbed thereon with an aqueous solution of sodium hydroxide having a concentration of 4% by weight or more.

2. The method according to claim 1 , wherein the aqueous solution having a pH of 9 or more is an aqueous sodium hydroxide solution.

3. A method for desorbing said silica, comprising the step of contacting cerium hydroxide adsorbed on said silica with a saturated aqueous sodium chloride solution.

4. The method according to any one of claims 1 to 3, wherein the cerium hydroxide is immobilized on a substrate.

5. A method for regenerating cerium hydroxide, comprising desorbing silica by the method according to any one of claims 1 to 4.

6. A silica removal device comprising a silica adsorption filter medium containing cerium hydroxide, An apparatus for carrying out the step of adsorbing silica onto the cerium hydroxide and the step of desorbing silica from the cerium hydroxide having silica adsorbed thereon by the method according to any one of claims 1 to 4.

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