Detergent, cleaning method for water treatment equipment, and cleaning method for silica-based scale

Abstract

The present invention provides a cleaning technique for silica-based scale. [Solution] The present invention can provide a cleaning agent for silica-based scale that contains a silicic acid compound. The present invention can also provide a cleaning method for water treatment equipment that uses a solution that contains a silicic acid compound. The present invention can also provide a cleaning method for silica-based scale that uses an agent that contains a silicic acid compound for a water system.

Description

[Technical field]

[0001] The present invention relates to a cleaning agent for silica-based scale, a cleaning method for water treatment equipment, and a cleaning method for silica-based scale. [Background technology]

[0002] Conventionally, it has been difficult to sufficiently remove silica-containing scale by cleaning with ordinary organic acids, alkalis, or surfactants, so cleaning with hydrofluoric acid or ammonium fluoride, which are environmentally hazardous and difficult to handle, cleaning with a heated highly alkaline solution, or scrubbing with a non-water-soluble suspension have been used. In order to solve these problems, a method has been developed to remove slime and silica deposits by using the synergistic effect of hydrogen peroxide and urea compounds, but this is not sufficiently effective against scale that is primarily made up of silica and inorganic substances.

[0003] The following Patent Documents 1 to 6 are cited as prior art. Patent Document 1 (JP Patent Publication 08-132093 A) proposes a cleaning composition that has an increased effect on removing both slime and scale and is also effective in removing rust, the cleaning composition containing hydrogen peroxide, condensed ammonium phosphate, and a urea compound as active ingredients. Patent Document 2 (JP Patent Publication 59-029093 A) proposes a method for removing scale, which is characterized by contacting silica or organic scale formed on the inner wall surface of a heated water system to which high-purity water with a dissolved oxygen content of 7 ppb or less is supplied with desalted water containing dissolved oxygen of 10 ppb or more at a temperature of 80°C or higher. Patent Document 3 (JP Patent Publication 05-137918 A) proposes a cleaning liquid for filter elements, which is characterized in that an organic corrosion inhibitor is added to nitric acid. Patent Document 4 (JP Patent Publication 11-189798 A) describes a method for preparing a surfactant comprising an anionic surfactant selected from an alkyl sulfonate (SAS), an alpha olefin sulfonate (AOS), or a linear alkylbenzene sulfonate (LAS) as a first component together with an acidic substance, and a polyoxyethylene alkanolamide (POE) (EO is 2 to 5 moles) (alkyl group is C 12 ~C 18 and an amine oxide having a specific structure as a third component, which supports a water-insoluble abrasive material in a stable manner under aqueous acidification. Patent Document 5 (JP 2003-41387 A) discloses a method for removing silica-based scale adhering to a metal surface, which comprises: (1) cleaning the silica-based scale containing silica and / or silicate adhering to the metal surface with a cleaning liquid containing a fluoride; and (2) passivating the metal surface with a passivation treatment liquid containing a fluoride and a peroxide. Patent Document 6 (JP Patent Publication 62-247089 A) discloses a scale remover that uses hydrochloric acid to which ammonium fluoride or acid ammonium fluoride has been added to remove silica scale adhering to bottle washing machines and other iron components. Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, a main object of the present invention is to provide a cleaning technique for silica-based scale. [Means for solving the problem]

[0005] In view of the above circumstances, the present inventors conducted extensive research and found that the use of a silicic acid compound can more effectively clean, reduce or remove silica-based scale, and completed the present invention. The present invention is as follows.

[0006] overview The present invention can provide a cleaning agent for silica-based scale, which contains a silicate compound.

[0007] The present invention can provide a method for cleaning a water treatment device using a solution containing a cleaning agent for silica-based scale that contains a silicic acid compound, or a solution containing a silicic acid compound.

[0008] The present invention can provide a method for cleaning silica-based scale by using an agent containing a silicic acid compound in an aqueous system. [Brief description of the drawings]

[0009] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0010] [Figure 1] FIG. 1 is a schematic diagram of an RO flat membrane evaluation cell assembly. [Diagram 2] FIG. 2 is a schematic diagram showing an RO flat membrane evaluation device. [Diagram 3]FIG. 3 is a photographic image of Samples 1-2 (membranes) before and after cleaning in the present disclosure 1-2 cleaning test and the conventional cleaning 1-2 cleaning test. FIG. 3A-3O are photographic images of Samples 1 and 2 (membranes) before and after cleaning in the present disclosure 1 and 2 cleaning test and the conventional cleaning 1 and 2 cleaning test, respectively. FIG. 3A is a photographic image of Sample 1 (membrane) before cleaning in the present disclosure 1 cleaning test. FIG. 3B is a photographic image of Sample 1 (membrane) after cleaning in the present disclosure 1 cleaning test. FIG. 3C is a photographic image of Sample 2 (membrane) before cleaning in the present disclosure 1 cleaning test. FIG. 3D is a photographic image of Sample 2 (membrane) after cleaning in the present disclosure 1 cleaning test. FIG. 3E is a photographic image of Sample 1 (membrane) before cleaning in the present disclosure 2 cleaning test. FIG. 3F is a photographic image of Sample 1 (membrane) after cleaning in the present disclosure 2 cleaning test. FIG. 3G is a photographic image of Sample 2 (membrane) before cleaning in the present disclosure 2 cleaning test. FIG. 3H is a photographic image of Sample 2 (membrane) after cleaning in the Disclosure 2 cleaning test. FIG. 3I is a photographic image of Sample 1 (membrane) after cleaning in the Conventional Clean 1 cleaning test. FIG. 3J is a photographic image of Sample 2 (membrane) before cleaning in the Conventional Clean 1 cleaning test. FIG. 3K is a photographic image of Sample 2 (membrane) after cleaning in the Conventional Clean 1 cleaning test. FIG. 3L is a photographic image of Sample 1 (membrane) before cleaning in the Conventional Clean 2 cleaning test. FIG. 3M is a photographic image of Sample 1 (membrane) after cleaning in the Conventional Clean 2 cleaning test. FIG. 3N is a photographic image of Sample 2 (membrane) before cleaning in the Conventional Clean 2 cleaning test. FIG. 3O is a photographic image of Sample 2 (membrane) after cleaning in the Conventional Clean 2 cleaning test. [Figure 4]FIG. 4 is a photographic image showing the properties of the remaining scale after cleaning of Sample 2 in the cleaning tests of the present disclosures 1 and 2 and the cleaning tests of conventional cleaning 1 and 2. FIG. 4A to FIG. 4D are photographic images showing the properties of the remaining scale after cleaning Sample 2 in the cleaning tests of the present disclosures 1 and 2 and the cleaning tests of conventional cleaning 1 and 2. FIG. 4A is a photographic image showing the properties of the remaining scale after cleaning of Sample 2 in the present disclosure 1. FIG. 4B is a photographic image showing the properties of the remaining scale after cleaning of Sample 2 in the present disclosure 2. FIG. 4C is a photographic image showing the properties of the remaining scale after cleaning of Sample 2 in conventional cleaning 1. FIG. 4D is a photographic image showing the properties of the remaining scale after cleaning of Sample 2 in conventional cleaning 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Description of the embodiments The present disclosure can provide a cleaning agent for silica-based scale, which contains a silicate compound. The cleaning agent may be used in a water treatment device or water system. The cleaning agent may have a pH of 10 or more, or the aqueous system using the cleaning agent may be adjusted to have a pH of 10 or more. The cleaning agent may contain 1,000 to 20,000 mg / L of silicic acid compounds calculated as total silica, or the cleaning agent may be used in an aqueous system so that the content of the silicic acid compound is 1,000 to 20,000 mg / L calculated as total silica. The cleaning agent may further contain one or more selected from a chelating agent, a surfactant, and a dispersant. The cleaning agent may further contain a percarbonate, or may be a cleaning agent that is used in combination with a solid agent (preferably a powder agent) containing a percarbonate.

[0012] The present disclosure can provide a method for cleaning a water treatment device using a solution containing a cleaning agent for silica-based scale that contains a silicic acid compound, or a solution containing a silicic acid compound. The solution may be adjusted to a pH of 10 or higher. The solution may contain a silicic acid compound at 1,000 to 20,000 mg / L in terms of total silica, or the solution may be added to the water to be treated in the water treatment device to adjust the water to a concentration of 1,000 to 20,000 mg / L in terms of total silica. Suitably, the solution further comprises a solid agent which, in use, comprises a percarbonate salt. The solution may further contain one or more selected from a chelating agent, a surfactant, and a dispersing agent. The solution may be one used for cleaning silica-based scale.

[0013] The present disclosure can provide a method for cleaning silica-based scale using an agent containing a silicate compound in a water system. The aqueous system may be adjusted to a pH of 10 or higher. The water system may be water to be treated or circulating water in a water system.

[0014] According to the present disclosure, a technique for cleaning silica-based scale can be provided.

[0015] Hereinafter, the embodiment for carrying out the present invention will be described. Note that the embodiment described below shows an example of a typical embodiment of the present invention, and the scope of the present invention is not limited by this. Furthermore, the upper and lower limit values ​​of the numerical values ​​can be arbitrarily combined as desired, and "to" in the numerical range means "greater than or equal to" or "less than or equal to".

[0016] 1. Overview of this technology The main objective of the present technology is to provide a cleaning technology for silica-based scale. In the present technology, a silicate compound is used to provide a cleaning technology for silica-based scale. The present technology is less susceptible to corrosion and deterioration of the water system during use, and therefore can be used more effectively in water systems or devices that are equipped in water systems.

[0017] Conventionally, in order to obtain a sufficient cleaning effect on scale, it was necessary to use a cleaning solution that has a high environmental impact and is difficult to handle, and the cleaning effect was particularly insufficient for scale mainly composed of silica and inorganic substances. In contrast, the present technology can be aimed at more effectively cleaning, reducing or removing silica-based scale that exists or occurs on a target, and this objective can be achieved.

[0018] Furthermore, conventional cleaning techniques have a large effect on corrosion or deterioration of resin materials (e.g., PVDF) and metal materials (e.g., stainless steel such as SUS) used in equipment provided in water systems and components of water treatment equipment (e.g., parts, tools, piping, etc.), and membranes used in membrane treatment (e.g., resin membranes such as polyamide membranes and PVDF membranes, etc.). In contrast, the present technology aims to more effectively clean, reduce, or remove silica-based scale present in targets such as water systems and equipment, as well as to reduce corrosion or deterioration of the targets or components used therein, and can achieve this aim.

[0019] As a more specific preferred embodiment of the present technology, a silica-based scale technology using a solution containing a silicic acid compound (preferably sodium or potassium metasilicate) and having a pH of 11.0 to 13.5 at 20° C. or higher, or a silica-based scale technology using a solution adjusted to such a solution, can be provided. More preferably, the technology contains or uses one or more selected from a chelating agent, a surfactant, and a dispersing agent, and / or contains or uses a percarbonate (preferably sodium percarbonate). In addition, the preferred solution in the present technology has an advantage that it can be easily prepared by dissolving or diluting a cleaning agent (preferably a solution or powder) prepared in advance, heating, etc. The preferred solution in the present technology may contain a silicic acid compound of preferably 1,000 to 20,000 mg / L (preferably 3,000 to 10,000 mg / L) in terms of total silica. Furthermore, the solution may contain one or more selected from a chelating agent, a surfactant, and a dispersing agent, and / or the solution may contain a percarbonate as a solid chemical (preferably a powder chemical), and may be a two-drug type drug kit containing the powder chemical.

[0020] Furthermore, this technology can provide a silica-based scale technology that can adjust the total silica equivalent concentration in the target to a specified concentration, thereby suppressing the decrease in effectiveness of cleaning the target due to a low concentration, or suppressing the occurrence of precipitation when neutralizing the pH during wastewater treatment due to a high concentration.

[0021] This technology can remove silica-containing scale, which is mainly composed of inorganic substances. This technology also provides a silica-based scale removal technology that has little effect on resin components such as polyamide membranes, PVDF membranes, and PVDF resin parts, and metal components such as stainless steel (SUS, etc.).

[0022] In this specification, the term "silica-based scale" refers to a substance formed by combining a silica-based substance (e.g., polymerized silica, calcium silicate, magnesium silicate, aluminum silicate, etc.) present in an aqueous system with a base or other components. In general, silica-based scale tends to precipitate in an aqueous system and adhere to or accumulate in places where water such as water to be treated or circulating water comes into contact with the water, such as the inside of various devices, piping, flow paths, membranes (prefilters, MF membranes, UF membranes, reverse osmosis membranes, etc.). With this technology, it is possible to more effectively implement silica-based scale countermeasures in aqueous systems. Examples of the silica-based scale countermeasures include one or more selected from cleaning, reduction, removal, etc. of silica-based scale present in aqueous systems, devices, etc.; and suppression, reduction, prevention, etc. of scale generation in aqueous systems, devices, etc.

[0023] In this specification, the measurement method of "total silica equivalent" is the "total silica" concentration in a solution or aqueous system, which is the total silica including ionic silica (ionic silicic acid), dissolved silica, and colloidal silica, and the total silica can be measured by the analytical method specified in JIS K 0101 44.3. The measurement method of "ionic silica equivalent" is the "ionic silica (ionic silicic acid)" concentration in a solution or aqueous system, and the ionic silica can be measured by the analytical method specified in JIS K 0101 44.3.

[0024] 2. Drugs according to this embodiment In the description of the agents and the like according to the present invention, the description of each component and each treatment method, such as silicic acid compounds, silica-based scale, pH, temperature, total silica equivalent concentration, dissolved matter concentration, and use concentration, which overlaps with the above-mentioned "1." and the following "3." and "4.", will be omitted as appropriate, but the description of "1.", "3.", "4.", etc. also applies to this embodiment and can be adopted as appropriate. In addition, in the description of the method in this embodiment, the description to be described later can be applied to this embodiment and can be adopted as appropriate.

[0025] The present embodiment can provide an agent containing a silicic acid compound (hereinafter also referred to as "the agent of the present embodiment"), preferably a cleaning agent for silica-based scale containing a silicic acid compound.

[0026] In this embodiment, it is suitable to use in a water treatment device or an aqueous system. In this embodiment, it is preferable that the cleaning agent has a pH of 10 or more or a pH of 11 or more, or that the aqueous system using the cleaning agent is adjusted to a pH of 10 or more or a pH of 11 or more. In this embodiment, the cleaning agent contains 1,000 to 20,000 mg / L of silicic acid compounds calculated as total silica, or the cleaning agent is used in an aqueous system so that the content of the silicic acid compound is 1,000 to 20,000 mg / L calculated as total silica. In this embodiment, the cleaning agent is preferably used in water having a temperature of 10 to 70°C.

[0027] In the present embodiment, it is preferable that the cleaning agent further contains one or more selected from a chelating agent, a surfactant, and a dispersing agent. In this embodiment, the cleaning agent is preferably a cleaning agent further containing percarbonate, or is preferably used in combination with percarbonate when used, and is preferably stored as a first agent (e.g., powder or liquid) containing a silicate compound and any appropriate optional ingredients, and a second agent containing percarbonate in a solid form (e.g., powder). In this embodiment, the cleaning agent may be in a unit package form. The unit package form preferably includes a first agent containing a silicic acid compound and a second agent containing a percarbonate as one unit package. For example, in the case of a one-dose type agent containing a first agent of a silicic acid compound and a second agent of a percarbonate, the agent may be in an integrated unit package form in which the separate packages are fixed and integrated on or within a single package (sheet, bag, etc.) without direct contact between the agents (for example, non-contact by packaging), or in a one-package unit package form in which separate drug packages are packaged together, or in a unit package form in which multiple agents are mixed together. For example, when an integrated unit package form such as a one-dose type agent containing a first agent of a silicic acid compound and a second agent of a percarbonate is added to water or a treatment target, the divided package portion of the form dissolves in the water or treatment target, and each agent in the package comes into contact with the water or treatment target and dissolves, thereby exerting the action of each agent.

[0028] The material used for the unit package is not particularly limited, but when it is to be added to the object to be treated or to water, a water-soluble resin or a material capable of forming a water-soluble film is suitable. Examples of the material include polyvinyl alcohol, polyvinylpyrrolidone, (vinylpyrrolidone / vinyl acetate) copolymer, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, gum arabic, etc., and one or more of these may be used.

[0029] 2-1.Silicate compounds The silicic acid compound used in this embodiment is not particularly limited, but examples thereof include silica (anhydrous silicic acid), silicic acid (e.g., orthosilicic acid (H4SiO4), pyrosiliic acid (H6Si2O7), metasilicic acid (H2SiO3), metadisiliic acid (H2Si2O5), etc.), polysilicic acid, and salts thereof, and one or more selected from these can be used. Among these, silicic acid or its salt, or metasilicic acid or its salt is preferred, and when the treatment target is alkaline during use, it is preferred that the silicic acid compound exists in the form of a silicate or metasilicate, and it is preferred to use a metasilicate when manufacturing a drug. The salt is not particularly limited, but examples thereof include one or more selected from alkali metal salts (e.g., Na salt, K salt, etc.), alkaline earth metals (e.g., Mg salt, Ca salt, etc.), and the like, and among these, alkali metal salts (preferably sodium salt) are preferred. In the case of the sodium salt, it is also called sodium silicate, and sodium silicate is generally a compound represented by the molecular formula Na2O·nSiO2·mH2O. The molar ratio in this case is not particularly limited, but for example, molar ratio = weight ratio (SiO2%·Na2O%) × (formula weight of Na2O / formula weight of SiO2), where n = about 0.5 to 4.0.

[0030] The form of the silicic acid compound in the drug in this embodiment is not particularly limited, and may be a solid (powder, granules, tablets, etc.), liquid, slurry, etc., and it is preferable that the drug containing the silicic acid compound is in a form that can be prepared into a liquid such as an aqueous solution and used. In the present embodiment, in the case of a solid drug, the amount of the silicic acid compound contained in the drug is not particularly limited, but is preferably 5 to 50%, more preferably 20 to 40%, calculated as the total silica. In the case of a liquid drug, the amount of the silicic acid compound contained in the liquid is not particularly limited, but is preferably about 1% to 25%, more preferably 5 to 20%, calculated as the total silica.

[0031] The use concentration of the silicic acid compound in this embodiment is not particularly limited, but it is preferable to adjust the silicic acid compound to be preferably 1,000 to 20,000 mg / L, more preferably 3,000 to 10,000 mg / L in terms of total silica. By adjusting the use concentration (adding a chemical, diluting with water, concentrating, etc.) when using the silicic acid compound for the treatment target, it is possible to more effectively wash the silica-based scale present in the treatment target. The use concentration at this time may be the total silica-equivalent concentration in the solution or in the aqueous system.

[0032] By using a silicic acid compound, it is possible to carry out measures against silica-based scales more effectively. As shown in the following [Examples], it was confirmed that the state of silica-based scales was clearly altered by using a silicic acid compound, and that the scales could be easily removed from the adhering portions even with the application of a small force. The mechanism of action in this embodiment is still under investigation and has not been clarified. However, the present inventors believe that due to the influence of silica in the silicic acid compound in the solution, not only is the silica-based scales that are very firmly attached to the water system (e.g., membranes, piping, etc.) partially dissolved in the solution containing the silicic acid compound, but the solution containing the silicic acid compound penetrates the silica-based scales, which softens the very firmly attached silica-based scales, and the silica-based scales after the treatment with the solution containing the silicic acid compound can be removed even with the application of a small force.

[0033] The silicic acid compound used in this embodiment has, for example, a cleaning action, a removal action, or a method for reducing silica-based scale, or an action for preventing the generation or clogging of scale caused by silica-based scale (for example, clogging of piping, membranes, etc.). Note that the generation or clogging of scale caused by silica-based scale includes, for example, fouling caused by the accumulation or non-removal of silica-based scale (including, for example, promotion of scaling, biofouling, organic matter filing, etc.). Therefore, the silicic acid compound can be contained in a cleaning agent, remover or reducer for silica-based scale, or an agent for preventing the generation or clogging of silica-based scale, or can be used in these agents. In this embodiment, the silicic acid compound itself can be used as the agent in this embodiment, or it can be used in combination with the silicic acid compound and other components, or it can be used as a multi-drug type drug kit consisting of a drug for the silicic acid compound and a drug for other components, and mixed when used. In this embodiment, a silicic acid compound or its use for use for purposes such as cleaning, removing or reducing silica-based scale, or preventing the generation or clogging of scale caused by silica-based scale may be provided. In addition, in this embodiment, the silicic acid compound can also be used to manufacture an agent or preparation such as the above-mentioned cleaning agent for silica-based scale. In addition, in this embodiment, a method such as a cleaning method for silica-based scale using a silicic acid compound can also be provided.

[0034] 2-2.Optional ingredients The drug or composition in this embodiment may contain various optional components as long as the desired technical effect and the effect of the present invention are not impaired. Suitable optional components for use in this embodiment include, for example, pH adjusters, surfactants; anionic surfactants such as alkylbenzenesulfonates; chelating agents such as tripolyphosphates, nitrilotriacetates, ethylenediaminetetraacetates ([4H], [2NA], [3NA], [4NA]), 2-hydroxyethylaminodiacetates, 3-hydroxy-2,2'-iminodisuccinic acid, iminodiacetic acid, and methylglycine diacetates; dispersants such as propylene glycol, polyethylene glycol, and polyacrylates; percarbonates; activators such as glucose pentaacetate, acetoxybenzenesulfonates, and ethylenediaminetetraacetates; hydrolases such as protease, amylolytic enzyme, lipase, and cellulose decomposing enzyme; and redeposition inhibitors such as polyvinylpyrrolidone, and one or more selected from these may be used. The content mass ratio or usage mass ratio of each component in the drug of this embodiment is not particularly limited. In addition, the various components used in this embodiment can be obtained by known manufacturing methods, and commercially available products may be used. The usage concentration of each component may be the concentration or content of each component in a solution or aqueous system. In addition, the content mass ratio may be the content ratio in a solution or aqueous system, and the usage mass ratio may be the usage ratio when used in a solution or aqueous system.

[0035] The drug or composition of the present embodiment preferably further contains one or more selected from a chelating agent, a surfactant, and a dispersing agent, and / or a percarbonate. In the present embodiment, the drug or composition containing a plurality of components may be in the above-mentioned unit package form as appropriate. When each component is contained in the drug or composition of the present embodiment, the drug or composition may be adjusted to have a high concentration of about 30 to 100 times the usage concentration of each component described below, and each component may be dissolved in a target or water so that the concentration of each component in the target or water is about 1 to 3% when used.

[0036] The chelating agent used in this embodiment is a water-soluble compound having two or more groups capable of forming a coordinate bond with a metal ion. Among these, ethylenediaminetetraacetate salts ([4H], [2NA], [3NA], [4NA]) are preferred, and among these, ethylenediaminetetraacetate 4Na is preferred. The concentration of the chelating agent used in this embodiment is not particularly limited, but it is preferable to adjust the chelating agent to preferably 10 to 10,000 mg / L, and more preferably 50 to 1,000 mg / L. The content mass proportion (usage mass proportion) of the chelating agent is preferably 0.05 to 100 parts by mass, and more preferably 0.5 to 35 parts by mass, per 100 parts by mass of total silica, and the "parts by mass" may be expressed as "mg / L."

[0037] The surfactant used in the present embodiment is not particularly limited, but may be, for example, an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant, etc., and one or more selected from these may be used. Among these, an anionic surfactant and / or a nonionic surfactant is preferred, and in the case of cleaning a reverse osmosis membrane, an anionic surfactant is more preferred. The concentration of the surfactant used in this embodiment is not particularly limited, but it is preferable to adjust the surfactant concentration to preferably 10 to 10,000 mg / L, and more preferably 50 to 300 mg / L. The content mass proportion of the surfactant (usage mass proportion) is preferably 0.05 to 1000 parts by mass, and more preferably 0.5 to 10 parts by mass, per 100 parts by mass of total silica, and the "parts by mass" may be expressed as "mg / L."

[0038] The dispersant used in the present embodiment is not particularly limited, and examples thereof include polymers such as polymaleic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), bis(poly-2-carboxyethyl)phosphinic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, phosphinocarboxylic acid copolymer, acrylic acid acrylamide copolymer, polyacrylic acid or its salt (for example, alkali metal salt such as sodium). One or more selected from these can be used, and among these, polyacrylic acid or its salt is preferred. The dispersant polymer preferably has a weight average molecular weight of 1,000 to 100,000, more preferably 4,000 to 20,000, but is not limited thereto. The weight average molecular weight of the polymer can be measured by gel permeation chromatography (GPC) analysis using standard polystyrene as a standard substance. The concentration of the dispersant used in this embodiment is not particularly limited, but it is preferable to adjust the dispersant to preferably 10 to 10,000 mg / L, and more preferably 50 to 1,000 mg / L. The content mass proportion of the dispersant (usage mass proportion) is preferably 0.05 to 1000 parts by mass, and more preferably 0.5 to 100 parts by mass, per 100 parts by mass of total silica, and the "parts by mass" may be expressed as "mg / L."

[0039] The percarbonate used in the present embodiment is not particularly limited, but examples of the salt include alkali metal salts (Na, K, etc.) and alkaline earth metal salts (Ca, Mg, etc.). Among these, alkali metal percarbonate salts (Na, K) are preferred, and sodium percarbonate is more preferred. The peroxide salt may be in the form of a liquid or solid (powder, granules, tablet), but in the case of generating foam in a water system during use, a solid (powder, etc.) is preferred. The carbonate peroxide salt may be packaged in the above-mentioned water-soluble resin or agent capable of forming a water-soluble film.

[0040] The concentration of the percarbonate used in this embodiment is not particularly limited, but it is preferable to adjust the concentration of the percarbonate to preferably 100 to 10,000 mg / L, and more preferably 1,000 to 5,000 mg / L. The content mass proportion of the percarbonate (usage mass proportion) is preferably 0.5 to 1000 parts by mass, and more preferably 30 to 170 parts by mass, per 100 parts by mass of total silica, and the "parts by mass" may be expressed as "mg / L."

[0041] In addition, the cleaning agent is preferably used in combination with a solid agent (preferably a powder agent) containing percarbonate. By using percarbonate in combination with a silicic acid compound, better silica-based scale countermeasures can be taken. Although the specific mechanism of action is under active investigation, it is believed that when a solution containing a silicic acid compound penetrates silica-based scale under highly alkaline conditions, oxygen bubbles are generated by the decomposition of percarbonate in the solution, which synergistically enhances the stripping effect on silica-based scale.

[0042] The form of the agent in this embodiment is not particularly limited, and may be any of liquid, solid (powder, granules, tablets, etc.), slurry, etc., and when used, the agent in this embodiment can be added, dissolved, or diluted to the object to be treated (for example, water present in the water system such as water to be treated or circulating water) or to water to prepare a solution for cleaning. For example, the agent in this embodiment may be added to water in equipment (pipes, tanks, etc.) provided in the water system to prepare water with a desired total silica equivalent concentration, and the prepared water may be circulated as the solution in this embodiment to clean the water system.

[0043] 2-3. Effects of this embodiment The agent in this embodiment can clean silica-based scales that exist or occur in the treatment target. The agent in this embodiment can also remove, reduce, peel off, or prevent adhesion of silica-based scales that exist in the treatment target (preferably an aqueous system).

[0044] Furthermore, the agent in this embodiment has the excellent effect of slowing or minimizing corrosion or deterioration (also referred to as low corrosion or low deterioration) of various materials (preferably metals and / or resins). In addition, in order to dissolve silica, acid treatment using fluorine compounds such as hydrofluoric acid and fluorides is generally performed, but acid treatment using fluorine compounds cannot be used for metal materials such as SUS because of its strong corrosion, and cannot be used for general resin materials because it is prone to deterioration. Compared with such acid treatment using fluorine compounds, the agent of this embodiment has the excellent advantage of low corrosion and low deterioration even when used in an alkaline range. Therefore, the agent of this embodiment can effectively clean silica-based scales present in a wide range of treatment targets such as equipment and water systems in which metals and / or resins are used as materials. The agent of this embodiment is suitably applied to metals and / or resins used as materials for water systems or water treatment facilities and devices (for example, water system piping, heat exchangers, refrigerators, air conditioners, tanks, etc.).

[0045] The metal is not particularly limited, and may be, for example, one or more metals selected from iron (carbon steel), stainless steel, etc. Among these, carbon steel and stainless steel are preferable. The low corrosiveness of a metal may be that the corrosion weight loss is 0.1% or less, 0.5% or less, or 1% or less in the corrosion resistance test in the following [Example], and it is preferable to apply the agent of this embodiment to those using such metal materials.

[0046] The resin is not particularly limited, and examples thereof include one or more resins selected from chlorinated resins (polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, etc.), polyolefin resins (polyethylene resins, polypropylene resins, polyvinylidene fluoride resins, etc.), and (meth)acrylic resins (e.g., polyacrylic ester resins, polymethacrylic ester resins, polyacrylamide resins, polyacrylonitrile resins, etc.). Among these, preferred are chlorinated resins such as polyvinyl chloride and polyvinylidene chloride; polyolefin resins such as polyethylene and polypropylene; and (meth)acrylic resins such as polyacrylic ester. The low deterioration of the resin may be a loss in resin volume of 0.1% or less, 0.5% or less, or 1% or less in the corrosion resistance test in the following [Examples], and it is preferable to apply the agent of this embodiment to those using such resin materials.

[0047] The agent in this embodiment can be used in a water system in which silica-based scale exists, regardless of the water quality conditions and operating conditions. The water system applicable to this embodiment is not particularly limited, but examples thereof include water treatment water systems such as systems equipped with various processes for water treatment, membrane treatment systems, etc.; circulating water systems equipped with cooling towers, boilers, etc. (cooling water systems, boiler water systems); and process water systems such as pulp process water systems and scrubber water systems in paper pulp production, etc., and the present embodiment can be applied to one or more types selected from these circulating water systems. In water treatment systems, the compound can be added to the water to be treated, preferably just before membrane treatment or between membrane treatment and the treatment preceding it. In circulating water systems, the compound can be added to circulating water or make-up water. In this embodiment, the location and method of adding the chemical agent are not particularly limited, and the chemical agent can be added as an aqueous solution prepared to a desired concentration at any desired location in the aqueous system used. Furthermore, this embodiment can be applied to the circulating water systems of heat exchangers in building air conditioning, general factories, petrochemical complexes, and the like, and can also remove, reduce, peel off, or prevent the adhesion of silica-based scale to devices such as heat exchanger bodies, circulating water pits, and cooling towers, as well as inside piping.

[0048] 3. Cleaning method according to the present invention In the description of the cleaning method according to the present invention, the description of each configuration and each treatment method such as silicic acid compounds, silica-based scale, pH, temperature, total silica equivalent concentration, dissolved matter concentration, and use concentration, which overlap with the above-mentioned "1." and "2." and the later-described "4.", etc., will be omitted as appropriate, but the description of "1.", "2.", "4.", etc. also applies to this embodiment and can be adopted as appropriate. In addition, in the description of the method in this embodiment, the description to be described later can be applied to this embodiment and can be adopted as appropriate. In addition, in this embodiment, for example, "(to) clean the water system" may be expressed as "process" or "step", "step" may be expressed as "(to) clean" or "process", and "process" may be expressed as "(to) clean" or "step. In addition, in this embodiment, "mechanism" and "means" may be expressed as a system, device, or part, "device" may be expressed as a system, mechanism, or part, and "part" may be expressed as a part or device to be provided in a mechanism, device, system, etc.

[0049] This embodiment can provide a method for cleaning a water treatment device or a method for cleaning silica-based scale, using a silicic acid compound, or a solution containing a silicic acid compound, or the agent of this embodiment. The solution containing a silicic acid compound may be a solution containing the agent of this embodiment (e.g., a cleaning agent for silica-based scale containing a silicic acid compound). Although this will be described below as a "solution containing a silicic acid compound", in this embodiment, it may also be a "solution containing a cleaning agent for silica-based scale containing a silicic acid compound". The present embodiment may be a method for cleaning an aqueous system, a method for removing, reducing or peeling silica-based scale in an aqueous system, or a method for preventing scale generation or clogging caused by silica-based scale.

[0050] The pH of the solution containing the silicic acid compound used in this embodiment is preferably in the alkaline region, with a preferred lower limit of preferably 10 or more, more preferably 11 or more, and even more preferably 11.5 or more, and a preferred upper limit of preferably 14 or less, 13.5 or less, with a preferred numerical range of pH 11 to 14. In this embodiment, it is preferred to adjust the solution containing the silicic acid compound to such a pH, and it is preferred that the pH of the solution (e.g., aqueous system, cleaning solution) is the pH when the solution is brought into contact with a treatment target such as a cleaning target (e.g., equipment, piping, membrane, etc.).

[0051] The water temperature of the solution containing the silicic acid compound is not particularly limited, but a suitable lower limit is preferably 10° C. or more, more preferably 20° C. or more, and more preferably 30° C. or more, and a suitable upper limit is preferably 70° C. or less, more preferably 60° C. or less, and more preferably 50° C. or less, with the suitable numerical range being 30 to 50° C. In the present embodiment, it is preferable to adjust the solution containing the silicic acid compound to such a water temperature, and it is preferable that the water temperature of the solution is the temperature when the solution is brought into contact with a treatment target such as a cleaning target.

[0052] The solution containing the silicic acid compound has a preferred lower limit of 100 mg / L or more, more preferably 500 mg / L or more, even more preferably 800 mg / L or more, more preferably 1,000 mg / L or more, even more preferably 1,500 mg / L or more, more preferably 2,000 mg / L or more, even more preferably 2,500 mg / L or more, and more preferably 3,000 mg / L or more, and a preferred upper limit of 50,000 mg / L or less, more preferably 40,000 mg / L or less, even more preferably 30,000 mg / L or less, more preferably 20,000 mg / L or less, and more preferably 10,000 mg / L or less, and the preferred numerical range is preferably 1,000 to 20,000 mg / L, more preferably 3,000 to 10,000 mg / L. In this embodiment, it is preferable to adjust the solution used in this embodiment by adding or mixing a silicic acid compound so that the solution concentration is equivalent to the total silica. It is preferable that the total silica concentration is the same as that of the solution (e.g., aqueous system, cleaning solution) when the solution is brought into contact with a target to be treated such as a target to be cleaned (e.g., equipment, piping, membrane, etc.).

[0053] When the solution containing the silicate compound is used by adding, blending or mixing a solid agent, it is preferable that the solution further contains a solid agent containing a percarbonate. It is preferable that the solution containing the silicic acid compound further contains one or more selected from a chelating agent, a surfactant, and a dispersing agent. The drug may be added as a single-dose drug or may be added as a multi-dose drug kit such as a two-dose drug kit composed of a plurality of drug products. It is more preferable that the second drug containing an optional ingredient (preferably a percarbonate) is added to the aqueous system at the same time as the first drug containing the silicic acid compound is added or at a different time. In addition, when it is a single-dose type, it may be in a unit package form, and when it is a multi-dose type, each drug may be film-coated with the above-mentioned water-soluble resin or water-soluble film-forming agent and dissolved by contacting with water when used.

[0054] The solution containing the silicic acid compound is preferably a cleaning liquid for silica-based scale, for example, a cleaning liquid for cleaning, reducing or removing, and preventing scale from parts (e.g., inside of equipment, parts, piping, membranes, etc.) through which water such as water to be treated, cooling water, circulating water, etc. in water systems and water treatment equipment flows.

[0055] The concentration of the chelating agent in the solution containing the silicic acid compound is not particularly limited, but a more preferred lower limit is preferably 10 mg / L or more, more preferably 30 mg / L or more, and even more preferably 50 mg / L or more, and a more preferred upper limit is preferably 10,000 mg / L or less, more preferably 5,000 mg / L or less, even more preferably 3,000 mg / L or less, and even more preferably 1,000 mg / L or less.

[0056] The concentration of the surfactant used in the solution containing the silicic acid compound is not particularly limited, but a more preferred lower limit is preferably 10 mg / L or more, more preferably 25 mg / L or more, and even more preferably 50 mg / L or more, and a more preferred upper limit is preferably 10,000 mg / L or less, more preferably 800 mg / L or less, even more preferably 500 mg / L or less, and even more preferably 300 mg / L or less.

[0057] The concentration of the dispersant used in the solution containing the silicic acid compound is not particularly limited, but a more preferred lower limit is preferably 10 mg / L or more, more preferably 20 mg / L or more, even more preferably 30 mg / L or more, more preferably 40 mg / L or more, and more preferably 50 mg / L or more, and a more preferred upper limit is preferably 10,000 mg / L or less, more preferably 5,000 mg / L or less, even more preferably 3,0000 mg / L or less, and more preferably 1,000 mg / L or less.

[0058] The concentration of the percarbonate used in the solution containing the silicic acid compound is not particularly limited, but a more preferred lower limit is preferably 100 mg / L or more, more preferably 500 mg / L or more, even more preferably 800 mg / L or more, and more preferably 1,000 mg / L or more, and a more preferred upper limit is preferably 10,000 mg / L or less, more preferably 8,000 mg / L or less, even more preferably 7,000 mg / L or less, and more preferably 5,000 mg / L or less.

[0059] The solution containing the silicic acid compound in this embodiment can be brought into continuous or intermittent contact (fluid flow, spray, convection, immersion, etc.) with the treatment target containing silica-based scale. In addition, in this embodiment, a mechanism configured to change the flow rate and flow rate of the solution containing the silicic acid compound may be provided, and the flow rate of the solution containing the silicic acid compound may be changed by this. As a change in the flow rate, for example, adjustment of a strong period and a weak period of the flow, or adjustment of an ON period and an OFF period of the flow, etc. are preferable. Here, "strong (more)" and "weak (less)" refer to a relative relationship, for example, a certain flow rate is stronger (more) or weaker (less) than a certain flow rate, and "certain (predetermined)" may be before and after over time (for example, a later flow rate is stronger (more) or weaker (less) than the previous flow rate). In addition, the OFF period may be a period during which the operation of the fluid, such as flow, spray, or convection, is OFF. For example, if the solution containing the silicic acid compound is in contact with the treatment target even during the OFF period, this OFF period may be the immersion period.

[0060] In this embodiment, the flow rate of the solution containing the silicic acid compound is not particularly limited, and can be set appropriately depending on the scale of the water system, the type of the water system, the type of equipment provided, and the like.

[0061] In this embodiment, the period during which the solution containing a silicic acid compound is brought into contact with or present on the treatment target containing silica-based scale is not particularly limited, but a longer contact period (hours) or number of days (days) is more preferable from the viewpoint of reducing silica-based scale, etc., and a suitable lower limit is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 3 hours or more, and from the viewpoint of work hours or resumption, etc., a suitable upper limit is preferably 2 days or less, more preferably 24 hours or less, even more preferably 18 hours or less, and even more preferably 12 hours or less.

[0062] This contact period is preferably accompanied by a fluid flow or fluid circulation. For example, by adjusting the flow rate with a control mechanism such as a pump or a control valve to turn the flow ON-OFF or to make the flow stronger or weaker, the silica-based scale can be peeled off more easily. The ON and OFF periods of the fluid flow are preferably 0.5 to 12 hours, more preferably 1 to 8 hours, and even more preferably 2 to 6 hours, and the OFF period is preferably 1 to 18 hours, more preferably 4 to 15 hours, and even more preferably 8 to 12 hours. For example, a flow (flow ON period) of 0.5 to 12 hours is performed, and after the flow is stopped, immersion (flow OFF period) is performed for 5 to 18 hours. By immersion, the silicate compound penetrates the silica-based scale, so that the silica-based scale that adheres when the flow is resumed is easily peeled off or dissolved.

[0063] The treatment object of this embodiment is not particularly limited, but is preferably an aqueous system, more preferably a water treatment device or water treatment system, and even more preferably a water treatment device equipped with a membrane treatment device. In addition, in order to carry out this embodiment, it is preferable to provide a mechanism for washing the treatment object (e.g., a separation membrane, piping, etc.) so that the fluid of the agent or solution of this embodiment flows through the treatment object. More preferably, a fluid circulation path and a fluid control mechanism (e.g., a pump, a flow control valve, etc.) are provided so that the fluid of the agent or solution of this embodiment can circulate while contacting the treatment object. Such a mechanism for contacting the treatment object with the fluid may utilize equipment or mechanisms present or provided in the aqueous system.

[0064] The water treatment device to be treated in this embodiment is not particularly limited, but is preferably, for example, a water treatment device equipped with a separation membrane for treating the water to be treated. Among these, it is preferable to treat a separation membrane to which silica-based scale is easily attached or accumulated. The separation membrane to be treated is not particularly limited, and may be, for example, an ultrafiltration membrane (UF membrane), a microfiltration membrane (MF membrane), a nanofiltration membrane (NF membrane), a reverse osmosis membrane (RO membrane), etc., and may be one or more selected from these. Among these, the reverse osmosis membrane is preferred because the agent containing a silicic acid compound has a good cleaning effect and a low deterioration effect.

[0065] Examples of separation membranes include membranes made of organic materials such as polyvinylidene fluoride (PVDF), polyethylene (PE), tetrafluoroethylene (PTFE), polypropylene (PP), cellulose acetate (CA), polyacrylonitrile (PAN), polyimide (PI), polysulfone (PS), and polyethersulfone (PES) or the above-mentioned resins; and membranes made of inorganic materials such as aluminum oxide (alumina: Al2O3), zirconium oxide (zirconia: ZrO2), titanium oxide (titania: TiO2), and stainless steel (SUS) or the above-mentioned metals.

[0066] The reverse osmosis membrane (RO membrane) is not particularly limited, and examples thereof include membranes in the form of a spiral, hollow fiber, flat membrane, or the like, with a skin layer made of a resin such as cellulose acetate, aromatic polyamide, or aromatic polyimide.

[0067] The water to be treated used in this embodiment is not particularly limited, and examples thereof include seawater, river water, well water, lake water, industrial water, city water, wastewater, and wastewater treatment water. One or more types selected from these can be used, and the water to be treated may contain organic matter. This embodiment can also be applied to industrial wastewater treatment, and to a system for obtaining treated water from which unnecessary substances such as organic compounds have been removed (e.g., reclaimed water, pure water, ultrapure water, etc.). This embodiment can also be applied to a system for obtaining treated water from which salt has been removed (e.g., drinking water, pure water, ultrapure water, etc.) by applying it to seawater desalination, and the water to be treated in this case may contain salt.

[0068] A water treatment system to which this embodiment can be applied preferably includes at least a membrane separation process for subjecting the water to be treated to membrane separation treatment, and preferably includes, as the membrane separation process, a prefilter treatment process and / or a reverse osmosis membrane treatment process. The water treatment system may further include one or more selected from an activated carbon treatment step (component activated carbon treatment step) for treating water to be treated (raw water) with activated carbon, a flocculation treatment step in which a flocculant is added to the water to be treated (raw water) in a flocculation device, a solid-liquid separation step in which the flocculated water is treated in a solid-liquid separation device, and various chemical addition steps. The water treatment system may also include an activated carbon tower (biological activated carbon tower) into which raw water flows, a reaction tank, a relay tank, a filter, and an RO device, and treated water is obtained. The concentrated water is discharged outside the water system through a concentrated water discharge line. A bypass pipe may be provided to introduce the outflow water from the activated carbon tower into the RO device (in this example, the front stage side of the filter 4).

[0069] In the cleaning method for a water treatment system having membrane separation of this embodiment, it is preferable to add the chemical of this embodiment before the prefilter treatment step and / or the RO membrane treatment step, or between the prefilter treatment step and the RO membrane treatment step (or before the RO membrane treatment), or it is preferable to circulate the chemical of this embodiment through the prefilter treatment step and / or the RO membrane treatment step.

[0070] In addition, the circulating water system to which this embodiment can be applied may be, for example, a detoxification scrubber facility configured to adsorb, wash with water, neutralize with chemicals, and release gas containing harmful substances generated into the atmosphere, or a humidity regulator for air conditioning. In addition, the method for cleaning a circulating water system of this embodiment preferably includes at least a step of adding the chemical to the circulating water system and contacting it with a target to be treated. In addition, the location of the chemical addition is not particularly limited, and is preferably a make-up water supply means, a chemical injection means, a circulating water channel, a transfer pump, or the like, and the chemical can be added at one or more locations selected from these.

[0071] In addition, the circulating cooling water system among the circulating systems to which this embodiment can be applied is not particularly limited, and may be either an open circulating cooling water system or a closed circulating cooling water system, and it is preferable that the open circulating cooling water system has a configuration in which cooling water can circulate in an open manner, and it is preferable that the closed circulating cooling water system has a configuration in which cooling water can circulate in a closed manner.

[0072] In addition, the method for cleaning a cooling water system of this embodiment preferably includes at least a step of adding the chemical agent to the cooling water system and contacting it with the object to be treated. The location of the chemical agent addition is not particularly limited and may be any location in the cooling water system, such as a blower, a water sprinkler, a pit, a make-up water supply means, a chemical agent injection means, a circulating water channel, a transfer pump, a heat exchanger, etc., and preferably, the chemical agent may be added at one or more locations selected from the make-up water supply means, the chemical agent injection means, the circulating water channel, the transfer pump, etc.

[0073] 4. Method for cleaning silica-based scale according to the present invention In the description of the cleaning method and the like according to the present invention, the description of each component and each treatment method, such as silicic acid compounds, silica-based scale, pH, temperature, total silica equivalent concentration, dissolved matter concentration, and use concentration, which overlap with the above-mentioned "1.", "2.", "3.", etc., will be omitted as appropriate, but the description of "1.", "2.", "3.", etc. also applies to this embodiment and can be adopted as appropriate. In addition, in the description of the method in this embodiment, the description to be described later can be applied to this embodiment and can be adopted as appropriate.

[0074] The present embodiment can provide a cleaning method for a water treatment device, using an agent containing a silicic acid compound for a water system. The aqueous system is preferably adjusted to a pH of 10 or higher. The water system is preferably water to be treated or circulating water, and more preferably water to be treated in a water treatment system (more preferably a membrane treatment system, etc.) or circulating water in a circulating water system (more preferably a cooling water system equipped with a heat exchanger, a boiler water system, a scrubber water system, etc.).

[0075] The concentration of the silicic acid compound used in this embodiment is not particularly limited, but it is preferable to use the silicic acid compound in an aqueous system at a concentration of 1,000 to 20,000 mg / L calculated as total silica.

[0076] This embodiment can provide a method for cleaning silica-based scale in an aqueous system, which includes a step of adding a chemical agent containing a silicic acid compound to the aqueous system so that the aqueous system has a predetermined total silica equivalent concentration. Furthermore, it is preferable to include a cleaning step in which, after the addition, the aqueous fluid (liquid) is circulated, the total silica equivalent concentration in the aqueous system increases, and then cleaning is performed until the total silica equivalent concentration becomes constant or reaches a set upper limit of the total silica equivalent concentration. In the chemical addition step, when the total silica equivalent concentration of the aqueous system containing the silicic acid compound is high, dilution with water and additional addition of the chemical agent may be used in combination to reach a predetermined concentration. When the total silica equivalent concentration in the aqueous system is in a stable state, an additional addition step of additionally adding the chemical agent of this embodiment may be included. In addition, when the total silica equivalent concentration in the aqueous system is only an increase in the total silica equivalent concentration of the additionally added chemical agent, the cleaning may be terminated. In addition, a discharge step may be included in which a part or all of the aqueous system or solution containing the dissolved or peeled silica-based scale is discharged from the system during or after the cleaning is completed. In terms of cleaning efficiency, the discharge step is preferably performed by discharging a part or the whole of the aqueous system based on the measurement results of the aqueous system. For example, one or more of the measurement results of the aqueous system may be used, selected from the total silica concentration, pH, and dissolved matter concentration. The discharge step may also be a liquid exchange step, and the liquid exchange step may involve, for example, replenishing the aqueous system with a cleaning solution or adding a chemical to the aqueous system to exchange the liquid in the aqueous system.

[0077] In addition, the present embodiment can also provide a method for cleaning silica-based scale, a method for cleaning silica-based scale in a water system, or a method for managing silica-based scale, which includes an adjustment step of adding a chemical to the water system to adjust the water system to a predetermined total silica equivalent concentration. By adding a chemical to the water system and / or diluting it with water, it is possible to prepare a cleaning water (cleaning solution) of the water system having a predetermined total silica equivalent concentration. By carrying out the adjustment step over time, it is possible to dissolve or peel off silica-based scale present in a membrane or pipe of the water system in the cleaning water of the water system. During or after cleaning, a part or the whole of the cleaning water or solution of the water system containing silica-based scale may be discharged outside the water system. In this way, it is possible to clean, remove, reduce, suppress, or prevent the generation of silica-based scale present in the water system.

[0078] In addition, this embodiment preferably includes a measuring step of measuring the total silica equivalent concentration in the water system and / or an adding step of adding a chemical to the water system. It is further preferable to include a pH measuring step of measuring the pH in the water system. The total silica equivalent concentration may be an ionic silica equivalent concentration. The total silica equivalent concentration measuring device is not particularly limited, but is preferably configured to be capable of measuring ionic silica (mg / L) and / or total silica (mg / L), and is more preferably a measuring device capable of measuring total silica. In addition, the pH measuring device is not particularly limited, but is preferably configured to be capable of measuring the pH in the water system. In addition, this embodiment may appropriately include a step of measuring the electrical conductivity in the water system and / or a step of measuring the BRIX in the water system, which can be measured using an electrical conductivity meter, a BRIX meter, etc., and it is also possible to measure the concentration of dissolved substances, etc. In addition, this embodiment may include a step of measuring the concentration of dissolved substances in the water system. In addition, the chemical addition device is not particularly limited, but one or more may be provided in the aqueous system, and it is preferable that the device is configured to be able to add chemicals such as silicic acid compounds and pH adjusters to the aqueous system. In addition, in this embodiment, the process may be carried out using a device configured to be able to perform flow (flow rate, etc.), immersion, spraying, etc., on the target of the portion (e.g., membrane, tool, piping, etc.) on which silica-based scale is attached in the aqueous system. In this embodiment, based on the measurement results of the measurement step, the amount of chemical added (or used) to the aqueous system or the amount of dilution with water (or used) can be adjusted in the addition step to a predetermined total silica equivalent concentration. Also, in the addition step, a pH adjuster can be added to the aqueous system to adjust it to a predetermined pH. These measuring devices and chemical addition devices are preferably managed and controlled by a control device (or control unit) provided in the device or system of this embodiment, and these devices can transmit and receive various data between each device as appropriate, and the control device preferably adjusts the total silica equivalent concentration, pH, chemical use, etc., of the aqueous system based on these various data.

[0079] Examples of the cleaning method in this embodiment are described below, but are not limited to these. The control unit used in this embodiment is configured to execute the method in this embodiment, and an operator (human) may execute the method in this embodiment as appropriate instead of the control unit. The use of the drug may include the concentration of use, contact time (use time), contact temperature, flow, etc., and may be selected appropriately from these. The control mechanism is capable of performing feedback control by executing such increase and decrease adjustments.

[0080] Example 1 of this embodiment will be described below. Examples 2 to 5 below can be adopted or incorporated as appropriate. In step 101, the control unit adjusts the cleaning solution by adding a silicic acid compound or water so that the cleaning solution has a predetermined total silica equivalent concentration. In step 101, the control unit may adjust the cleaning solution to a predetermined total silica equivalent concentration based on the measurement result of the total silica equivalent concentration, and may further instruct the measurement unit to measure the total silica equivalent concentration and transmit the measurement result to the control unit. In addition, the control unit may adjust the cleaning solution by appropriately adding optional components, etc. In step 102, the control unit causes the cleaning solution to come into contact with the treatment object for a predetermined period of time, and then ends the cleaning.

[0081] Example 2 of this embodiment will be described below. It is preferable to further include a step of pH measurement and pH adjustment in the above Example 1. The above and following Examples 1, 3 to 5 can be adopted or incorporated as appropriate. In the following, the step of adjusting the total silica equivalent concentration and the step of adjusting the pH can be interchanged or performed at the same time. In step 201, the control unit adjusts the cleaning solution by adding a silicic acid compound or water so that the cleaning solution has a predetermined total silica equivalent concentration. In step 202, the control unit adds a pH adjuster (acid or alkali) to adjust the cleaning solution to a predetermined pH. Note that in step 202, the control unit may adjust the pH to the predetermined pH based on the pH measurement result, or may measure the pH and instruct the measurement unit to transmit the measurement result to the control unit. In step 203, the control unit causes the cleaning solution to come into contact with the treatment object for a predetermined period of time, and then ends the cleaning.

[0082] Example 3 of this embodiment will be described below. The above and following Examples 1, 2, 4, and 5 may be adopted or incorporated as appropriate. The control unit may incorporate and perform step 201 and / or step 202 of Example 2 before and / or after step 301. In step 301, when the cleaning solution becomes lower than a predetermined pH from the alkaline region based on the result of the pH measurement, the control unit discharges a part or all of the cleaning solution from the system so as to replace or change it with a new cleaning solution. After the discharge, the control unit adds a silicic acid compound, a pH adjuster, the agent of this embodiment, etc. to the cleaning solution in the system to prepare a new cleaning solution. In step 303, the control unit causes the cleaning solution to come into contact with the treatment object for a predetermined period of time, and then ends the cleaning.

[0083] Example 4 of this embodiment will be described below. Examples 1 to 3 above and Example 5 below can be adopted or incorporated as appropriate. In step 401, the control unit adds a pH adjuster (acid or alkali) to adjust the cleaning solution to a predetermined pH. Step 401 may be skipped. In step 402, the control unit executes the measurement device to measure the total silica equivalent concentration in the water (eg, an aqueous system) to which the silicic acid compound is added. In step 403, the control unit executes the process of adding the agent of the present embodiment or water to the cleaning solution so that the measurement result of the total silica concentration becomes a predetermined total silica concentration in the cleaning solution that has been set, and starting cleaning by a fluid flow, etc. The predetermined total silica concentration in the cleaning solution that has been set may be data that has been previously stored and accessed and acquired. In step 404, the control unit obtains current total silica equivalent concentration data by monitoring the total silica equivalent concentration in the cleaning solution with a measuring device during cleaning, compares the current total silica equivalent concentration data with the total silica equivalent concentration data of the previous measurement, and determines whether the total silica equivalent concentration in the cleaning solution has changed (increased or remained the same). It is preferable that the various acquired data be stored in the storage unit. In step 405, if the total silica equivalent concentration after step 404 has increased from the previously measured total silica equivalent concentration, the control unit executes monitoring until the increase in the total silica equivalent concentration stops.

[0084] In step 406, the control unit determines that the amount of the agent used is insufficient and further adds the agent of this embodiment when the total silica equivalent concentration is maintained after step 404. Step 406 may be skipped as appropriate. In step 407, the control unit executes to end the cleaning when the total silica concentration increases only by the amount of the agent added during cleaning, even if the agent of this embodiment is added, or when the total silica concentration reaches a predetermined upper limit value. Step 407 may be skipped as appropriate.

[0085] In step 408, if the total silica equivalent concentration does not increase or reaches a predetermined upper limit of the total silica equivalent concentration, the process ends. After completion or during cleaning, all or part of the cleaning solution with an increased total silica equivalent concentration may be discharged outside the water system, and the cleaning solution in the water system may be replaced with a new cleaning solution or new cleaning solution may be added to the water system as appropriate, and the process may be restarted from step 401. In addition, in order to determine the state or timing of discharging the cleaning solution or replacing the solution, a step may be incorporated in Example 4 when the pH of the cleaning solution becomes a predetermined value or less as in Example 3, or when the dissolved concentration of the cleaning solution reaches an upper limit as in Example 5.

[0086] Moreover, Example 5 of this embodiment will be described below. It is preferable to further include a step of measuring the concentration of dissolved substances and a step of exchanging the liquid according to the concentration of dissolved substances in the above Example 1. The above Examples 1 to 4 can be adopted or incorporated as appropriate. In addition, the step of adjusting the total silica equivalent concentration and the step of measuring the concentration of dissolved substances can be interchanged in order or performed at the same time. In step 501, the control unit measures the concentration of a dissolved substance in the cleaning solution. The dissolved substance concentration may be an electrical conductivity or a BRIX value. In step 502, the control unit replaces all or part of the cleaning solution when the concentration of the dissolved substances in the cleaning solution reaches a predetermined upper limit based on the measurement result of the dissolved substances in the cleaning solution. The liquid replacement may be, for example, discharging all or part of the cleaning solution in which the concentration of the dissolved substances in the cleaning solution has become high out of the water system, and appropriately replacing the cleaning solution in the water system with a new cleaning solution or adding a new chemical to the water system. This makes it possible to reduce the concentration of the dissolved substances in the cleaning solution. After that, the process may be restarted from step 501, or the cleaning solution may be completely discharged to end the cleaning.

[0087] 5. Other embodiments of the present invention In the description of the cleaning method in this embodiment, the description of each component and each treatment method such as silicic acid compounds, silica-based scale, pH, temperature, total silica equivalent concentration, dissolved matter concentration, use concentration, cleaning method, etc., which overlaps with the above-mentioned "1." to "4.", etc., will be omitted as appropriate, but the description of "1." to "4.", etc. also applies to this embodiment and can be adopted as appropriate. In addition, in the description of the example of the green liquor treatment method in this embodiment, the description described later can be applied to this embodiment and can be adopted as appropriate.

[0088] The cleaning management system according to this embodiment is preferably provided with a cleaning management device having at least the control unit described above. The cleaning management system of this embodiment may further include a communication unit that enables wireless and / or wired transmission and reception between the control unit or the cleaning management device having the control unit and another unit or another device.

[0089] The method according to this embodiment can also be realized by a device including a CPU or a control unit in a device for managing the cleaning processing status (for example, a computer, PLC, server, cloud service, etc.). The method according to this embodiment can also be stored as a program in hardware resources including a recording medium (non-volatile memory (such as a USB memory), HDD, CD, DVD, Blu-ray, etc.) and realized by a control unit. It is also possible to provide a device including the control unit or the system, such as a management system for the status of cleaning, etc., which controls the use of a predetermined amount of chemicals in a water system, etc., by the control unit. The management device may also include an input unit such as a keyboard, a communication unit such as a network, a display unit such as a display, etc.

[0090] The cleaning management system according to the present embodiment can be executed by using a program and hardware. An embodiment of the computer 1 according to the present embodiment (not shown) is not limited to this, but may include at least a CPU as a component of the computer 1, and may further include one or two components selected from a RAM, a storage unit, an output unit, an input unit, a communication unit, a ROM, and a measurement unit, among which it is preferable to include a RAM, a storage unit, an output unit, and an input unit, and it is preferable to further include at least one of a communication unit, a measurement unit, a ROM, etc. Each component is preferably connected by a bus as a data transmission path, for example.

[0091] The present technology can also employ the following configuration. [1] An agent containing a silicic acid compound. The agent is preferably a cleaning agent for silica-based scale, a silica-based scale inhibitor, or a silica-based scale remover. Furthermore, the agent is an agent having low corrosiveness or low deterioration, and more preferably an agent having low corrosiveness or deterioration to metals or resins. [2] The agent according to [1] above, used in a water treatment device or a water system. The water system is preferably one or more selected from a water treatment system (e.g., a membrane treatment system, etc.) and a circulating water system (e.g., a cooling water system equipped with a heat exchanger, a boiler water system, a scrubber water system, a pulp process water system, etc.), and the water system is preferably water to be treated and / or circulating water. [3] The agent according to [1] or [2] above, wherein the cleaning agent has a pH of 10 or higher, or an aqueous system using the cleaning agent is adjusted to have a pH of 10 or higher. [4] The agent according to any one of [1] to [3], wherein the cleaning agent contains 1,000 to 20,000 mg / L of silicic acid compounds calculated as total silica, or the cleaning agent is used in an aqueous system so as to give a concentration of 1,000 to 20,000 mg / L calculated as total silica. [5] The cleaning agent according to any one of [1] to [4], further comprising one or more selected from the group consisting of a chelating agent, a surfactant, and a dispersant. The cleaning agent is preferably in the form of a solid or a solution. [6] The cleaning agent according to any one of [1] to [5] above, which further contains percarbonate, or which is used in combination with a solid agent (preferably a powder agent) containing percarbonate. More preferably, the cleaning agent is a multi-drug kit consisting of a first agent containing a silicic acid compound and a second agent containing percarbonate, and more preferably, the second agent may be either a liquid or a solid as long as it is in a form capable of generating foam. [7] The cleaning agent according to any one of [1] to [6], which is used in an aqueous system at a water temperature of 10° C. or higher.

[0092] [8] A method for cleaning a water treatment device using a solution containing a cleaning agent for silica-based scale containing a silicic acid compound, or a solution containing a silicic acid compound. The water treatment device is preferably a prefilter treatment device and / or a reverse osmosis membrane treatment device. [9] The method for cleaning a water treatment device according to [8], wherein the solution is adjusted to a pH of 10 or higher.

[10] The method for cleaning a water treatment device according to [8] or [9], wherein the solution contains a silicic acid compound at 1,000 to 20,000 mg / L in terms of total silica, or the solution is added to the water to be treated in the water treatment device to adjust the water to a concentration of 1,000 to 20,000 mg / L in terms of total silica.

[11] The method for cleaning a water treatment device according to any one of [8] to

[10] above, wherein the temperature of the solution is 10° C. or higher. Note that the configurations according to [1] to

[10] above may be appropriately adopted.

[12] The method for cleaning a water treatment device according to any one of [8] to

[11] above, wherein the solution further contains a percarbonate, or further contains a solid agent that contains a percarbonate when used.

[13] The method for cleaning a water treatment device according to any one of [8] to

[12] above, wherein the solution further contains one or more selected from a chelating agent, a surfactant, and a dispersant.

[14] The method for cleaning a water treatment device according to any one of the above [8] to

[13] , which is for cleaning silica-based scale.

[0093]

[15] A method for cleaning silica-based scale, comprising using an agent containing the above-mentioned silicate compound in an aqueous system.

[16] The method for cleaning silica-based scale according to

[15] above, wherein the aqueous solution is adjusted to a pH of 10 or higher and / or a water temperature of 10°C or higher.

[17] The method for cleaning silica-based scale according to

[15] or

[16] , wherein the water system is preferably water to be treated or circulating water, and more preferably water to be treated in a water treatment system (membrane treatment system), or circulating water in a circulating water system (such as a cooling water system equipped with a heat exchanger, a boiler water system, or a scrubber water system).

[18] The method for cleaning silica-based scale according to any one of

[15] to

[17] above, further comprising adjusting a total silica-equivalent concentration in the aqueous system to a predetermined concentration. The predetermined concentration is preferably 1,000 to 20,000 mg / L in terms of total silica.

[0094]

[19] A method for cleaning a water treatment device according to any one of [8] to

[14] above, or a method for removing silica-based scale according to any one of

[15] to

[18] above, using the agent according to any one of [1] to [7] above.

[20] A silicic acid compound for use in a chemical, or for cleaning, preventing or removing silica-based scale, or use thereof.

[21] The silicic acid compound according to

[20] , wherein the pH of the aqueous system using the agent is 10 or more, or the aqueous system using the agent is adjusted to have a pH of 10 or more.

[22] The silicic acid compound according to any one of

[19] to

[21] , wherein the agent contains the silicic acid compound in an amount of 1,000 to 20,000 mg / L calculated as total silica, or the silicic acid compound is used in an aqueous system so as to give a concentration of 1,000 to 20,000 mg / L calculated as total silica.

[0095]

[23] The silicic acid compound according to any one of

[19] to

[22] , further comprising one or more selected from the group consisting of a chelating agent, a surfactant, and a dispersing agent. It is also preferable that the silicic acid compound is used in combination with a solid agent containing a percarbonate. The components may be packaged separately or together in a unit package.

[0096]

[24] A silicic acid compound or its use for producing a drug, or for use in producing a drug. Use of a silicic acid compound in a drug. The drug is preferably a cleaning agent for silica-based scale, a silica-based scale inhibitor, or a silica-based scale remover. Furthermore, the drug is a drug with low corrosiveness or low deterioration, and more preferably a drug with low corrosiveness or deterioration to metals or resins.

[0097] ·

[25] A drug kit comprising a first drug containing a silicic acid compound and a second drug in a solid form containing percarbonate. The second drug in a powder form is preferably used in combination when used in an aqueous system. The drug kit may be a drug kit that is a multi-liquid type drug, and may be mixed at the time of use to form a drug containing the first drug and the second drug, or may be mixed as separate drugs for the treatment target. For example, it is more preferable to add the second drug to the treatment target at the same time as or at a different time from the addition of the first drug to the treatment target. The first and second drugs may each be a single-dose drug in a unitary package form, either integrated or packaged.

[26] The preferred chemical kit according to

[25] above is preferably a silica-based scale cleaner kit, a silica-based scale inhibitor kit, or a silica-based scale remover kit. Furthermore, the chemical kit is a chemical that has low corrosiveness or low deterioration when the first chemical and the second chemical are mixed and used, and more preferably has low corrosiveness or deterioration to metals or resins.

[27] The first agent according to

[25] or

[26] may further contain one or more selected from a chelating agent, a surfactant, and a dispersing agent, and each of them may be separately contained in a third agent, a fourth agent, and a fifth agent for use. Note that the first, second, etc. are numbers given for convenience, and are not particularly limited to numbers, order, etc.

[28] A method for cleaning silica-based scale, comprising a step of adjusting a total silica-equivalent concentration in an aqueous system. A method for cleaning silica-based scale, comprising a step of adjusting a total silica-equivalent concentration in an aqueous system, and a discharge or liquid exchange step of discharging or exchanging a part or all of the aqueous system. It is preferable that the discharge or liquid exchange step discharges a part or all of the aqueous system based on one or more measurement results selected from the total silica-equivalent concentration, pH, and dissolved substance concentration. EXAMPLES

[0098] The following examples and comparative examples are provided to illustrate the present invention, but the scope of the present invention is not limited to these examples.

[0099] [Example 1] A cleaning test was conducted using inorganic scale mainly made of silica that had actually formed in a typical water treatment device that has an RO membrane that is prone to generating silica-based scale due to silica concentration. The membranes of the two samples from the facilities where silica clogging had occurred were disassembled and analyzed for scale, and the results are shown in Table 1. The collected samples were subjected to measurement of dry weight (105℃), and then to measurement of ignition loss (weight loss at 600±25℃). After the weight loss measurement, the samples were heated and dissolved in strong acid, and the weight of the dissolved residue was measured. The ion concentration of the dissolved sample was then quantified using ICP emission spectrometry, and converted into the oxide form. Separately, the inorganic carbon of the samples after the dry weight measurement was measured using total organic carbon (TOC).

[0100] [Table 1]

[0101] <Experimental conditions> 1. Cleaning test 1-1. Comparative test using flat membranes For each sample, the cleaning agent was evaluated using a flat membrane prepared by dismantling an actual RO membrane. Since the adhesion of dirt and scale to RO membranes has a large effect on the membrane's permeability and salt removal ability, it is easy to see changes in scale removal ability.

[0102] The cleaning test was carried out under the following conditions: For the flat membrane, the cell in Figure 1, which allows performance measurement of the RO membrane (TMG20-400, manufactured by TORAY: low pressure membrane: cross-linked fully aromatic polyamide composite membrane) in the flat membrane state, was used to carry out performance measurements (permeation flow rate, salt rejection rate) and cleaning tests. The conditions are shown below in [Conditions for performance evaluation], [Operating conditions for cleaning], and [Table 2]. The evaluation part of the RO membrane is the inside part of the O-ring, which is about 10 cm in diameter. In addition, the cell (cell tester 1, 2) in which the RO membrane was set was set in the circulation system device, and the cleaning solution was circulated using the performance evaluation pump and the CIP (clean in place) pump to clean the RO membrane (see Figure 2). The stored water in the tank was adjusted to the cleaning solution in Table 2 and circulated, and the stored water in the tank was appropriately collected and subjected to water quality analysis, etc.

[0103] In addition, Disclosure 3 and Disclosure 4 are obtained by further mixing 1% of a dispersant (polyacrylic acid, weight average molecular weight of about 4,000) with Disclosure 1 and Disclosure 2 as cleaning solutions. Disclosure 3 and Disclosure 4 will be able to exhibit cleaning effects equal to or greater than Disclosure 1 and Disclosure 2, respectively. In addition, a cleaning solution can be prepared by replacing the anionic surfactant of Disclosure 2 with a nonionic surfactant, and the cleaning solution can be added to a device having a circulating water mechanism to clean the inside of the circulating flow path. The first agent of sodium metasilicate powder and the second agent of sodium percarbonate powder can be packaged with a water-soluble resin, respectively, and fixed on a water-soluble resin sheet to produce an integrated unit package form, and by adding them to a water system, each is dissolved to prepare a cleaning solution, and each cleaning action can be better exhibited.

[0104] The evaluation items in Table 3 (Nor. Flux (m / d), Rejection (%)) are taken from Non-Patent Document 1: “FilmTec TMThe values ​​were calculated according to "5.6.6 Plant Performance Normalization" in the Reverse Osmosis Membranes Technical Manual Version 4, October 2020, DuPont de Nemours, Inc., P138-142. In addition, the pH, conductivity (mS / m), iron, ionic silica (mg / L), and total silica (mg / L) in Table 6 were measured by pH: pH meter (glass electrode), conductivity (mS / m): electric conductivity meter (electrode type), iron: ICP emission analysis, total silica: analysis method specified in JIS K 0101 44.3, and ionic silica was measured by the analysis method specified in JIS K 0101 44.3.

[0105] [Conditions for performance evaluation] Pressure: 0.69 MPa Flow rate: 2.8 L / min Water temperature: 25℃ Solution: NaCl 500 mg / L

[0106] [Operating conditions during cleaning] Pressure: 0.1~0.2 MPa Flow rate: 3.2~3.4 L / min Water temperature: 35℃ Cleaning time: 6hr circulation + 1 night soak + 1hr circulation

[0107] [Table 2]

[0108] 1-2. Cleaning test using membrane module A cleaning test was carried out using the present disclosure 2 on a membrane module extracted from the same equipment as Sample 2.

[0109] [Conditions for performance evaluation] Pressure: 0.76 MPa Water supply flow rate: approx. 5m 3 / h Recovery rate 15% Water temperature: 25℃ Solution: NaCl 500mg / L

[0110] [Operating conditions during cleaning] Pressure: 0.1-1.0MPa Flow rate: 9~10m 3 / h Water temperature: 35℃ Cleaning time: 6 hours (h) circulation + 1 night soak + 1 hour (h) circulation

[0111] 1-3.Corrosion resistance test A solution six times more concentrated than that of Disclosure 2 was prepared, and a corrosion resistance evaluation test of the material was carried out. Test pieces of each material, measuring 30 mm x 50 mm x 1 to 3 mm, were placed so that about half of them were immersed in the solution, and were then covered with plastic wrap to prevent evaporation of the solution and placed in a thermostatic chamber at 40°C. After storing the test pieces stationary for 14 days, the corrosion resistance is evaluated based on the appearance, size, weight, etc. of the test pieces.

[0112] <Results / Discussion> 1. Cleaning test 1-1. Comparison test results using flat membranes As shown in Tables 3 and 4, it was confirmed that the performance of RO membranes was greatly improved by using the cleaning agent disclosed in this disclosure, compared to the cleaning test in which the pH was adjusted to the same level as the developed product using NaOH, a conventional cleaning agent, and the cleaning test in which a chelating agent or surfactant was added. It was also confirmed that the effect was further improved by combining the cleaning agent disclosed in this disclosure with sodium percarbonate. When the properties of the scale that remained after cleaning were compared, it was confirmed that the properties of the scale had clearly changed after cleaning according to the present invention, as shown in Table 5, and that the scale could be removed from the membrane surface with little force. Although the principle behind the effects of the present disclosure is unclear, it is believed that the silica in the sodium metasilicate not only partially dissolves the silica-based scale, but also softens the scale as the cleaning liquid penetrates into it. It is believed that sodium percarbonate was effective in promoting the removal of such silica-based scale because, under highly alkaline conditions, oxygen bubbles produced by the decomposition of percarbonate were generated in the cleaning solution that penetrated the scale, enhancing the stripping effect.

[0113] [Table 3]

[0114] [Table 4]

[0115] [Table 5]

[0116] 1-2. Cleaning test results using membrane modules The performance of the module before and after cleaning is summarized in Table 6. After cleaning, the performance improved significantly, similar to the flat membrane test using Sample 2. In addition, samples were taken at each elapsed time during module cleaning and the results of the analysis are shown in Table 7. The results showed that the silica concentration in the cleaning solution gradually increased, confirming that the cleaning agent was dissolving the silica.

[0117] [Table 6]

[0118] [Table 7]

[0119] 1-3.Corrosion resistance test results Results are shown for SUS304, SUS316, SS400 (carbon steel), Hastelloy C, PVDF, PVC, PE, PP, and acrylic. Regarding various materials, Tables 8 and 9 below show that this cleaning agent has low corrosiveness to materials commonly used in water treatment facilities and can be widely used. It is known that PVDF loses strength when immersed in alkaline conditions, but it has been determined that there is no problem with its use as a cleaning agent.

[0120] [Table 8]

[0121] [Table 9]

Claims

1. A cleaning agent for silica-based scale that contains silicate compounds.

2. 10. The cleaning agent according to claim 1 for use in a water treatment device or an aqueous system.

3. The cleaning agent according to claim 1 , wherein the cleaning agent has a pH of 10 or more, or an aqueous system using the cleaning agent is adjusted to have a pH of 10 or more.

4. The cleaning agent according to claim 1, wherein the cleaning agent contains 1,000 to 20,000 mg / L of the silicic acid compound calculated as a total silica equivalent, or the cleaning agent is used in an aqueous system so that the content of the silicic acid compound is 1,000 to 20,000 mg / L calculated as a total silica equivalent.

5. The cleaning agent according to claim 1 , further comprising one or more selected from the group consisting of a chelating agent, a surfactant, and a dispersant, and the cleaning agent is in the form of a solid or a solution.

6. The cleaning agent according to claim 1 , which further contains a percarbonate, or which is used in combination with a solid agent containing a percarbonate.

7. A method for cleaning a water treatment device using a solution containing a cleaning agent for silica-based scale that contains a silicic acid compound, or a solution containing a silicic acid compound.

8. The method for cleaning a water treatment device according to claim 7 , wherein the solution is adjusted to a pH of 10 or higher.

9. The method for cleaning a water treatment device according to claim 7, wherein the solution contains 1,000 to 20,000 mg / L of a silicic acid compound in terms of total silica, or the solution is added to the water to be treated in the water treatment device to adjust the water to a concentration of 1,000 to 20,000 mg / L in terms of total silica.

10. 8. The method of claim 7, wherein the solution further comprises a solid agent comprising percarbonate in use.

11. The method for cleaning a water treatment device according to claim 7 , wherein the solution further contains one or more selected from the group consisting of a chelating agent, a surfactant, and a dispersant.

12. The method for cleaning a water treatment device according to claim 7, which is for cleaning silica-based scale.

13. A method for cleaning silica-based scale using a chemical containing a silicate compound in a water system.

14. The method for cleaning silica-based scale according to claim 13, wherein the aqueous solution is adjusted to a pH of 10 or higher.

15. The method for cleaning silica-based scale according to claim 13, wherein the aqueous system is water to be treated or circulating water in an aqueous system.

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