Phosphorus removal and recovery method, and method for producing phosphorus removal and recovery agent
The method enhances phosphorus removal by preparing a residue from combustion ash and carbon source in a chlorine atmosphere, forming calcium hydrogen phosphate, addressing sludge and adsorption capacity issues in existing methods, and increasing recovery efficiency.
Patent Information
- Application Number
- JP2024025101
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-02-22
- Publication Date
- 2025-09-03
AI Technical Summary
Conventional phosphorus removal methods face issues such as sludge generation, reagent costs, operational complexity, and limited adsorption capacity, particularly when using fly ash with varying calcium content.
A phosphorus removal and recovery method involving a residue produced by mixing combustion ash containing calcium with a carbon source and heating in a chlorine-containing atmosphere to volatilize silicon and aluminum as chlorides, while retaining calcium, followed by reacting with phosphoric acid to form sparingly soluble calcium hydrogen phosphate.
Increases the calcium content and enhances the amount of phosphorus removed and recovered, addressing the limitations of existing methods by improving efficiency and reducing the need for frequent adsorbent replacement.
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Figure 2025128464000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a phosphorus removal and recovery method for removing and recovering phosphorus (P) from water to be treated by bringing a phosphorus removal and recovery agent into contact with the water to be treated, which contains phosphoric acid (H3PO4), to react and produce a poorly soluble phosphorus compound, and to a method for producing the phosphorus removal and recovery agent used in the method. [Background technology]
[0002] Conventionally, a method for converting water-soluble phosphorus into sparingly soluble compounds and separating the resulting compounds by solid-liquid separation has been known as a phosphorus removal and recovery technology. The conversion of water-soluble phosphorus into sparingly soluble compounds can be broadly divided into physicochemical and biological methods. Physicochemical methods include coagulation sedimentation, crystallization dephosphorization, and adsorption dephosphorization, while biological methods include phostrip and anaerobic-aerobic dephosphorization. Among these, adsorption dephosphorization methods include phosphorus adsorption techniques using limestone, seashells, and other calcium compounds. Furthermore, in recent years, research has been conducted into the adsorption and removal of phosphorus using fly ash derived from coal or biomass combustion that contains a relatively high percentage of calcium (Ca) (see, for example, Non-Patent Documents 1 and 2). [Prior art documents] [Patent documents]
[0003] [Non-Patent Document 1] Lu et al., Journal of Hazardous Materials, 161, 95-101 (2009) [Non-patent document 2] Park et al., The Korean Society for Applied Biological Chemistry, 64:43 (2021) Summary of the Invention [Problem to be solved by the invention]
[0004] However, among the conventional techniques, the coagulation and sedimentation methods and biological methods have the problem of generating sludge. Furthermore, the crystallization dephosphorization method requires pretreatment, such as the removal of carbonate ions and pH adjustment, which poses problems such as the need for reagent costs and operational management. On the other hand, the adsorption dephosphorization method does not generate sludge and has a relatively simple device configuration, but has the problem of requiring periodic replacement or regeneration of the adsorbent due to the limited adsorption capacity of the adsorbent. Even in adsorption removal using fly ash, the calcium content in fly ash varies widely, ranging from several to several tens of percent, so if the calcium content in the fly ash is low, the amount of phosphorus removed and recovered is low.
[0005] The present invention has been made in light of the above-mentioned problems, and aims to provide a phosphorus removal and recovery method that can increase the calcium content and increase the amount of phosphorus removed and recovered, and a method for producing a phosphorus removal and recovery agent. [Means for solving the problem]
[0006] The first phosphorus removal and recovery method of the present invention removes and recovers phosphorus from the water to be treated, by bringing a phosphorus removal and recovery agent into contact with the water to be treated, which contains phosphoric acid, to react and produce sparingly soluble phosphorus compounds. The phosphorus removal and recovery agent is a residue obtained by mixing combustion ash containing calcium as a component with a carbon source and heating the mixture in a chlorine-containing atmosphere at a temperature at which silicon (Si) and aluminum (Al) volatilize as chlorides but calcium does not volatilize as chloride.
[0007] The second phosphorus removal and recovery method of the present invention removes and recovers phosphorus from water to be treated that contains phosphoric acid, and includes a phosphorus removal and recovery agent production step of producing a phosphorus removal and recovery agent, and a sparingly soluble phosphorus compound reaction and generation step of adding the phosphorus removal and recovery agent to the water to be treated and reacting to generate a sparingly soluble phosphorus compound. The phosphorus removal and recovery agent production step includes a step of mixing combustion ash containing calcium as a component with a carbon source, and obtaining a residue after heat treatment in a chlorine-containing atmosphere at a temperature at which silicon and aluminum volatilize as chlorides but calcium does not volatilize as chloride, and a step of burning the residue and removing the carbon source.
[0008] The method for producing a phosphorus removal and recovery agent of the present invention produces a phosphorus removal and recovery agent that removes and recovers phosphorus from water to be treated by contacting the agent with water to be treated that contains phosphoric acid and reacting to produce a poorly soluble phosphorus compound. The method includes the steps of: mixing combustion ash containing calcium as a component with a carbon source; and obtaining a residue after heat treatment in a chlorine-containing atmosphere at a temperature at which silicon and aluminum volatilize as chlorides but calcium does not volatilize as chloride; and combusting the residue and removing the carbon source. [Effects of the Invention]
[0009] According to the present invention, the phosphorus removal and recovery agent is prepared by mixing combustion ash containing calcium as a component with a carbon source, and then heat-treating the mixture in a chlorine-containing atmosphere at a temperature at which silicon and aluminum volatilize as chlorides but calcium does not volatilize as chloride, resulting in a residue that is used. This increases the calcium content and the amount of phosphorus removed and recovered. [Brief explanation of the drawings]
[0010] [Figure 1] 1 is a flow chart showing steps of a phosphorus removal and recovery method according to one embodiment of the present invention and a method for producing a phosphorus removal and recovery agent used therein. [Figure 2] FIG. 2 is a characteristic diagram showing the phosphorus removal and recovery rate in Example 1 in comparison with Comparative Example 1. [Figure 3]FIG. 10 is a characteristic diagram showing the phosphorus removal and recovery rate in Example 2 in comparison with Comparative Example 2. [Figure 4] FIG. 10 is a characteristic diagram showing the phosphorus removal and recovery rate in Example 3 in comparison with Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION
[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0012] 1 shows a phosphorus removal and recovery method according to one embodiment of the present invention, and steps in a method for producing a phosphorus removal and recovery agent used therein. The phosphorus removal and recovery method according to this embodiment involves contacting phosphoric acid-containing water to be treated with a phosphorus removal and recovery agent to react and produce sparingly soluble phosphorus compounds, thereby removing and recovering phosphorus from the water to be treated. The phosphorus removal and recovery agent is a residue obtained by mixing combustion ash containing calcium as a component with a carbon source and heating the mixture in a chlorine-containing atmosphere at a temperature at which silicon and aluminum volatilize as chlorides but calcium does not volatilize as chloride.
[0013] Specifically, the phosphorus removal and recovery method according to this embodiment includes, for example, a phosphorus removal and recovery agent manufacturing process (step S110) for manufacturing a phosphorus removal and recovery agent, and a sparingly soluble phosphorus compound reaction and generation process (step S120) for reacting and generating a sparingly soluble phosphorus compound using the phosphorus removal and recovery agent.
[0014] The phosphorus removal and recovery agent manufacturing process (step S110) preferably includes, for example, a crushing process (step S111) of crushing combustion ash containing calcium as an ingredient, a mixing process (step S112) of mixing a carbon source with the combustion ash containing calcium as an ingredient, a volatilization process (step S113) of obtaining a residue after heat-treating the combustion ash containing calcium as an ingredient in a chlorine-containing atmosphere at a temperature at which silicon and aluminum volatilize as chlorides but calcium does not volatilize as chloride, and a combustion process (step S114) of burning the obtained residue and removing the carbon source.
[0015] Examples of combustion ash containing calcium include coal ash (fly ash) and wood ash. Coal ash is ash generated when coal is burned, and wood ash is ash generated when wood fuel is burned. The composition of combustion ash containing calcium varies depending on the material, but it typically contains silicon dioxide (SiO2) and aluminum oxide (Al2O3) as its main components, as well as other oxides such as iron oxide (Fe2O3), titanium oxide (TiO2), calcium oxide (CaO), magnesium oxide (MgO), sodium oxide (Na2O), and potassium oxide (KO).
[0016] In the pulverization step (step S111), the combustion ash is preferably pulverized to a crystallite diameter (i.e., crystallite size) containing valuable components of 30 nm or less. This is because adjusting the crystallite diameter can improve reactivity, increase the volatilization rate of silicon and aluminum chlorides that react with chlorine, and increase the calcium content. The crystallite diameter can be calculated, for example, from the Scherrer equation shown in formula (1) based on the width of the diffraction line in X-ray diffraction. In formula (1), D is the crystallite diameter (nm), K is the Scherrer constant, λ is the wavelength of the X-ray (nm), B is the broadening of the diffraction line (rad), and θ is the Bragg angle (rad). D=Kλ / Bcosθ (1)
[0017] The pulverization is preferably carried out using, for example, a planetary ball mill. This is because it is difficult to achieve a crystallite diameter of 30 nm or less using a ball mill, whereas the use of a planetary ball mill makes it easy to achieve a crystallite diameter of 30 nm or less. The pulverization time is preferably, for example, 2 hours or more, because the crystallite diameter can be reduced to 30 nm or less.
[0018] The reason for mixing the carbon source in the mixing step (step S112) is to promote the reaction between the components in the combustion ash and chlorine. The carbon source used in the mixing step is preferably, for example, carbon obtained by pyrolyzing an organic compound such as phenolphthalein, or amorphous carbon such as coal, charcoal, coke, or activated carbon. The amount of carbon source mixed is preferably, for example, in excess of the stoichiometric amount required to chlorinate all oxides in the combustion ash. The pulverized combustion ash has a crystallite diameter of 30 nm or less, which improves the reactivity between the components in the combustion ash and chlorine, so it is preferable to mix an amount in excess of the stoichiometric amount. It is preferable to use, for example, a powdered carbon source. The carbon source may be mixed before or after the pulverization step, but is preferably mixed after the pulverization step. This is because, when a powdered carbon source is used, there is no need to pulverize the carbon source.
[0019] The volatilization step (step S113) is performed to obtain a residue with a high calcium content by volatilizing the silicon and aluminum contained in the combustion ash as chlorides. The volatilization step is preferably performed after the pulverization step and the mixing step. The heat treatment temperature in the volatilization step is preferably 800°C or higher and 1000°C or lower. This is because, within this temperature range, silicon dioxide (SiO2) and aluminum oxide (Al2O3), which are contained in the combustion ash in large amounts, react with chlorine and quickly volatilize, and most calcium oxide (CaO) remains as an oxide without becoming calcium chloride (CaCl2). The boiling points of silicon tetrachloride (SiCl4) are 58°C, aluminum chloride (AlCl3) is 180°C, iron chloride (FeCl3) is 315°C, titanium tetrachloride (TiCl4) is 136°C, and calcium chloride is 1412°C.
[0020] In the volatilization step, chlorine gas may be supplied alone or mixed with an inert gas such as nitrogen gas. The supply amount of chlorine gas and the reaction time can be appropriately adjusted. The reaction apparatus may be any type provided with a reaction section for reacting the raw material with chlorine, and may be a continuous or batch type.
[0021] The combustion step (step S114) is intended to remove the carbon source contained in the residue and increase the proportion of calcium in the residue. Combustion is carried out in an oxygen-containing atmosphere, such as the air. The combustion temperature is set to a temperature at which the carbon source burns or higher, preferably between 800°C and 1000°C.
[0022] In the poorly soluble phosphorus compound reaction production step (step S120), for example, the phosphorus removal and recovery agent, i.e., the residue, produced in the phosphorus removal and recovery agent production step (step S110) is brought into contact with the water to be treated to react and produce poorly soluble phosphorus compounds. Specifically, for example, the phosphorus removal and recovery agent is preferably added to the water to be treated and mixed by shaking or the like, and if necessary, heated to increase reactivity. The heating temperature is preferably, for example, 20°C or higher and 30°C or lower.
[0023] This causes the phosphoric acid contained in the water to react with the calcium contained in the phosphorus removal and recovery agent, as shown in the chemical formula below, to produce poorly soluble calcium hydrogen phosphate (CaHPO4·2H2O). The produced calcium hydrogen phosphate precipitates and is separated from the water to be treated and recovered by filtration using a filter or other means. Ca 2+ + H + + PO4 3- +2H2O → CaHPO4 2H2O
[0024] As described above, according to this embodiment, the phosphorus removal and recovery agent is prepared by mixing combustion ash containing calcium as a component with a carbon source, and then subjecting the mixture to heat treatment in a chlorine-containing atmosphere at a temperature at which silicon and aluminum volatilize as chlorides but calcium does not volatilize as chloride, and using the resulting residue. This increases the calcium content and the amount of phosphorus removed and recovered. [Example]
[0025] (Examples 1, 2, and 3) Powdered solid carbon as a carbon source was mixed with combustion ash containing calcium as a component in a ratio of 1 part by mass of solid carbon to 1 part by mass of combustion ash containing calcium as a component (step S112). The mixture was then placed in a reaction vessel, and a chlorine-containing gas was supplied. The mixture was heated to 1000°C to obtain a residue after heat treatment (step S113). The reaction time was 1 hour. Tivoli ash, which is coal ash, was used as the combustion ash containing calcium as a component in Example 1, Rotosous ash, which is coal ash, was used in Example 2, and wood ash was used in Example 3. The resulting residue was then combusted in the atmosphere at 815°C to remove the carbon source (step S114). The resulting residue was used as a phosphorus removal and recovery agent.
[0026] The calcium content of the phosphorus removal and recovery agent obtained in Examples 1, 2, and 3, and the combustion ash containing calcium as a component before treatment, was examined. The results are shown in Table 1. In Table 1, the calcium content is expressed in terms of oxide. As shown in Table 1, in each of Examples 1, 2, and 3, the calcium content in the residue was increased to about twice that before treatment.
[0027] [Table 1]
[0028] Next, the resulting phosphorus removal and recovery agent was contacted with a phosphate ion aqueous solution containing phosphoric acid dissolved in water to react and generate poorly soluble phosphate compounds (step S120). Specifically, the phosphorus removal and recovery agent was added to the phosphate ion aqueous solution, which was then placed in a container and shaken at 20°C and a shaking speed of 175 rpm. The initial phosphate ion concentration of the phosphate ion aqueous solution was 10 mg / L in Example 1 and 1000 mg / L in Examples 2 and 3. The hydrogen ion concentration of the phosphate ion aqueous solution was adjusted to pH 6 in Examples 1 and 2. 1 g of the phosphorus removal and recovery agent was added per 125 mL of the phosphate ion aqueous solution, while 0.5 g of the phosphorus removal and recovery agent was added per 125 mL of the phosphate ion aqueous solution in Example 3. The phosphate ion concentration in the phosphate ion aqueous solution was examined by varying the reaction time in Examples 1, 2, and 3. FIG. 2 shows the relationship between the phosphorus removal and recovery rate and the reaction time in Example 1, FIG. 3 shows the relationship between the phosphorus removal and recovery rate and the reaction time in Example 2, and FIG. 4 shows the relationship between the phosphorus removal and recovery rate and the reaction time in Example 3.
[0029] For Comparative Examples 1, 2, and 3, which correspond to Examples 1, 2, and 3, the same procedures as in Examples 1, 2, and 3 were used to generate sparingly soluble phosphate compounds and examine the phosphate ion concentration, except that combustion ash containing calcium before treatment was used as the phosphate removal and recovery agent. The combustion ash containing calcium was Tivoli ash in Comparative Example 1, Rotosous ash in Comparative Example 2, and wood ash in Comparative Example 3. In Comparative Example 3, 1 g of phosphorus removal and recovery agent was added to 125 mL of aqueous phosphate ion solution. In other words, the proportion of phosphorus removal and recovery agent was twice that of Example 3. Figure 2 shows the results of Comparative Example 1 together with Example 1, Figure 3 shows the results of Comparative Example 2 together with Example 2, and Figure 4 shows the results of Comparative Example 3 together with Example 3.
[0030] 2 and 3, in Examples 1 and 2, in which a carbon source was mixed with coal ash as a phosphorus removal and recovery agent, the mixture was heat-treated in a chlorine-containing atmosphere, and the residue obtained after heat treatment at 815°C to remove the carbon source was used, the phosphorus removal and recovery rate was significantly increased compared to Comparative Examples 1 and 2, in which untreated coal ash was used. Furthermore, in Example 3, in which a carbon source was mixed with wood ash, the mixture was heat-treated in a chlorine-containing atmosphere, and the residue obtained after heat treatment at 815°C to remove the carbon source was used, similar results to those in Examples 1 and 2 were obtained, as shown in FIG. 4.
[0031] That is, it was found that by mixing combustion ash containing calcium as a component with a carbon source, and then heating the mixture in a chlorine-containing atmosphere at a temperature at which silicon and aluminum volatilize as chlorides but calcium does not volatilize as chloride, the calcium content can be increased and the amount of phosphorus removed and recovered can be increased.
[0032] Although the present invention has been described above using embodiments, the present invention is not limited to the above embodiments and can be modified in various ways. For example, the above embodiments and examples specifically describe the steps of the phosphorus removal and recovery method and the method for producing a phosphorus removal and recovery agent used therein, but it is not necessary to include all steps, and other steps may also be included. For example, the above embodiments specifically describe the case where the phosphorus removal and recovery method includes, for example, a phosphorus removal and recovery agent production step (step S110) and a poorly soluble phosphorus compound reaction production step (step S120), but it may also include only the poorly soluble phosphorus compound reaction production step (step S120). Furthermore, the above embodiments and examples specifically describe the conditions for each step, but they may be different.
Claims
1. A method for removing and recovering phosphorus (P) from water to be treated, comprising contacting the water to be treated containing phosphoric acid with a phosphorus removal and recovery agent to react and produce a poorly soluble phosphorus compound, the method comprising: The phosphorus removal and recovery method is characterized in that the phosphorus removal and recovery agent is a residue obtained by mixing combustion ash containing calcium (Ca) as a component with a carbon source and heating the mixture in a chlorine-containing atmosphere at a temperature at which silicon (Si) and aluminum (Al) volatilize as chlorides but calcium does not volatilize as chloride.
2. A method for removing and recovering phosphorus (P) from water to be treated that contains phosphoric acid, comprising: a phosphorus removal and recovery agent production step of producing a phosphorus removal and recovery agent; and a sparingly soluble phosphorus compound reaction and production step of adding the phosphorus removal and recovery agent to the water to be treated and reacting and producing a sparingly soluble phosphorus compound, The phosphorus removal and recovery agent manufacturing process includes a step of mixing a carbon source with combustion ash containing calcium (Ca) as a component, and obtaining a residue after heat treatment in a chlorine-containing atmosphere at a temperature at which silicon (Si) and aluminum (Al) volatilize as chlorides but calcium does not volatilize as chloride, and a step of burning the residue and removing the carbon source. A method for removing and recovering phosphorus.
3. 3. The phosphorus removal and recovery method according to claim 2, wherein the heat treatment temperature of the combustion ash is 800°C or higher and 1000°C or lower.
4. 3. The phosphorus removal and recovery method according to claim 2, wherein the combustion temperature of the residue is 800°C or higher and 1000°C or lower.
5. A method for producing a phosphorus removal and recovery agent, which removes and recovers phosphorus (P) from water to be treated containing phosphoric acid by contacting the agent with the water to be treated to react and generate a poorly soluble phosphorus compound, comprising: a step of mixing a carbon source with combustion ash containing calcium (Ca) as a component, and heat-treating the mixture in a chlorine-containing atmosphere at a temperature at which silicon (Si) and aluminum (Al) volatilize as chlorides but calcium does not volatilize as chloride, thereby obtaining a residue; burning the residue to remove the carbon source; A method for producing a phosphorus removal and recovery agent, comprising:
6. 6. The method for producing a phosphorus removal and recovery agent according to claim 5, wherein the heat treatment temperature of the combustion ash is 800°C or higher and 1000°C or lower.
7. 6. The method for producing a phosphorus removal and recovery agent according to claim 5, wherein the combustion temperature of the residue is 800°C or higher and 1000°C or lower.