A method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials

Abstract

The present invention relates to the technical field of solid waste resource utilization, and discloses a method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials, comprising: acid leaching, oxidation of acid leaching liquid, alkalization, hydrolysis, polymerization, maturation, solidification, phosphorus extraction, phosphorus recovery, aluminum recovery, reuse of alkaline waste liquid and replacement of cement clinker with residual fly ash. The present invention not only realizes high-value resource utilization of sludge incineration fly ash, but also reduces the content of P, Fe, Al and heavy metals in sludge incineration fly ash, greatly reducing the risk of heavy metal leaching. At the same time, the method has the advantages of low cost, simple and easy operation of preparation process, no special requirements for equipment, good controllability of process parameters, and easy industrialization, thus realizing waste treatment with waste, and the extraction and recovery of phosphorus from fly ash opens up new raw materials for phosphate fertilizer production. At the same time, the residual fly ash after the extraction of phosphorus, aluminum and iron can be completely used to replace cement clinker, and the obtained product has good mechanical properties and the heavy metal leaching toxicity meets the national standard.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization, and in particular to a method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials. Background Art

[0002] Sludge often contains pathogenic microorganisms, harmful heavy metals, and some difficult-to-decompose substances. If not promptly treated, it can easily cause secondary pollution to the environment and threaten human health. Currently, sludge treatment and disposal methods include sanitary landfill, land use, incineration, and building material utilization. Among them, sludge drying and incineration technology can completely decompose organic matter in sludge, oxidize toxic and harmful substances, and completely kill pathogenic microorganisms, thereby minimizing sludge volume and achieving both harmlessness and volume reduction.

[0003] Currently, the annual production of sludge incineration fly ash reaches nearly 6 million tons, and its primary disposal method is landfill. However, sludge incineration ash still contains large amounts of heavy metals. Direct landfill not only occupies a large amount of land and causes soil degradation, but also causes heavy metals to leach out and contaminate soil and groundwater after being washed by rainwater. Furthermore, because sludge itself is an active flocculent substance composed of fine particles such as microbial cells, the ash particles produced after sludge incineration are very fine and easily dispersed by wind. Improper disposal can cause secondary pollution to the environment. Since sewage treatment plants use a large amount of iron and aluminum salts as flocculants to treat domestic sewage, this not only causes phosphorus in the sewage to deposit in the sludge, but also results in high aluminum and iron content in the sludge. As the sludge is incinerated, these phosphorus, aluminum, and iron will eventually be enriched in the fly ash, resulting in high phosphorus, aluminum, and iron content in the sludge incineration fly ash.

[0004] Therefore, how to provide a method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials is a technical problem that needs to be solved. Summary of the Invention

[0005] The embodiment of the present invention provides a method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials, so as to solve the technical problems in the prior art of being unable to reasonably control the pollution caused by sludge incineration fly ash and being unable to improve the utilization rate of sludge incineration fly ash.

[0006] In order to achieve the above object, the present invention provides a method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials, the method comprising the following steps:

[0007] S1, acid leaching: sludge incineration fly ash and dilute sulfuric acid are mixed at a solid-liquid ratio of 5-20, placed on a magnetic stirrer and stirred at a speed of 500 r / min, the reaction temperature is 25-60 ° C, the reaction time is 1 hour-7 hours, and the pH of the solution is controlled at 2.5-3.5 at the end of the reaction. After the reaction, filter to obtain an acid leaching solution and filter residue;

[0008] S2, acid leaching solution oxidation: the acid leaching solution obtained in S1 was cooled, placed on a magnetic stirrer and stirred at 500 r / min, and 20%-40% hydrogen peroxide was added in batches and reacted for 20 min-40 min to fully oxidize the divalent iron ions to trivalent iron ions;

[0009] S3, alkalization, hydrolysis, polymerization: Place the liquid obtained in S2 on a magnetic stirrer and stir at 500 r / min and raise the temperature to 40°C-90°C. During stirring, add NaOH at a ratio of m(OH) / m(Fe)=1.6-2.6 to carry out alkalization reaction. After the alkalization is completed, control the reaction time to 30 min-240 min and the reaction temperature to 40°C-90°C for hydrolysis and polymerization reaction;

[0010] S4, aging and solidification: The liquid obtained in S3 was allowed to stand at room temperature for 24 hours to mature to obtain a reddish-brown polyferric sulfate liquid, which was then vacuum-dried at 40°C to obtain a light yellow polyferric sulfate solid;

[0011] S5, phosphorus extraction: the filter residue obtained in S1 was mixed with 0.2-1.5 mol / L NaOH solution at a liquid-to-solid ratio of 5-20, stirred on a magnetic stirrer at a speed of 500 r / min, the reaction temperature was 25°C-60°C, and the reaction time was 0.5 h-4 h. After the reaction was completed, the mixture was filtered to obtain a filtrate and a filter residue;

[0012] S6, phosphorus recovery: adding CaCl2 to the filtrate in S5 at a ratio of m(Ca) / m(P)=1-2 to obtain a turbid liquid, filtering the turbid liquid to obtain a filtrate and a filter residue, and drying the obtained filter residue to obtain hydroxyapatite, a phosphorus recovery product;

[0013] S7, aluminum recovery: continuously introduce CO2 into the filtrate obtained in S6 for 0.5h-2h. After the reaction is completed, filter the solution to obtain a filtrate and a filter residue, and dry the obtained filter residue to obtain aluminum recovery product aluminum hydroxide;

[0014] S8, alkaline waste liquid reuse: adding a certain amount of NaOH to the filtrate obtained in S7 and using it as the NaOH solution in S5;

[0015] S9, residual fly ash replaces cement clinker: the filter residue in S5 is dried and then used to replace cement clinker at a ratio of 20%-60% for building material utilization.

[0016] Preferably, in one embodiment, in said S1, the solid-liquid ratio of fly ash to dilute sulfuric acid is 10, the acid leaching reaction temperature is 25°C, the reaction time is 5h, and the reaction endpoint pH is 3.

[0017] Preferably, in one embodiment, the acid leaching solution in S2 should be cooled to room temperature.

[0018] Preferably, in one embodiment, the NaOH concentration in S5 is 1 mol / L, the liquid-solid ratio is 20, the reaction temperature is 25° C., and the reaction time is 5 h-7 h.

[0019] Preferably, in one embodiment, the CO2 in S7 is high-concentration CO2.

[0020] Preferably, in one embodiment, the alkaline waste liquid in S8 should be recycled after adding NaOH.

[0021] The present invention provides a method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials. Compared with the prior art, the method has the following beneficial effects:

[0022] The present invention discloses a method for recovering phosphorus, aluminum, and iron from sludge incineration fly ash and utilizing them as building materials. This method not only achieves high-value resource utilization of sludge incineration fly ash, but also reduces the contents of phosphorus, iron, aluminum, and heavy metals in the sludge incineration fly ash, significantly reducing the risk of heavy metal leaching. Furthermore, the method has the advantages of low cost, a simple and easy preparation process, no special equipment requirements, good controllability of process parameters, and ease of industrialization.

[0023] In addition, the present invention utilizes the polyferric sulfate produced from sludge incineration fly ash to treat domestic sewage, industrial wastewater, etc., realizing waste treatment with waste, and the extraction and recovery of phosphorus from the fly ash opens up new raw materials for the production of phosphate fertilizers. At the same time, the remaining fly ash after the extraction of phosphorus, aluminum and iron can be completely used to replace cement clinker. The obtained product has good mechanical properties and the heavy metal leaching toxicity meets the national standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic flow chart of a method for recovering phosphorus, aluminum, and iron from sludge incineration fly ash and utilizing them as building materials is shown in an embodiment of the present invention; DETAILED DESCRIPTION

[0025] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following embodiments are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0026] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0027] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. Throughout this application, unless otherwise specified, "plurality" means two or more.

[0028] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0029] The following is a description of preferred embodiments of the present invention with reference to the accompanying drawings.

[0030] Example 1: Figure 1 As shown, this embodiment discloses a method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials, the method comprising the following steps:

[0031] S1: Acid leaching: 50 g of sludge incineration fly ash was mixed with 0.065 mol / L dilute sulfuric acid at a solid-liquid ratio of 10, and the mixture was stirred on a magnetic stirrer at a speed of 500 r / min. The reaction temperature was 25°C, the reaction time was 5 h, and the reaction end point pH was 3. After the reaction was completed, the mixture was filtered to obtain an acid leaching solution and a filter residue.

[0032] S2, acid extract oxidation: Pipette 20 ml of the acid extract obtained in S1 into a conical flask and cool it. Place it on a magnetic stirrer and stir it at 500 rpm. Add 120 μl of hydrogen peroxide to the conical flask in four portions over 30 minutes to fully oxidize the divalent iron ions to trivalent iron ions.

[0033] S3, alkalization, hydrolysis, polymerization: The liquid obtained in S2 was placed on a magnetic stirrer and stirred at 500 r / min and heated to 50°C. During stirring, NaOH was added at a ratio of m(OH) / m(Fe)=1.8 for alkalization reaction. After the alkalization was completed, the reaction time was controlled to 120 min and the reaction temperature was controlled to 50°C for hydrolysis and polymerization reaction;

[0034] S4, aging and curing: the liquid obtained in S3 was allowed to stand at room temperature for 24 hours to mature, to obtain a reddish-brown polyaluminium ferric sulfate liquid;

[0035] S5, phosphorus extraction: The filter residue obtained in S1 was mixed with 1 mol / L NaOH solution at a liquid-to-solid ratio of 1:15, stirred on a thermostatic magnetic stirrer at 500 rpm, the reaction temperature was 30°C, the reaction time was 2 h, and after the reaction was completed, the mixture was filtered;

[0036] S6, phosphorus recovery: adding CaCl2 to the filtrate at m(Ca) / m(P)=1.5 to obtain a turbid solution, filtering the turbid solution to obtain a filtrate and a filter residue, and drying the obtained filter residue to obtain hydroxyapatite, a phosphorus recovery product;

[0037] S7, aluminum recovery: continuously introduce CO2 into the filtrate obtained in S6 for 1 hour. After the reaction is completed, filter the solution to obtain a filtrate and a filter residue, and dry the obtained filter residue to obtain aluminum recovery product aluminum hydroxide;

[0038] S8, alkaline waste liquid reuse: adding a certain amount of NaOH to the filtrate obtained in S7 and using it as the NaOH solution in S5;

[0039] S9, residual fly ash replaces cement clinker: the filter residue in S5 is dried and replaced with cement clinker at a ratio of 30% for use as building materials.

[0040] In this embodiment, the phosphorus leaching rate in S5 was 87.29%, the aluminum leaching rate was 41.27%, the solid products in S6 and S7 were hydroxyapatite and aluminum hydroxide according to XRD analysis, the cement test block prepared by replacing cement clinker in S9 had a 28-day compressive strength of 14.6 MPa, and the heavy metal leaching concentrations of the acid leaching solution in S1 are shown in Table 1:

[0041]

[0042] From the above, it can be seen that the present invention not only realizes the high-value resource utilization of sludge incineration fly ash, but also reduces the P, Fe, Al and heavy metal contents in sludge incineration fly ash, greatly reducing the risk of heavy metal leaching; in addition, the remaining fly ash after the extraction of phosphorus, aluminum and iron can be completely used to replace cement clinker, and the obtained product has good mechanical properties and a compressive strength of up to 14.6 MPa.

[0043] Example 2: This example discloses a method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials, the method comprising the following steps:

[0044] S1: Acid leaching: 50 g of sludge incineration fly ash was mixed with 0.075 mol / L dilute sulfuric acid at a solid-liquid ratio of 15, and stirred at 500 r / min on a constant temperature magnetic stirrer. The reaction temperature was 25°C, the reaction time was 5 h, and the reaction end point pH was 2.8. After the reaction was completed, the mixture was filtered to obtain the acid leaching solution and filter residue;

[0045] S2, acid extract oxidation: Pipette 20 ml of the acid extract obtained in S1 into a conical flask and cool it. Place it on a magnetic stirrer and stir it at 500 rpm. Add 120 μl of hydrogen peroxide to the conical flask in four portions over 30 minutes to fully oxidize the divalent iron ions to trivalent iron ions.

[0046] S3, alkalization, hydrolysis, polymerization: The liquid obtained in S2 was placed on a magnetic stirrer and stirred at 500 r / min and heated to 50°C. During stirring, NaOH was added at a ratio of m(OH) / m(Fe)=2 for alkalization reaction. After alkalization, the reaction time was controlled to 100 min and the reaction temperature was controlled to 60°C for hydrolysis and polymerization reaction;

[0047] S4, aging and curing: the liquid obtained in S3 was allowed to stand at room temperature for 24 hours to mature, to obtain a reddish-brown polyaluminium ferric sulfate liquid;

[0048] S5, phosphorus extraction: The filter residue obtained in S1 was mixed with 0.5 mol / L NaOH solution at a liquid-to-solid ratio of 1:15, and stirred on a thermostatic magnetic stirrer at a speed of 500 r / min. The reaction temperature was 25°C and the reaction time was 1 h. After the reaction was completed, the mixture was filtered to obtain a filtrate and a filter residue.

[0049] S6, phosphorus recovery: adding CaCl2 to the filtrate at m(Ca) / m(P)=1.5 to obtain a turbid solution, filtering the turbid solution to obtain a filtrate and a filter residue, and drying the obtained filter residue to obtain hydroxyapatite, a phosphorus recovery product;

[0050] S7, aluminum recovery: continuously introduce CO2 into the filtrate obtained in S6 for 1 hour. After the reaction is completed, filter the solution to obtain a filtrate and a filter residue, and dry the obtained filter residue to obtain aluminum recovery product aluminum hydroxide;

[0051] S8, alkaline waste liquid reuse: adding a certain amount of NaOH to the filtrate obtained in S7 and using it as the NaOH solution in S5;

[0052] S9, the remaining fly ash replaces cement clinker: the filter residue in S5 is dried and used to replace cement clinker at a ratio of 40% for building material utilization.

[0053] In this embodiment, the phosphorus leaching rate in S5 is 69.31%, the aluminum leaching rate in S5 is 30.13%, the solid products in S6 and S7 are hydroxyapatite and aluminum hydroxide by XRD analysis, the cement test block prepared by replacing cement clinker in S9 has a 28-day compressive strength of 10.64 MPa, and the heavy metal leaching concentration of the acid leaching solution in S1 is shown in Table 2.

[0054]

[0055] exist

[0056] Comparative Example 1: This example discloses a method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials, the method comprising the following steps:

[0057] S1: Acid leaching: 50 g of sludge incineration fly ash was mixed with 0.2 mol / L dilute sulfuric acid at a solid-liquid ratio of 4, stirred at 400 r / min on a constant temperature magnetic stirrer, the reaction temperature was 20°C, the reaction time was 8 h, the reaction end point pH was 1.8, and the mixture was filtered after the reaction was completed;

[0058] S2, acid extract oxidation: Pipette 20 ml of the acid extract obtained in S1 into a conical flask and cool it. Place it on a magnetic stirrer and stir it at 500 rpm. Add 120 μl of hydrogen peroxide to the conical flask in four portions over 40 minutes to fully oxidize the divalent iron ions to trivalent iron ions.

[0059] S3, alkalization, hydrolysis, polymerization: The liquid obtained in S2 was placed on a magnetic stirrer and stirred at 500 r / min and heated to 50°C. During stirring, NaOH was added at a ratio of m(OH) / m(Fe)=1.5 for alkalization reaction. After the alkalization was completed, the reaction time was controlled to 120 min and the reaction temperature was controlled to 30°C for hydrolysis and polymerization reaction;

[0060] S4, aging and curing: the liquid obtained in S3 was allowed to stand at room temperature for 20 hours to mature, to obtain a reddish-brown polyaluminium ferric sulfate liquid;

[0061] S5, phosphorus extraction: The filter residue obtained in S1 was mixed with 0.5 mol / L NaOH solution at a liquid-to-solid ratio of 2:5, stirred on a thermostatic magnetic stirrer at 400 rpm, the reaction temperature was 25°C, the reaction time was 2 h, and after the reaction was completed, the mixture was filtered;

[0062] S6, phosphorus recovery: adding CaCl2 to the filtrate at m(Ca) / m(P)=0.8 to obtain a turbid solution, filtering the turbid solution, and drying the filter residue to obtain hydroxyapatite, a phosphorus recovery product;

[0063] S7, aluminum recovery: CO2 is continuously introduced into the filtrate obtained in S6 for 2.5 hours. After the reaction is completed, the solution is filtered and the obtained filter residue is dried to obtain aluminum hydroxide as an aluminum recovery product;

[0064] S8, alkaline waste liquid reuse: adding a certain amount of NaOH to the filtrate obtained in S7 and using it as the NaOH solution in S5;

[0065] S9, residual fly ash replaces cement clinker: the filter residue in S5 is dried and used to replace cement clinker at a ratio of 70% for building material utilization.

[0066] In this comparative example: the phosphorus leaching rate in S5 is 0.99%, the aluminum leaching rate in S5 is 3.04%, the solid products in S6 and S7 are hydroxyapatite and aluminum hydroxide after XRD analysis, and the cement test block prepared by replacing cement clinker in S9 has a 28-day compressive strength of 1.21 MPa.

[0067] In summary, by comparing Example 1 and Example 2 with the comparative example, it can be seen that the solid-liquid ratio, dilute sulfuric acid concentration, and m(OH) / m(Fe) ratio of sludge incineration fly ash and dilute sulfuric acid, and the liquid-solid ratio and NaOH solution concentration of the filter residue in S5 and the NaOH solution have a significant effect on the phosphorus leaching rate, aluminum leaching rate, and cement compressive strength. The phosphorus leaching rate and aluminum leaching rate extracted by the method of the present invention are much better than those in comparative example 1, and the 28-day compressive strength of the prepared cement test block is also much higher than that in comparative example 1.

[0068] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0069] Although the present invention has been described above with reference to exemplary embodiments, various modifications may be made and equivalent components may be substituted without departing from the scope of the present invention. In particular, the various features of the disclosed embodiments may be combined with one another in any manner, provided no structural conflicts exist. These combinations are not fully described in this specification solely for the sake of space and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

[0070] Those skilled in the art will understand that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will still be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials, comprising the following steps: S1, acid leaching: sludge incineration fly ash and dilute sulfuric acid are mixed at a solid-liquid ratio of 5-20, placed on a magnetic stirrer and stirred at a speed of 500 r / min, the reaction temperature is 25-60 ° C, the reaction time is 1 hour-7 hours, and the pH of the solution is controlled at 2.5-3.5 at the end of the reaction. After the reaction, filter to obtain an acid leaching solution and filter residue; S2, acid leaching solution oxidation: the acid leaching solution obtained in S1 is cooled, placed on a magnetic stirrer and stirred at 500 rpm, and 20%-40% hydrogen peroxide is added in batches for 20-40 minutes to fully oxidize the divalent iron ions to trivalent iron ions; S3, alkalization, hydrolysis, polymerization: Place the liquid obtained in S2 on a magnetic stirrer and stir at 500 r / min and raise the temperature to 40°C-90°C. During stirring, add NaOH at a ratio of m(OH) / m(Fe)=1.6-2.6 to carry out alkalization reaction. After the alkalization is completed, control the reaction time to 30min-240min and the reaction temperature to 40°C-90°C for hydrolysis and polymerization reaction; S4, aging and solidification: The liquid obtained in S3 was allowed to stand at room temperature for 24 hours to mature to obtain a reddish-brown polyferric sulfate liquid, which was then vacuum-dried at 40°C to obtain a light yellow polyferric sulfate solid; S5, phosphorus extraction: the filter residue obtained in S1 is mixed with 0.2-1.5 mol / L NaOH solution at a liquid-to-solid ratio of 5-20, stirred on a magnetic stirrer at a speed of 500 r / min, the reaction temperature is 25°C-60°C, and the reaction time is 0.5 h-4 h. After the reaction is completed, the mixture is filtered to obtain a filtrate and a filter residue; S6, phosphorus recovery: adding CaCl2 to the filtrate in S5 at a ratio of m(Ca) / m(P)=1-2 to obtain a turbid liquid, filtering the turbid liquid to obtain a filtrate and a filter residue, and drying the obtained filter residue to obtain a phosphorus recovery product, hydroxyapatite; S7, aluminum recovery: continuously introduce CO2 into the filtrate obtained in S6 for 0.5h-2h. After the reaction is completed, filter the solution to obtain a filtrate and a filter residue, and dry the obtained filter residue to obtain aluminum recovery product aluminum hydroxide; S8, alkaline waste liquid reuse: adding a certain amount of NaOH to the filtrate obtained in S7 and using it as the NaOH solution in S5; S9, Residual fly ash replaces cement clinker: the filter residue in S5 is dried and used to replace cement clinker at a ratio of 20%-60% for building material utilization; In S1, the solid-liquid ratio of fly ash to dilute sulfuric acid is 10, the acid leaching reaction temperature is 25°C, the reaction time is 5h, and the reaction endpoint pH is 3; The acid leaching solution in S2 should be cooled to room temperature; the NaOH concentration in S5 is 1 mol / L, the liquid-solid ratio is 20, the reaction temperature is 25°C, and the reaction time is 5h-7h; The CO2 in S7 is high-concentration CO2.

2. The method for recovering phosphorus, aluminum and iron from sludge incineration fly ash and utilizing them as building materials according to claim 1, characterized in that: The alkaline waste liquid in S8 should be recycled after adding NaOH.

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