Method for extracting phosphorus from sludge incineration ash and recycling residues of sludge incineration ash

Abstract

The invention discloses a method for extracting phosphorus from sludge incineration ash and recycling residues, and belongs to the field of sludge recycling. The method comprises the following steps: firstly, conditioning municipal sludge to dehydrate by adopting calcium salt, reducing the water content of the sludge and fixing phosphorus in a liquid phase; then, the obtained calcium-containing sludge and an alkali metal reagent are mixed and incinerated, and insoluble metal phosphate in the sludge is promoted to be converted into water-soluble phosphate; the incineration ash is subjected to water leaching treatment, and a phosphorus-rich solution can be obtained through separation (the phosphorus recovery rate is gt; 90%) and leaching residues; finally, the leaching residues are directly mixed with cement, sand and water in proportion, and the strength of the prepared mortar test block meets the GB 175-2007 standard requirement. In the sludge treatment process, efficient recycling of phosphorus resources in the sludge and complete recycling of incineration ash leaching residues are synchronously achieved, the method has the advantages of being simple in process and controllable in cost, the mature incineration process is coupled, and industrial application is easy to achieve.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of sludge resource utilization, and particularly relates to a method for extracting phosphorus from sludge incineration ash and resource utilization of residues thereof. BACKGROUND

[0002] Phosphorus is one of the essential elements for all living things, and is also a non-naturally renewable resource. According to the current mining rate, it is reported that the global proven reserves of phosphorus ore will be exhausted in 50-100 years, and the risk of phosphorus resource shortage is increasingly prominent. Municipal sludge is a potential secondary phosphorus source, and the recovery of phosphorus therefrom is of great significance for alleviating the crisis of phosphorus ore resources, promoting sludge resource utilization, and controlling phosphorus pollution. However, the phosphorus in municipal sludge exists in complex forms, which is difficult to directly recover and utilize. Existing researches mainly use acid / alkali treatment, anaerobic digestion, and hydrothermal treatment to transfer phosphorus in the solid phase of sludge to the liquid phase, and then recover phosphorus from the phosphorus-rich liquid by precipitation, adsorption, crystallization, and other methods. However, these methods generally have the problems of low phosphorus recovery efficiency, long cycle, high energy consumption, and the like.

[0003] In recent years, heat treatment technology has been favored by more and more researchers because it can realize efficient reduction, harmless treatment, and resource utilization of sludge. Under this background, the research focus of phosphorus recovery has gradually shifted to the heat treatment products of sludge. For example, patent CN113072267A proposes a new method for sludge resource utilization by using iron salt to modify sludge-alkali metal to activate iron-containing sludge pyrolysis-water immersion phosphorus recovery, which successfully converts sludge into phosphorus-rich solution and porous biochar functional material. However, the specific surface area of the porous biochar functional material obtained by this method is only 50-200 m 2 / g, which is relatively low compared with the specific surface area of biochar obtained by pyrolysis of other agricultural and forestry biomass or biochar obtained by pyrolysis of modified sludge (the specific surface area can be up to 1000 m 2 / g or more), which may limit its high-value-added resource utilization approach and is not conducive to large-scale utilization. At the same time, from the perspective of industrialization, the number of sludge pyrolysis projects actually put into production in China is relatively small, and most of the researches are still in the laboratory research or pilot-scale stage, lacking systematic research and practical experience of industrial application of large-scale projects, which is difficult to directly provide effective reference and guidance for large-scale industrial production.

[0004] Compared with sludge pyrolysis technology, sludge incineration technology has more successful cases and rich practical experience in actual engineering application. Patent CN 118619226 A proposes a method for selectively leaching and recovering phosphorus resources from sludge incineration ash. The method mixes sludge incineration ash with calcium oxide, presses into shape, high-temperature modification, dilute acid leaching, and a series of steps such as precipitation separation, and finally obtains phosphate products. However, this method has complex processing flow, and the acid leaching process may leach out impurity elements such as metals, making it difficult to remove impurities and resulting in low product purity. At the same time, the above method mainly focuses on the recovery of phosphorus in sludge, and it is difficult to achieve large-scale safe resource utilization of the remaining sludge. Although patent CN 119774950 A proposes a method for preparing cement mortar using sludge incineration ash, research shows that directly using phosphorus-rich sludge incineration ash for cement mortar may interfere with the cement hydration process, thereby affecting the engineering performance of the material, limiting its application potential in the construction field.

[0005] In summary, the existing sludge phosphorus recovery method has the problems of low phosphorus recovery efficiency, long processing flow, and difficulty or poor effect in resource utilization of the remaining residue after phosphorus recovery, which cannot meet the needs of actual production and environmental protection. SUMMARY

[0006] In view of the deficiencies and improvement needs of the prior art, the purpose of the present application is to provide a method for extracting phosphorus from sludge incineration ash and resource utilization of its residue, which improves the overall process design and proposes a new method of calcium salt conditioning sludge dewatering-sludge co-incineration with alkali metal reagent-water leaching phosphorus recovery-incineration ash leaching residue resource utilization. Compared with the prior art, it can effectively solve the problems of low phosphorus recovery efficiency, long processing flow, and insufficient resource utilization of the remaining residue after phosphorus recovery. The method has a simple process, can simultaneously achieve efficient recovery (>90%) of phosphorus resources in sludge and complete resource utilization (replacing part of cement as building material) of incineration ash leaching residue during sludge treatment and disposal, and has significant economic and environmental benefits.

[0007] To achieve the above-mentioned purpose, the present application provides a method for extracting phosphorus from sludge incineration ash and resource utilization of its residue, characterized in that the method first adds calcium salt to municipal sludge for conditioning and dewatering; then mixes the calcium-containing sludge with an alkali metal reagent and incinerates it to obtain sludge incineration ash; then performs water leaching treatment on the sludge incineration ash, and solid-liquid separation to obtain a phosphorus-rich solution and incineration ash leaching residue; finally, the incineration ash leaching residue can be directly mixed, stirred, and cured with ordinary Portland cement, standard sand, and water in a certain proportion to prepare a cement mortar test block.

[0008] Preferably, the calcium salt is one or more of calcium chloride, calcium sulfate, calcium carbonate or calcium oxide; the calcium salt is added in an amount of 1:5 to 20 (w / w) of the dry sludge.

[0009] The alkali reagent is selected from one or more of potassium hydroxide, potassium carbonate, potassium bicarbonate, sodium hydroxide, sodium carbonate, sodium bicarbonate or potassium-sodium alkali residue.

[0010] The calcium-containing sludge is further subjected to dewatering, drying, grinding and sieving before co-incineration with the alkali reagent.

[0011] The alkali reagent is completely mixed with the calcium-containing sludge, and the ratio of the amount of the alkali reagent to the mass of ash in the calcium-containing sludge is 1:2 to 2:1.

[0012] The sieving is performed through a 100-mesh sieve.

[0013] The incineration is performed in a muffle furnace at a temperature of 750 to 900℃.

[0014] The solid-liquid ratio used in the water immersion treatment is 10 to 30 g / L, and the water immersion time is 30 to 60 min.

[0015] The incineration ash leaching residue is directly mixed with ordinary Portland cement, standard sand and water at a mass ratio of 5 to 8:15 to 25:55 to 65:15 to 20, stirred, poured into a mold after uniform stirring, vibrated on a vibrating table to remove air bubbles, leveled, placed in an incubator for curing and demolding, and a cement mortar test block is obtained.

[0016] Specifically, the advantages of the present application are as follows: the calcium salt is used to condition the sludge for dewatering, which can effectively destroy the colloidal stability of the sludge, improve the flocculation structure and filter cake properties, and significantly improve the dewatering performance of the sludge and reduce the subsequent sludge drying energy consumption through multiple effects such as charge neutralization, bridging, replacement, hydrophobicization and generation of rigid skeleton; on the other hand, the dissolved phosphorus in the sludge liquid phase will also combine with calcium to form calcium phosphate precipitate in the calcium-containing sludge, improving the recovery rate of phosphorus in the sludge. During the incineration of the sludge, organic phosphorus is also decomposed into phosphorus-containing oxides, which combine with metals in the sludge to form orthophosphates (iron phosphate, aluminum phosphate and calcium phosphate); then, the alkali reagent reacts with the orthophosphates to convert the insoluble metal phosphates into water-soluble potassium phosphate. Since the water immersion liquid after incineration of the alkali reagent is alkaline, it can selectively leach out phosphorus (water-soluble potassium / sodium phosphate) and effectively inhibit the dissolution of metals and other impurities, significantly simplifying the subsequent treatment process of the phosphorus-rich liquid. At the same time, the addition of calcium in the sludge and the dissolution of phosphorus in the incineration ash are both conducive to promoting the hydration process of cement and improving its setting strength, providing conditions for the resource utilization of the sludge incineration ash leaching residue.

[0017] The reaction of the alkali reagent with different kinds of metal phosphate in the sludge in the present application is mainly completed by formula (1-18), which converts the insoluble metal phosphate in the sludge into water-soluble sodium / potassium phosphate, and then the phosphorus in the sludge incineration ash can be dissolved by simple water immersion.

[0018] 2FePO4+6KOH=2K3PO4+Fe2O3+3H2O (1)

[0019] 2AlPO4+6KOH=2K3PO4+Al2O3+3H2O (2)

[0020] Ca3(PO4)2+6KOH=2K3PO4+3CaO+3H2O (3)

[0021] 2FePO4+3K2CO3=2K3PO4+Fe2O3+3CO2 (4)

[0022] 2AlPO4+3K2CO3=2K3PO4+Al2O3+3CO2 (5)

[0023] Ca3(PO4)2+3K2CO3=2K3PO4+3CaCO3 (6)

[0024] 2FePO4+6KHCO3=2K3PO4+Fe2O3+3H2O+6CO2 (7)

[0025] 2AlPO4+6KHCO3=2K3PO4+Al2O3+3H2O+6CO2 (8)

[0026] Ca3(PO4)2+6KHCO3=2K3PO4+3CaCO3+3H2O+3CO2 (9)

[0027] 2FePO4+6NaOH=2Na3PO4+Fe2O3+3H2O (10)

[0028] 2AlPO4+6NaOH=2Na3PO4+Al2O3+3H2O (11)

[0029] Ca3(PO4)2+6NaOH=2Na3PO4+3CaO+3H2O (12)

[0030] 2FePO4+3Na2CO3=2Na3PO4+Fe2O3+3CO2 (13)

[0031] 2AlPO4+3Na2CO3=2Na3PO4+Al2O3+3CO2 (14)

[0032] Ca3(PO4)2+ 3Na2CO3= 2Na3PO4+ 3CaCO3 (15)

[0033] 2FePO4+ 6NaHCO3= 2Na3PO4+ Fe2O3+ 3H2O + 6CO2 (16)

[0034] 2AlPO4+ 6NaHCO3= 2Na3PO4+ Al2O3+ 3H2O + 6CO2 (17)

[0035] Ca3(PO4)2+ 6NaHCO3= 2Na3PO4+ 3CaCO3+ 3H2O + 3CO2 (18)

[0036] In summary, compared with the prior art, the present application can achieve the following beneficial effects:

[0037] 1. Efficient phosphorus recovery and simultaneous realization of residue resourceization

[0038] Through calcium salt conditioning sludge dewatering + alkali reagent co-incineration + water immersion treatment, the phosphorus recovery rate can reach more than 90%. At the same time, the water immersion residue of incineration ash can directly replace part of the cement to prepare qualified building materials, realizing the complete resourceization of phosphorus and inorganic components in sludge incineration ash.

[0039] 2. Good impurity separation effect and simplified process

[0040] The water immersion process is carried out under alkaline conditions, which can selectively leach out phosphorus while effectively inhibiting the leaching of metal and other impurity elements. Compared with acid leaching method, the difficulty of removing impurities from the subsequent phosphorus-rich liquid is greatly reduced, the product purity is improved, and only simple impurity removal and crystallization steps are required.

[0041] 3. Integrated design reduces overall process cost and improves marketization potential

[0042] Through integrated design from source to terminal (calcium salt dewatering to reduce energy consumption-alkali reagent co-incineration to avoid acid leaching-leaching residue utilization to save treatment cost), energy saving and resource recycling are realized, and the overall cost is significantly reduced. At the same time, relying on the widely used mature sludge incineration process, it is easier to be adopted by existing facilities, promoting marketization application and popularization. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The figure is a schematic diagram of the method steps of the present application.

[0044] Figure 2 The figure is a Gibbs free energy change diagram of possible reactions of potassium metal promoting phosphorus conversion in the sludge incineration process

the legends in the figure correspond to chemical reaction formulas (1)-(9) respectively

[0045] Figure 3The diagram shows the Gibbs free energy changes of possible reactions during the phosphorus conversion process promoted by sodium metal in sludge incineration. [The legends in the diagram correspond to chemical reaction formulas (10) to (18) respectively]. Detailed Implementation

[0046] To fully illustrate the purpose, technical solution, and beneficial effects of the present invention, a detailed description is provided below in conjunction with the accompanying drawings and embodiments. It should be understood that the listed embodiments are intended to explain the present invention and not to limit it. Furthermore, the technical features included in each embodiment can be arbitrarily combined without conflicting with each other.

[0047] The method for phosphorus extraction from sludge incineration ash and resource utilization of its residue in this invention includes four steps: calcium salt modification to promote sludge dewatering to obtain calcium-containing sludge, co-incineration of the calcium-containing sludge with alkali metal reagents, water leaching of incineration ash to separate phosphorus-rich solution and leaching residue, and resource utilization of incineration ash leaching residue. Specifically:

[0048] Step S1: Condition the sludge with calcium salt, then dewater, dry, grind, and sieve it to obtain calcium-containing sludge. The calcium salt is one or more of calcium chloride, calcium sulfate, calcium carbonate, or calcium oxide. The preferred ratio of calcium salt mass to sludge dry basis mass is 1:5 to 20.

[0049] Step S2: Mix calcium-containing sludge with alkali metal reagent and incinerate in a muffle furnace at a temperature of 750-900℃ to obtain sludge incineration ash; the alkali metal reagent is selected from one or more of potassium hydroxide, potassium carbonate, potassium bicarbonate, sodium hydroxide, sodium carbonate, sodium bicarbonate or potassium sodium alkali residue, and the ratio of the amount of alkali metal reagent added to the mass of ash in calcium-containing sludge is 1:2 to 2:1.

[0050] Step S3: The sludge incineration ash is leached in water with a solid-liquid ratio of 10-30 g / L for 30-60 min. After leaching, solid-liquid separation is performed to obtain a phosphorus-rich solution and incineration ash leaching residue.

[0051] Step S4: Directly mix and stir the incineration ash leachate residue with ordinary silicate cement, standard sand, and water in a mass ratio of 5-8:15-25:55-65:15-20. After stirring evenly, pour the mixture into a mold, vibrate it on a compaction table to remove air bubbles, scrape the surface smooth, place it in an incubator for curing, and then demold it to obtain a cement mortar test block.

[0052] The following are specific examples:

[0053] Example 1

[0054] This embodiment describes a method for phosphorus extraction from sludge incineration ash and resource utilization of its residue, which is carried out according to the following steps:

[0055] (1) Calcium oxide was used to condition municipal sludge (the municipal sludge raw material was taken from the secondary sedimentation tank of the Gaobeidian Wastewater Treatment Plant in Beijing, the same below). The amount of calcium oxide added was 5% of the initial dry basis mass of the municipal sludge. After conditioning, it was dewatered by plate and frame dewatering. The moisture content of the sludge after dewatering was 78.9%, and the phosphorus retention rate of the sludge solid phase was 99.1%. The dewatered sludge cake was then dried, ground, and passed through a 100-mesh sieve. The material passing through the sieve was used for subsequent incineration experiments (the test results of the basic characteristics of the sludge before and after calcium salt conditioning are shown in Table 1 below).

[0056] (2) Sludge incineration experiment using a muffle furnace. Calcium-containing sludge was mixed with potassium bicarbonate reagent and co-incinerated. The ratio of potassium bicarbonate added to the ash mass in the calcium-containing sludge was 1:1. The incineration temperature was 850℃ and maintained for 1 hour to obtain sludge incineration ash.

[0057] (3) The sludge incineration ash was leached with water at a solid-liquid ratio of 10 g / L for 30 min. After leaching, solid-liquid separation was performed to obtain a phosphorus-rich solution and leaching residue of incineration ash. The phosphorus leaching rate in the sludge incineration ash was 96.5%, and the phosphorus recovery rate from sludge to phosphorus-rich solution was 95.6% (the content of each element in the leaching solution is shown in Table 2 below).

[0058] (4) The leaching residue of incineration ash is mixed with ordinary silicate cement, standard sand and water in a mass ratio of 5:20:60:15. After mixing evenly, the mixture is poured into a mold, vibrated on a vibrating table to remove air bubbles, the surface is smoothed, and the mixture is placed in an incubator for curing and demolding to obtain cement mortar test blocks. The flexural strength of the mortar test blocks after curing for 3 days and 28 days is 5.6 MPa and 11.5 MPa, respectively, and the compressive strength after curing for 3 days and 28 days is 25.4 MPa and 47.8 MPa, respectively, which meet the strength requirements in the national standard GB 175-2007.

[0059] Table 1. Basic characteristics of the raw sludge and calcium-conditioned sludge used in Example 1

[0060]

[0061] Table 2. Analysis of main components (mg / L) of sludge incineration ash leachate from Example 1.

[0062]

[0063] Example 2

[0064] (1) Calcium chloride was used to condition municipal sludge. The amount of calcium chloride added was 20% of the initial dry weight of municipal sludge. After conditioning, the sludge was dewatered using a plate and frame dewatering machine. The moisture content of the sludge after dewatering was 75.3%, and the phosphorus retention rate of the sludge solid phase was 99.7%. The dewatered sludge cake was then dried, ground, and passed through a 100-mesh sieve. The material passing through the sieve was used for subsequent incineration experiments.

[0065] (2) Sludge incineration experiment using a muffle furnace. Calcium-containing sludge was mixed with potassium hydroxide reagent and co-incinerated. The ratio of potassium hydroxide added to the ash mass in the calcium-containing sludge was 1:2. The incineration temperature was 750℃ and maintained for 1 hour to obtain sludge incineration ash.

[0066] (3) The sludge incineration ash was leached with water at a solid-liquid ratio of 30 g / L for 60 min. After leaching, solid-liquid separation was performed to obtain a phosphorus-rich solution and leaching residue from the incineration ash. The phosphorus leaching rate in the sludge incineration ash was 92.1%, and the phosphorus recovery rate from sludge to phosphorus-rich solution was 91.8%.

[0067] (4) The leaching residue of incineration ash was mixed with ordinary silicate cement, standard sand and water in a mass ratio of 8:17:55:20. After stirring evenly, the mixture was poured into a mold, vibrated on a vibrating table to remove air bubbles, the surface was smoothed, and the mixture was placed in an incubator for curing and demolding to obtain cement mortar test blocks. The flexural strength of the mortar test blocks after curing for 3 days and 28 days was 4.9 MPa and 10.7 MPa, respectively, and the compressive strength after curing for 3 days and 28 days was 23.6 MPa and 45.1 MPa, respectively, which met the strength requirements in the national standard GB 175-2007.

[0068] Example 3

[0069] (1) Calcium oxide was used to condition municipal sludge (the municipal sludge raw material was taken from the secondary sedimentation tank of the Gaobeidian Wastewater Treatment Plant in Beijing, the same below). The amount of calcium oxide added was 15% of the initial dry weight of the municipal sludge. After conditioning, it was dewatered by plate and frame dewatering. The moisture content of the sludge after dewatering was 73.6%, and the phosphorus retention rate of the solid phase of the sludge was 99.5%. The dewatered sludge cake was then dried, ground, and passed through a 100-mesh sieve. The material passing through the sieve was used for subsequent incineration experiments.

[0070] (2) Sludge incineration experiment using muffle furnace. Calcium-containing sludge was mixed with potassium sodium alkali residue (indigo alkali residue, yellow alkaline sludge discharged during the concentration of alkali solution in the indigo production process) and co-incinerated. The ratio of the amount of potassium sodium alkali residue added to the mass of ash in calcium-containing sludge was 2:1. The incineration temperature was 900℃ and maintained for 1 hour to obtain sludge incineration ash.

[0071] (3) The sludge incineration ash was leached with water at a solid-liquid ratio of 20 g / L for 60 min. After leaching, solid-liquid separation was performed to obtain a phosphorus-rich solution and leaching residue from the incineration ash. The phosphorus leaching rate in the sludge incineration ash was 93.7%, and the phosphorus recovery rate from sludge to phosphorus-rich solution was 93.2%.

[0072] (4) The leaching residue of incineration ash is mixed with ordinary silicate cement, standard sand and water in a mass ratio of 5:20:60:15. After stirring evenly, the mixture is poured into a mold, vibrated on a vibrating table to remove air bubbles, the surface is smoothed, and the mixture is placed in an incubator for curing and demolding to obtain cement mortar test blocks. The flexural strength of the mortar test blocks after curing for 3 days and 28 days is 5.9 MPa and 11.7 MPa, respectively, and the compressive strength after curing for 3 days and 28 days is 26.1 MPa and 47.9 MPa, respectively, which meet the strength requirements in the national standard GB 175-2007.

[0073] Example 4

[0074] (1) Calcium oxide was used to condition municipal sludge (the municipal sludge raw material was taken from the secondary sedimentation tank of the Gaobeidian Wastewater Treatment Plant in Beijing, the same below). The amount of calcium oxide added was 15% of the initial dry weight of the municipal sludge. After conditioning, it was dewatered by plate and frame dewatering. The moisture content of the sludge after dewatering was 73.6%, and the phosphorus retention rate of the solid phase of the sludge was 99.5%. The dewatered sludge cake was then dried, ground, and passed through a 100-mesh sieve. The material passing through the sieve was used for subsequent incineration experiments.

[0075] (2) Sludge incineration experiment using a muffle furnace. Calcium-containing sludge was mixed with potassium bicarbonate and co-incinerated. The ratio of potassium bicarbonate added to the ash mass in the calcium-containing sludge was 1:1. The incineration temperature was 850℃ and maintained for 1 hour to obtain sludge incineration ash.

[0076] (3) The sludge incineration ash was leached with water at a solid-liquid ratio of 20 g / L for 30 min. After leaching, solid-liquid separation was performed to obtain a phosphorus-rich solution and leaching residue from the incineration ash. The phosphorus leaching rate in the sludge incineration ash was 95.3%, and the phosphorus recovery rate from sludge to phosphorus-rich solution was 94.8%.

[0077] (4) The leaching residue of incineration ash is mixed with ordinary silicate cement, standard sand and water in a mass ratio of 5:15:65:15. After stirring evenly, the mixture is poured into a mold, vibrated on a vibrating table to remove air bubbles, the surface is smoothed, and the mixture is placed in an incubator for curing and demolding to obtain cement mortar test blocks. The flexural strength of the mortar test blocks after curing for 3 days and 28 days is 5.3 MPa and 10.8 MPa, respectively, and the compressive strength after curing for 3 days and 28 days is 23.4 MPa and 45.5 MPa, respectively, which meet the strength requirements in the national standard GB 175-2007.

[0078] Comparative Example 1

[0079] The method and steps were the same as in Example 1, except that calcium salts were not added to condition the sludge in step 1, and the municipal sludge was directly dewatered using a plate and frame dewatering system. After dewatering, the sludge moisture content was 90.4%, and the solid phosphorus retention rate was 90.7%. The final phosphorus leaching rate in the incineration ash was 95.8%, and the phosphorus recovery rate from sludge to phosphorus-rich liquid was 86.9%. The flexural strength of the mortar test blocks after curing for 3 days and 28 days was 4.4 MPa and 7.2 MPa, respectively, and the compressive strength after curing for 3 days and 28 days was 20.5 MPa and 41.6 MPa, respectively, which did not meet the strength requirements in the national standard GB 175-2007.

[0080] Comparative Example 2

[0081] The method and steps are the same as in Example 1, except that no alkali metal reagent is added in step 2, and the calcium-containing sludge is directly incinerated. The phosphorus leaching rate in the final incineration ash is only 2.3%. The flexural strength of the mortar test blocks after curing for 3 days and 28 days is 4.9 MPa and 10.8 MPa, respectively, and the compressive strength after curing for 3 days and 28 days is 23.1 MPa and 45.9 MPa, respectively.

[0082] Comparative Example 3

[0083] The method and steps are the same as in Example 1, except that the incineration temperature is set to 700℃ in step 2. The phosphorus leaching rate in the final incineration ash is only 63.9%. The flexural strength of the mortar test blocks after curing for 3 days and 28 days is 5.1MPa and 11.2MPa, respectively, and the compressive strength after curing for 3 days and 28 days is 24.3MPa and 46.1MPa, respectively.

[0084] Comparative Example 4

[0085] The method and steps are the same as in Example 1, except that an excessive amount of incinerator ash leaching residue is added in step 4 (the mass ratio of incinerator ash leaching residue to ordinary Portland cement, standard sand, and water is 10:15:60:15). The final flexural strength of the mortar test blocks after curing for 3 days and 28 days was 4.3 MPa and 6.5 MPa, respectively, and the compressive strength after curing for 3 days and 28 days was 16.4 MPa and 40.9 MPa, respectively, which did not meet the strength requirements in the national standard GB 175-2007.

[0086] It should be added that the phosphorus-rich solutions obtained in the above embodiments of the present invention have extremely low impurity ion content (Table 1). Therefore, by simply controlling the solution pH and adding ferrous salts, the phosphorus-rich solution can be purified and crystallized to obtain high-quality phosphorus products. Furthermore, the flexural strength, compressive strength, and heavy metal leaching amount of the incineration ash leaching residue after resource utilization in the above embodiments all meet the national standard GB 175-2007 and the environmental protection industry standard HJ / 300-2007.

[0087] It should be understood that the above embodiments are only for better illustrating the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for enhanced phosphorus leaching from sludge incineration ash, characterized in that, Includes the following steps: (1) Calcium salt conditioning and dehydration: Calcium salt conditioner is added to municipal sludge to obtain calcium-containing sludge; (2) Co-incineration with alkali metal reagents: calcium-containing sludge is mixed with alkali metal reagents and incinerated to obtain sludge incineration ash; (3) Water leaching for phosphorus extraction: The incineration ash is subjected to water leaching treatment, and solid-liquid separation is performed to obtain a phosphorus-rich solution and leaching residue.

2. The method according to claim 1, characterized in that, The calcium salt is one or more of calcium chloride, calcium sulfate, calcium carbonate, or calcium oxide; the amount of calcium salt added is such that the ratio of calcium salt mass to sludge dry basis mass is 1:5 to 20.

3. The method according to claim 1, characterized in that, The alkali metal reagent is at least one of potassium hydroxide, potassium carbonate, potassium bicarbonate, sodium hydroxide, sodium carbonate, sodium bicarbonate, or potassium sodium alkali residue, and its addition amount is in the mass ratio of calcium-containing sludge ash to 1:2 to 2:

1.

4. The method according to claim 1, characterized in that, Before being co-incinerated with alkali metal reagents, the calcium-containing sludge underwent dehydration, drying, grinding, and sieving, with the sieving process involving passing through a 100-mesh sieve.

5. The method according to claim 1, characterized in that, The incineration is carried out in a muffle furnace at a temperature of 750–900°C.

6. The method according to claim 1, characterized in that, The solid-liquid ratio used in the water immersion treatment is 10–30 g / L, and the immersion time is 30–60 min.

7. A method for the resource utilization of incineration ash leaching residue, characterized in that, Cement mortar test blocks were prepared using leaching residue produced by any one of the methods of claims 1 to 6 as a raw material to replace part of the cementitious material.

8. The method according to claim 7, characterized in that, The leaching residue of incinerator ash is mixed with ordinary silicate cement, standard sand and water in a mass ratio of 5-8:15-25:55-65:15-20, stirred and cured to prepare cement mortar test blocks.

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