A method for recovering aluminum phosphate from sludge

Abstract

This invention relates to the field of sludge resource utilization technology, and more particularly to a method for recovering aluminum phosphate from sludge. The technical solution provided by this invention involves incinerating dried sludge to obtain sludge incineration ash, then leaching the ash with a target organic acid of a predetermined concentration, followed by solid-liquid separation to obtain a phosphorus-containing leachate. This phosphorus-containing leachate is then subjected to hydrothermal synthesis to obtain industrial-grade aluminum phosphate. Therefore, the above technical solution involves directly performing hydrothermal synthesis treatment on the phosphorus-containing leachate obtained after leaching with a target organic acid of a predetermined concentration, thus shortening the process flow for preparing industrial-grade aluminum phosphate.

Description

Technical Field

[0001] This invention relates to the field of sludge resource utilization technology, and in particular to a method for recovering aluminum phosphate from sludge. Background Technology

[0002] Pollutants and nutrients in wastewater aggregate under the action of rapidly multiplying bacteria and chemical agents, eventually forming sludge. With the rapid development of industries such as functional materials, refractory materials, ceramics, and novel molecular sieves, the production of industrial-grade aluminum phosphate is also constantly increasing, leading to a greater demand for its raw materials (such as phosphorus).

[0003] In related technologies, the main method for recovering phosphorus from sludge and preparing industrial-grade aluminum phosphate is the wet chemical method; however, this method has a long process flow.

[0004] Therefore, there is an urgent need for a method to recover aluminum phosphate from sludge to solve this technical problem. Summary of the Invention

[0005] This invention provides a method for recovering aluminum phosphate from sludge, which can shorten the process flow for preparing industrial-grade aluminum phosphate.

[0006] This invention provides a method for recovering aluminum phosphate from sludge, comprising:

[0007] The dried sludge is incinerated to obtain sludge incineration ash;

[0008] The sludge incineration ash is leached with a target organic acid of a preset concentration, and a phosphorus-containing leachate is obtained after solid-liquid separation.

[0009] The phosphorus-containing leachate was subjected to hydrothermal synthesis to obtain industrial-grade aluminum phosphate.

[0010] As can be seen from the above scheme, the method for recovering aluminum phosphate from sludge provided by the present invention involves incinerating dried sludge to obtain sludge incineration ash, then leaching the sludge incineration ash with a target organic acid of a preset concentration, and obtaining a phosphorus-containing leachate after solid-liquid separation. The phosphorus-containing leachate is then subjected to hydrothermal synthesis to obtain industrial-grade aluminum phosphate. Therefore, the above technical solution involves directly performing hydrothermal synthesis treatment on the phosphorus-containing leachate after leaching with a target organic acid of a preset concentration, thus shortening the process flow for preparing industrial-grade aluminum phosphate. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of a method for recovering aluminum phosphate from sludge according to an embodiment of the present invention;

[0013] Figure 2 A comparison chart of aluminum phosphate recovered by this method and commercial-grade aluminum phosphate provided for embodiments of the present invention;

[0014] Figure 3 This is a diagram illustrating the thermodynamic equilibrium calculation system for the precipitation reaction between impurity components and target phosphorus-containing products in a phosphorus-containing leachate, provided in an embodiment of the present invention.

[0015] Figure 4 The Gibbs free energy variation diagram of the aluminum phosphate precipitation reaction provided in the embodiments of the present invention;

[0016] Figure 5 The reaction equilibrium constant diagram for the aluminum phosphate precipitation reaction provided in the embodiments of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Please see Figure 1 One embodiment of the present invention provides a method for recovering aluminum phosphate from sludge, the method comprising:

[0019] Step 100: Incinerate the dried sludge to obtain sludge incineration ash;

[0020] Step 102: Leach the sludge incineration ash using a target organic acid of a preset concentration, and obtain a phosphorus-containing leachate after solid-liquid separation;

[0021] Step 104: Perform hydrothermal synthesis on the phosphorus-containing leachate to obtain industrial-grade aluminum phosphate.

[0022] In this embodiment, dried sludge is incinerated to obtain sludge incineration ash. The sludge incineration ash is then leached with a target organic acid of a predetermined concentration. After solid-liquid separation, a phosphorus-containing leachate is obtained. This phosphorus-containing leachate is then subjected to hydrothermal synthesis to obtain industrial-grade aluminum phosphate. Therefore, the above technical solution involves direct hydrothermal synthesis of the phosphorus-containing leachate obtained after leaching with a target organic acid of a predetermined concentration, thus shortening the process flow for preparing industrial-grade aluminum phosphate.

[0023] In some implementations, the incineration temperature is 750–900°C to ensure the incineration effect of the dried sludge.

[0024] In one embodiment of the present invention, the target organic acid includes at least one of oxalic acid, citric acid, acetic acid, and ascorbic acid.

[0025] In this embodiment, the sludge accumulates a large amount of aluminum from the external environment during its formation, resulting in a higher molar amount of aluminum than phosphorus in the sludge itself. This means that if aluminum and phosphorus in the sludge can be leached out simultaneously, there is no need to add an external aluminum source during the subsequent precipitation process, thus saving process costs. To achieve the above objective, the type and concentration of the target organic acid were optimized, and it was determined that the target organic acid would be used to leach the sludge incineration ash. These target organic acids can achieve complete phosphorus leaching through their strong acidity, reducing properties, and chelating characteristics of acid radicals, while ensuring that sufficient aluminum enters the phosphorus-containing leachate simultaneously. The organic acid radicals in the target organic acid react with the aluminum phosphate in the sludge incineration ash to form a precipitation reaction, and the target organic acid can be destroyed under hydrothermal conditions, thereby achieving the simultaneous precipitation of aluminum and phosphorus.

[0026] In related technologies, some leachates typically add metal source reagents in corresponding molar proportions. However, Al salts, represented by AlCl3, are priced as high as 7000 yuan / ton, significantly increasing the process cost of the recovery process, which is also complex and lengthy. During leaching, elements such as Fe, Ca, and Mg in the sludge leach out simultaneously with P. To avoid the formation of impurities, it is often necessary to remove impurities through methods such as pH adjustment pre-precipitation or cation exchange resin methods. The pH is then adjusted to the optimal precipitation range for the target product to obtain the highest possible yield. However, the target organic acid in this embodiment can achieve simultaneous leaching of phosphorus and aluminum elements in sludge incineration ash without the addition of an external Al source, pH adjustment, or filtrate purification. This method effectively simplifies the treatment process and reduces treatment costs.

[0027] In one embodiment of the present invention, the preset concentration is 0.04 to 0.15 mol / L. At this concentration, the leaching effect of the target organic acid on phosphorus in sludge incineration ash can be guaranteed.

[0028] In one embodiment of the present invention, the solid-liquid ratio of sludge incineration ash to target organic acid is 1:50 to 1:200, the leaching time is 2 to 4 hours, and the tumbling and shaking rate is 60 to 200 rpm, so as to ensure the leaching effect of target organic acid on phosphorus in sludge incineration ash.

[0029] In one embodiment of the present invention, the pH value of the phosphorus-containing leachate is 1 to 2.

[0030] In this embodiment, by adding a target organic acid to make the pH value of the phosphorus-containing leachate 1 to 2, it can help recover aluminum phosphate from sludge incineration ash at room temperature, while ensuring that the phosphorus leaching rate of sludge incineration ash can reach more than 90% and the aluminum leaching rate can reach more than 70%.

[0031] Thermodynamic calculations show that, under hydrothermal reaction conditions, AlPO4 exhibits an independent precipitation range under acidic conditions of relatively strong target organic acids at pH 1–2. Figure 3 As shown (the width of the horizontal bar for each substance represents the degree of precipitation reaction under the corresponding pH conditions), other phosphorus-containing products (such as Fe3(PO4)2, MgNH4PO4, Ca5(PO4)3OH) and solid impurities (such as Fe(OH)3, Al(OH)3, Mg(OH)2, CaC2O4) cannot undergo precipitation reactions within this range. Therefore, by controlling the concentration of the target organic acid and ensuring that the pH value of the phosphorus-containing leachate is within this range, the individual precipitation of AlPO4 can be achieved, thereby ensuring the purity of the phosphorus-containing leachate.

[0032] In some embodiments, the phosphorus-containing leachate can be filtered using a filter head such as 0.45 μm to remove any solid particles that have not been completely separated from the phosphorus-containing leachate.

[0033] In one embodiment of the present invention, a phosphorus-containing leachate is used for the cyclic leaching of new sludge incineration ash.

[0034] In this embodiment, the cyclic leaching of phosphorus from the phosphorus-containing leachate and its reuse in sludge incineration ash can reduce reagent consumption.

[0035] In one embodiment of the present invention, when the pH value of the phosphorus-containing leachate is greater than 2, the phosphorus-containing leachate circulation leaching is stopped.

[0036] In this embodiment, if the pH value of the phosphorus-containing leachate is greater than 2, the individual precipitation of AlPO4 cannot be guaranteed, and the purity of the phosphorus-containing leachate is also affected. When the pH value of the phosphorus-containing leachate is less than 2 and greater than 1, the phosphorus-containing leachate can be used for the cyclic leaching of new sludge incineration ash.

[0037] In one embodiment of the present invention, the molar ratio of aluminum to phosphorus in the phosphorus-containing leachate is greater than 1:1.

[0038] In some implementations, if the molar ratio of aluminum to phosphorus in the phosphorus-containing leachate is less than 1:1, AlCl3 needs to be added to bring the molar ratio to 1:1. In this case, the amount of additional aluminum required is generally less than 20% of the total aluminum required for preparing industrial-grade aluminum phosphate.

[0039] In one embodiment of the present invention, the reaction temperature for hydrothermal synthesis is 150–210°C, and the reaction time is 2–24 h, to ensure that the phosphorus-containing leachate reacts fully.

[0040] In one embodiment of the present invention, step 104 may specifically include:

[0041] A hydrothermal synthesis was performed on a phosphorus-containing leachate to obtain a hydrothermal synthesis product.

[0042] The hydrothermal synthesis product was subjected to solid-liquid separation to obtain a solid product;

[0043] The solid product was washed a predetermined number of times with a deionized water mixture, and the washed solid product was freeze-dried to obtain industrial-grade aluminum phosphate.

[0044] In this embodiment, under the heating conditions of a target organic acid at a preset concentration, the precipitation reactions of related impurities and other phosphorus-containing products besides AlPO4 can be further suppressed. In the phosphorus-containing leachate, Al ions exist in the form of Al-acid anion ligands (taking the oxalic acid system as an example, Al exists as Al(C2O4)3). 3- This coordination compound exists without binding to phosphorus. Under hydrothermal conditions, the organic acid anions decompose, causing Al... 3+ It is released again, and can then react with (phosphate) PO4. 3- A precipitation reaction occurs to form AlPO4. The precipitation of AlPO4 is reversible at low temperatures (equilibrium constant lgK < 5), which leads to low AlPO4 yield and slow synthesis rate. However, the hydrothermal method can achieve an equilibrium constant lgK > 5 at temperatures above 150℃, resulting in a more complete synthesis reaction and a faster reaction rate. Figure 4 (When △G < 0, the reaction is considered to proceed spontaneously) and Figure 5 (When lgK>5, the precipitation reaction is considered to be more complete).

[0045] The hydrothermal-produced aluminum phosphate exhibits a uniform microcrystalline particle structure, and the products all show highly crystalline, flower-like microcrystalline particles at the microscopic level. Al, P, and O elements show a uniform symbiotic distribution, such as... Figure 2As shown, this is to give aluminum phosphate better microstructure and product performance.

[0046] exist Figure 2 In the diagram, a and b represent a comparison of the macroscopic morphology of aluminum phosphate obtained by this method and commercial-grade aluminum phosphate, respectively; c and d represent a comparison of the microscopic morphology of aluminum phosphate obtained by this method and commercial-grade aluminum phosphate, respectively; e represents the elemental distribution uniformity test of aluminum phosphate obtained by this method and a comparison of the crystal structure of commercial-grade aluminum phosphate; f represents a comparison of the crystal structure of aluminum phosphate recovered by this method and commercial-grade aluminum phosphate. Figure 2 It can be seen that the aluminum phosphate prepared in the embodiments of the present invention has greatly improved uniformity.

[0047] In this embodiment of the invention, the impurity content of aluminum phosphate can meet the standards of industrial aluminum phosphate and analytical reagent (TZJCX0002-2022), as shown in Table 1 (which shows the content of industrial grade aluminum phosphate, analytical reagent grade, and the product recovered by this method).

[0048] Table 1 Comparison of Aluminum Phosphate and Standard Limits

[0049]

[0050] In this embodiment, vacuum filtration is used to separate the hydrothermal synthesis products into solid and liquid components, so as to achieve better separation of the solid and liquid components of the hydrothermal synthesis products.

[0051] In this embodiment, washing with deionized water can remove impurity ions from the solid product.

[0052] In this embodiment, the washed solid product is freeze-dried to remove moisture and obtain industrial-grade aluminum phosphate.

[0053] In some embodiments, the phosphorus-containing leachate is placed directly in a sealed container for hydrothermal reaction, and the reaction process does not require stirring.

[0054] Using the above method, extensive calculations and experiments were conducted on the ionic thermodynamic reaction equilibrium system in the phosphorus-containing leachate. By selecting the type and concentration of the target organic acid, sludge incineration ash was leached to ensure the simultaneous leaching of phosphorus and aluminum from the ash. This allowed the phosphorus-containing leachate to reach hydrothermal conditions for hydrothermal synthesis, achieving the direct synthesis of aluminum phosphate using only the aluminum element within the sludge incineration ash. This method eliminates the need for external aluminum sources, saving reagent costs, and also eliminates the need for pH adjustment and filtrate purification to remove impurities, shortening the process flow for recovering phosphorus from sludge and preparing industrial-grade aluminum phosphate. This method not only realizes the resource utilization of sludge but also achieves the goal of producing industrial-grade aluminum phosphate.

[0055] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering aluminum phosphate from sludge, characterized in that, include: The dried sludge is incinerated to obtain sludge incineration ash; The sludge incineration ash is leached with a target organic acid of a preset concentration, and a phosphorus-containing leachate is obtained after solid-liquid separation. The phosphorus-containing leachate was subjected to hydrothermal synthesis to obtain industrial-grade aluminum phosphate; The target organic acid includes at least one of oxalic acid, citric acid, acetic acid, and ascorbic acid; The pH value of the phosphorus-containing leachate is 1~2.

2. The method according to claim 1, characterized in that, The preset concentration is 0.04~0.15 mol / L.

3. The method according to claim 1, characterized in that, The solid-liquid ratio of the sludge incineration ash to the target organic acid is 1:50 to 1:200, the leaching time is 2 to 4 hours, and the tumbling and shaking rate is 60 to 200 rpm.

4. The method according to claim 1, characterized in that, The phosphorus-containing leachate is used for the cyclic leaching of new sludge incineration ash.

5. The method according to claim 4, characterized in that, When the pH value of the phosphorus-containing leachate is greater than 2, the circulation and leaching of the phosphorus-containing leachate shall be stopped.

6. The method according to claim 1, characterized in that, The molar ratio of aluminum to phosphorus in the phosphorus-containing leachate is greater than 1:

1.

7. The method according to claim 1, characterized in that, The hydrothermal synthesis reaction temperature is 150~210℃, and the reaction time is 2~24h.

8. The method according to any one of claims 1-7, characterized in that, The process of hydrothermal synthesis of the phosphorus-containing leachate to obtain industrial-grade aluminum phosphate includes: The phosphorus-containing leachate was subjected to hydrothermal synthesis to obtain the hydrothermal synthesis product; The hydrothermal synthesis product was subjected to solid-liquid separation to obtain a solid product; The solid product is washed a predetermined number of times with a deionized water mixture, and the washed solid product is freeze-dried to obtain industrial-grade aluminum phosphate.

Images