Method and equipment for recovering alkali elements from coal cinder

Abstract

The application provides a method and equipment for recovering alkali metal elements in coal cinder, and the method comprises the following steps: mixing coal cinder powder with water for water immersion digestion, and obtaining first filtrate and first residue after solid-liquid separation; mixing the first residue with an ammonium acetate solution for leaching treatment, and obtaining second filtrate and second residue after solid-liquid separation; mixing the second residue with an organic acid digestion solution containing citric acid and EDTA for organic acid digestion, and obtaining third filtrate and third residue after solid-liquid separation. The method can comprehensively and efficiently recover various different forms of alkali metal elements in coal cinder, and improve the recovery rate of alkali metal elements in coal cinder.

Description

Technical Field

[0001] This application relates to the field of resource utilization technology for solid waste from coal combustion, and in particular to methods and equipment for recovering alkali metal elements from coal slag. Background Technology

[0002] The Zhundong region of Xinjiang boasts abundant coal reserves and low mining costs. However, the high content of alkali metal oxides in the coal makes it prone to coking and fouling during boiler combustion, generating large amounts of ash containing alkali metals (such as sodium and potassium), which constitutes solid waste from coal-fired power plants. Normally, power plant ash can be converted into building materials, but the low level of infrastructure development in Xinjiang, especially in the Zhundong region, prevents this resource conversion, forcing power plants to resort to backfilling for solid waste disposal. This results in resource waste and environmental harm.

[0003] Alkali metal recovery and residue conversion from coal slag can not only reduce resource waste but also increase power plant revenue. However, most existing alkali metal recovery technologies have some shortcomings. For example, some technologies only target the recovery of a single form of alkali metal, failing to comprehensively handle alkali metals in different forms present in coal slag; the use of strong acids and alkalis for digestion is energy-intensive and causes severe equipment corrosion; furthermore, the alkali metal recovery rate of traditional methods is typically below 60%. Therefore, developing a highly efficient, energy-saving method and equipment for recovering alkali metal elements from coal slag with minimal equipment corrosion is of significant practical importance. Summary of the Invention

[0004] Based on this, this application provides a method and equipment for recovering alkali metal elements from coal slag, aiming to solve the technical problem that the existing technology is not comprehensive enough in recovering various forms of alkali metal elements from coal slag and has a low recovery rate.

[0005] To address the above problems, the technical solution proposed in this application is as follows:

[0006] According to a first aspect of this application, a method for recovering alkali metal elements from coal slag is provided, comprising the following steps:

[0007] The coal slag powder was mixed with water and subjected to water leaching digestion. After solid-liquid separation, the first filtrate and the first residue were obtained.

[0008] The first residue was mixed with ammonium acetate solution for leaching treatment, and after solid-liquid separation, the second filtrate and the second residue were obtained.

[0009] The second residue was mixed with an organic acid digestion solution containing citric acid and EDTA for organic acid digestion. After solid-liquid separation, a third filtrate and a third residue were obtained.

[0010] In some embodiments, the solid-liquid mass-volume ratio of coal slag powder to water in water leaching digestion is 1 kg: (4 L~8 L).

[0011] In some embodiments, the stirring rate during water immersion digestion is 50 rpm to 100 rpm.

[0012] In some implementations, the water immersion digestion time is 20 min to 40 min.

[0013] In some embodiments, the particle size of the coal slag powder is 0.1 mm to 2 mm.

[0014] In some embodiments, the slag powder is the ash produced after the combustion of coal containing alkali metal elements.

[0015] In some embodiments, the mass ratio of the first residue to the ammonium acetate solution in the leaching process is 1:(6~8).

[0016] In some embodiments, the stirring rate during the leaching process is 80 rpm to 150 rpm.

[0017] In some embodiments, the immersion treatment time is 30 min to 60 min.

[0018] In some embodiments, the concentration of ammonium acetate in the ammonium acetate solution is 0.6 mol / L to 1 mol / L.

[0019] In some embodiments, the mass ratio of the second residue to the organic acid digestion solution in the organic acid digestion is 1:(3~6).

[0020] In some embodiments, the stirring rate during organic acid digestion is 120 rpm to 180 rpm.

[0021] In some implementations, the digestion time of organic acids is 2 to 3 hours.

[0022] In some embodiments, the concentration of citric acid in the organic acid digestion solution is 0.15 mol / L to 0.2 mol / L, and the concentration of EDTA is 0.05 mol / L to 0.1 mol / L.

[0023] In some implementations, the recycling method further includes the following steps:

[0024] The first filtrate, the second filtrate, and the third filtrate are mixed to obtain a mixed filtrate;

[0025] The mixed filtrate was treated with ion exchange using a cation exchange column to obtain the effluent;

[0026] The effluent was evaporated and crystallized to obtain an alkali metal salt.

[0027] In some implementations, the recycling method further includes the following steps:

[0028] The third residue was mixed with high-calcium fly ash with a calcium mass fraction of 15%~25% and an alkaline activator to obtain a mixture;

[0029] The mixture was subjected to a depolymerization reaction in a saturated steam environment to obtain Na-A zeolite;

[0030] The Na-A zeolite was dried until the water content was below 5% by mass.

[0031] According to a second aspect of this application, a recovery device is provided for the method of recovering alkali metal elements from coal slag according to the first aspect of this application, including a staged digestion device, the staged digestion device comprising:

[0032] The water immersion digestion unit is used to mix coal slag powder with water for water immersion digestion and solid-liquid separation;

[0033] The ammonium acetate leaching unit is used to mix the first residue obtained after water leaching digestion and solid-liquid separation with an ammonium acetate solution for leaching treatment and solid-liquid separation.

[0034] The organic acid digestion unit is used to mix the second residue obtained after leaching and solid-liquid separation with an organic acid digestion solution containing citric acid and EDTA for organic acid digestion and solid-liquid separation.

[0035] In some embodiments, the recycling equipment further includes a targeted recycling device, which includes:

[0036] A cation exchange column is used to perform ion exchange treatment on the first filtrate obtained after water leaching digestion and solid-liquid separation, the second filtrate obtained after leaching treatment and solid-liquid separation, and the third filtrate obtained after organic acid digestion and solid-liquid separation.

[0037] An evaporation crystallization apparatus is used to evaporate and crystallize the effluent obtained from ion exchange treatment.

[0038] In some embodiments, the recycling equipment further includes a residue conversion device, which comprises:

[0039] A mixing tank is used to mix the third residue obtained after digestion and solid-liquid separation of organic acids with high-calcium fly ash and an alkaline activator to obtain a mixture.

[0040] A hydrothermal reactor is used to depolymerize mixtures to obtain Na-A zeolite.

[0041] A dryer is used to dry Na-A zeolite.

[0042] In some embodiments, the recycling equipment also includes a slag collection and crushing device and a waste heat recovery device;

[0043] The coal slag collection and crushing device includes a compression crushing device and a rolling crushing device; the compression crushing device is used to compress and crush the ash produced after coal combustion; the rolling crushing device is used to roll and crush the ash after compression crushing to obtain coal slag powder.

[0044] The waste heat recovery device is used to recover waste heat from coal slag powder, reducing the temperature of the coal slag powder to 300℃~500℃.

[0045] Compared with traditional technologies, this application has at least the following beneficial effects:

[0046] By subjecting coal slag powder to water leaching digestion, water-soluble alkali metal compounds in the coal slag can be dissolved into the first filtrate. The first residue is then mixed with ammonium acetate solution for leaching treatment. The ammonium acetate solution facilitates the exchange reaction between ion-exchangeable alkali metals in the coal slag and the ammonium acetate, allowing the ion-exchangeable alkali metals to be leached into the second filtrate. The second residue is then mixed with an organic acid digestion solution containing citric acid and EDTA for organic acid digestion. This organic acid digestion solution disrupts the silica-alumina encapsulation structure in the coal slag, releasing the alkali metals within this structure into the third filtrate. Through the above-mentioned water leaching digestion, ammonium acetate leaching treatment, and organic acid digestion, water-soluble alkali metal compounds, ion-exchangeable alkali metals, and alkali metals within the silica-alumina encapsulation structure in the coal slag can be dissolved into the first, second, and third filtrates, respectively, achieving comprehensive and efficient recovery of various forms of alkali metal elements from the coal slag and improving the recovery rate of alkali metal elements in the coal slag. Furthermore, this recovery method does not require strong acids or alkalis, resulting in minimal corrosion to equipment. Attached Figure Description

[0047] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0048] Figure 1 This is a schematic diagram of the structure of a recycling device according to one embodiment of this application.

[0049] Explanation of reference numerals in the attached figures:

[0050] 10. Recycling equipment; 11. Grading digestion device; 111. Water leaching digestion unit; 112. Ammonium acetate leaching unit; 113. Organic acid digestion unit; 12. Targeted recovery device; 13. Residue conversion device; 131. Mixing tank; 132. Hydrothermal reactor; 133. Dryer; 14. Cinder collection and crushing device; 141. Extrusion crushing device; 142. Rolling crushing device; 15. Waste heat recovery device; 20. Boiler. Detailed Implementation

[0051] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0052] Furthermore, 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 technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0053] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0055] Currently, technologies for recovering alkali metals from coal slag typically only target single-form alkali metals, failing to comprehensively address the diverse forms of alkali metals present in coal slag, resulting in low recovery rates. Furthermore, traditional technologies often employ strong acids and alkalis for digestion, leading to high energy consumption and severe equipment corrosion. Therefore, it is necessary to develop a highly efficient, energy-saving method for recovering alkali metals from coal slag that minimizes equipment corrosion.

[0056] One embodiment of this application provides a method for recovering alkali metal elements from coal slag, the method comprising the following steps S100 to S300:

[0057] Step S100: Mix coal slag powder with water for water leaching digestion, and obtain the first filtrate and the first residue after solid-liquid separation.

[0058] Step S200: The first residue is mixed with ammonium acetate solution for leaching treatment, and the second filtrate and the second residue are obtained after solid-liquid separation.

[0059] Step S300: The second residue is mixed with an organic acid digestion solution containing citric acid and EDTA for organic acid digestion. After solid-liquid separation, a third filtrate and a third residue are obtained.

[0060] The method for recovering alkali metal elements from coal slag described in this application first involves mixing coal slag powder with water for water leaching digestion, which dissolves water-soluble alkali metal compounds in the coal slag in the water. After solid-liquid separation, the water-soluble alkali metal compounds enter the first filtrate. Next, the first residue is mixed with ammonium acetate solution for leaching treatment. The ammonium acetate solution causes an exchange reaction between the ion-exchangeable alkali metals in the coal slag and the ammonium acetate, thereby leaching the ion-exchangeable alkali metals into the second filtrate. Then, the second residue is mixed with an organic acid digestion solution containing citric acid and EDTA for organic acid digestion. This organic acid digestion solution disrupts the silica-alumina encapsulation structure in the coal slag, thereby releasing the alkali metals within the silica-alumina encapsulation structure into the third filtrate.

[0061] By sequentially performing water leaching digestion, ammonium acetate solution leaching treatment, and organic acid digestion, water-soluble alkali metal compounds, ion-exchangeable alkali metals, and alkali metals encapsulated in silica-alumina structures in coal slag can be dissolved into the first, second, and third filtrates, respectively. This achieves comprehensive and efficient recovery of various forms of alkali metal elements from coal slag, improving the recovery rate of alkali metal elements in coal slag. Furthermore, this recovery method does not require the use of strong acids or alkalis, resulting in minimal corrosion to equipment.

[0062] In some embodiments, the solid-liquid mass-volume ratio of coal slag powder to water in water leaching digestion is 1 kg: (4 L~8 L). Controlling the solid-liquid mass-volume ratio of coal slag powder to water in water leaching digestion within the above range is beneficial for fully dissolving water-soluble alkali metal compounds in the coal slag powder in the water and fully recovering water-soluble alkali metal compounds from the coal slag.

[0063] It is understandable that the solid-liquid mass-volume ratio of coal slag powder to water can be 1kg:4L, 1kg:4.5L, 1kg:5L, 1kg:5.5L, 1kg:6L, 1kg:6.5L, 1kg:7L, 1kg:7.5L, 1kg:8L, or any ratio within the range formed by any two of the above ratios.

[0064] In some embodiments, the stirring rate during water immersion digestion is 50 rpm to 100 rpm. Controlling the stirring rate within this range during water immersion digestion is more conducive to the complete dissolution of water-soluble alkali metal compounds in the coal slag powder in the water. The stirring method can be mechanical stirring.

[0065] It is understandable that the stirring rate during the water immersion digestion process can be 50 rpm, 55 rpm, 58 rpm, 60 rpm, 65 rpm, 68 rpm, 70 rpm, 75 rpm, 78 rpm, 80 rpm, 85 rpm, 88 rpm, 90 rpm, 95 rpm, 98 rpm, 100 rpm, or any value within the range formed by any two of the above values.

[0066] In some embodiments, the water immersion digestion time is 20 min to 40 min. It is understood that the water immersion digestion time can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, 40 min, or any value within the range formed by any two of the above values.

[0067] In some embodiments, the particle size of the coal slag powder is 0.1 mm to 2 mm. Controlling the particle size of the coal slag powder within this range is beneficial for ensuring sufficient contact between the coal slag and water, ammonium acetate solution, organic acid digestion solution, etc., so as to fully dissolve various forms of alkali metals in the coal slag and improve the alkali metal recovery rate.

[0068] In some embodiments, the slag powder is the ash produced after the combustion of coal containing alkali metal elements. Specifically, coal containing alkali metal compounds is used as fuel, and the boiler ash produced after combustion is crushed to a specific particle size to obtain slag powder. In some specific examples, the coal containing alkali metal elements is coal mined in the eastern part of the Junggar Basin (Zhundong) in Xinjiang, which contains a relatively high amount of alkali metal compounds. The recovery method of this application can be applied to coal-fired boilers burning high-alkali coal from Zhundong, and has broad market application prospects.

[0069] In some embodiments, the slag powder is prepared by the following method: first, a crushing device is used to collect slag with larger particle size from a coal-fired boiler and to perform preliminary crushing on the slag; then, a rolling crushing device is used to further crush the preliminary crushed slag to a particle size range of 0.1 mm to 2 mm; the crushed slag is then sent to a waste heat recovery device to exchange heat between the high-temperature slag and low-temperature air, thereby reducing the slag temperature to 300°C to 500°C.

[0070] By reducing the slag temperature to 300℃~500℃ through the waste heat recovery device, on the one hand, the silicon-aluminum coating structure in the coal slag powder can be relaxed, which is more conducive to the leaching of alkali metal elements in the silicon-aluminum coating structure during the organic acid digestion step; on the other hand, the heated air can be transported to the boiler furnace for waste heat recovery and utilization.

[0071] It is understandable that the temperature of the coal slag powder is 300℃~500℃ before it is mixed with water for water leaching digestion. Since water leaching digestion of coal slag powder requires a specific temperature, maintaining this temperature through heating would require additional energy input. This application directly collects slag from the boiler, crushes it, and recovers waste heat to obtain coal slag powder at a specific temperature, reducing the additional energy input required for the subsequent digestion process and thus lowering recycling costs.

[0072] In some embodiments, the mass ratio of the first residue to the ammonium acetate solution in the leaching process is 1:(6~8). Controlling the mass ratio of the first residue to the ammonium acetate solution in the leaching process within the above range is beneficial for fully leaching the ion-exchangeable alkali metals in the first residue into the second filtrate, and for improving the recovery rate of alkali metals in the coal slag.

[0073] Among them, ion-exchangeable alkali metals in coal slag refer to alkali metal ions that bind to the negatively charged sites on the surface of ash slag in the form of free cations after coal combustion through electrostatic adsorption. Ion-exchangeable alkali metals do not enter the interior of silicate and aluminosilicate mineral lattices, and do not form stable oxide, sulfate, or chloride crystals. They only attach to the active adsorption sites of ash slag through reversible ion exchange.

[0074] It is understood that the mass ratio of the first residue to the ammonium acetate solution in the leaching process can be 1:6, 1:6.2, 1:6.5, 1:6.8, 1:7, 1:7.2, 1:7.5, 1:7.8, 1:8, or any ratio within the range formed by any two of the above ratios.

[0075] In some embodiments, the concentration of ammonium acetate in the ammonium acetate solution is 0.6 mol / L to 1 mol / L. Using an ammonium acetate solution of this concentration facilitates the complete leaching of ion-exchangeable alkali metals from the first residue into the second filtrate. The concentration of ammonium acetate in the ammonium acetate solution can be 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1 mol / L, or any ratio within the range formed by any two of the above values.

[0076] In some embodiments, the stirring rate during the leaching process is 80 rpm to 150 rpm. Controlling the stirring rate in the leaching step within this range is more conducive to ensuring that the ion-exchangeable alkali metals in the first residue are fully leached into the second filtrate. The stirring method can be mechanical stirring.

[0077] It is understood that the stirring rate of the leaching process can be 80 rpm, 85 rpm, 88 rpm, 90 rpm, 95 rpm, 98 rpm, 100 rpm, 105 rpm, 108 rpm, 110 rpm, 115 rpm, 118 rpm, 120 rpm, 125 rpm, 128 rpm, 130 rpm, 135 rpm, 138 rpm, 140 rpm, 145 rpm, 148 rpm, 150 rpm, or any value within the range formed by any two of the above values.

[0078] In some embodiments, the leaching treatment time is 30 min to 60 min. It is understood that the leaching treatment time can be 30 min, 32 min, 35 min, 38 min, 40 min, 42 min, 45 min, 48 min, 50 min, 52 min, 55 min, 58 min, 60 min, or any value within the range formed by any two of the above values.

[0079] In some embodiments, the mass ratio of the second residue to the organic acid digestion solution in the organic acid digestion is 1:(3~6). Performing organic acid digestion with the second residue and the organic acid digestion solution within the above-mentioned mass ratio range is beneficial for the organic acid digestion solution to fully disrupt the silica-alumina encapsulation structure in the second residue, allowing the alkali metals in the silica-alumina encapsulation structure to be fully released into the third filtrate, thereby improving the recovery rate of alkali metals in the coal slag.

[0080] The silica-alumina encapsulation structure in coal slag refers to the core-shell microstructure formed after coal combustion at high temperatures. This structure consists of an amorphous silica-alumina glass phase and crystalline aluminosilicates (mullite, feldspar, quartz) forming a continuous, dense outer shell that encapsulates alkali metal salts, elemental alkali metals, iron / calcium-containing minerals, and unburned carbon particles. Alkali metal elements within this silica-alumina encapsulation structure typically cannot be extracted through water leaching or ammonium acetate leaching.

[0081] It is understandable that the mass ratio of the second residue to the organic acid digestion solution can be 1:3, 1:3.2, 1:3.5, 1:3.8, 1:4, 1:4.2, 1:4.5, 1:4.8, 1:5, 1:5.2, 1:5.5, 1:5.8, 1:6, or any ratio within the range formed by any two of the above ratios.

[0082] In some embodiments, the concentration of citric acid in the organic acid digestion solution is 0.15 mol / L to 0.2 mol / L, and the concentration of EDTA is 0.05 mol / L to 0.1 mol / L. Controlling the concentrations of citric acid and EDTA in the organic acid digestion solution within these ranges is more conducive to the digestion of the silica-alumina encapsulated structure in the second residue, leaching out the alkali metal elements and improving the recovery rate of alkali metals.

[0083] The organic acid digestion solution can be prepared by adding 0.05 mol / L of disodium EDTA solution to a citric acid solution with a concentration of 0.1 mol / L to 0.3 mol / L in a certain proportion, and stirring at 60°C for 120 min to 180 min.

[0084] In some embodiments, the stirring rate in the organic acid digestion step is 120 rpm to 180 rpm. Controlling the stirring rate in the organic acid digestion step within this range is more conducive to the thorough digestion of the silicon-aluminum encapsulation structure in the second residue, allowing the alkali metal elements in the silicon-aluminum encapsulation structure to enter the third filtrate. The stirring method can be ultrasonic or mechanical stirring.

[0085] It is understandable that the stirring rate in the organic acid digestion step can be 120 rpm, 125 rpm, 128 rpm, 130 rpm, 135 rpm, 138 rpm, 140 rpm, 145 rpm, 148 rpm, 150 rpm, 155 rpm, 158 rpm, 160 rpm, 165 rpm, 168 rpm, 170 rpm, 175 rpm, 178 rpm, 180 rpm, or any value within the range formed by any two of the above values.

[0086] In some embodiments, the digestion time of the organic acid is 2h to 3h. It is understood that the digestion time of the organic acid can be 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, 3h, or any value within the range formed by any two of the above values.

[0087] In some embodiments, the recycling method further includes the following steps:

[0088] Step S400: Mix the first filtrate, the second filtrate and the third filtrate to obtain a mixed filtrate; perform ion exchange treatment on the mixed filtrate using a cation exchange column to obtain an effluent; evaporate and crystallize the effluent to obtain an alkali metal salt.

[0089] By mixing the first filtrate obtained after water leaching digestion and solid-liquid separation, the second filtrate obtained after ammonium acetate solution leaching and solid-liquid separation, and the third filtrate obtained after organic acid digestion and solid-liquid separation, and then subjecting the mixture to ion exchange treatment, alkali metal ions (Na+) in the filtrate can be removed. + K + Li + The alkali metal salts are enriched and filtered to remove interference from the detection of metal ions such as calcium, magnesium, and iron ions; then the effluent is evaporated and crystallized to obtain the recovered alkali metal salts.

[0090] In some specific examples, the cation exchange column uses NH4 + Type cation exchange column.

[0091] In some embodiments, the recycling method further includes the following steps:

[0092] Step S500: Mix the third residue with high-calcium fly ash with a calcium mass fraction of 15%~25% and an alkali activator to obtain a mixture; carry out the above mixture under a saturated steam environment for depolymerization reaction to obtain Na-A zeolite; dry the obtained Na-A zeolite to a water mass fraction of less than 5%.

[0093] By synergistically combining the third residue with high-calcium fly ash and an alkaline activator, the silica-alumina components in the third residue undergo depolymerization and rearrangement under saturated steam conditions, generating Na-A type zeolite with high specific surface area and ion exchange capacity. This process achieves high-value utilization of residual silica-alumina resources in the third residue, improving overall recovery efficiency while reducing waste emissions. The resulting Na-A zeolite, after drying, can be directly used in water treatment, catalysis, or gas adsorption, expanding the comprehensive utilization of coal slag.

[0094] Among them, Na-A zeolite refers to type A sodium zeolite, also known as 4A molecular sieve.

[0095] One embodiment of this application provides a recovery device 10 used in the method for recovering alkali metal elements from coal slag described above. Please refer to... Figure 1 The recycling equipment 10 includes a graded digestion device 11, which includes a water immersion digestion unit 111, an ammonium acetate leaching unit 112, and an organic acid digestion unit 113.

[0096] The water leaching digestion unit 111 is used to mix coal slag powder with water for water leaching digestion and then perform solid-liquid separation to leach water-soluble alkali metal compounds from the coal slag powder; the ammonium acetate leaching unit 112 is used to mix the first residue obtained after water leaching digestion and solid-liquid separation with ammonium acetate solution for leaching treatment and then perform solid-liquid separation to leach ion-exchangeable alkali metals from the first residue; the organic acid digestion unit 113 is used to mix the second residue obtained after leaching treatment and solid-liquid separation with an organic acid digestion solution containing citric acid and EDTA for organic acid digestion and then perform solid-liquid separation to release alkali metals in the silicon-aluminum encapsulated structure of the second residue.

[0097] By employing the aforementioned water leaching digestion unit 111, ammonium acetate leaching unit 112, and organic acid digestion unit 113 to form a staged digestion device 11, water-soluble alkali metal compounds, ion-exchangeable alkali metals, and alkali metals encapsulated in silica-alumina structures in coal slag powder can be leached out separately. This achieves comprehensive and efficient recovery of various forms of alkali metal elements from coal slag, improving the recovery rate of alkali metal elements in coal slag. Furthermore, this recovery equipment 10 has a simple structure, does not require strong acids or alkalis, and exhibits minimal corrosion.

[0098] Please see Figure 1 In some embodiments, the recovery device 10 further includes a targeted recovery device 12, which includes a cation exchange column and an evaporation crystallization device.

[0099] The cation exchange column is used to perform ion exchange treatment on the first filtrate obtained after water leaching and solid-liquid separation in the water leaching digestion unit 111, the second filtrate obtained after leaching and solid-liquid separation in the ammonium acetate leaching unit 112, and the third filtrate obtained after organic acid digestion and solid-liquid separation in the organic acid digestion unit 113, to obtain an effluent mainly containing alkali metal salts; the evaporation crystallization device is used to evaporate and crystallize the effluent obtained from the ion exchange treatment to obtain alkali metal salts.

[0100] In some specific examples, the cation exchange column is NH4. + Type cation exchange column.

[0101] Please see Figure 1In some embodiments, the recycling device 10 further includes a residue conversion device 13, which includes a mixing tank 131, a hydrothermal reactor 132, and a dryer 133.

[0102] The mixing tank 131 is used to mix the third residue obtained after digestion and solid-liquid separation of organic acid with high-calcium fly ash and alkali activator to obtain a mixture; the hydrothermal reactor 132 is used to carry out the above mixture through a depolymerization reaction to obtain Na-A zeolite; the dryer 133 is used to dry the obtained Na-A zeolite so that the water content of Na-A zeolite is below 5%.

[0103] Please see Figure 1 In some embodiments, the recycling device 10 also includes a slag collection and crushing device 14 and a waste heat recovery device 15.

[0104] The slag collection and crushing device 14 includes a compression crushing device 141 and a rolling crushing device 142. The compression crushing device 141 is used to initially compress and crush the ash produced by the combustion of the boiler 20. The rolling crushing device 142 is used to further roll and crush the compressed ash to obtain slag powder of the desired particle size. The ash is a large amount of alkali metal-rich slag produced by the boiler 20 during the combustion of high-alkali coal. The waste heat recovery device 15 is used to recover waste heat from the slag powder and reduce the temperature of the slag powder to 300℃~500℃. The waste heat recovery device 15 can be connected to the boiler 20 to send the recovered waste heat into the furnace of the boiler 20 for utilization.

[0105] Please see Figure 1 In some specific examples, the feed end of the extrusion crusher 141 is connected to the slag discharge port of the boiler 20, and the feed end of the rolling crusher 142 is connected to the discharge end of the extrusion crusher 141; the discharge end of the rolling crusher 142 is connected to the feed end of the waste heat recovery device 15, and the gas discharge end of the waste heat recovery device 15 is connected to the furnace of the boiler 20; the coal slag powder processed by the waste heat recovery device 15 sequentially enters the water leaching digestion unit 111, the ammonium acetate leaching unit 112, and the organic acid digestion unit. Unit 113 performs the processing; the third residue obtained after solid-liquid separation after digestion in the organic acid digestion unit 113 enters the mixing tank 131, the discharge end of the mixing tank 131 is connected to the feed end of the hydrothermal reactor 132, and the discharge end of the hydrothermal reactor 132 is connected to the feed end of the dryer 133; the filtrate obtained after solid-liquid separation in the water leaching digestion unit 111, the ammonium acetate leaching unit 112 and the organic acid digestion unit 113 enters the targeted recovery device 12, and after ion exchange and evaporation crystallization, alkali metal salts are obtained.

[0106] The present application will be further described below with reference to specific embodiments and comparative examples, but should not be construed as limiting the scope of protection of the present application.

[0107] Example 1:

[0108] (1) Crushing of coal slag

[0109] The slag produced by the combustion of coal in the boiler is collected and crushed in an extrusion crushing device to crush the larger particles in the slag. Then the slag is sent to a rolling crushing device for further crushing to obtain coal slag powder with a particle size of 0.1mm to 2mm.

[0110] (2) Waste heat recovery

[0111] The aforementioned coal slag powder is sent to a waste heat recovery device, where the high-temperature coal slag powder is exchanged with low-temperature air to reduce the temperature of the coal slag powder to 300℃~500℃, thus loosening the silicon-aluminum coating structure in the coal slag powder. The air after heat exchange is then transported to the furnace of the boiler for use.

[0112] (3) Staged digestion

[0113] (3.1) The coal slag powder recovered from the waste heat in step (2) is transported to the water immersion digestion unit and mixed with room temperature water at a solid-liquid mass-volume ratio of 1 kg: 4 L. Mechanical stirring is used, the stirring speed is set to 50 rpm, and the water immersion treatment is carried out for 40 min. The solution and solid residue are separated by filtration to obtain the first filtrate and the first residue.

[0114] (3.2) The first residue described above is fed into the ammonium acetate leaching unit. The mass ratio of the first residue to the ammonium acetate solution is controlled at 1:6. The concentration of the ammonium acetate solution used is 0.6 mol / L. Mechanical stirring is used, and the stirring speed is set to 80 rpm. The leaching process is carried out for 60 min. The solution and solid residue are separated by filtration to obtain the second filtrate and the second residue.

[0115] (3.3) The second residue described above is transferred to the organic acid digestion unit. The mass ratio of the second residue to the organic acid digestion solution is controlled at 1:3. The concentration of citric acid in the organic acid digestion solution is 0.15 mol / L and the concentration of EDTA is 0.05 mol / L. The organic acid digestion is carried out for 3 hours by using ultrasonic and mechanical stirring at a stirring rate of 120 rpm. The solution and solid residue are separated by filtration to obtain the third filtrate and the third residue.

[0116] (4) Residue conversion

[0117] The third residue obtained in step (3) is sent to a mixing tank and mixed with high-calcium fly ash (calcium mass fraction 15%) and alkali activator (6 mol / L NaOH solution) at a mass ratio of 1:0.4:0.1 to obtain a mixture. The mixture is sent to a hydrothermal reactor and subjected to a depolymerization reaction for 180 min under saturated steam at a steam pressure of 1 MPa to obtain Na-A zeolite. The Na-A zeolite is then sent to a dryer for drying to reduce the water content of the Na-A zeolite to below 5%.

[0118] (5) Filtrate treatment

[0119] The first, second, and third filtrates obtained in step (3) are mixed and sent to the targeted recovery device. The mixed filtrate is first passed through NH4. + Ion exchange is performed using a cation exchange column. The effluent after ion exchange is collected and sent to an evaporator crystallizer for evaporation and crystallization to obtain alkali metal salts.

[0120] Example 2:

[0121] This embodiment is basically the same as embodiment 1, except that: in step (3.1), the solid-liquid mass-volume ratio of coal slag powder and room temperature water is 1kg:8L, and the stirring speed is 100rpm.

[0122] Example 3:

[0123] This embodiment is basically the same as embodiment 1, except that: in step (3.2), the mass ratio of the first residue to the ammonium acetate solution is 1:8, and the stirring speed is 150 rpm.

[0124] Example 4:

[0125] This embodiment is basically the same as embodiment 1, except that: in step (3.3), the mass ratio of the second residue to the organic acid digestion solution is 1:6, and the stirring rate is 180 rpm.

[0126] Comparative Example 1:

[0127] (1) Crushing of coal slag

[0128] The slag produced by the combustion of coal in the boiler is collected and crushed in an extrusion crushing device to crush the larger particles in the slag. Then the slag is sent to a rolling crushing device for further crushing to obtain coal slag powder with a particle size of 0.1mm to 2mm.

[0129] (2) Waste heat recovery

[0130] The aforementioned coal slag powder is sent to a waste heat recovery device, where the high-temperature coal slag powder is exchanged with low-temperature air to reduce the temperature of the coal slag powder to 300℃~500℃, thus loosening the silicon-aluminum coating structure in the coal slag powder. The air after heat exchange is then transported to the furnace of the boiler for use.

[0131] (3) Water immersion digestion

[0132] The coal slag powder recovered from waste heat in step (2) was mixed with room temperature water at a solid-liquid mass-to-volume ratio of 1 kg:4 L. The mixture was mechanically stirred at a stirring speed of 50 rpm and then immersed in water for 40 min. The solution and solid residue were separated by filtration to obtain filtrate and residue.

[0133] (4) Filtrate treatment

[0134] The filtrate obtained in step (3) is passed through NH4 + Ion exchange is performed using a cation exchange column. The effluent obtained from the ion exchange is collected and sent to an evaporator crystallizer for evaporation and crystallization to obtain alkali metal salts.

[0135] Alkali metal element recovery rate test method:

[0136] Alkali metal element recovery rate R = (CF1 + CF2 + CF3) / C0 × 100%

[0137] CF1: Alkali metals in water leaching filtrate;

[0138] CF2: Alkali metal in ammonium acetate filtrate;

[0139] CF3: Citric acid + EDTA filtrate alkali metal;

[0140] C0: Alkali metals are completely digested in the raw slag.

[0141] The digestion process conditions and alkali metal recovery rates of the recovery methods in the above embodiments and comparative examples are shown in Table 1.

[0142] Table 1

[0143]

[0144] Note: In Table 1, " / " indicates that it does not exist.

[0145] As shown in Table 1, the recovery methods of each embodiment of this application have high alkali metal element recovery rates, all exceeding 65%. In contrast, the recovery rate of alkali metal elements in Comparative Example 1, which uses a single water immersion treatment, is significantly lower.

[0146] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0147] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for recovering alkali metal elements from coal slag, characterized in that, Includes the following steps: The coal slag powder was mixed with water and subjected to water leaching digestion. After solid-liquid separation, the first filtrate and the first residue were obtained. The first residue was mixed with ammonium acetate solution for leaching treatment, and after solid-liquid separation, a second filtrate and a second residue were obtained. The second residue was mixed with an organic acid digestion solution containing citric acid and EDTA for organic acid digestion. After solid-liquid separation, a third filtrate and a third residue were obtained.

2. The method for recovering alkali metal elements from coal slag according to claim 1, characterized in that, The recycling method satisfies one or more of the following: (1) The solid-liquid mass-volume ratio of the coal slag powder to water in the water immersion digestion is 1 kg: (4 L~8 L). (2) The stirring rate during the water immersion digestion is 50 rpm to 100 rpm; (3) The water immersion digestion time is 20 min to 40 min; (4) The particle size of the coal slag powder is 0.1 mm to 2 mm; (5) The coal slag powder is the ash produced after the combustion of coal containing alkali metal elements.

3. The method for recovering alkali metal elements from coal slag according to claim 1, characterized in that, The recycling method satisfies one or more of the following: (1) The mass ratio of the first residue to the ammonium acetate solution in the leaching process is 1:(6~8). (2) The stirring rate during the leaching process is 80 rpm to 150 rpm; (3) The leaching treatment time is 30 min to 60 min; (4) The concentration of ammonium acetate in the ammonium acetate solution is 0.6 mol / L to 1 mol / L.

4. The method for recovering alkali metal elements from coal slag according to claim 1, characterized in that, The recycling method satisfies one or more of the following: (1) The mass ratio of the second residue to the organic acid digestion solution in the organic acid digestion is 1:(3~6). (2) The stirring rate during the digestion of the organic acid is 120 rpm to 180 rpm; (3) The digestion time of the organic acid is 2h~3h; (4) The concentration of citric acid in the organic acid digestion solution is 0.15 mol / L to 0.2 mol / L, and the concentration of EDTA is 0.05 mol / L to 0.1 mol / L.

5. The method for recovering alkali metal elements from coal slag according to any one of claims 1 to 4, characterized in that, The recycling method further includes the following steps: The first filtrate, the second filtrate, and the third filtrate are mixed to obtain a mixed filtrate; The mixed filtrate was subjected to ion exchange treatment using a cation exchange column to obtain the effluent. The effluent was evaporated and crystallized to obtain an alkali metal salt.

6. The method for recovering alkali metal elements from coal slag according to any one of claims 1 to 4, characterized in that, The recycling method further includes the following steps: The third residue is mixed with high-calcium fly ash with a calcium mass fraction of 15%~25% and an alkaline activator to obtain a mixture; The mixture was subjected to a depolymerization reaction in a saturated steam environment to obtain Na-A zeolite; The Na-A zeolite is dried until the water content is below 5% by mass.

7. A recovery device used in a method for recovering alkali metal elements from coal slag as described in any one of claims 1 to 6, characterized in that, The device includes a staged digestion apparatus, which comprises: The water immersion digestion unit is used to mix coal slag powder with water for water immersion digestion and solid-liquid separation; The ammonium acetate leaching unit is used to mix the first residue obtained after water leaching digestion and solid-liquid separation with an ammonium acetate solution for leaching treatment and solid-liquid separation. The organic acid digestion unit is used to mix the second residue obtained after leaching and solid-liquid separation with an organic acid digestion solution containing citric acid and EDTA for organic acid digestion and solid-liquid separation.

8. The recycling equipment according to claim 7, characterized in that, The recycling equipment further includes a targeted recycling device, which comprises: A cation exchange column is used to perform ion exchange treatment on the first filtrate obtained after water leaching digestion and solid-liquid separation, the second filtrate obtained after leaching treatment and solid-liquid separation, and the third filtrate obtained after organic acid digestion and solid-liquid separation. An evaporation crystallization apparatus is used to evaporate and crystallize the effluent obtained from ion exchange treatment.

9. The recycling equipment according to claim 7, characterized in that, The recycling equipment also includes a residue conversion device, which comprises: A mixing tank is used to mix the third residue obtained after digestion and solid-liquid separation of organic acids with high-calcium fly ash and an alkaline activator to obtain a mixture. A hydrothermal reactor is used to depolymerize the mixture to obtain Na-A zeolite; A dryer is used to dry the Na-A zeolite.

10. The recycling equipment according to any one of claims 7 to 9, characterized in that, The recycling equipment also includes a slag collection and crushing device and a waste heat recovery device; The coal slag collection and crushing device includes an extrusion crushing device and a rolling crushing device; the extrusion crushing device is used to extrude and crush the ash produced after coal combustion; the rolling crushing device is used to roll and crush the extruded and crushed ash to obtain coal slag powder. The waste heat recovery device is used to recover waste heat from the coal slag powder, thereby reducing the temperature of the coal slag powder to 300℃~500℃.

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