Methods for separating potassium and sodium from fly ash

Abstract

This invention belongs to the field of fly ash treatment technology, specifically disclosing a method for separating potassium and sodium from fly ash, including the following steps: adjusting the acid concentration in the fly ash washing solution to 40-65% and the temperature to 40-65℃, adding a sodium precipitating agent and maintaining the reaction temperature, and filtering to obtain sodium salt and potassium-containing waste liquid. This invention utilizes precipitation to recover sodium ions from fly ash washing solution. After filtration, sodium salt precipitate and potassium-containing waste liquid are obtained. During this process, the reaction is controlled under acidic conditions to prevent potassium ion precipitation. At 40-60℃, the sodium precipitating agent reacts with sodium ions to obtain sodium salt precipitate with large crystals, which allows for more convenient and thorough filtration, resulting in better separation of potassium and sodium ions in the fly ash washing solution. The sodium salt precipitate is further washed with a displacement agent to replace the potassium ions attached to the surface of the sodium salt precipitate with sodium, improving the purity of the sodium salt product. Finally, multiple water washings are performed to reduce the acidity of the sodium salt precipitate, resulting in a sodium salt product with stable quality.

Description

Technical Field

[0001] This invention belongs to the field of fly ash treatment technology, specifically relating to a method for separating potassium and sodium from fly ash. Background Technology

[0002] Fly ash primarily originates from the precipitates collected by flue gas purification systems during waste incineration and from the bottom ash settling at the base of flues and chimneys. Its chemical composition depends on fuel type, combustion conditions, and ash collection methods. Common components include chlorides, sodium salts, potassium salts, calcium salts, and carbonates. Landfilling is a common method for fly ash disposal, but fly ash contains high concentrations of heavy metals, as well as persistent organic pollutants such as dioxins and furans. These substances are highly hazardous and can enter the environment through landfill, threatening ecosystems and human health. Furthermore, fly ash landfill not only occupies significant land resources but also fails to fundamentally solve the fly ash pollution problem. Therefore, some regions have explicitly restricted fly ash landfilling, shifting towards resource utilization. Research indicates that the potassium and sodium salt content in incinerated fly ash can reach over 20%, and recovering these salts is beneficial for resource recycling.

[0003] Potassium and sodium both belong to Group IA of the periodic table, and their atoms each have only one electron in their outermost shell. Therefore, their chemical properties are similar. This leads to the current technology where potassium and sodium recovered from fly ash are often separated together in combination, requiring further separation to obtain potassium and sodium separately. This process is cumbersome and costly. Evaporation and concentration is a commonly used method, but its quality is unstable due to the influence of other pollutants in the fly ash. Furthermore, potassium and sodium salts in fly ash have different solubilities and concentrations, requiring potassium or sodium supplementation during evaporation and concentration to balance them. This results in high processing costs, poor process continuity, and poor product stability.

[0004] Based on this, the present invention is proposed. Summary of the Invention

[0005] Based on the above reasons, the purpose of this invention is to provide a method for separating potassium and sodium from fly ash. The method uses precipitation to separate sodium ions, and controls the reaction conditions to make sodium precipitate while potassium does not precipitate, thereby continuously and stably separating potassium and sodium from fly ash to obtain a sodium product with stable quality.

[0006] This invention is achieved through the following technical solution:

[0007] A method for separating potassium and sodium from fly ash includes the following steps: adjusting the acid concentration in the fly ash washing solution to 40-65% and the temperature to 40-65℃, adding a sodium precipitating agent to maintain the reaction temperature, and filtering to obtain sodium salt precipitate and potassium-containing waste liquid.

[0008] Furthermore, the fly ash washing solution is obtained by washing with fly ash water and then filtering.

[0009] Preferably, the sodium precipitation agent is one or more of ammonium dihydrogen phosphate, fluorosilicic acid, potassium hexafluorophosphate, and organic sulfonic acid substances.

[0010] Furthermore, the sodium salt precipitate is washed with a displacement agent and then washed with water to obtain the sodium salt product.

[0011] Preferably, the displacement agent is a saturated sodium sulfate solution and an acid solution with a concentration of 40-60%.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] This invention utilizes a precipitation method to recover sodium ions from fly ash washing liquid. After filtration, sodium salt precipitate and potassium-containing waste liquid are obtained. The reaction is controlled under acidic conditions to prevent potassium ion precipitation. At 40-60℃, the sodium precipitating agent reacts with sodium ions to produce a sodium salt precipitate with large crystals, allowing for more convenient and thorough filtration and better separation of potassium and sodium ions in the fly ash washing liquid. The sodium salt precipitate is further washed with a displacement agent to replace the potassium ions adhering to its surface with sodium, improving the purity of the sodium salt product. Finally, multiple water washes reduce the acidity of the sodium salt precipitate, resulting in a stable sodium salt product. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0015] It should be noted that in existing technologies, fly ash is typically recovered and reused as a mixed potassium and sodium salt. Further evaporation and concentration are required to obtain pure potassium and sodium salts, a complex and discontinuous process. Due to the difficulty of separation, the quality of the resulting product is also unstable. Based on this, the present invention discloses a method for separating potassium and sodium from fly ash without evaporation and concentration. By controlling the reaction conditions during the sodium ion precipitation reaction, potassium precipitation is prevented, thereby obtaining a stable sodium salt precipitate. The potassium ions remain in the filtrate and can be separated using commonly used potassium removal methods in the art.

[0016] The embodiments of the present invention provide a method for separating potassium and sodium from fly ash, comprising the following steps: adjusting the acid concentration in the fly ash washing solution to 40-65% and the temperature to 40-65℃, adding a sodium precipitating agent to maintain the reaction temperature, and filtering to obtain sodium salt precipitate and potassium-containing waste liquid.

[0017] In this embodiment, fly ash contains a large amount of alkaline substances, and its washing solution is usually alkaline. The present invention first adjusts the acid concentration of the fly ash washing solution because potassium ions have high solubility in acidic environments and are difficult to precipitate. When the acid concentration is 40-65%, the environment of the washing solution is adjusted to be acidic. By adjusting the temperature, the sodium salt precipitate obtained by the sodium precipitation agent reaction is made to have a large crystal form, which is easy to filter. This avoids poor filtration effect due to small crystal form, which would prevent effective separation of sodium ions. Finally, the sodium ions in the fly ash are removed in the form of precipitation, while the potassium ions remain in the solution, thus achieving the purpose of separating potassium and sodium in fly ash.

[0018] It is understood that the method for adjusting the acidity of the washing solution described in this invention is a method commonly used by those skilled in the art, such as directly adding an acid solution or introducing an acidic gas into the washing solution.

[0019] In some specific embodiments, the fly ash washing solution is obtained by filtration after washing with fly ash. The fly ash washing solution of the present invention can be obtained directly by mixing fly ash with water in any proportion and filtering. The mixing proportion can be adjusted according to the type of fly ash. Alternatively, it can be a pre-treated fly ash treatment solution containing potassium and sodium ions.

[0020] In some preferred embodiments, the sodium precipitating agent is one or more of ammonium dihydrogen phosphate, fluorosilicic acid, potassium hexafluorophosphate, and organic sulfonic acids. This invention selects a sodium precipitating agent that can fully react with sodium ions under acidic conditions to precipitate them, continuously precipitating sodium ions during the reaction process to achieve the purpose of sodium removal.

[0021] In some specific embodiments, the sodium salt precipitate is washed with a displacement agent and then washed with water to obtain the sodium salt product. After filtration, a small amount of impurities inevitably adhere to the surface of the sodium salt precipitate. Therefore, this invention washes the obtained sodium salt precipitate with a displacement agent to replace the potassium ions adhering to the surface of the sodium salt precipitate with sodium, thereby improving the purity of the sodium salt product. Finally, it is washed multiple times with water to reduce the acidity of the sodium salt precipitate, resulting in a sodium salt product with stable quality.

[0022] In some preferred embodiments, the displacement agent is a saturated sodium sulfate solution and an acid solution with a concentration of 40-60%. During washing, a saturated sodium sulfate solution is used first, where the sulfate ion concentration is high, making the displacement reaction more likely. Then, a 40-60% acid solution is used, which can react with most metal ions, improving the washing effect. The acid solution is a common acid solution in the art.

[0023] The following will disclose specific embodiments for implementing this application, along with corresponding comparative examples to demonstrate the relevant technical effects of this application.

[0024] Example 1

[0025] Fly ash was mixed with 3 times its volume of water and washed. The resulting washing liquid was filtered and poured into a reaction tank. Concentrated sulfuric acid was added to adjust the acid concentration to 50%. The mixture was heated until the temperature in the reaction tank reached 50°C. Fluorosilicic acid, a sodium precipitant, was added and stirred and kept at the temperature for 60 minutes. The potassium-containing waste liquid and sodium fluorosilicate precipitate were separated by filtration. The sodium fluorosilicate precipitate was first washed with a saturated sodium sulfate solution, then washed with a 50% sulfuric acid solution, and finally rinsed with running water to obtain the sodium fluorosilicate product.

[0026] In Example 1, fluorosilicate ions can combine with sodium ions in fly ash to form a sparingly soluble sodium fluorosilicate precipitate, thereby removing sodium ions from the fly ash system. Acidic conditions can prevent side reactions such as hydrolysis of sodium fluorosilicate, ensuring the smooth progress of the precipitation reaction. Controlling the reaction temperature is beneficial for forming a sodium fluorosilicate precipitate with larger crystals.

[0027] Example 2

[0028] Fly ash was mixed with 4 times its volume of water and washed. The resulting washing liquid was filtered and poured into a reaction tank. Concentrated nitric acid was added to adjust the acid concentration to 40%. The mixture was heated until the temperature in the reaction tank reached 60°C. Ammonium dihydrogen phosphate, a sodium precipitant, was added and stirred and kept at the temperature for 60 minutes. The potassium-containing waste liquid and disodium hydrogen phosphate precipitate were separated by filtration. The disodium hydrogen phosphate precipitate was first washed with a saturated sodium sulfate solution, then washed with a 60% phosphoric acid solution, and finally rinsed with running water to obtain the disodium hydrogen phosphate product.

[0029] Under acidic and heated conditions, phosphate ions in ammonium dihydrogen phosphate can react with sodium ions in fly ash to form sodium phosphate precipitate. In Example 2, disodium hydrogen phosphate precipitate was formed. As the reaction proceeds, sodium ions are continuously precipitated, achieving the purpose of desodiumification. Temperature control during the reaction can accelerate the reaction rate, making the precipitation reaction more complete and resulting in larger crystals. An acidic environment helps to inhibit the hydrolysis of phosphate ions, ensuring the effective reaction between phosphate ions and sodium ions.

[0030] Example 3

[0031] Fly ash was mixed with 5 times its volume of water and washed. The resulting washing liquid was filtered and poured into a reaction tank. Concentrated sulfuric acid was added to adjust the acid concentration to 60%. The mixture was heated until the temperature in the reaction tank reached 40°C. Potassium hexafluorophosphate, a sodium precipitant, was added and stirred and kept at the temperature for 60 minutes. The potassium-containing waste liquid and sodium hexafluorophosphate precipitate were separated by filtration. The sodium hexafluorophosphate precipitate was first washed with a saturated sodium sulfate solution, then washed with a 40% hydrochloric acid solution, and finally rinsed with running water to obtain the sodium hexafluorophosphate product.

[0032] In Example 3, under acidic heating conditions, fluorophosphate ions are provided, which combine with sodium ions in fly ash to form sodium hexafluorophosphate precipitate. Because sodium hexafluorophosphate has relatively low solubility, it can precipitate from the solution under acidic and heated conditions, thereby achieving the removal of sodium from the fly ash. The acidic environment inhibits the hydrolysis of fluorophosphate ions, while heating accelerates the reaction rate, promoting a more complete precipitation reaction.

[0033] Example 4

[0034] Fly ash was mixed with 3 times its volume of water and washed. The resulting washing liquid was filtered and poured into a reaction tank. Concentrated sulfuric acid was added to adjust the acid concentration to 50%. The mixture was heated until the temperature in the reaction tank reached 50°C. Toluenesulfonic acid, a sodium precipitant, was added and stirred and kept at the temperature for 50 minutes. The potassium-containing waste liquid and sodium sulfonate precipitate were separated by filtration. The sodium sulfonate precipitate was first washed with a saturated sodium sulfate solution, then washed with a 60% nitric acid solution, and finally rinsed with running water to obtain the sodium sulfonate product.

[0035] In Example 4, under acidic and heated conditions, the sulfonic acid groups in toluenesulfonic acid can undergo an ion exchange reaction with sodium ions in fly ash to form sodium sulfonate precipitate. Heating enhances the reactivity of the sulfonic acid groups with sodium ions, improving the sodium removal efficiency, while the acidic environment helps maintain the stability of its molecular structure and reactivity.

[0036] Test case

[0037] This experimental example will determine the sodium recovery rate of the sodium salt products obtained in Examples 1-4. The sodium recovery rate is calculated as follows: (Sodium content in the sodium salt product × Sodium salt product mass) / (Sodium content in fly ash × Fly ash mass) × 100%. The results are shown in Table 1. As can be seen from Table 1, the method of this invention can achieve a sodium recovery rate of over 90% in fly ash, efficiently recovering sodium from fly ash. The process steps are simple and continuous, and the final sodium salt product has high stability.

[0038] Table 1. Detection of sodium recovery rate

[0039] .

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for separating potassium from sodium in fly ash, characterized in that, The method comprises the following steps: mixing fly ash with 3 times of water for water washing, filtering the obtained water washing liquid, pouring the water washing liquid into a reaction tank, adding concentrated sulfuric acid, adjusting the acid concentration to 50%, heating to a temperature of 50 DEG C in the reaction tank, adding a sodium precipitating agent fluorosilicic acid, stirring and keeping warm for 60 min, and filtering and separating potassium-containing waste liquid and sodium fluorosilicate precipitate; the sodium fluorosilicate precipitate is washed with saturated sodium sulfate solution first, then washed with a 50% sulfuric acid solution, and then washed with flowing water to obtain a sodium fluorosilicate product.