Method for separating potassium and sodium in fly ash

Abstract

The invention belongs to the technical field of fly ash treatment, and particularly discloses a method for separating potassium and sodium in fly ash, which comprises the following steps: adjusting the acid concentration of fly ash washing liquid to be 40-65% and the temperature to be 40-65 DEG C, adding a sodium precipitation agent for heat preservation reaction, and filtering to obtain sodium salt and potassium-containing waste liquid. Sodium ions in the fly ash water washing liquid are recycled through a precipitation method, sodium salt precipitates and potassium-containing waste liquid are obtained after filtering, the reaction is controlled under the acidic condition in the process, potassium ion precipitation is prevented, the sodium salt precipitates with large crystal forms are obtained through the reaction of a sodium precipitation agent and the sodium ions at the temperature of 40-60 DEG C, filtering can be more convenient and thorough, and the potassium-containing waste liquid can be recycled. And the effect of separating potassium ions and sodium ions in the fly ash washing liquid is better. Further washing the sodium salt precipitate by using a displacer, replacing potassium ions attached to the surface of the sodium salt precipitate with sodium, improving the purity of the sodium salt product, and finally washing for multiple times to reduce the acidity of the sodium salt precipitate, thereby obtaining the sodium salt product with stable quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of fly ash treatment, and particularly relates to a method for separating potassium and sodium in fly ash. Background Art

[0002] The sources of fly ash are mainly the captives of the flue gas purification system generated during the garbage incineration process and the bottom ash settled at the bottom of the flue and chimney. Its chemical composition is related to the fuel type, combustion conditions and ash collection method. Common components include chlorides, sodium salts, potassium salts, calcium salts, carbonates, etc. Landfill is a common method for fly ash treatment, but fly ash contains high concentrations of heavy metals and persistent organic pollutants such as dioxins and furans. These substances are highly harmful and may enter the environment through landfill, posing a threat to the ecosystem and human health. At the same time, fly ash landfill not only occupies a large amount of land resources but also cannot fundamentally solve the pollution problem of fly ash. Therefore, some regions have clearly restricted the burial of fly ash and shifted the fly ash treatment towards resource utilization. Research results show that the potassium and sodium salt content in incinerated fly ash is as high as more than 20%. Recycling potassium and sodium salts in fly ash is conducive to the recycling of resources.

[0003] Both potassium and sodium belong to Group IA elements in the periodic table. They both have only one electron in their outermost atomic layer, so their chemical properties are similar. As a result, in the prior art, potassium and sodium recovered from fly ash are mostly separated together in a combined form and then further separated to obtain potassium and sodium, with a cumbersome process and high cost. The evaporation concentration method is a commonly used method, but it is affected by the content of other pollutants in fly ash, resulting in unstable quality of the separated potassium salt and sodium salt. Moreover, the solubility and concentration of potassium salt and sodium salt in fly ash are different. During the evaporation concentration process, it is necessary to balance the two by adding potassium or sodium, resulting in high treatment costs, poor process continuity and poor product stability.

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

[0005] For the above reasons, the purpose of the present invention is to provide a method for separating potassium and sodium in fly ash, which uses the precipitation method to separate sodium ions, controls the reaction conditions to precipitate sodium while potassium does not precipitate, and then continuously and stably separates potassium and sodium in fly ash to obtain a sodium product with stable quality.

[0006] The present invention is achieved by the following technical solutions: A method for separating potassium and sodium in 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°C, adding a sodium precipitation agent and carrying out a heat preservation reaction, and filtering to obtain a sodium salt precipitate and a potassium-containing waste liquid.

[0007] Further, the fly ash washing solution is obtained by filtering after washing the fly ash.

[0008] Preferably, the sodium precipitant is one or more of ammonium dihydrogen phosphate, fluosilicic acid, potassium hexafluorophosphate, and organic sulfonic acid substances.

[0009] Further, after washing the sodium salt precipitate with a displacement agent, it is then washed with water to obtain a sodium salt product.

[0010] Preferably, the displacement agent is a saturated sodium sulfate solution and an acid solution with a concentration of 40 - 60%.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses a precipitation method to recover sodium ions from the fly ash washing liquid. After filtration, a sodium salt precipitate and a potassium-containing waste liquid are obtained. In this process, the reaction is controlled under acidic conditions to prevent potassium ions from precipitating. At 40 - 60 °C, the sodium precipitant reacts with sodium ions to obtain a sodium salt precipitate with large crystal forms, which can be filtered more conveniently and thoroughly, and the separation effect of potassium ions and sodium ions in the fly ash washing liquid is better. Further, the sodium salt precipitate is 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, it is washed with water multiple times to reduce the acidity of the sodium salt precipitate, obtaining a sodium salt product with stable quality. Specific Embodiments

[0012] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that these descriptions are exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention. For those not specified in the embodiments, they are carried out under conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0013] It should be noted that in the prior art, fly ash is usually recycled in the form of a potassium-sodium mixed salt, and pure potassium salt and sodium salt can only be obtained through further evaporation and concentration separation. The process is complex and discontinuous. Due to the difficulty of separation, the quality of the obtained products is also unstable. Based on this, the present invention discloses a method for separating potassium and sodium in fly ash without evaporation and concentration. By controlling the reaction conditions during the process of precipitating sodium ions, potassium precipitation is prevented, and then a sodium salt precipitate with stable quality is obtained. The potassium ions are left in the filtrate and can be separated by common potassium removal methods in the art.

[0014] The embodiment of the present invention provides a method for separating potassium and sodium in fly ash, including the following steps: adjusting the acid concentration in the fly ash washing liquid to 40 - 65% and the temperature to 40 - 65 °C, adding a sodium precipitant and carrying out a heat preservation reaction, and filtering to obtain a sodium salt precipitate and a potassium-containing waste liquid.

[0015] In this embodiment, the fly ash contains a large amount of alkaline substances, and its washing liquid is usually alkaline. First, the acid concentration of the fly ash washing liquid is adjusted in the present invention. Since potassium ions have high solubility in an acidic environment and are difficult to precipitate, when the acid concentration is 40 - 65%, the environment of the washing liquid is adjusted to be acidic. By adjusting the temperature, the crystal form of the sodium salt precipitate obtained from the heat preservation reaction of the sodium precipitation agent is large and easy to filter, avoiding poor filtration effect due to small crystal form and ineffective 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, achieving the purpose of separating potassium and sodium in the fly ash.

[0016] It can be understood that the method for adjusting the acidity of the washing liquid described in the present invention is a commonly used method by those skilled in the art, such as directly adding an acid solution or introducing an acidic gas into the washing liquid, etc.

[0017] In some specific embodiments, the fly ash washing liquid is obtained by filtering after washing the fly ash. The fly ash washing liquid described in the present invention can be directly obtained by mixing fly ash with water in any proportion and then filtering. The mixing ratio can be adjusted according to the type of fly ash, or it can be a fly ash treatment liquid containing potassium ions and sodium ions after pretreatment.

[0018] In some preferred embodiments, the sodium precipitation agent is one or more of ammonium dihydrogen phosphate, fluorosilicic acid, potassium hexafluorophosphate, and organic sulfonic acid substances. In the present invention, a sodium precipitation agent that can fully react with sodium ions to precipitate under acidic conditions is selected, and sodium ions are continuously precipitated during the reaction to achieve the purpose of sodium removal.

[0019] In some specific embodiments, after washing the sodium salt precipitate with a displacement agent, it is then washed with water to obtain a sodium salt product. After filtration, a small amount of impurities will inevitably adhere to the surface of the sodium salt precipitate. Therefore, in the present invention, the obtained sodium salt precipitate is 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, it is washed with water multiple times to reduce the acidity of the sodium salt precipitate and obtain a sodium salt product with stable quality.

[0020] In some preferred embodiments, the displacement agent is a saturated sodium sulfate solution and an acid solution with a concentration of 40 - 60%. When washing, first use the saturated sodium sulfate solution. Since the sulfate ion concentration is high, the displacement reaction is more likely to occur. Then use the 40 - 60% acid solution, which can react with most metal ions to enhance the washing effect. The acid solution is a common acid solution in the art.

[0021] Next, specific examples for implementing the present application will be disclosed, as well as corresponding comparative examples to prove the relevant technical effects of the present application.

[0022] Example 1 Mix the fly ash with three times its weight of water for washing. Pour the washed liquid obtained by suction filtration into the reaction tank, add concentrated sulfuric acid, adjust the acid concentration to 50%, heat to a temperature of 50 °C in the reaction tank, add the sodium-precipitating agent fluosilicic acid, stir and keep the temperature for reaction for 60 min, and filter to separate the potassium-containing waste liquid and the sodium fluosilicate salt precipitate; wash the sodium fluosilicate salt precipitate first with saturated sodium sulfate solution, then with 50% sulfuric acid solution, and then rinse the sodium fluosilicate salt precipitate with running water to obtain the sodium fluosilicate salt product.

[0023] In Example 1, the fluosilicate ions can combine with the sodium ions in the fly ash to form an insoluble sodium fluosilicate salt precipitate, thereby removing the sodium ions from the fly ash system. The acidic condition can prevent side reactions such as hydrolysis of sodium fluosilicate and ensure the smooth progress of the precipitation reaction. Controlling the reaction temperature is conducive to the formation of sodium fluosilicate salt precipitate with larger crystal forms.

[0024] Example 2 Mix the fly ash with four times its weight of water for washing. Pour the washed liquid obtained by suction filtration into the reaction tank, add concentrated nitric acid, adjust the acid concentration to 40%, heat to a temperature of 60 °C in the reaction tank, add the sodium-precipitating agent ammonium dihydrogen phosphate, stir and keep the temperature for reaction for 60 min, and filter to separate the potassium-containing waste liquid and the disodium hydrogen phosphate precipitate; wash the disodium hydrogen phosphate precipitate first with saturated sodium sulfate solution, then with 60% phosphoric acid solution, and then rinse the disodium hydrogen phosphate precipitate with running water to obtain the disodium hydrogen phosphate product.

[0025] Under acidic and heating conditions, the phosphate ions in ammonium dihydrogen phosphate can react with the sodium ions in the fly ash to form a sodium phosphate salt precipitate. In Example 2, disodium hydrogen phosphate precipitate is formed. As the reaction proceeds, the sodium ions are continuously precipitated to achieve the purpose of sodium removal. Controlling the temperature during the reaction can accelerate the reaction rate, make the precipitation reaction more complete, and form larger crystal forms. The acidic environment helps to inhibit the hydrolysis of phosphate ions and ensure the effective reaction between phosphate ions and sodium ions.

[0026] Example 3 Mix the fly ash with five times its weight of water for washing. Pour the washed liquid obtained by suction filtration into the reaction tank, add concentrated sulfuric acid, adjust the acid concentration to 60%, heat to a temperature of 40 °C in the reaction tank, add the sodium-precipitating agent potassium hexafluorophosphate, stir and keep the temperature for reaction for 60 min, and filter to separate the potassium-containing waste liquid and the sodium hexafluorophosphate precipitate; wash the sodium hexafluorophosphate precipitate first with saturated sodium sulfate solution, then with 40% hydrochloric acid solution, and then rinse the sodium hexafluorophosphate precipitate with running water to obtain the sodium hexafluorophosphate product.

[0027] In Example 3, under acidic heating conditions, fluorophosphate ions can be provided, which combine with sodium ions in the fly ash to form sodium hexafluorophosphate precipitate. Since the solubility of sodium hexafluorophosphate is relatively low, it can precipitate from the solution under acidic and heating conditions, thereby achieving the removal of sodium from the fly ash. The acidic environment can inhibit the hydrolysis of fluorophosphate ions, and heating can accelerate the reaction rate, promoting the precipitation reaction to be more complete.

[0028] Example 4 Mix the fly ash with three times the amount of water for washing, pour the washed liquid obtained by suction filtration into the reaction tank, add concentrated sulfuric acid to adjust the acid concentration to 50%, heat to a temperature of 50 °C in the reaction tank, add the sodium precipitation agent p-toluenesulfonic acid, stir and keep the reaction for 50 min, filter to separate the potassium-containing waste liquid and the sodium sulfonate precipitate; wash the sodium sulfonate precipitate first with saturated sodium sulfate solution, then wash the sodium sulfonate precipitate with 60% nitric acid solution, and then rinse the sodium sulfonate precipitate with running water to obtain the sodium sulfonate product.

[0029] In Example 4, under acidic and heating conditions, the sulfonic acid group in p-toluenesulfonic acid can undergo an ion exchange reaction with sodium ions in the fly ash to form a sodium sulfonate salt precipitate. Heating can enhance the reaction activity of the sulfonic acid group and sodium ions, improve the sodium removal efficiency, and at the same time the acidic environment is beneficial to maintaining the stability and reaction activity of its molecular structure.

[0030] Test Example In this test example, the sodium recovery rate of the sodium salt products obtained according to Examples 1-4 was measured. The detection of the sodium recovery rate = (sodium content in the sodium salt product × mass of the sodium salt product) / (sodium content in the fly ash × mass of the fly ash) × 100%; the measurement results are shown in Table 1. It can be seen from Table 1 that the method of the present invention can make the sodium recovery rate in the fly ash exceed 90%, can efficiently recover sodium in the fly ash, the process steps are simple and continuous, and the finally obtained sodium salt product has high stability.

[0031] Table 1 Detection of Sodium Recovery Rate 。

[0032] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for separating potassium and sodium from fly ash, characterized in that: The following steps are involved: The acid concentration in the fly ash washing liquid is adjusted to 40-65%, the temperature is 40-65°C, a sodium precipitant is added to keep the temperature for reaction, and the sodium salt precipitate and potassium-containing waste liquid are obtained by filtration.

2. The separation method according to claim 1, characterized in that The fly ash water washing liquid is obtained by washing the fly ash with water and filtering it.

3. The separation method according to claim 1, characterized in that The sodium precipitation agent is one or more of ammonium dihydrogen phosphate, fluorosilicic acid, potassium hexafluorophosphate, and organic sulfonic acid substances.

4. The separation method according to claim 1, characterized in that The sodium salt precipitate is washed with a replacement agent and then washed with water to obtain a sodium salt product.

5. The separation method according to claim 4, characterized in that The displacing agent is a saturated sodium sulfate solution and an acid solution with a concentration of 40-60%.