A method for recovering sodium sulfate from waste salt

Abstract

The present application relates to the technical field of resource utilization of industrial waste salt, and specifically discloses a method for recovering sodium sulfate from waste salt, comprising the following steps: Step 1: Put the waste salt raw material and pure water into a dissolving device in a certain proportion for dissolution, heat the device to 38-42°C, and stir for 20-30 minutes to dissolve the waste salt solid; Step 2: After the waste salt in the device is dissolved, filter and remove the insoluble matter in the waste salt raw material; Step 3: Add a regulator to make the solution look like a colorless clear liquid; Step 4: Place the solution in a 3-6°C environment for freezing and crystallization. The purpose of this patent is to solve the problem that the purity of sodium sulfate obtained by the existing method for recovering sodium sulfate from waste salt is low and the recovery rate is not high.

Description

Technical Field

[0001] The invention relates to the technical field of resource utilization of industrial waste salt, and in particular to a method for recovering sodium sulfate from waste salt. Background Art

[0002] In industrial production, the amount of industrial waste salt generated every year in various chemical, pharmaceutical, and pesticide manufacturing processes is astonishing, reaching a scale of about 1.2 million tons / year. This figure only represents the newly added waste salt production, and the total amount of waste salt that has not been properly treated and accumulated over the years is even more shocking. It is estimated that it has exceeded the 10 million tons mark. One of the common salt slags is waste salt slag containing sodium sulfate, and the sodium sulfate content is usually not less than 60% (wt%). Since sodium sulfate waste salt slag contains a large amount of impurities, it cannot be directly used as an industrial raw material or auxiliary material; in addition, the high moisture content and easy hardening characteristics further increase the difficulty of disposing of sodium sulfate waste salt slag.

[0003] The traditional method uses the principle that the solubility of sodium sulfate in water reaches a maximum value of 48g / 100mL at 40°C and 4.9g / 100mL at 0°C. Sodium sulfate crystals are obtained by first heating up the solution and then cooling it down for crystallization. However, due to the presence of low-valent ion impurities in the raw materials, the solution after the waste salt raw materials are dissolved is yellow. Since the impurities are not removed, the obtained sodium sulfate crystals have more impurities, the appearance color is light yellow, the quality is poor, and the purity is low. Summary of the invention

[0004] In view of the shortcomings of the prior art, the technical problem solved by the present invention is to provide a method for recovering sodium sulfate from waste salt, thereby solving the problem that the sodium sulfate obtained by the existing method for recovering sodium sulfate from waste salt has low purity and low recovery rate.

[0005] In order to solve the above problems, the technical solution adopted by the present invention is: a method for recovering sodium sulfate from waste salt, comprising the following steps:

[0006] Step 1: Put the waste salt raw material and pure water in a certain proportion into a dissolving device for dissolution, heat the device to 38-42°C, and stir for 20-30 minutes to dissolve the waste salt solid;

[0007] Step 2: After the waste salt in the device is dissolved, filter and remove insoluble matter in the waste salt raw material;

[0008] Step 3: Add a regulator to make the solution appear as a colorless clear liquid;

[0009] Step 4: Place the solution in a 3-6°C environment to freeze and crystallize.

[0010] The beneficial effects of this scheme are: by adopting the process of this scheme to recover sodium sulfate from waste salt, a high-quality sodium sulfate product with a transparent oblique crystal appearance is obtained; not only has a good appearance, but more importantly, its purity is extremely high, and the sodium sulfate content of the product reaches more than 98%, which is very suitable for use as an industrial raw material. In addition, the yield of the product exceeds 70%, which has a high economic value, so that more useful components can be extracted from each unit weight of waste salt, thereby improving the resource utilization rate and economic benefits of waste salt.

[0011] Compared with the traditional method, this solution has obvious advantages in many aspects. In terms of product quality, the use of a regulator for color removal makes the final sodium sulfate purer; in terms of production efficiency, the new process significantly improves the yield between waste salt raw materials and finished sodium sulfate products, reducing energy consumption and production costs; the entire preparation process is simple, requires less equipment investment, occupies a small area, and is easy to adjust the scale according to actual needs or combine with other production lines, which greatly facilitates the implementation and promotion of enterprises.

[0012] Furthermore, the solid-liquid ratio of the waste salt raw material to pure water is 1:2.1-1:2.5. The waste salt can be dissolved quickly by using the solid-liquid ratio in this range.

[0013] Furthermore, in step 3, the regulator is sulfuric acid, and the pH value of the solution is adjusted to 2-3 by sulfuric acid, so that the solution becomes a colorless clear liquid.

[0014] By using sulfuric acid as a regulator and adjusting the pH value to decolorize the solution, a small amount of sulfuric acid is used, the production cost is low, and the product yield can reach more than 70%, and the product purity can reach more than 98%. This process not only has good economic benefits, but also can meet high-standard production needs.

[0015] Furthermore, the regulator in step 3 is hydrogen peroxide. By using hydrogen peroxide as a regulator to decolorize the solution, the product yield can reach more than 72%, and the product purity can reach more than 99%. The dual advantages of high purity and high yield make the final product far superior to the products produced by traditional methods in quality.

[0016] Furthermore, in step 4, the solution is first placed at room temperature for crystallization, and then placed in an environment of 3-6°C for further freezing crystallization. By first placing the solution at room temperature for guided crystallization, the formation process of the crystal nucleus can be optimized, creating favorable conditions for subsequent freezing crystallization; the crystal nucleus formed in the guided crystallization stage provides uniform nucleation points for freezing crystallization, which helps to reduce defects and unevenness in the crystal growth process; and the crystals that are subsequently placed in a low-temperature environment for freezing crystallization are well formed.

[0017] Furthermore, in step 4, the solution is continuously stirred in an environment of 3-6°C until crystallization occurs. By continuously stirring, the solute in the solution is more evenly distributed, avoiding the occurrence of local oversaturation or undersaturation. The uniform solute distribution helps the crystals grow evenly in all directions, thereby forming a regular crystal morphology.

[0018] Furthermore, in step 3, the mass ratio of hydrogen peroxide to solution is 1:6-1:9. The product yield within this ratio range is high, and the yield can reach 72%-77%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a crystal diagram of the product of Example 1-3.

[0020] Figure 2 This is the appearance of the solution when the pH value is adjusted to 2.65, 6.99, 9.17, and 11.21. DETAILED DESCRIPTION

[0021] The following is further described in detail through specific implementation methods:

[0022] The material of this embodiment is derived from the miscellaneous salt of a certain unit in Jiangxi. The test data is shown in the following table;

[0023]

[0024] Example 1, a method for recovering sodium sulfate from waste salt, comprising the following steps:

[0025] Step 1: Dissolve the waste salt raw material and pure water at a solid-liquid ratio of 1:2.32, heat the device to 40°C, and stir for 20 minutes to dissolve the waste salt solid;

[0026] Step 2: After the waste salt in the device is dissolved, filter and remove the insoluble matter in the waste salt raw material to obtain 250g of solution;

[0027] Step 3: Add 27.8 g of hydrogen peroxide to the solution so that the solution appears as a colorless clear liquid; the mass ratio of hydrogen peroxide to the solution is 1:8.99;

[0028] Step 4: First, place the solution at room temperature to crystallize, and then place it in a refrigerator at 5°C to continue freezing and crystallizing. After solid-liquid separation, 139.94 g of crystals are obtained.

[0029] Embodiment 2 is similar to Embodiment 1-1 and is not described in detail. The difference is that:

[0030] Step 3: Add 38.01 g of hydrogen peroxide to the solution so that the solution appears as a colorless clear liquid; the mass ratio of hydrogen peroxide to the solution is 1:6.58;

[0031] Step 4: First, the solution was placed at room temperature for crystallization, and then placed in a 5°C environment for further freezing and crystallization. After solid-liquid separation, 143.27 g of crystals were obtained.

[0032] Embodiment 3 is similar to Embodiment 1-1 and Embodiment 1-2 and is not described in detail. The difference is that:

[0033] Step 3: Add 30 g of hydrogen peroxide to the solution so that the solution appears as a colorless clear liquid; the mass ratio of hydrogen peroxide to solution is 1:8.33;

[0034] Step 4: First, place the solution at room temperature for crystallization, and then place it in a 5°C environment to continue freezing and crystallization. After solid-liquid separation, 141.3 g of crystals are obtained.

[0035] The crystals of the products obtained in Examples 1-3 are shown in FIG. Figure 1 shown.

[0036] Comparative experiment 1: In this experiment, waste salt was dissolved at a solid-liquid ratio of about 1:2.4; 250g of waste salt was weighed and dissolved in 606g of water, and stirred and dissolved at room temperature for about 30 minutes until it was completely dissolved. Filter, divide the filtrate into three equal parts, that is, each part is 285g, and place them in a three-effect evaporator to evaporate part of the water to make the solution a saturated solution, and the solution is not salty. Then place it at 4℃, 10℃ and room temperature for cooling and crystallization, and the specific experimental results are shown in Table 1.

[0037] Table 1 Comparative Experiment 1 Experimental results

[0038]

[0039] Embodiment 4, a method for recovering sodium sulfate from waste salt, comprising the following steps:

[0040] Step 1: Dissolve the waste salt raw material and pure water at a solid-liquid ratio of 1:2.32, heat the device to 40°C, and stir for 20 minutes to dissolve the waste salt solid;

[0041] Step 2: After the waste salt in the device is dissolved, filter and remove the insoluble matter in the waste salt raw material to obtain 80g of solution;

[0042] Step 3: Add 2 ml of sulfuric acid (AR) solution to the solution to make the pH value of the solution 2.65, so that the solution appears as a colorless clear liquid;

[0043] Step 4: Place the solution in a 5°C environment for freezing and crystallization. After solid-liquid separation, oblique crystals are obtained that are pure white.

[0044] Comparative Experiment 2: In this experiment, waste salt was dissolved at a solid-liquid ratio of about 1:2.32: Stir and dissolve at room temperature for about 30 minutes until it is completely dissolved. Filter and divide the filtrate into three equal parts, i.e., 80g each. 6ml, 9.5ml, and 12ml of 0.5mol / L sodium hydroxide solution were added respectively. The pH values ​​were adjusted to 6.99, 9.17, and 11.21 respectively. The solution was placed in a 5℃ environment for freezing and crystallization. The experimental results of Example 4 and Comparative Experiment 2 are shown in the following table. The experimental solution is as follows: Figure 2 shown.

[0045] Table 2 Experimental results of Example 4 and comparative experiment 2

[0046]

[0047] It can be seen from the above comparative experiment 2 and Example 4 that no matter the pH value of the solution is too acidic or too alkaline, the color of the solution will become lighter, but the solution precipitates crystals better under acidic conditions, while the crystals precipitated under alkaline conditions have defects in appearance and are impure.

[0048] The product yield and product quality of the samples of Examples 1-4 and Comparative Examples 1-4 are measured and the results are shown in Tables 3-5 below;

[0049] Table 3

[0050]

[0051] Table 4

[0052]

[0053] Table 5

[0054]

[0055] From the experimental results in Tables 3-5, it can be seen that after the hydrogen peroxide oxidation solution is used for decolorization in Example 1-3, a single crystallization is directly performed to obtain a product with a sodium sulfate content of more than 99%, and a product yield of more than 72%. The obtained product is excellent in terms of product quality, appearance, and yield. In Example 4, sulfuric acid is used to adjust the pH value of the solution to between 2 and 3, and a single crystallization is directly performed, which not only makes the product excellent in appearance, but also has a yield of up to 70.59%, and a sodium sulfate content of more than 98.9%.

[0056] Although the product yield obtained in Comparative Examples 1-3 can reach more than 59%, the product appearance is poor and is slightly yellow, which limits the application scope of this product in certain fields with extremely strict requirements on raw materials; from Comparative Example 4, it can be seen that although the product appearance is improved, it still has variegated colors, and the product yield is not high, less than 60%; therefore, in actual production, it may face the problem of excessively high costs.

[0057] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for recovering sodium sulfate from waste salt, characterized in that: The steps include: Step 1: Put the waste salt raw material and pure water in a certain proportion into a dissolving device for dissolution, heat the device to 38-42°C, and stir for 20-30 minutes to dissolve the waste salt solid; Step 2: After the waste salt in the device is dissolved, filter and remove insoluble matter in the waste salt raw material; Step 3: Add a regulator to make the solution appear as a colorless clear liquid; Step 4: Place the solution in a 3-6°C environment to freeze and crystallize.

2. The method for recovering sodium sulfate from waste salt according to claim 1, characterized in that: The solid-liquid ratio of the waste salt raw material to pure water is 1:2.1-1:2.

5.

3. The method for recovering sodium sulfate from waste salt according to claim 1, characterized in that: In step 3, the regulator is sulfuric acid, and the pH value of the solution is adjusted to 2-3 by sulfuric acid, so that the solution becomes a colorless clear liquid.

4. The method for recovering sodium sulfate from waste salt according to claim 1, characterized in that: In step 3, the regulator is hydrogen peroxide.

5. The method for recovering sodium sulfate from waste salt according to claim 4, characterized in that: In step 4, the solution is first placed at room temperature for crystallization, and then placed in a 3-6° C. environment for further freezing and crystallization.

6. The method for recovering sodium sulfate from waste salt according to claim 4, characterized in that: In step 4, the solution is continuously stirred at 3-6° C. until crystallization occurs.

7. The method for recovering sodium sulfate from waste salt according to claim 4, characterized in that: In step 3, the mass ratio of hydrogen peroxide to solution is 1:6-1:9.

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