Method for treating desulfurization waste liquid

Abstract

The application provides a desulfurization waste liquid treatment method, and belongs to the technical field of waste water treatment. The desulfurization waste liquid is subjected to step-by-step salt extraction to obtain ammonium thiosulfate, ammonium thiocyanate and ammonium sulfate; the ammonium thiosulfate is purified by using ethanol to obtain pure ammonium thiosulfate; the ammonium thiocyanate is purified by using ethyl acetate-acetone and ethyl acetate step by step to obtain pure ammonium thiocyanate; and the ammonium sulfate is purified by using a water-acetone mixed solution to obtain pure ammonium sulfate. The application first subjects ammonium thiosulfate, ammonium thiocyanate and ammonium sulfate in the desulfurization waste liquid to rough extraction by using step-by-step salt extraction, and then subjects the ammonium thiosulfate, ammonium thiocyanate and ammonium sulfate to purification by using specific solvents, so that pure ammonium thiosulfate, pure ammonium thiocyanate and pure ammonium sulfate with high purity are obtained, and the added value of the products is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a desulfurization waste liquid treatment method. BACKGROUND

[0002] Due to the increasing demand for coke in steel enterprises, the coke industry has become popular, but a large amount of impure coke oven gas is generated in the coking process, so the purification process has begun to develop rapidly. Especially the HPF desulfurization process has been widely used in China. Therefore, how to improve the recovery rate and purity of the by-product salt in the desulfurization waste liquid is an important issue that needs to be solved in the coking industry. SUMMARY

[0003] In view of the above problems, the present application provides a desulfurization waste liquid treatment method.

[0004] To achieve the above purpose, the technical scheme adopted by the present application is:

[0005] A desulfurization waste liquid treatment method, comprising the following steps:

[0006] Desulfurization waste liquid is subjected to step-by-step salt extraction to obtain ammonium thiosulfate, ammonium thiocyanate and ammonium sulfate;

[0007] Ammonium thiosulfate is purified by adding ethanol to dissolve ammonium thiocyanate and ammonium sulfate impurities, cooling, filtering, and obtaining pure ammonium thiosulfate;

[0008] Ammonium thiocyanate is purified by adding an ethyl acetate-ketone mixed solution to dissolve ammonium thiocyanate, cooling to room temperature, removing insoluble ammonium thiosulfate and ammonium sulfate by filtration, concentrating the filtrate to dryness, adding ethyl acetate to heat and dissolve residual impurities, then cooling, filtering, and obtaining pure ammonium thiocyanate;

[0009] Ammonium sulfate is purified by adding a water-ketone mixed solution to dissolve impurities, cooling, filtering, and obtaining pure ammonium sulfate.

[0010] Further, in the ammonium thiocyanate purification process, the concentration of ethyl acetate in the ethyl acetate-ketone mixed solution is 2-4 vol%.

[0011] Further, in the ammonium thiocyanate purification process, the weight ratio of ammonium thiocyanate to ethyl acetate-ketone mixed solution is 1:3-5;

[0012] The weight ratio of the concentrate to ethyl acetate is 1:2-3.

[0013] Further, in the purification process of the ammonium sulfate crude product, the concentration of water in the water-acetone mixed solution is 3-6 vol%.

[0014] Further, in the purification process of the ammonium sulfate crude product, the weight ratio of the ammonium sulfate crude product to the water-acetone mixed solution is 1:3-5.

[0015] Further, in the purification process of the ammonium sulfate crude product, the weight ratio of the ammonium sulfate crude product to the water-acetone mixed solution is 1:3-5.

[0016] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0017] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0018] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0019] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0020] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0021] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0022] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0023] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0024] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0025] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0026] Further, in the purification process of the ammonium sulfate crude product, the temperature of heating is 50-55℃, and the time is 0.5-1h.

[0027] The desulfurization waste liquid treatment method has the following beneficial effects:

[0028] The present application first adopts section salt extraction to coarsely extract ammonium thiosulfate, ammonium thiocyanate and ammonium sulfate in the desulfurization waste liquid, and then adopts specific solvents to purify ammonium thiosulfate, ammonium thiocyanate and ammonium sulfate, so as to obtain ammonium thiosulfate, ammonium thiocyanate and ammonium sulfate with high purity, and effectively improve the product added value. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a process flow chart of the treatment method of the desulfurization waste liquid in the embodiment 1 of the present application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application are described clearly and completely below. In the following description, a lot of specific details are set forth in order to fully understand the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0031] Embodiment 1: A preparation method of desulfurization waste liquid

[0032] The present embodiment is a treatment method of desulfurization waste liquid, as shown in Figure 1 for example, taking the desulfurization waste liquid containing 158.96 g / L ammonium thiocyanate, 85.47 g / L ammonium thiosulfate and 112.37 g / L ammonium sulfate, the specific treatment method includes the following steps:

[0033] S1, section salt extraction of desulfurization waste liquid

[0034] Take 2000L desulfurization waste liquid and pump it into a filter to preliminarily remove suspended sulfur, tar and other impurities, then pump the purified filtrate into a decolorization kettle, add activated carbon, and then stir and heat to decolorize under normal pressure (95-100℃, the temperature of heating decolorization in the present embodiment is 100℃), suspended sulfur, tar, hydroquinone and the like are basically removed under the action of activated carbon; the water vapor and part of the volatile substances volatilized from the decolorization kettle are captured by a condenser and then discharged into a clear liquid pool; after the activated carbon decolorization is completed, it is discharged into a suction filter, and after the activated carbon is separated, the obtained desulfurization liquid enters an evaporation kettle, and under the condition of negative pressure stirring, it is evaporated and concentrated to some microcrystals at 75℃ for the first time, and the concentrated liquid is sent to a crystallization kettle for the first time at 40℃ for 4h, and after the first centrifugal separation, 164.64kg of ammonium thiosulfate crude product is obtained, with a purity of 89.37%;

[0035] The solution after the first centrifugal separation is evaporated and concentrated to some microcrystals at 75℃ under the condition of negative pressure stirring for the second time, and then sent to a crystallization kettle for the second time at 20℃ for 4h, and after the second centrifugal separation, 283.84kg of ammonium thiocyanate crude product is obtained, with a purity of 85.76%;

[0036] The solution after the second centrifugal separation is returned to the evaporation kettle, and is evaporated and concentrated at 75°C under negative pressure and stirring to form a small amount of crystals. The crystals are sent to a crystallization kettle, and are crystallized at 0°C for the third time. The third centrifugal separation is performed to obtain 205.14 kg of the ammonium sulfate crude product with a purity of 82.69%.

[0037] S2, purification of the ammonium thiosulfate crude product

[0038] The 50 kg of the ammonium thiosulfate crude product is added with 200 kg of ethanol. The ammonium thiocyanate and ammonium sulfate impurities are dissolved by heating and refluxing for 0.5 h. The temperature is lowered to 0°C, and is maintained for 4 h. Filtration is performed, and a small amount of ethanol is used for washing. Thus, 43.21 kg of the ammonium thiosulfate pure product is obtained, with a recovery rate of 86.42%, a purity of 98.37%, and an actual recovery rate of 95.12%.

[0039] The filtrate is evaporated and concentrated to obtain a concentrate. The concentrate can be used for further purification of the ammonium thiocyanate crude product by using the method for purifying the ammonium thiocyanate crude product. The solvent is recovered and mixed with a new solvent to continue to be used for purification of the ammonium thiosulfate crude product.

[0040] S3, purification of the ammonium thiocyanate crude product

[0041] The 100 kg of the ammonium thiocyanate crude product is added with 400 kg of an ethyl acetate-ketone mixed solution containing ethyl acetate with a concentration of 3 vol%. The ammonium thiocyanate is dissolved by heating and refluxing for 0.5 h. The temperature is lowered to room temperature. The insoluble ammonium thiosulfate and ammonium sulfate are removed by filtration. The filtrate is concentrated to dryness to obtain a concentrate. The ethyl acetate-ketone mixed solution is recovered and used for purification of the ammonium thiocyanate crude product.

[0042] The concentrate is added with 3 times by weight of ethyl acetate, and is heated to dissolve the residual impurities again. The temperature is lowered to 0°C, and is maintained for 4 h. Filtration is performed to obtain 84.51 kg of the ammonium thiocyanate pure product, with a recovery rate of 84.51%, a purity of 99.43%, and an actual recovery rate of 97.98%.

[0043] The ethyl acetate is recovered and used for purification of the ammonium thiocyanate crude product.

[0044] S4, purification of the ammonium sulfate crude product

[0045] The 100 kg of the ammonium sulfate crude product is added with 200 kg of a water-ketone mixed solution containing water with a concentration of 5 vol%. The impurities are dissolved by heating and stirring at 53°C for 0.5 h. The temperature is lowered to 12°C, and is maintained for 4 h. Filtration is performed, and a small amount of the 5 vol% water-ketone solution is used for washing. Thus, 80.48 kg of the ammonium sulfate pure product is obtained, with a recovery rate of 80.48%, a purity of 98.72%, and an actual recovery rate of 96.08%.

[0046] The filtrate is recovered and used for purification of the ammonium sulfate crude product.

[0047] The filtrate was reused for 10 times, and then concentrated by evaporation to obtain a concentrate which was used as the ammonium thiocyanate crude product for further purification.

[0048] The actual recovery rate (%) = the weight of the pure product x the purity of the pure product ÷ (the weight of the crude product x the purity of the crude product) x 100%.

[0049] Treatment methods of the desulfurization waste liquid in Examples 2-5

[0050] Examples 2-5 are each a treatment method of a desulfurization waste liquid, and the steps thereof are basically the same as those of Example 1, except that the raw material usage and some process parameters are different. See Table 1 for details.

[0051] Table 1: List of process parameters in Examples 2-5

[0052]

[0053]

[0054] The contents of other parts of Examples 2-5 and the types of raw materials used are the same as those of Example 1, and will not be repeated here.

[0055] Experimental Example 1

[0056] Comparative Examples 1-4 are comparative tests of the treatment method of the desulfurization waste liquid in Example 1, and the ammonium thiocyanate crude product, the ammonium thiocyanate crude product and the ammonium sulfate crude product obtained in Example 1 are used as raw materials for purification. The only difference is that:

[0057] The specific process of steps S2-S4 in Comparative Example 1 is as follows:

[0058] Among them, S2, purification of ammonium thiosulfate crude product

[0059] 5 kg of ammonium thiosulfate crude product was taken and 20 kg of methanol was added. The impurities such as ammonium thiocyanate and ammonium sulfate were dissolved by heating under reflux for 0.5 h. The temperature was lowered to 0°C and maintained for 4 h. Filtration was performed and a small amount of methanol was used for washing. 3.754 kg of ammonium thiosulfate pure product was obtained with a recovery rate of 75.08% and a purity of 91.69%, and the actual recovery rate was 77.03%.

[0060] S3, purification of ammonium thiocyanate crude product

[0061] 10 kg of ammonium thiocyanate crude product was taken and 40 kg of ethyl acetate-ketone mixed solution containing ethyl acetate with a concentration of 13 vol% was added. The ammonium thiocyanate was dissolved by heating under reflux for 0.5 h. The temperature was lowered to room temperature, and the insoluble ammonium thiosulfate and ammonium sulfate were removed by filtration. The filtrate was concentrated to dryness to obtain a concentrate, and the ethyl acetate-ketone mixed solution was recovered for purification of ammonium thiocyanate crude product.

[0062] The concentrate was added with 3 times weight of ethyl acetate and heated to dissolve the residual impurities again. After cooling to 0°C and maintaining for 4 hours, filtration was performed to obtain 8.962 kg of ammonium thiocyanate product with a recovery rate of 89.62%, a purity of 87.98% and an actual recovery rate of 91.94%.

[0063] S4, purification of ammonium sulfate crude product

[0064] The 10 kg of ammonium sulfate crude product was added with 20 kg of water-acetone mixed solution containing water with a concentration of 15 vol%, heated to 53°C and stirred to dissolve the impurities for 0.5 h. After cooling to 12°C and maintaining for 4 hours, filtration was performed with a small amount of 15 vol% water-acetone solution for washing to obtain 6.364 kg of ammonium sulfate product with a recovery rate of 63.64%, a purity of 91.56% and an actual recovery rate of 70.47%.

[0065] The specific process of steps S3-S4 in Comparative Example 2 is as follows:

[0066] S3, purification of ammonium thiocyanate crude product

[0067] The 10 kg of ammonium thiocyanate crude product was added with 40 kg of acetone, heated to reflux to dissolve the ammonium thiocyanate for 0.5 h, cooled to room temperature, and filtration was performed to remove the insoluble ammonium thiosulfate and ammonium sulfate. The filtrate was concentrated to dryness to obtain a concentrate, and the ethyl acetate-acetone mixed solution was recovered for purification of ammonium thiocyanate crude product.

[0068] The concentrate was added with 3 times weight of ethyl acetate and heated to dissolve the residual impurities again. After cooling to 0°C and maintaining for 4 hours, filtration was performed to obtain 6.357 kg of ammonium thiocyanate product with a recovery rate of 63.57%, a purity of 92.67% and an actual recovery rate of 68.69%.

[0069] S4, purification of ammonium sulfate crude product

[0070] The 10 kg of ammonium sulfate crude product was added with 20 kg of acetone, heated to 53°C and stirred to dissolve the impurities for 0.5 h. After cooling to 12°C and maintaining for 4 hours, filtration was performed with a small amount of acetone for washing to obtain 8.539 kg of ammonium sulfate product with a recovery rate of 85.39%, a purity of 85.66% and an actual recovery rate of 88.46%.

[0071] The specific process of step S4 in Comparative Example 3 is as follows:

[0072] The 10 kg of ammonium sulfate crude product was added with 20 kg of water-acetone mixed solution containing water with a concentration of 5 vol%, heated to 53°C and stirred to dissolve the impurities for 0.5 h. After cooling to 0°C and maintaining for 4 hours, filtration was performed with a small amount of 5 vol% water-acetone solution for washing to obtain 8.775 kg of ammonium sulfate product with a recovery rate of 87.75%, a purity of 90.54% and an actual recovery rate of 96.08%.

[0073] The specific process of step S4 in Comparative Example 4 is as follows:

[0074] Take 10 kg of ammonium sulfate crude product, add 20 kg of 5 vol% water-acetone mixed solution containing water, heat to 53°C, stir and dissolve impurities for 0.5 h, cool to 20°C and maintain for 4 h, filter and wash with a small amount of 5 vol% water-acetone solution, obtain 2.769 kg of ammonium sulfate pure product, the recovery rate is 27.69%, the purity is 98.83%, and the actual recovery rate is 33.09%.

[0075] From Comparative Examples 1-4, it can be seen that changing the type of solvent and the crystallization temperature in the purification process will cause the purity or actual recovery rate of the obtained ammonium thiosulfate pure product, ammonium thiocyanate pure product and ammonium sulfate pure product to decrease to different degrees, which is not conducive to the recovery and application of ammonium thiosulfate, ammonium thiocyanate and ammonium sulfate.

[0076] Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor belong to the scope of protection of the present application.

Claims

1. A method for treating desulfurization wastewater, characterized in that, The processing method includes the following steps: Segmented salt extraction from desulfurization wastewater: The desulfurization wastewater is subjected to segmented salt extraction to obtain crude ammonium thiosulfate, crude ammonium thiocyanate and crude ammonium sulfate; Purification of crude ammonium thiosulfate: Ethanol is added to crude ammonium thiosulfate, the mixture is heated under reflux to dissolve impurities, cooled to 0-4℃, and filtered to obtain pure ammonium thiosulfate; the weight ratio of crude ammonium thiosulfate to ethanol is 1:3-5. Purification of crude ammonium thiocyanate: An ethyl acetate-acetone mixture was added to the crude ammonium thiocyanate, and the mixture was heated under reflux to dissolve. After cooling to room temperature, the mixture was filtered to remove insoluble ammonium thiosulfate and ammonium sulfate. The filtrate was concentrated to dryness. The concentrate was then added to ethyl acetate and heated to dissolve residual impurities again. The solution was then cooled to 0-4°C and filtered to obtain pure ammonium thiocyanate. The concentration of ethyl acetate in the ethyl acetate-acetone mixture was 2-4 vol%. The weight ratio of crude ammonium thiocyanate to the ethyl acetate-acetone mixture was 1:3-5. The weight ratio of the concentrate to ethyl acetate was 1:2-3. Purification of crude ammonium sulfate: Add a water-acetone mixed solution to the crude ammonium sulfate, heat to 50-55℃ to dissolve impurities for 0.5-1h, cool to 10-15℃, filter, and obtain pure ammonium sulfate; the water-acetone mixed solution contains 3-6 vol% water; the weight ratio of crude ammonium sulfate to water-acetone mixed solution is 1:3-5.

2. The method for treating desulfurization wastewater according to claim 1, characterized in that, In the purification process of crude ammonium thiosulfate, after filtering the pure ammonium thiosulfate, the resulting filtrate is evaporated and concentrated, and the solvent is recovered for the purification of crude ammonium thiosulfate. In the purification process of crude ammonium thiocyanate, after filtering to remove insoluble ammonium thiosulfate and ammonium sulfate, the ethyl acetate-acetone mixed solution is recovered during the concentration of the filtrate for the purification of crude ammonium thiocyanate. In the purification process of crude ammonium sulfate, after filtering the pure ammonium sulfate, the resulting filtrate is recycled for further purification of crude ammonium sulfate.

3. The method for treating desulfurization wastewater according to claim 1, characterized in that, The specific process of staged salt extraction from the desulfurization wastewater is as follows: After the desulfurization waste liquid is initially removed of impurities, the purified filtrate is decolorized by activated carbon. The resulting desulfurization liquid is concentrated by the first evaporation until some microcrystals precipitate, followed by the first crystallization and the first centrifugation to obtain crude ammonium thiosulfate. The solution after the first centrifugation was concentrated by a second evaporation until some microcrystals precipitated, followed by a second crystallization and a second centrifugation to obtain crude ammonium thiocyanate. The solution after the second centrifugation was concentrated by a third evaporation until some microcrystals precipitated, followed by a third crystallization and a third centrifugation to obtain crude ammonium sulfate.

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