A method for preparing calcium sulfate based on semi-dry desulfurization ash, acid waste water and desulfurization waste water

Abstract

The application provides a calcium sulfate preparation method based on semi-dry desulfurization ash, acid-making wastewater and desulfurization wastewater, which uses semi-dry desulfurization ash containing CaSO4·0.5H2O and Ca(OH)2, strong acid acid-making wastewater containing H2SO4 and desulfurization wastewater containing Cl ‑ and Ca 2+ as main raw materials, and obtains high-purity calcium sulfate dihydrate (dihydrate gypsum) through a synergistic process of "waste acid dissolving ash, waste calcium supplement, catalytic oxidation and crystal control purification", so as to realize resource utilization of the three kinds of waste / wastewater. The content of CaSO4·2H2O in the obtained calcium sulfate dihydrate product is all above 99.2%, the whiteness is all above 92.3, and the compressive strength is all 14.2 MPa kg / m 3 The content of As is below 0.08%, the content of Pb is below 0.12%, the content of MgO is below 0.10%, the content of Na2O is below 0.02%, and the content of Cl is all below 0.01%. It fully meets the building gypsum standard of GB / T 37785-2019, and can be used in the building material industry.

Description

Technical Field

[0001] This application relates to the field of solid waste and wastewater resource treatment technology, and in particular to a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater. Background Technology

[0002] Semi-dry desulfurization ash is a mixture mainly composed of CaSO2·0.5H2O and Ca(OH)2. Due to its high heavy metal content, comprehensive utilization is difficult, and its poor stability makes long-term storage prone to environmental pollution.

[0003] In response, a method and apparatus for preparing calcium sulfate whiskers using sintering flue gas desulfurization ash (application number CN202211354173.4) is disclosed in the prior art. This method utilizes the Cl already present in the semi-dry desulfurization ash of sintering flue gas. - Mg 2+ K + Na + Plasma, without the addition of auxiliary reagents, prepares desulfurization ash slurry, followed by an acidic hydrothermal reaction to generate calcium sulfate whiskers, thus achieving comprehensive utilization of sintering flue gas desulfurization ash. However, this technical route does not consider how to remove other harmful impurities (such as As and Pb) contained in the desulfurization ash, resulting in insufficient purity of the prepared calcium sulfate, which cannot meet the requirements of the construction industry and greatly limits its utilization value. Secondly, the separation of chloride salts in high-chlorine wastewater is achieved through ion exchange resin, which has low extraction efficiency. Finally, this method adds a large amount of inorganic acid and alkali during the preparation process, leading to the generation of a large amount of wastewater with different characteristics, which requires specific wastewater treatment processes, making the entire process relatively cumbersome. Summary of the Invention

[0004] This application aims to address the technical problems in existing processes for preparing calcium sulfate based on semi-dry desulfurization ash, such as insufficient product purity and subsequent wastewater generation requiring specific wastewater treatment. It proposes a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater. This method utilizes the synergistic treatment of these three wastes to prepare high-purity calcium sulfate dihydrate (gypsum dihydrate), achieving resource utilization of these three types of wastewater. Simultaneously, the preparation process generates no additional waste or wastewater, truly achieving the technical effect of "treating waste with waste" and zero emissions.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] A method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater includes the following steps:

[0007] S1. Mix semi-dry desulfurization ash with acid production wastewater, add concentrated sulfuric acid to adjust the pH value to 2-5, and stir to form a primary slurry, wherein the solid-liquid ratio of the semi-dry desulfurization ash and the acid production wastewater is 1:(3-8).

[0008] S2. Introduce oxygen or air into the primary slurry and add a catalyst, then react at 50-80℃ for 1-4 hours to oxidize the calcium sulfite in the primary slurry to calcium sulfate.

[0009] S3. Add precipitant and flocculant to the primary slurry after the reaction in S2 for flocculation. Then, after solid-liquid separation for 10-30 minutes, secondary slurry and heavy metal sludge are obtained. The heavy metal sludge is washed 1-3 times, and the washing liquid is returned to the secondary slurry. The sludge is solidified with cement and then sintered.

[0010] S4. Add desulfurization wastewater to the secondary slurry and adjust the supersaturation to 1.2-1.5. Add 0.1-1.0% calcium sulfate dihydrate seed crystals and induce crystallization for 2-3 hours.

[0011] S5. The secondary slurry that has completed crystallization in S4 is treated with a reverse osmosis membrane to obtain a tertiary slurry and a high-Cl slurry. - Wastewater, including tertiary slurry containing Cl - Concentration <100mg / L, high Cl - Cl in wastewater - Concentration > 5%;

[0012] S6. The high Cl - Wastewater is recycled into the mixture of the secondary slurry and the desulfurization wastewater in step S4 until the high Cl content in step S5 is reached. - Cl in wastewater - After the concentration is >30%, the high Cl - Wastewater is evaporated, crystallized, and recovered to obtain industrial chloride salts;

[0013] S7. The three-stage slurry is subjected to pressure filtration to separate the filtrate and filter cake, wherein the filtrate is recycled to the high-Cl solution in S5. - In the wastewater, the filter cake is washed and dried to obtain calcium sulfate dihydrate product.

[0014] Furthermore, in step S1, the semi-dry desulfurization ash is first screened to a particle size ≤200 mesh before being mixed with the acid production wastewater.

[0015] Furthermore, the oxygen or air flow rate in S2 is 0.5-1.0 L / (min·L slurry).

[0016] Furthermore, the catalyst is an iron salt or a manganese salt, and the catalyst concentration is 0.01-0.1 mol / L.

[0017] Furthermore, the precipitant is sodium sulfide or TMT-15.

[0018] Furthermore, the flocculant is polyaluminum chloride and polyacrylamide, and the weight ratio of polyaluminum chloride to polyacrylamide is 3:(1-3).

[0019] Furthermore, the sintering temperature is 800-1000℃.

[0020] Furthermore, the calcium sulfate dihydrate seed crystals are calcium sulfate dihydrate microcrystals with a particle size of 10-50 μm.

[0021] Furthermore, the number of times the washing is performed in S7 is two or more.

[0022] Furthermore, the drying temperature in S7 is 100-120°C.

[0023] The beneficial effects of this application are:

[0024] This application utilizes semi-dry desulfurization ash containing CaSO4·0.5H2O and Ca(OH)2, strongly acidic acid production wastewater containing H2SO4, and Cl... - and Ca 2+ Using desulfurization wastewater as the main raw material, and through a synergistic process of "waste acid dissolution, waste calcium replenishment, catalytic oxidation, and crystal-controlled purification," high-purity calcium sulfate dihydrate (gypsum dihydrate) that meets the GB / T 37785-2019 standard for building gypsum and can be used in the building materials industry is prepared, achieving resource utilization of the above three types of waste / wastewater. Furthermore, in this application, the utilization rate of semi-dry desulfurization ash is >90%, the recovery rates of H2SO4 in acid-producing wastewater and Ca+ in desulfurization wastewater are both >85%, the heavy metal solidification rate is >99%, and no additional waste or wastewater is generated after preparation, truly achieving the technical effect of "treating waste with waste" and zero discharge.

[0025] Compared to the traditional limestone-gypsum method, this application reduces raw material costs by more than 40%, achieving both environmental and economic benefits, and providing an innovative solution for solid waste / wastewater treatment in industries such as coal-fired power plants and steel metallurgy. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flow chart of the calcium sulfate preparation process provided in the embodiments of this application.

[0028] Figure 2 The image shows the XRD pattern of the calcium sulfate dihydrate product obtained in Example 1. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In the description of this application, the experimental methods, unless otherwise specified, are conventional methods; the reagents and materials, unless otherwise specified, are all commercially available.

[0030] The following disclosure provides many different implementations or examples for carrying out this application. Of course, these are merely examples and are not intended to limit the scope of this application. Those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0031] In the following embodiments of this application, the semi-dry desulfurization ash used is a byproduct generated after sintering flue gas is desulfurized by SDA semi-dry method; the acid production wastewater is the wastewater generated during the production of sulfuric acid for impurity removal in the process of sulfur resource reuse during desulfurization of coking flue gas by activated coke; and the desulfurization wastewater is the wastewater discharged from power plant flue gas during limestone-gypsum desulfurization.

[0032] Example 1

[0033] This application provides a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater, such as... Figure 1 As shown, it includes the following steps:

[0034] S1. The semi-dry desulfurization ash is crushed and screened to a particle size of ≤200 mesh. The screened semi-dry desulfurization ash is mixed with acid production wastewater at a solid-liquid ratio of 1:3. Concentrated sulfuric acid is added to adjust the pH value to 2, and the mixture is stirred to form a primary slurry.

[0035] S2. Oxygen is introduced into the primary slurry, and ferric chloride is added as a catalyst. The mixture is then reacted at 50°C for 4 hours to oxidize calcium sulfite in the primary slurry to calcium sulfate. The oxygen flow rate is 0.5 L / (min·L slurry), and the catalyst concentration is 0.01 mol / L.

[0036] S3. Sodium sulfide is added to the primary slurry after the reaction in S2 as a precipitant, and polyaluminum chloride and polyacrylamide are mixed in a weight ratio of 3:1 as a flocculant for flocculation. After solid-liquid separation for 10 minutes, secondary slurry and heavy metal sludge are obtained. The heavy metal sludge is washed 3 times, and the washing liquid is recycled back to the secondary slurry. The sludge is solidified with cement and then sintered at 950℃.

[0037] S4. Add desulfurization wastewater to the secondary slurry and adjust the supersaturation of the system to 1.2. Add 0.1% of calcium sulfate dihydrate microcrystals with a particle size of 10μm as calcium sulfate dihydrate seed crystals and induce crystallization for 2 hours.

[0038] S5. The secondary slurry that has completed crystallization in S4 is treated with a reverse osmosis membrane to obtain a tertiary slurry and a high-Cl slurry. - Wastewater, including tertiary slurry containing Cl - Concentration <100mg / L, high Cl - Cl in wastewater - Concentration > 5%;

[0039] S6. The high Cl - Wastewater is recycled into the mixture of the secondary slurry and the desulfurization wastewater in step S4 until the high Cl content in step S5 is reached. - Cl in wastewater - After the concentration is >30%, the high Cl - Wastewater is evaporated, crystallized, and recovered to obtain industrial chloride salts;

[0040] S7. The three-stage slurry is subjected to pressure filtration to separate the filtrate and filter cake, wherein the filtrate is recycled to the high-Cl solution in S5. - In the wastewater, the filter cake is washed with deionized water in a three-stage countercurrent process and then dried at 105°C for 8 hours to obtain calcium sulfate dihydrate product.

[0041] After the above process, the utilization rate of the semi-dry desulfurization ash is 93.6%, and the recovery rate of H2SO4 in the acid production wastewater and Ca in the desulfurization wastewater is [not specified]. 2+ The recovery rates were 87.9% and 91.6%, respectively, and the solidification rate of the heavy metals was 99.8%.

[0042] Example 2

[0043] This application provides a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater, such as... Figure 1 As shown, it includes the following steps:

[0044] S1. The semi-dry desulfurization ash is crushed and screened to a particle size of ≤200 mesh. The screened semi-dry desulfurization ash is mixed with acid production wastewater at a solid-liquid ratio of 1:5. Concentrated sulfuric acid is added to adjust the pH value to 3, and the mixture is stirred to form a primary slurry.

[0045] S2. Oxygen is introduced into the primary slurry, and ferric chloride is added as a catalyst. The mixture is then reacted at 60°C for 3 hours to oxidize calcium sulfite in the primary slurry to calcium sulfate. The oxygen flow rate is 0.8 L / (min·L slurry), and the concentration of the catalyst is 0.05 mol / L.

[0046] S3. TMT-15 is added to the primary slurry after the reaction in S2 as a precipitant, and polyaluminum chloride and polyacrylamide are mixed in a weight ratio of 3:2 as a flocculant for flocculation. After solid-liquid separation for 20 minutes, secondary slurry and heavy metal sludge are obtained. The heavy metal sludge is washed twice, and the washing liquid is recycled back to the secondary slurry. The sludge is solidified with cement and then sintered at 950℃.

[0047] S4. Add desulfurization wastewater to the secondary slurry and adjust the supersaturation of the system to 1.4. Add 0.5% of calcium sulfate dihydrate microcrystals with a particle size of 30μm as calcium sulfate dihydrate seed crystals and induce crystallization for 3 hours.

[0048] S5. The secondary slurry that has completed crystallization in S4 is treated with a reverse osmosis membrane to obtain a tertiary slurry and a high-Cl slurry. - Wastewater, including tertiary slurry containing Cl - Concentration <100mg / L, high Cl - Cl in wastewater - Concentration > 5%;

[0049] S6. The high Cl - Wastewater is recycled into the mixture of the secondary slurry and the desulfurization wastewater in step S4 until the high Cl content in step S5 is reached. - Cl in wastewater - After the concentration is >30%, the high Cl - Wastewater is evaporated, crystallized, and recovered to obtain industrial chloride salts;

[0050] S7. The three-stage slurry is subjected to pressure filtration to separate the filtrate and filter cake, wherein the filtrate is recycled to the high-Cl solution in S5. - In the wastewater, the filter cake is washed with deionized water in a three-stage countercurrent process and then dried at 105°C for 8 hours to obtain calcium sulfate dihydrate product.

[0051] After the above process, the utilization rate of semi-dry desulfurization ash is 94.6%, and the recovery rate of H2SO4 in acid production wastewater and Ca in desulfurization wastewater is [not specified]. 2The recovery rates were 88.5% and 92.1%, respectively, and the heavy metal solidification rate was 99.7%.

[0052] Example 3

[0053] This application provides a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater, such as... Figure 1 As shown, it includes the following steps:

[0054] S1. The semi-dry desulfurization ash is crushed and screened to a particle size of ≤200 mesh. The screened semi-dry desulfurization ash is mixed with acid production wastewater at a solid-liquid ratio of 1:8. Concentrated sulfuric acid is added to adjust the pH value to 5, and the mixture is stirred to form a primary slurry.

[0055] S2. Oxygen is introduced into the primary slurry, and manganese chloride is added as a catalyst. The mixture is then reacted at 80°C for 2 hours to oxidize calcium sulfite in the primary slurry to calcium sulfate. The oxygen flow rate is 1.0 L / (min·L slurry), and the catalyst concentration is 0.1 mol / L.

[0056] S3. Sodium sulfide is added to the primary slurry after the reaction in S2 as a precipitant, and polyaluminum chloride and polyacrylamide are mixed in a weight ratio of 1:1 as a flocculant for flocculation. After solid-liquid separation for 10 minutes, secondary slurry and heavy metal sludge are obtained. The heavy metal sludge is washed 3 times, and the washing liquid is recycled back to the secondary slurry. The sludge is solidified with cement and then sintered at 950℃.

[0057] S4. Add desulfurization wastewater to the secondary slurry and adjust the supersaturation of the system to 1.2. Add 0.1% of calcium sulfate dihydrate microcrystals with a particle size of 10μm as calcium sulfate dihydrate seed crystals and induce crystallization for 2 hours.

[0058] S5. The secondary slurry that has completed crystallization in S4 is treated with a reverse osmosis membrane to obtain a tertiary slurry and a high-Cl slurry. - Wastewater, including tertiary slurry containing Cl - Concentration <100mg / L, high Cl - Cl in wastewater - Concentration > 5%;

[0059] S6. The high Cl - Wastewater is recycled into the mixture of the secondary slurry and the desulfurization wastewater in step S4 until the high Cl content in step S5 is reached. - Cl in wastewater - After the concentration is >30%, the high Cl - Wastewater is evaporated, crystallized, and recovered to obtain industrial chloride salts;

[0060] S7. The three-stage slurry is subjected to pressure filtration to separate the filtrate and filter cake, wherein the filtrate is recycled to the high-Cl solution in S5. - In the wastewater, the filter cake is washed with deionized water in a three-stage countercurrent process and then dried at 105°C for 8 hours to obtain calcium sulfate dihydrate product.

[0061] After the above process, the utilization rate of the semi-dry desulfurization ash is 95.2%, and the recovery rate of H2SO4 in the acid production wastewater and Ca in the desulfurization wastewater is [not specified]. 2 The recovery rates were 88.9% and 92.4%, respectively, and the heavy metal solidification rate was 99.8%.

[0062] Performance testing

[0063] To verify the product quality obtained in each embodiment, the calcium sulfate dihydrate products obtained in Examples 1-3 were tested for composition and performance. The contents of CaSO4·2H2O, MgO, Na2O, and Cl were tested according to the methods in the national standard GB / T 37785-2019 "Flue Gas Desulfurization Gypsum". Whiteness was tested according to the methods in the national standard GB / T 5950-2008 "Methods for Measuring Whiteness of Building Materials and Non-metallic Mineral Products". Compressive strength was tested according to the methods in the national building materials industry standard GB 9776-88 "Building Gypsum". As and Pb contents were tested according to the methods in the national environmental protection standard HJ 557-2010 "Solid Waste Leaching Toxicity Leaching Method - Horizontal Oscillation Method". The test results for each embodiment are as follows:

[0064] Table 1. Product component content and performance test results for each embodiment.

[0065]

[0066] As can be seen from the product test results of Examples 1-3 in Table 1, the calcium sulfate dihydrate products prepared using the method of this application all have a CaSO4·2H2O content of over 99.2%, a whiteness of over 92.3, and a compressive strength of 14.2 MPa / m³. 3 The As content is below 0.08%, even reaching 0.03%; the Pb content is below 0.12%; the MgO content is below 0.10%; the Na₂O content is below 0.02%; and the Cl content is all <0.01%. Therefore, the calcium sulfate dihydrate product prepared using the method described in this application fully meets the performance requirements of the GB / T 37785-2019 standard for building gypsum and can be used in the building materials industry.

[0067] Figure 2 The image shows the XRD pattern of the calcium sulfate dihydrate product obtained in Example 1. The figure further verifies that the main component of the product is calcium sulfate dihydrate (gypsum).

[0068] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0069] The above provides a detailed description of a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater, as provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. 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 of the technical features. These 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 this application.

Claims

1. A method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater, characterized in that, Includes the following steps: S1. Mix the semi-dry desulfurization ash with the acid production wastewater, and add concentrated sulfuric acid to adjust the pH value to 2-5. Stir to form a primary slurry, wherein the solid-liquid ratio of the semi-dry desulfurization ash to the acid production wastewater is 1:(3-8). S2. Introduce oxygen or air into the primary slurry and add a catalyst, then react at 50-80℃ for 1-4 hours to oxidize the calcium sulfite in the primary slurry to calcium sulfate. S3. Add precipitant and flocculant to the primary slurry after the reaction in S2 for flocculation. Then, after solid-liquid separation for 10-30 minutes, secondary slurry and heavy metal sludge are obtained. The heavy metal sludge is washed 1-3 times, and the washing liquid is returned to the secondary slurry. The sludge is solidified with cement and then sintered. S4. Add desulfurization wastewater to the secondary slurry and adjust the supersaturation to 1.2-1.

5. Add 0.1-1.0% calcium sulfate dihydrate seed crystals and induce crystallization for 2-3 hours. S5. The secondary slurry that has completed crystallization in S4 is treated with a reverse osmosis membrane to obtain a tertiary slurry and a high-Cl slurry. - Wastewater, including tertiary slurry containing Cl - Concentration <100 mg / L, high Cl - Cl in wastewater - Concentration > 5%; S6. The high Cl - Wastewater is recycled into the mixture of the secondary slurry and the desulfurization wastewater in step S4 until the high Cl content in step S5 is reached. - Cl in wastewater - After the concentration is >30%, the high Cl - Wastewater is evaporated, crystallized, and recovered to obtain industrial chloride salts; S7. The three-stage slurry is subjected to pressure filtration to separate the filtrate and filter cake, wherein the filtrate is recycled to the high-Cl solution in S5. - In the wastewater, the filter cake is washed and dried to obtain calcium sulfate dihydrate product; The catalyst is an iron salt or a manganese salt, and the precipitant is sodium sulfide or TMT-15.

2. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater as described in claim 1, characterized in that: In step S1, the semi-dry desulfurization ash is screened to a particle size of ≤200 mesh before being mixed with acid production wastewater.

3. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater as described in claim 1, characterized in that: The oxygen or air flow rate in S2 is 0.5-1.0 L / (min·L slurry).

4. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater as described in claim 1, characterized in that: The catalyst concentration is 0.01-0.1 mol / L.

5. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater as described in claim 1, characterized in that: The flocculant is polyaluminum chloride and polyacrylamide, and the weight ratio of polyaluminum chloride to polyacrylamide is 3:(1-3).

6. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater as described in claim 1, characterized in that: The sintering temperature is 800-1000℃.

7. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater as described in claim 1, characterized in that: The calcium sulfate dihydrate seed crystals are calcium sulfate dihydrate microcrystals with a particle size of 10-50 μm.

8. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater as described in claim 1, characterized in that: The number of times the washing is performed in S7 is two or more.

9. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater, and desulfurization wastewater as described in claim 1, characterized in that: The drying temperature in S7 is 100-120℃.

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