Calcium sulfate preparation method based on semi-dry desulfurization ash, acid-making wastewater and desulfurization wastewater

Abstract

The embodiment of the invention provides a calcium sulfate preparation method based on semi-dry desulfurization ash, acid-making wastewater and desulfurization wastewater. According to the method, semi-dry desulfurization ash containing CaSO-0. 5H-O and Ca (OH)-, strongly acidic acid-making wastewater containing H2SO4 and desulfurization wastewater containing Cl-and Ca < 2 + > are used as main raw materials, and high-purity calcium sulfate dihydrate (dihydrate gypsum) is prepared through a synergistic process of dissolving ash with waste acid, supplementing a source with waste calcium, performing catalytic oxidation and performing crystal control purification. The resource utilization of the three wastes / wastewater is realized. In the obtained calcium sulfate dihydrate product, the content of CaSO4. 2H2O is 99.2% or above, the whiteness is 92.3 or above, the compressive strength is 14.2 MPa kg / m < 3 > or above, the content of As is 0.08% or below, the content of Pb is 0.12% or below, the content of MgO is 0.10% or below, the content of Na2O is 0.02% or below, and the content of Cl is 1t. And 0.01% of the total weight. The gypsum completely meets the building gypsum standard of GB / T 37785-2019, and can be used in the building material industry.

Description

Technical Field

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

[0002] Semi-dry desulfurization ash is a mixture mainly composed of CaSO□·0.5H□O and Ca(OH)□. Its high heavy metal content makes its comprehensive utilization difficult. At the same time, its poor stability makes its long-term storage prone to environmental pollution.

[0003] In this regard, the prior art discloses a method and device for preparing calcium sulfate whiskers using sintering flue gas desulfurization ash (application number CN202211354173.4). This method utilizes the Cl - Mg 2+ , K + 、Na + Plasma, without adding auxiliary reagents, prepares the desulfurization ash slurry and then undergoes an acidic hydrothermal reaction to generate calcium sulfate whiskers, thereby realizing the comprehensive utilization of sintering flue gas desulfurization ash. However, the above technical route does not consider how to remove other harmful impurities (such as As, Pb, etc.) contained in the desulfurization ash. The purity of the prepared calcium sulfate is insufficient and cannot meet the requirements of the construction industry, which greatly limits its utilization value; secondly, the separation of chloride salts in high-chloride wastewater is achieved by ion exchange resin, and the extraction efficiency is low; finally, this method adds a large amount of inorganic acid and alkali during the preparation process, which will result in a large amount of wastewater with different characteristics. The wastewater needs to be treated through its specific wastewater treatment process, which makes the entire process relatively cumbersome. Summary of the Invention

[0004] In order to solve the technical problems in the prior art of preparing calcium sulfate based on semi-dry desulfurization ash, such as the insufficient purity of the product obtained, the subsequent generation of wastewater, and the need to adopt a specific process to treat the wastewater, this application proposes a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater. By synergistically treating semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater to prepare high-purity calcium sulfate dihydrate (dihydrate gypsum), the resource utilization of the above three wastes / wastewaters is realized. At the same time, no additional waste or wastewater is generated during the preparation process, truly achieving the technical effect of "waste treatment with waste" and zero emissions.

[0005] In order to achieve the above-mentioned purpose, this application adopts the following technical solutions:

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

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

[0008] S2. introducing oxygen or air into the primary slurry, adding a catalyst and reacting at 50-80° C. for 1-4 hours to oxidize the calcium sulfite in the primary slurry into calcium sulfate;

[0009] S3, adding a precipitant and a flocculant to the primary slurry after the reaction in S2 for flocculation, followed by solid-liquid separation for 10-30 minutes to obtain a secondary slurry and heavy metal sludge, washing the heavy metal sludge 1-3 times, returning the washing liquid to the secondary slurry, and solidifying the sludge with cement and then sintering it;

[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 by reverse osmosis membrane to obtain tertiary slurry and high Cl - Wastewater, including Cl in the tertiary slurry - Concentration <100 mg / L, high Cl - Cl in wastewater - Concentration>5%;

[0012] S6, the high Cl - The wastewater is circulated and added to the mixed solution of the secondary slurry of S4 and the desulfurization wastewater until the high Cl in S5 is - Cl in wastewater - When the concentration is greater than 30%, the high Cl - The wastewater is evaporated and crystallized to recover industrial chloride salt;

[0013] S7, the three slurries are subjected to filter press separation to obtain filtrate and filter cake, wherein the filtrate is circulated and added to the high Cl in S5 - The filter cake is washed and dried in the wastewater to obtain calcium sulfate dihydrate product.

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

[0015] Furthermore, the flow rate of oxygen or air 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 polyaluminium chloride and polyacrylamide, and the weight ratio of polyaluminium chloride to polyacrylamide is 3:(1-3).

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

[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 washing steps in S7 is more than two times.

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

[0023] The beneficial effects of this application are:

[0024] This application uses semi-dry desulfurization ash containing CaSO□·0.5H□O and Ca(OH)□, strongly acidic acid production wastewater containing H2SO4 and strong acidic acid production wastewater containing Cl - and Ca 2+ The desulfurization wastewater is used as the main raw material and is prepared through the collaborative process of "waste acid ash dissolution, waste calcium source supplementation, catalytic oxidation, and crystal control purification" to obtain high-purity calcium sulfate dihydrate (dihydrate gypsum) that meets the "GB / T 37785-2019" building gypsum standard. It can be used in the building materials industry to achieve resource utilization of the above three wastes / wastewaters. In this application, the semi-dry desulfurization ash utilization rate is greater than 90%, the H2SO4 in the acid wastewater and the Ca+ recovery rate in the desulfurization wastewater are both greater than 85%, and the heavy metal solidification rate is greater than 99%. After the preparation is completed, no additional waste or wastewater is generated, truly achieving the technical effect of "waste treatment with waste" and zero emissions.

[0025] Compared with the traditional limestone-gypsum method, this application reduces raw material costs by more than 40%, has both environmental and economic benefits, and provides an innovative solution for solid waste / wastewater treatment in coal-fired power plants, steel and metallurgy industries, and other industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present application. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

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

[0028] Figure 2 The XRD pattern of the calcium sulfate dihydrate product obtained in Example 1 is shown. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present application will be clearly and completely described below in combination with the technical solutions of the embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative work 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, can be obtained from commercial channels.

[0030] The disclosure below provides many different embodiments or examples for implementing the present application. Of course, they are merely examples and are not intended to limit the present application. Those skilled in the art will appreciate the application of other processes and / or the use of other materials.

[0031] The semi-dry desulfurization ash used in the following embodiments of this application is a by-product produced after the sintering flue gas is desulfurized by the SDA semi-dry method, the acid-making wastewater is the wastewater produced when sulfuric acid is produced and impurities are removed during the sulfur resource recycling process when the coking flue gas is desulfurized by activated coke, and the desulfurization wastewater is the wastewater discharged when the power plant flue gas is desulfurized by the limestone-gypsum method.

[0032] Example 1

[0033] The present invention provides a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater. Figure 1 As shown, the following steps are included:

[0034] S1. Crushing and screening the semi-dry desulfurization ash to a particle size of ≤200 mesh, mixing the screened semi-dry desulfurization ash with acid production wastewater at a solid-liquid ratio of 1:3, adding concentrated sulfuric acid to adjust the pH value to 2, and stirring to form a primary slurry;

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

[0036] S3, adding sodium sulfide as a precipitant, and polyaluminum chloride and polyacrylamide in a weight ratio of 3:1 as a flocculant to the primary slurry after the reaction in S2 for flocculation, followed by solid-liquid separation for 10 minutes to obtain a secondary slurry and heavy metal sludge, washing the heavy metal sludge three times, recycling the washing liquid back to the secondary slurry, and sintering the sludge at 950°C after cement solidification;

[0037] S4, adding desulfurization wastewater to the secondary slurry and adjusting the system supersaturation to 1.2, adding 0.1% of calcium sulfate dihydrate microcrystals with a particle size of 10 μm as calcium sulfate dihydrate seeds, and inducing crystallization for 2 hours;

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

[0039] S6, the high Cl - The wastewater is circulated and added to the mixed solution of the secondary slurry of S4 and the desulfurization wastewater until the high Cl in S5 is - Cl in wastewater - When the concentration is greater than 30%, the high Cl - The wastewater is evaporated and crystallized to recover industrial chloride salt;

[0040] S7, the three slurries are subjected to filter press separation to obtain filtrate and filter cake, wherein the filtrate is circulated and added to the high Cl in S5 - In the wastewater, the filter cake is washed with deionized water three times in countercurrent and dried at 105° C. for 8 h to obtain a calcium sulfate dihydrate product.

[0041] After the above process treatment, the utilization rate of the semi-dry desulfurization ash is 93.6%, the recovery rate of H2SO4 in the acid wastewater and the recovery rate of Ca2PO4 in the desulfurization wastewater are 93.6%. 2+ The recovery rates were 87.9% and 91.6% respectively, and the heavy metal solidification rate was 99.8%.

[0042] Example 2

[0043] The present invention provides a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater. Figure 1 As shown, the following steps are included:

[0044] S1. Crushing and screening the semi-dry desulfurization ash to a particle size of ≤200 mesh, mixing the screened semi-dry desulfurization ash with acid production wastewater at a solid-liquid ratio of 1:5, adding concentrated sulfuric acid to adjust the pH value to 3, and stirring to form a primary slurry;

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

[0046] S3. To the primary slurry after the reaction in S2, TMT-15 is added as a precipitant, and polyaluminum chloride and polyacrylamide are mixed in a weight ratio of 3:2 as a flocculant for flocculation. Then, solid-liquid separation is performed for 20 minutes to obtain a secondary slurry and heavy metal sludge. 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 sintered at 950°C.

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

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

[0049] S6, the high Cl - The wastewater is circulated and added to the mixed solution of the secondary slurry of S4 and the desulfurization wastewater until the high Cl in S5 is - Cl in wastewater - When the concentration is greater than 30%, the high Cl - The wastewater is evaporated and crystallized to recover industrial chloride salt;

[0050] S7, the three slurries are subjected to filter press separation to obtain filtrate and filter cake, wherein the filtrate is circulated and added to the high Cl in S5 - In the wastewater, the filter cake is washed with deionized water three times in countercurrent and dried at 105° C. for 8 h to obtain a calcium sulfate dihydrate product.

[0051] After the above process treatment, the utilization rate of semi-dry desulfurization ash is 94.6%, the recovery rate of H2SO4 in acid wastewater and the recovery rate of Ca in desulfurization wastewater are 94.6%. 2+The recovery rates were 88.5% and 92.1% respectively, and the heavy metal solidification rate was 99.7%.

[0052] Example 3

[0053] The present invention provides a method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater. Figure 1 As shown, the following steps are included:

[0054] S1. Crushing and screening the semi-dry desulfurization ash to a particle size of ≤200 mesh, mixing the screened semi-dry desulfurization ash with acid production wastewater at a solid-liquid ratio of 1:8, adding concentrated sulfuric acid to adjust the pH value to 5, and stirring to form a primary slurry;

[0055] S2. introducing oxygen into the primary slurry, adding manganese chloride as a catalyst, and reacting at 80° C. for 2 hours to oxidize the calcium sulfite in the primary slurry to calcium sulfate; wherein the oxygen introduction rate is 1.0 L / (min·L slurry) and the catalyst concentration is 0.1 mol / L;

[0056] S3, adding sodium sulfide as a precipitant, and polyaluminum chloride and polyacrylamide in a weight ratio of 1:1 as a flocculant to the primary slurry after the reaction in S2 for flocculation, followed by solid-liquid separation for 10 minutes to obtain a secondary slurry and heavy metal sludge, washing the heavy metal sludge three times, recycling the washing liquid back to the secondary slurry, and sintering the sludge at 950°C after cement solidification;

[0057] S4, adding desulfurization wastewater to the secondary slurry and adjusting the system supersaturation to 1.2, adding 0.1% of calcium sulfate dihydrate microcrystals with a particle size of 10 μm as calcium sulfate dihydrate seeds, and inducing crystallization for 2 hours;

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

[0059] S6, the high Cl - The wastewater is circulated and added to the mixed solution of the secondary slurry of S4 and the desulfurization wastewater until the high Cl in S5 is - Cl in wastewater - When the concentration is greater than 30%, the high Cl - The wastewater is evaporated and crystallized to recover industrial chloride salt;

[0060] S7, the three slurries are subjected to filter press separation to obtain filtrate and filter cake, wherein the filtrate is circulated and added to the high Cl in S5 - In the wastewater, the filter cake is washed with deionized water three times in countercurrent and dried at 105° C. for 8 h to obtain a calcium sulfate dihydrate product.

[0061] After the above process treatment, the utilization rate of the semi-dry desulfurization ash is 95.2%, the recovery rate of H2SO4 in the acid wastewater and the recovery rate of Ca2PO4 in the desulfurization wastewater are 95.2%. 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 quality of the products obtained in each example, the calcium sulfate dihydrate products obtained in Examples 1-3 were tested for component content and performance. The CaSO4·2H2O, MgO, Na2O, and Cl contents were tested according to the methods specified in the national standard GB / T 37785-2019 "Flue Gas Desulfurization Gypsum," the whiteness was tested according to the method specified in the national standard GB / T 5950-2008 "Method for Measurement of Whiteness of Building Materials and Non-metallic Mineral Products," the compressive strength was tested according to the method specified in the national building materials industry standard GB 9776-88 "Building Gypsum," and the As and Pb contents were tested according to the method specified in the national environmental protection standard HJ 557-2010 "Toxicity Leaching Method for Solid Waste - Horizontal Oscillation Method." The test results for each example are as follows:

[0064] Table 1 Component content and performance test results of each example product

[0065]

[0066] From the product test results of Examples 1-3 in Table 1, it can be seen that the content of CaSO4·2H2O in the calcium sulfate dihydrate products prepared by the method of the present application is all above 99.2%, the whiteness is all above 92.3, and the compressive strength is all 14.2MPakg / m 3 As above, the As content is below 0.08%, and can even reach 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%. It can be seen that the performance of the calcium sulfate dihydrate product prepared by the method of the application fully complies with the "GB / T 37785-2019" building gypsum standard and can be used in the building materials industry.

[0067] Figure 2 This is the XRD pattern of the calcium sulfate dihydrate product obtained in Example 1, which further verifies that the main component of the product is calcium sulfate dihydrate (gypsum).

[0068] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0069] The above is a detailed introduction to the calcium sulfate preparation method based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater provided in the embodiments of the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solution and core ideas of the present application; ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater, characterized in that: The steps include: S1. Mixing semi-dry desulfurization ash with acid-making wastewater, adding concentrated sulfuric acid to adjust the pH value to 2-5, and stirring to form a primary slurry, wherein the solid-liquid ratio of the semi-dry desulfurization ash and the acid-making wastewater is 1:(3-8); S2. introducing oxygen or air into the primary slurry, adding a catalyst and reacting at 50-80° C. for 1-4 hours to oxidize the calcium sulfite in the primary slurry into calcium sulfate; S3, adding a precipitant and a flocculant to the primary slurry after the reaction in S2 for flocculation, followed by solid-liquid separation for 10-30 minutes to obtain a secondary slurry and heavy metal sludge, washing the heavy metal sludge 1-3 times, returning the washing liquid to the secondary slurry, and solidifying the sludge with cement and then sintering it; 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, treating the secondary slurry that has completed crystallization in S4 with a reverse osmosis membrane to obtain a tertiary slurry and high-Cl- wastewater, wherein the Cl- concentration in the tertiary slurry is less than 100 mg / L, and the Cl- concentration in the high-Cl- wastewater is greater than 5%; S6, circulating the high Cl- wastewater into the mixed solution of the secondary slurry and the desulfurization wastewater in S4 until the Cl- concentration in the high Cl- wastewater in S5 is greater than 30%, evaporating and crystallizing the high Cl- wastewater to recover industrial chloride salt; S7, the three slurries are subjected to filter press separation to obtain a filtrate and a filter cake, wherein the filtrate is circulated and added to the high Cl- wastewater in S5, and the filter cake is washed and dried to obtain a calcium sulfate dihydrate product.

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

3. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater according to claim 1, characterized in that: The flow rate of oxygen or air 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 according to claim 1, characterized in that: The catalyst is an iron salt or a manganese salt, and 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 according to claim 1, characterized in that: The precipitant is sodium sulfide or TMT-15.

6. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater according to claim 1, characterized in that: The flocculants are polyaluminium chloride and polyacrylamide, and the weight ratio of the polyaluminium chloride to the polyacrylamide is 3:(1-3).

7. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater according to claim 1, characterized in that: The sintering temperature is 800-1000°C.

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

9. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater according to claim 1, characterized in that: The number of times of washing in S7 is more than two times.

10. The method for preparing calcium sulfate based on semi-dry desulfurization ash, acid production wastewater and desulfurization wastewater according to claim 1, characterized in that: The drying temperature in S7 is 100-120°C.

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