Method for preparing alpha-type semi-hydrated gypsum through hydrothermal treatment of incineration fly ash

Abstract

The invention relates to a method for preparing alpha-type semi-hydrated gypsum through hydrothermal treatment of incineration fly ash. Chlorine salt, heavy metal and dioxin in the incineration fly ash are removed through three-step hydrothermal treatment, and calcium is converted into high-strength gypsum in situ. According to the method, fly ash treatment and byproduct utilization are integrated, sodium sulfate, sulfuric acid and a crystal modifier are added in the hydrothermal process, and non-calcium minerals are converted into zeolite substances beneficial to a gypsum system; non-gypsum calcium in the fly ash is converted into calcium sulfate, and then the calcium sulfate is converted into alpha-type semi-hydrated gypsum. Alkali metal salts are dissolved in the hydrothermal process, and dioxin is oxidized and decomposed. Compared with an existing main incineration fly ash resource utilization technology, the method has the advantages of being low in fly ash treatment temperature, low in carbon emission and high in product additional value.

Description

Technical Field

[0001] The invention relates to a method for treating incineration fly ash, and in particular to a method for preparing alpha-type hemihydrate gypsum by hydrothermal treatment of incineration fly ash. Background Art

[0002] Fly ash from the incineration of domestic waste mainly comes from light and fine powder collected by the flue gas purification device of the incinerator. Due to the high concentration of heavy metals and dioxins and other harmful substances, fly ash from the incineration of domestic waste is included in the "National List of Hazardous Wastes", code 772-002-18. At present, the main method of harmless disposal of fly ash from incineration is chelation landfill, that is, adding chelating agents to the fly ash for mixing, so that the soluble heavy metals in it are converted into insoluble complexes, thereby reducing its environmental risks, and then transported to the landfill area. The problems of chelation landfill are: the long-term stability of the chelated product is poor; it occupies the precious land resources of the city. This will lead to a large number of chelated fly ash in the existing landfill area. Invalidation and increased environmental risks. A large number of incineration plants will face the dilemma of saturation of the existing fly ash landfill area and no land for expansion or new construction. In view of the above two problems, the landfill disposal of incineration fly ash is difficult to sustain, and resource utilization is particularly urgent.

[0003] At present, there are three main technologies for resource utilization of incineration fly ash at home and abroad, high-temperature melting, cement kiln co-treatment and sintering to prepare ceramsite. The basic principle is to decompose dioxins at high temperature and solidify heavy metals in the product. The high-temperature melting process temperature is about 1500℃, the high-temperature melting process has good independence and high safety of the melt, but there are problems such as poor operation stability, difficulty in resource utilization of the melt, large amount of secondary fly ash, high energy consumption and high operating cost. The cement kiln co-treatment process temperature is about 1400℃, which has the advantages of low investment cost and good operation stability, but there are problems such as dependence on cement production process and poor independence, difficulty in resource utilization of crystallized salt, low value of cement products, increased environmental risks and high operating costs. The sintering process temperature for preparing ceramsite is about 1200℃, which has the advantages of good process independence and good operation stability, but there are problems such as high operating cost, increased environmental risks of ceramsite products, large amount of secondary fly ash and high energy consumption. Although the three existing technologies can realize the resource utilization of fly ash, they all have problems such as high energy consumption, high cost and high carbon emissions caused by high heat treatment temperature. This patent realizes the harmless disposal of fly ash from garbage incineration and the in-situ preparation of high-strength gypsum building materials. The process temperature for preparing high-strength gypsum building materials is within 300°C, and the final product, α-type hemihydrate gypsum, has high added value and is clean. Compared with the process of high-temperature melting, cement production and sintering to prepare ceramsite, it can effectively solve the above-mentioned contradictions of high energy consumption, high cost and high carbon emissions. In addition, heavy metal hydrothermal dissolution, dioxin hydrothermal decomposition, high-salt wastewater, and removal of heavy metals and slightly soluble calcium sulfate can be evaporated to produce salt, which can further improve the economy of the process. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing α-type hemihydrate gypsum by hydrothermal treatment of incineration fly ash, so as to solve the problem of difficult landfill and resource utilization of incineration fly ash.

[0005] A method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash, comprising the steps of: S1: Mix the incineration fly ash, sodium sulfate and water to make pulp; S2: subjecting the slurry obtained in S1 to a first-stage pressurized hydrothermal reaction to convert silicon, aluminum, magnesium and iron impurities in the fly ash into zeolite substances and converting part of the calcium substances into calcium sulfate; S3: adding sulfuric acid to the slurry treated by S2 to carry out a second stage of pressurized hydrothermal reaction, converting the calcium substances that were not converted into calcium sulfate in the first stage into calcium sulfate and dissolving heavy metals; S4: adding a crystal conversion agent to the slurry treated in S3 to carry out a third stage of pressurized hydrothermal reaction to convert calcium sulfate into α-type calcium sulfate hemihydrate; S5: filtering the product after the treatment in S4 to perform liquid-solid separation, and obtaining a solid of α-type calcium sulfate hemihydrate, which is dried and ground into powder to prepare gypsum.

[0006] Furthermore, the sodium sulfate in S1 refers to waste sodium sulfate produced in industrial production, and the sodium sulfate content is greater than 85%. The addition ratio is 0.3g Na 2 SO 4 / 1g fly ash ~ 0.7g Na 2 SO 4 / 1g fly ash.

[0007] Furthermore, in S2, the temperature of the first stage is controlled at 100-200°C; the pressure is controlled at 0-5MPa; the pH is controlled at 7-14; the liquid-solid ratio is controlled at 3-30; and the reaction time is controlled at 0.5-1.5h.

[0008] Furthermore, the sulfuric acid in S3 refers to waste sulfuric acid produced in industrial production, with a sulfuric acid content greater than 5%; the addition ratio is controlled at 0.3 g H 2 SO 4 / 1g fly ash ~ 0.7g H 2 SO 4 / 1g fly ash.

[0009] Furthermore, the temperature of the second stage in S3 is controlled at 200-300°C; the pressure is controlled at 0-10MPa; the pH is controlled at 2-7; the liquid-solid ratio is controlled at 10-30; and the reaction time is controlled at 2-8h.

[0010] Furthermore, the crystal-changing agent in S4 includes stearic acid, sodium citrate, sodium dodecylbenzene sulfonate, and maleic acid, and the addition ratio is controlled at 0.001 g / 1 g fly ash to 0.03 g / 1 g fly ash.

[0011] Furthermore, the temperature of the third stage in S4 is controlled at 90-150°C; the pressure is controlled at 0-5MPa; the pH is controlled at 2-8; the liquid-solid ratio is controlled at 3-30; the reaction time is controlled at 0.5-4h; and the temperature of the liquid-solid separation of the product is controlled at 80-100°C.

[0012] Furthermore, in S5, the product after treatment in S4 is filtered for liquid-solid separation, and the obtained liquid is high-salt wastewater. Sodium carbonate and sodium sulfide are added to the high-salt wastewater and then filtered to recover heavy metals. The filtrate is evaporated to recover NaCl and KCl, and the water vapor is recovered for pulping the incineration fly ash. Beneficial Effects

[0013] The present invention relates to a method for preparing α-type hemihydrate gypsum by hydrothermal treatment of incineration fly ash. The incineration fly ash is subjected to three steps of hydrothermal treatment to remove chloride salts, heavy metals and dioxins therein, and the calcium is in situ converted into high-strength gypsum (α-type hemihydrate gypsum), and the generated high-salt wastewater is purified to recover NaCl, KCl and heavy metals therein. The present invention integrates fly ash treatment and by-product utilization. Sodium sulfate, sulfuric acid and a crystal conversion agent are added during the hydrothermal process to convert non-calcium minerals (Si, Al, Mg, Fe, etc.) into zeolite substances that are beneficial to the gypsum system; non-gypsum calcium (CaClOH, Ca(OH)2, CaCO3) in the fly ash is converted into calcium sulfate, and the calcium sulfate is then converted into α-type hemihydrate gypsum. The hydrothermal process dissolves alkali metal salts (NaCl and KCl) and heavy metals, and oxidatively decomposes dioxins. The main components of the wastewater produced by hydrothermal treatment are NaCl and KCl, as well as heavy metals and slightly soluble calcium. Sodium carbonate and sodium sulfide are added to the wastewater to remove and recover heavy metals. The purified salt solution is evaporated and salted to obtain NaCl crystals and KCl crystals. Compared with the current main incineration fly ash resource utilization technologies (such as high-temperature melting, cement kiln co-treatment and sintering to prepare ceramsite), the present invention has the advantages of low fly ash treatment temperature, low carbon emissions and high product added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the principle of a method for preparing α-type hemihydrate gypsum by hydrothermal treatment of incineration fly ash according to an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The following is a description of the implementation of the present invention by way of specific examples, which further illustrate and describe the technology of the present invention. Example 1

[0016] A method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash, comprising the steps of: S1: Mix the incineration fly ash, sodium sulfate and water to make pulp; S2: subjecting the slurry obtained in S1 to a first-stage pressurized hydrothermal reaction to convert silicon, aluminum, magnesium and iron impurities in the fly ash into zeolite substances and converting part of the calcium substances into calcium sulfate; S3: adding sulfuric acid to the slurry treated by S2 to carry out a second stage of pressurized hydrothermal reaction, converting the calcium substances that were not converted into calcium sulfate in the first stage into calcium sulfate and dissolving heavy metals; S4: adding a crystal conversion agent to the slurry treated in S3 to carry out a third stage of pressurized hydrothermal reaction to convert calcium sulfate into α-type calcium sulfate hemihydrate; S5: filtering the product after the treatment in S4 to perform liquid-solid separation, and obtaining a solid of α-type calcium sulfate hemihydrate, which is dried and ground into powder to prepare gypsum.

[0017] Furthermore, the sodium sulfate in S1 refers to waste sodium sulfate produced in industrial production, and the sodium sulfate content is greater than 85%. The addition ratio is 0.3g Na 2 SO 4 / 1g fly ash ~ 0.7g Na 2 SO 4 / 1g fly ash.

[0018] Furthermore, in S2, the temperature of the first stage is controlled at 100-200°C; the pressure is controlled at 0-5MPa; the pH is controlled at 7-14; the liquid-solid ratio is controlled at 3-30; and the reaction time is controlled at 0.5-1.5h.

[0019] Furthermore, the sulfuric acid in S3 refers to waste sulfuric acid produced in industrial production, with a sulfuric acid content greater than 5%; the addition ratio is controlled at 0.3 g H 2 SO 4 / 1g fly ash ~ 0.7g H 2 SO 4 / 1g fly ash.

[0020] Furthermore, the temperature of the second stage in S3 is controlled at 200-300°C; the pressure is controlled at 0-10MPa; the pH is controlled at 2-7; the liquid-solid ratio is controlled at 10-30; and the reaction time is controlled at 2-8h.

[0021] Furthermore, the crystal-changing agent in S4 includes stearic acid, sodium citrate, sodium dodecylbenzene sulfonate, and maleic acid, and the addition ratio is controlled at 0.001 g / 1 g fly ash to 0.03 g / 1 g fly ash.

[0022] Furthermore, the temperature of the third stage in S4 is controlled at 90-150°C; the pressure is controlled at 0-5MPa; the pH is controlled at 2-8; the liquid-solid ratio is controlled at 3-30; the reaction time is controlled at 0.5-4h; and the temperature of the liquid-solid separation of the product is controlled at 80-100°C.

[0023] Furthermore, in S5, the product after treatment in S4 is filtered for liquid-solid separation, and the obtained liquid is high-salt wastewater. Sodium carbonate and sodium sulfide are added to the high-salt wastewater and then filtered to recover heavy metals. The filtrate is evaporated to recover NaCl and KCl, and the water vapor is recovered for pulping the incineration fly ash. Example 2

[0024] like Figure 1 As shown, the method for preparing α-type hemihydrate gypsum by hydrothermal treatment of incineration fly ash comprises the following steps: mixing incineration fly ash, sodium sulfate and water, maintaining the hydrothermal reaction at a reaction temperature of 100-200°C for 0.5-1.5h, then adding sulfuric acid, maintaining the hydrothermal reaction at a reaction temperature of 200-300°C for 2-8h, then adding a crystal-changing agent, maintaining the hydrothermal reaction at a reaction temperature of 90-150°C for 0.5-4h after mixing, removing water, crystal-changing agent and the like to obtain α-gypsum crystals; grinding and modifying the prepared α-gypsum crystals to obtain α-high-strength gypsum powder. Example 3

[0025] CaSO in fly ash from a waste incineration plant 4 The content of calcium reaches 34%, and the content of other calcium reaches 35%. The fly ash from incineration is mixed with sodium sulfate at a rate of 0.5 Na 2 SO 4 g / 1g fly ash was mixed at a liquid-solid ratio of 30 mL / g, and then hydrothermally reacted at 200 °C for 0.5 h and heated to 0.6 g H 2 SO 4 Sodium sulfate was added to 1g fly ash, and the mixture was hydrothermally reacted at 280℃ for 2h. Then sodium citrate was added at 0.003g / 1g fly ash, and the mixture was hydrothermally reacted at 130℃ for 1.5h. The hydrothermally synthesized product was filtered and washed with hot water at 90℃. The washed semi-hydrated gypsum was quickly transferred to a dryer to obtain α-type semi-hydrated gypsum.

[0026] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash, characterized in that: Includes steps: S1: Mix the incineration fly ash, sodium sulfate and water to make pulp; S2: subjecting the slurry obtained in S1 to a first-stage pressurized hydrothermal reaction to convert silicon, aluminum, magnesium and iron impurities in the fly ash into zeolite substances and converting part of the calcium substances into calcium sulfate; S3: adding sulfuric acid to the slurry treated by S2 to carry out a second stage of pressurized hydrothermal reaction, converting the calcium substances that were not converted into calcium sulfate in the first stage into calcium sulfate and dissolving heavy metals; S4: adding a crystal conversion agent to the slurry treated in S3 to carry out a third stage of pressurized hydrothermal reaction to convert calcium sulfate into α-type calcium sulfate hemihydrate; S5: filtering the product after the treatment in S4 to perform liquid-solid separation, and obtaining a solid of α-type calcium sulfate hemihydrate, which is dried and ground into powder to prepare gypsum.

2. The method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash according to claim 1, characterized in that: The sodium sulfate mentioned in S1 refers to waste sodium sulfate generated in industrial production, with a sodium sulfate content greater than 85%, and an addition ratio of 0.3 g Na2SO4 / 1 g fly ash to 0.7 g Na2SO4 / 1 g fly ash.

3. The method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash according to claim 1, characterized in that: In S2, the temperature of the first stage is controlled at 100~200°C; the pressure is controlled at 0~5MPa; the pH is controlled at 7~14; the liquid-solid ratio is controlled at 3~30; and the reaction time is controlled at 0.5~1.5h.

4. The method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash according to claim 1, characterized in that: The sulfuric acid mentioned in S3 refers to waste sulfuric acid generated in industrial production, with a sulfuric acid content greater than 5%; the addition ratio is controlled at 0.3g H2SO4 / 1g fly ash~0.7g H2SO4 / 1g fly ash.

5. The method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash according to claim 1, characterized in that: The temperature of the second stage in S3 is controlled at 200~300°C; the pressure is controlled at 0~10MPa; the pH is controlled at 2~7; the liquid-solid ratio is controlled at 10~30; and the reaction time is controlled at 2~8h.

6. The method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash according to claim 1, characterized in that: The crystal-changing agent in S4 includes stearic acid, sodium citrate, sodium dodecylbenzene sulfonate, and maleic acid, and the addition ratio is controlled at 0.001 g / 1 g fly ash to 0.03 g / 1 g fly ash.

7. The method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash according to claim 1, characterized in that: The temperature of the third stage in S4 is controlled at 90~150℃; the pressure is controlled at 0~5MPa; the pH is controlled at 2~8; the liquid-solid ratio is controlled at 3~30; the reaction time is controlled at 0.5~4h; and the temperature of the liquid-solid separation of the product is controlled at 80~100℃.

8. The method for preparing α-hemihydrate gypsum by hydrothermal treatment of incineration fly ash according to claim 1, characterized in that: In S5, the product after treatment in S4 is filtered for liquid-solid separation, and the obtained liquid is high-salt wastewater. After sodium carbonate and sodium sulfide are added to the high-salt wastewater, heavy metals are recovered by filtration. The filtrate is evaporated to recover NaCl and KCl, and the water vapor is recovered for pulping the incineration fly ash.

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