Heterogeneous modification method for semi-dry flue gas desulfurization gypsum

Abstract

The invention discloses a semi-dry method flue gas desulfurization gypsum multiphase modification method, and belongs to the technical field of flue gas desulfurization gypsum resource utilization. The method comprises the following steps: (1) mixing semi-dry flue gas desulfurization gypsum with water to prepare slurry I, standing the slurry I, and carrying out solid-liquid separation on the slurry I to obtain a precipitate I and a liquid; (2) carrying out catalytic oxidation modification on the precipitate I; introducing electrolytic aluminum desulfurization flue gas into the liquid until the pH value of the liquid is 7-8, stopping introducing gas, and standing the liquid for 30 minutes; and (3) carrying out solid-liquid separation on the liquid to obtain a precipitate II and a supernatant, collecting the precipitate II for storage, and collecting the supernatant for preparing the slurry with the semi-dry flue gas desulfurization gypsum. According to the method disclosed by the invention, CaSO3 and Ca (OH) 2 in the semi-dry FGD gypsum can be effectively separated and independently used, so that multiple types of products with higher additional value are generated after the semi-dry FGD gypsum is subjected to multi-phase modification, and the application scene of resource utilization of the semi-dry FGD gypsum is enriched.

Description

Technical Field

[0001] The invention belongs to the technical field of resource utilization of flue gas desulfurization gypsum and relates to a semi-dry flue gas desulfurization gypsum multiphase modification method. Background Art

[0002] The production process of electrolytic aluminum industry is cryolite-alumina molten salt electrolysis. During the electrolysis process, a large amount of SO is generated due to anodic oxidation. 2 In order to ensure that the flue gas generated in the aluminum electrolysis process meets the emission standards, reduce pollutant emissions, and reduce the impact of flue gas on the environment, desulfurization of the flue gas generated in the aluminum electrolysis process has become an indispensable process section in the aluminum electrolysis plant. Taking into account factors such as cost and desulfurization efficiency, aluminum electrolysis plants usually adopt a semi-dry desulfurization process, and the desulfurization gypsum produced is semi-dry flue gas desulfurization gypsum (semi-dry FGD gypsum). According to the standard "GB / T 37785-2019 Flue Gas Desulfurization Gypsum", FGD gypsum products are mainly divided into three grades: one, two, and three according to the content of calcium sulfate dihydrate. To achieve the third grade FGD gypsum, the content of calcium sulfate dihydrate must be not less than 85%, and the CaSO in the semi-dry FGD gypsum produced by the aluminum electrolysis plant is 1.5447 g / cm2. 3 and Ca(OH) 2 High content, CaSO 4 The content is low, only between 30-50%, and it is impossible to recycle the semi-dry FGD gypsum. At present, the semi-dry FGD gypsum produced by the electrolytic aluminum plant cannot meet the standard requirements, resulting in a large amount of semi-dry FGD gypsum produced by the electrolytic aluminum plant being stored, which seriously occupies the site and also causes the Ca(OH) in the FGD gypsum to 2 Therefore, increasing the CaSO in semi-dry FGD gypsum 4 content, and also the Ca(OH) 2 It is of great practical significance to fully utilize the secondary utilization value of FGD gypsum and finally consume the stockpiled FGD gypsum.

[0003] Therefore, it is necessary to provide a method for multiphase modification of semi-dry flue gas desulfurization gypsum to increase the CaSO 4 Content, and Ca(OH) 2 To utilize. Summary of the invention

[0004] In order to overcome the problems in the background technology, the present invention comprises the following steps: 2 It is separated from FGD gypsum and then used to remove CO contained in the flue gas from electrolytic aluminum desulfurization. 2 With Ca(OH) 2 Reaction to obtain the product CaCO with higher added value 3, and utilize the SO contained in the flue gas of electrolytic aluminum desulfurization 2 Lowering the pH value of the catalytic oxidation system creates an acidic environment that is conducive to improving the efficiency of the catalytic oxidation reaction. By adding a catalyst and utilizing the O contained in the flue gas from the electrolytic aluminum desulfurization 2 CaSO 3 Catalytic oxidation to increase the CaSO in FGD gypsum 4 content, so that the FGD gypsum itself meets the use standard requirements, and ultimately achieves the purpose of consuming the stockpiled FGD gypsum.

[0005] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0006] The multiphase modification method comprises the following steps:

[0007] (1) The semi-dry flue gas desulfurization gypsum and water are mixed at a mass ratio of 1:500 to prepare slurry I, and then the slurry I is allowed to stand for 30 minutes, and then the slurry I is subjected to solid-liquid separation to obtain a precipitate I and a liquid. In the semi-dry flue gas desulfurization gypsum produced by the electrolytic aluminum industry, Ca(OH) 2 、CaSO 3 、CaSO 4 The content is about 30%, and because the semi-dry flue gas desulfurization gypsum contains Ca(OH) 2 On the one hand, it will create catalytic oxidation of CaSO 3 The required acidic environment is hindered, and on the other hand, it is not conducive to the single Ca(OH) 2 Therefore, firstly, Ca(OH) 2 Separation from FGD gypsum. Since Ca(OH) 2 The solubility in water is 1.73 g / L, CaSO 3 The solubility in water is 0.0036 g / L. 3 The solubility is very low. When semi-dry FGD gypsum is mixed with water, most of the CaSO 3 It exists in the form of solid precipitation. Therefore, after solid-liquid separation, the precipitate I is mainly CaSO 3 , Ca(OH) 2 Mainly exists in liquid, so CaSO 3 With Ca(OH) 2 To separate.

[0008] (2) subjecting the precipitate I obtained in step (1) to catalytic oxidation modification.

[0009] The desulfurization flue gas from electrolytic aluminum is introduced into the liquid obtained in step (1) until the pH value of the liquid is 7-8, then the aeration is stopped and the liquid is allowed to stand for 30 minutes. The liquid contains a relatively high concentration of Ca(OH) 2 , CO in flue gas from desulfurization of electrolytic aluminum 2 The concentration is about 40g / m 3 , relative to SO 2 For 2 The gas concentration is much higher, which can more thoroughly react with Ca(OH) 2 The reaction generates high concentrations of CaCO 3 . High concentration of CaCO 3 It has added value due to its versatility and advantages in specific applications.

[0010] (3) The liquid in step (2) is subjected to solid-liquid separation to obtain a precipitate II and a supernatant, the precipitate II is collected and stored, and the supernatant is collected and used in the step (1) to prepare a slurry with semi-dry flue gas desulfurization gypsum. Ca(OH) 2 and CO 2 The CaCO generated after the reaction 3 It has low solubility in water and exists almost in the form of solid precipitation. The main component of the precipitate II obtained after solid-liquid separation of the liquid is CaCO 3 , can be collected and stored for later use. At the same time, the supernatant contains CaSO 4 When it is returned to step (1) to neutralize the semi-dry flue gas desulfurization gypsum to prepare slurry I, the CaSO precipitated after saturation 4 Will remain in the precipitate I and will not affect the CaCO 3 purity.

[0011] Preferably, in step (2), the specific method for catalytically oxidizing and modifying the precipitate I comprises the following steps:

[0012] S1: The precipitate I is mixed with water in a mass ratio of 1:5-1:10 to prepare a slurry II.

[0013] S2: Add the desulfurized flue gas from electrolytic aluminum to the slurry II obtained in step S1 until the pH of the slurry II is 6, add a catalyst to the slurry II, and then continue to add the desulfurized flue gas from electrolytic aluminum for 4 hours before stopping the ventilation. The desulfurized flue gas from electrolytic aluminum contains SO 2 and CO 2 After the desulfurization flue gas of electrolytic aluminum is introduced into slurry II, SO 2 It dissolves in water to form sulfurous acid, which is unstable and can be further oxidized to form sulfuric acid, which can reduce the pH of slurry II. 2Dissolved in water, it generates carbonic acid, which also helps to lower the pH of slurry II, thereby creating an acidic environment for catalytic oxidation reactions.

[0014] S3: After stopping ventilation, the slurry II is allowed to stand for 30 minutes, and the slurry II is subjected to solid-liquid separation to obtain a precipitate III and a supernatant, and the supernatant is recovered and used to prepare the slurry II with the precipitate I in step S1;

[0015] S4: Drying the precipitate III obtained in step S3 to complete the catalytic oxidation modification of the precipitate I.

[0016] Preferably, in step S2, the catalyst is MnSO 4 The mass of the catalyst added is 0.2-1% of the mass of the semi-dry flue gas desulfurization gypsum. Through the catalytic oxidation reaction, CaSO 3 Oxidized to CaSO 4 , while using MnSO 4 As a catalyst, Mn can be introduced 2+ To change CaSO 3 The oxidation mechanism and oxidation process ensure that CaSO 3 Maintain a high oxidation rate level in a wider concentration and time range. The flue gas from electrolytic aluminum desulfurization contains O 2 , can be used as CaSO 3 Oxidant. MnSO 4 The catalytic principle of the catalyst is as follows:

[0017] Mn 2+ +O 2 →Mn 3+ +O 2 ·-

[0018] Mn 3+ +CaSO 3 →Mn 2+ +CaSO 4

[0019] Mn 2+ →Mn 3+ →Mn 2+

[0020] In an acidic environment, Mn 2+ More stable, high-valent manganese (such as Mn 3+ or Mn 4+ ) is formed and exists. In addition, CaSO 3 The solubility is higher under acidic conditions, so in an acidic environment, it can effectively increase the CaSO 3The catalytic oxidation rate of is as follows:

[0021]

[0022] SO 3 2- (aq)+2H + (aq)→H 2 SO 3 (aq)

[0023] Preferably, in step S4, the drying temperature is 70-100° C. and the drying time is 2 h.

[0024] As a preferred embodiment, in the electrolytic aluminum desulfurization flue gas, CO 2 The concentration is 40g / m 3 , SO 2 Concentration is 100-160 mg / m 3 , O 2 The volume accounts for 21% of the total volume of electrolytic aluminum desulfurization flue gas.

[0025] Preferably, the temperature of the electrolytic aluminum desulfurization flue gas is 70-100°C.

[0026] Preferably, the inlet flow rate of the electrolytic aluminum desulfurization flue gas is 250 ml / min.

[0027] Preferably, the solid-liquid separation method adopts filter press.

[0028] Beneficial effects of the present invention:

[0029] 1. The present invention uses the flue gas from electrolytic aluminum desulfurization to perform multiphase modification on semi-dry FGD gypsum. Although the flue gas from electrolytic aluminum desulfurization meets the emission standards after desulfurization, it still contains SO 2 and CO 2 The further utilization of the flue gas from aluminum electrolysis desulfurization can further reduce or even eliminate harmful substances in the flue gas from desulfurization, further reducing the impact of flue gas emissions on the environment. In addition, the use of the flue gas from aluminum electrolysis desulfurization to treat semi-dry FGD gypsum allows FGD gypsum to be recycled, which is an effective way to treat waste with waste.

[0030] 2. The present invention converts CaSO 3 With Ca(OH) 2 After separation, Ca(OH) can be used independently 2 As raw material to prepare CaCO with higher added value 3 , broadening the resource utilization of FGD gypsum. In addition, the alkaline substance Ca(OH) 2The removal of makes it easier to quickly lower the pH value, thus creating good conditions for creating the acidic conditions required for the subsequent precipitate modification process, which helps to improve the overall efficiency of multiphase modification.

[0031] 3. The present invention removes the CaSO in FGD gypsum 3 Catalytic oxidation to form CaSO 4 It not only reduces the content of unstable substances in FGD gypsum, but also increases the content of available effective ingredients in FGD gypsum, so that FGD gypsum meets the requirements of use standards and the stockpiled FGD gypsum can be consumed.

[0032] 4. The present invention makes full use of the aluminum electrolytic flue gas after the desulfurization process to achieve a comprehensive utilization of waste treatment, and the CaSO in the semi-dry FGD gypsum 4 The increase in content and the added value product CaCO 3 The production of gypsum provides a new idea for solving the problem of difficulty in utilizing semi-dry FGD gypsum in the electrolytic aluminum industry and broadening the comprehensive utilization channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 These are the XRD and XRF test and analysis results of semi-dry FGD gypsum from an aluminum smelter.

[0034] Figure 2 These are the XRD and XRF detection and analysis results of the precipitate III of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with specific embodiments.

[0036] Example 1

[0037] In this example, semi-dry FGD gypsum stored in an electrolytic aluminum plant was used. First, XRD and XRF detection and analysis were performed on the unmodified semi-dry FGD gypsum in this example. The results are as follows: Figure 1 As shown, through Figure 1 The quantitative results of the composition of unmodified semi-dry FGD gypsum are shown in Table 1.

[0038] Table 1

[0039]

[0040]

[0041] In this embodiment, the semi-dry FGD gypsum is subjected to multiphase modification by the following method:

[0042] (1) 180 g of semi-dry FGD gypsum was weighed and mixed with 90,000 g of water to prepare slurry I. The slurry I was then allowed to stand for 30 min and then filtered to obtain a precipitate I and a liquid.

[0043] (2) introducing electrolytic aluminum desulfurization flue gas at a temperature of 70° C. into the liquid obtained in step (1) at a flow rate of 250 ml / min until the pH value of the liquid is 7-8, then stopping the ventilation and then allowing the liquid to stand for 30 min;

[0044] (3) The liquid in step (2) is filtered to obtain a precipitate II and a supernatant, the precipitate II is collected and stored, and the supernatant is collected and used to prepare a slurry with semi-dry flue gas desulfurization gypsum in step (1).

[0045] (4) Weigh 180 g of precipitate I and mix with 900 g to prepare slurry II.

[0046] (5) Use an aerator to aerate slurry II at a flow rate of 250 ml / min with electrolytic aluminum desulfurization flue gas at a temperature of 70°C. Monitor the pH value of slurry II in real time. When pH = 6, add 0.36 g MnSO 4 Continue to use the aerator to aerate the electrolytic aluminum desulfurization flue gas into the slurry II for 4 hours, and then stop ventilation.

[0047] (6) The slurry II was allowed to stand for 30 min, and the slurry II was filtered to obtain a precipitate III and a supernatant. The supernatant was recovered and used to prepare the slurry II with the precipitate I in step (4). The precipitate III was tested and the results were as follows: Figure 2 As shown, through Figure 2 The quantitative results of the composition of unmodified semi-dry FGD gypsum are shown in Table 2.

[0048] Table 2

[0049] phase of matter Mass fraction % <![CDATA[CaSO 4 ·2H 2 Or]]> 96.6 <![CDATA[CaCO 3 ]]> 3.4

[0050] It can be seen from Table 2 that the precipitate III contains almost no CaCO 3 , it can be proved that in step (3), a large amount of CaCO 3 A precipitate II was generated and formed which was collected by filtration.

[0051] Example 2

[0052] This example uses the same semi-dry FGD gypsum raw material and electrolytic aluminum desulfurization flue gas as in Example 1 to conduct the experiment.

[0053] In this embodiment, the semi-dry FGD gypsum is subjected to multiphase modification by the following method:

[0054] (1) 180 g of semi-dry FGD gypsum was weighed and mixed with 90,000 g of water to prepare slurry I. The slurry I was then allowed to stand for 30 min and then filtered to obtain a precipitate I and a liquid.

[0055] (2) introducing electrolytic aluminum desulfurization flue gas at a temperature of 85° C. into the liquid obtained in step (1) at a flow rate of 250 ml / min until the pH value of the liquid is 7-8, then stopping the ventilation and then allowing the liquid to stand for 30 min;

[0056] (3) The liquid in step (2) is filtered to obtain a precipitate II and a supernatant, the precipitate II is collected and stored, and the supernatant is collected and used to prepare a slurry with semi-dry flue gas desulfurization gypsum in step (1).

[0057] (4) Weigh 180 g of precipitate I and mix with 1260 g to prepare slurry II.

[0058] (5) Use an aerator to aerate slurry II at a flow rate of 250 ml / min with the desulfurization flue gas of aluminum electrolysis at a temperature of 85 °C. Monitor the pH value of slurry II in real time. When the pH value reaches 6, add 0.9 g MnSO 4 Continue to use the aerator to aerate the electrolytic aluminum desulfurization flue gas into the slurry II for 4 hours, and then stop ventilation.

[0059] (6) The slurry II was allowed to stand for 30 min, and the slurry II was filtered to obtain a precipitate III and a supernatant. The supernatant was recovered and used to prepare the slurry II with the precipitate I in step (4).

[0060] In this embodiment, the multi-phase modification effect on the semi-dry FGD gypsum is similar to that in Embodiment 1.

[0061] Example 3

[0062] This example uses the same semi-dry FGD gypsum raw material and electrolytic aluminum desulfurization flue gas as in Example 1 to conduct experiments.

[0063] In this embodiment, the semi-dry FGD gypsum is subjected to multi-phase modification by the following method:

[0064] (1) 180 g of semi-dry FGD gypsum was weighed and mixed with 90,000 g of water to prepare slurry I. The slurry I was then allowed to stand for 30 min and then filtered to obtain a precipitate I and a liquid.

[0065] (2) introducing electrolytic aluminum desulfurization flue gas at a temperature of 100° C. into the liquid obtained in step (1) at a flow rate of 250 ml / min until the pH value of the liquid is 7-8, then stopping the ventilation and then allowing the liquid to stand for 30 min;

[0066] (3) The liquid in step (2) is filtered to obtain a precipitate II and a supernatant, the precipitate II is collected and stored, and the supernatant is collected and used to prepare a slurry with semi-dry flue gas desulfurization gypsum in step (1).

[0067] (4) Weigh 180 g of precipitate I and mix with 1800 g to prepare slurry II.

[0068] (5) Use an aerator to aerate slurry II at a flow rate of 250 ml / min with the desulfurization flue gas of aluminum electrolysis at a temperature of 100 °C. Monitor the pH value of slurry II in real time. When the pH value reaches 6, add 1.8 g MnSO 4 Continue to use the aerator to aerate the electrolytic aluminum desulfurization flue gas into the slurry II for 4 hours, and then stop ventilation.

[0069] (6) The slurry II was allowed to stand for 30 min, and the slurry II was filtered to obtain a precipitate III and a supernatant. The supernatant was recovered and used to prepare the slurry II with the precipitate I in step (4).

[0070] In this embodiment, the multi-phase modification effect on the semi-dry FGD gypsum is similar to that in Embodiment 1.

[0071] In summary, the method of the present invention can be used to carry out multiphase modification of semi-dry FGD gypsum to effectively separate CaSO 3 With Ca(OH) 2 , Ca(OH) 2 Can be used independently to prepare CaCO 3 At the same time, it effectively increases the CaSO in FGD gypsum 4 content, so that FGD gypsum meets the requirements of the use standards, thereby making the resource utilization of FGD gypsum more diversified and having a wider range of applications.

Claims

1. A method for multiphase modification of semi-dry flue gas desulfurization gypsum, characterized in that: The multiphase modification method comprises the following steps: (1) mixing semi-dry flue gas desulfurization gypsum and water at a mass ratio of 1:500 to prepare slurry I, then standing the slurry I for 30 minutes, and then performing solid-liquid separation on the slurry I to obtain a precipitate I and a liquid; (2) subjecting the precipitate I obtained in step (1) to catalytic oxidation modification; Adding the desulfurization flue gas of aluminum electrolysis into the liquid obtained in step (1) until the pH value of the liquid is 7-8, stopping the ventilation, and then letting the liquid stand for 30 minutes; (3) The liquid in step (2) is subjected to solid-liquid separation to obtain a precipitate II and a supernatant, the precipitate II is collected for storage, and the supernatant is collected for use in preparing a slurry with semi-dry flue gas desulfurization gypsum in step (1).

2. The method for multiphase modification of semi-dry flue gas desulfurization gypsum according to claim 1, characterized in that: In the step (2), the specific method for catalytic oxidation modification of the precipitate I comprises the following steps: S1: Mixing the precipitate I with water in a mass ratio of 1:5-1:10 to prepare slurry II; S2: introducing the desulfurized flue gas from electrolytic aluminum into the slurry II obtained in step S1 until the pH of the slurry II is 6, adding a catalyst into the slurry II, and then continuing to introduce the desulfurized flue gas from electrolytic aluminum for 4 hours, and then stopping the ventilation; S3: After stopping ventilation, the slurry II is allowed to stand for 30 minutes, and the slurry II is subjected to solid-liquid separation to obtain a precipitate III and a supernatant, and the supernatant is recovered and used to prepare the slurry II with the precipitate I in step S1; S4: Drying the precipitate III obtained in step S3 to complete the catalytic oxidation modification of the precipitate I.

3. A method for multiphase modification of semi-dry flue gas desulfurization gypsum according to claim 2, characterized in that: In the step S2, the catalyst is MnSO4, and the mass of the added catalyst is 0.2-1% of the mass of the semi-dry flue gas desulfurization gypsum.

4. The method for multiphase modification of semi-dry flue gas desulfurization gypsum according to claim 2, characterized in that: In step S4, the drying temperature is 70-100° C. and the drying time is 2 hours.

5. A method for multiphase modification of semi-dry flue gas desulfurization gypsum according to claim 1 or 2, characterized in that: The CO2 concentration in the electrolytic aluminum desulfurization flue gas is 40g / m 3 , SO2 concentration is 100-160mg / m 3 , the volume of O2 accounts for 21% of the total volume of electrolytic aluminum desulfurization flue gas.

6. A method for multiphase modification of semi-dry flue gas desulfurization gypsum according to claim 1 or 2, characterized in that: The temperature of the electrolytic aluminum desulfurization flue gas is 70-100°C.

7. A method for multiphase modification of semi-dry flue gas desulfurization gypsum according to claim 1 or 2, characterized in that: The inlet flow rate of the electrolytic aluminum desulfurization flue gas is 250 ml / min.

8. A method for multiphase modification of semi-dry flue gas desulfurization gypsum according to claim 1 or 2, characterized in that: The solid-liquid separation method adopts filter pressing.

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