Heavy metal stabilizer as well as preparation method and application thereof

Abstract

The invention relates to a heavy metal stabilizer and a preparation method and application thereof, and relates to the technical field of heavy metal stabilizers. The preparation method comprises the following steps: weighing sepiolite, adding hydrochloric acid, carrying out constant-temperature water bath, carrying out centrifugal separation to obtain a precipitate, drying the precipitate, and grinding to obtain the heavy metal stabilizer for sludge pyrolysis. Natural sepiolite is used as a base material, acid activation treatment is carried out through hydrochloric acid to obtain the heavy metal stabilizer, the heavy metal stabilizer is used in sludge pyrolysis, in the pyrolysis process, the heavy metal stabilizer fixes heavy metal in a pyrolysis product carbon in a stable form through the effects of surface adsorption, ion complexation, high-temperature packaging and the like, and the heavy metal stabilizer is used for sludge pyrolysis. Therefore, the emission of heavy metals in the pyrolysis process is reduced, and the ecological risk and the use risk of the pyrolysis product carbon are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heavy metal stabilizer, and particularly relates to a heavy metal stabilizer and a preparation method and application thereof. BACKGROUND

[0002] With the promotion of new urbanization, the production of municipal sludge is increasing. Municipal sludge is complex in composition and contains a large amount of toxic and harmful substances. Proper disposal of these sludge has become a major problem facing urban development. Sludge pyrolysis technology can effectively reduce the volume of sludge, kill bacteria and parasites, and significantly reduce the emission of gaseous pollutants. Its solid product (pyrolytic carbon) has been widely used in carbon sequestration, pollutant adsorption and soil remediation. However, municipal sludge contains heavy metals, which will be enriched in pyrolytic carbon under low-temperature pyrolysis conditions. When pyrolytic carbon containing heavy metals is used for soil remediation or water adsorption, these heavy metals may be released again, causing serious threats to the ecological environment and human health. Studies have shown that the ecological risk of heavy metals in pyrolytic carbon is determined by their existing form. If more heavy metals can exist in stable forms in pyrolytic carbon, it will not only help to control the release of heavy metals during pyrolysis, but also reduce the risk of using pyrolytic carbon, further achieving the harmless and resourceful treatment goal of municipal sludge.

[0003] Patent (CN 111620532 A) introduces a fly ash modified material and its preparation method and its application in sludge pyrolysis process for heavy metal adsorption. Na2CO3 is used to decompose and destroy the sintered interface on the surface of fly ash at high temperature, and the volatilized CO2 gas can provide pores and increase the specific surface area of the adsorption material surface, exposing more adsorption active sites, which is conducive to the storage of reaction products and the further penetration of volatile heavy metals into the material, increasing the reaction efficiency, thereby improving the utilization rate of the adsorption material. In addition, the alkaline condition is conducive to the absorption of Cl element, preventing its combination with volatile or semi-volatile heavy metals, thereby inhibiting the volatilization of heavy metal chlorides. The preparation process of the modified fly ash in the patent is complex, and the application temperature window range is narrow, only for pyrolysis environment with temperature greater than 800℃.

[0004] Currently, there are two main technical approaches for controlling heavy metals in sludge pyrolysis processes: The first is heavy metal volatilization removal technology. This involves high-temperature pyrolysis (≥ 800℃) or the addition of chlorides (such as CaCl2, PVC) during pyrolysis to volatilize heavy metals in the sludge as gaseous chlorides, which are then captured and removed by a condensation and exhaust gas purification system (bag filter + activated carbon adsorption). This technology has a high removal rate for low-boiling-point metals (such as Cd, Hg), but it has significant drawbacks: the high temperature and chloride ion environment easily promote the formation of dioxin precursors from organic matter and chlorine sources; maintaining the high temperature requires additional fuel consumption, increasing exhaust gas treatment costs; and smaller metal aerosol particles can easily penetrate the purification device, posing a risk of secondary pollution. The second approach is heavy metal stabilization technology, which involves adding high-temperature resistant clay minerals (such as modified kaolin, attapulgite) or biochar to the pyrolysis furnace. This utilizes adsorption, ion exchange, and high-temperature encapsulation to fix heavy metals in the pyrolysis carbon matrix, forming stable oxidizable and residual states. This technology can passivate heavy metals at medium and low temperatures, reducing energy consumption and the risk of dioxin formation, and effectively reducing the leaching rate of heavy metals in pyrolytic char. However, this technology is currently limited to the use of kaolin-based additives, mainly aluminosilicates. Natural kaolin has limited adsorption capacity for heavy metals, and although complex modifications can improve it to some extent, its low specific surface area limits the synergistic adsorption enhancement for multiple heavy metals.

[0005] The purpose of this invention is to provide a heavy metal stabilizer for sludge pyrolysis, its preparation method, and its application, overcoming the shortcomings of existing technologies. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a heavy metal stabilizer, its preparation method, and its application. The present invention uses natural sepiolite as a base material, and obtains a heavy metal stabilizer through acid activation treatment with hydrochloric acid. This stabilizer is then used in sludge pyrolysis. During pyrolysis, the heavy metal stabilizer of the present invention fixes heavy metals in a stable form within the pyrolysis product carbon through surface adsorption, ion complexation, and high-temperature encapsulation, thereby reducing heavy metal emissions during pyrolysis and mitigating the ecological and usage risks of the pyrolysis product carbon.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: The first objective of this invention is to provide a method for preparing a heavy metal stabilizer, comprising the following steps: weighing sepiolite, adding hydrochloric acid for constant temperature water bath, then centrifuging to obtain a precipitate, drying and grinding the precipitate to obtain a heavy metal stabilizer from sludge pyrolysis.

[0008] The beneficial effects of this invention are: This invention uses natural sepiolite as the base material, and removes Mg through acid activation treatment with hydrochloric acid. 2+It also generates additional Si–OH hydroxyl groups, increasing the specific surface area and surface hydroxyl density of natural sepiolite, constructing more surface complexation sites and through-pores, thereby significantly enhancing the ability of natural sepiolite to capture and encapsulate volatile and semi-volatile heavy metals.

[0009] Based on the above technical solution, the present invention can be further improved as follows.

[0010] Furthermore, the mass ratio of the sepiolite to the hydrochloric acid is 1~2:1~2, and the concentration of the hydrochloric acid is 3mol / L~4mol / L.

[0011] Furthermore, the centrifugation rate is 2000 rpm to 4000 rpm.

[0012] Furthermore, the particle size of the heavy metal stabilizer is 100 mesh to 180 mesh.

[0013] The beneficial effect of adopting the above-mentioned further scheme is that after the precipitate is ground and dried, a heavy metal stabilizer with a particle size of x~100 mesh is obtained.

[0014] Furthermore, the constant temperature water bath lasts for 20 to 28 hours, and the temperature is 10°C to 30°C.

[0015] The advantages of adopting the above-mentioned further scheme are: this process does not require high-temperature calcination or special equipment, the raw materials are widely available, the preparation conditions are mild, the operation is convenient, it significantly reduces the formulation cost and production difficulty, and is suitable for large-scale addition.

[0016] Furthermore, the drying temperature is 90℃~110℃, and the time is 20 h~28 h.

[0017] A second objective of this invention is to provide a heavy metal stabilizer.

[0018] A third objective of this invention is to provide an application of a heavy metal stabilizer, wherein the heavy metal stabilizer is used in sludge pyrolysis.

[0019] The beneficial effects of this invention are: when the heavy metal stabilizer prepared by this invention is used in sludge pyrolysis, the heavy metal stabilizer effectively fixes the heavy metals in the pyrolysis carbon through multiple mechanisms such as surface adsorption, ion complexation and high-temperature encapsulation during the pyrolysis process, significantly increasing the proportion of its residual state and reducing the risk of environmental release.

[0020] The fourth objective of this invention is to provide a method for sludge pyrolysis, wherein the specific steps of sludge pyrolysis are as follows: mixing sludge with the heavy metal stabilizer and pyrolyzing under an inert atmosphere.

[0021] Furthermore, the heating process involves raising the temperature from room temperature to the pyrolysis temperature.

[0022] The beneficial effects of adopting the above-mentioned further scheme are as follows: after mixing the heavy metal stabilizer of the present invention with sludge, a pyrolysis reaction is carried out in an inert anaerobic environment. During the pyrolysis process, the heavy metal stabilizer effectively fixes the heavy metals in the pyrolysis carbon through multiple mechanisms such as surface adsorption, ion complexation and high-temperature encapsulation, which significantly increases the proportion of its residual state and reduces the risk of environmental release.

[0023] Furthermore, the mass ratio of the sludge to the heavy metal stabilizer is 8~15:1.

[0024] Furthermore, the pyrolysis temperature is 400℃~600℃, the time is 0.5 h~1.5 h, and the heating rate is 8℃ / min~12℃ / min.

[0025] The beneficial effects of adopting the above-mentioned further solution are as follows: Compared with the existing technology that relies on high temperature (≥800℃) or external chlorine source to volatilize and remove metals, the present invention can solidify heavy metals through a triple mechanism of physical adsorption, ion complexation and high temperature sintering in a lower pyrolysis temperature range of 400℃~600℃, avoiding fuel consumption and potential chloride reaction caused by high temperature operation, thereby effectively inhibiting the formation of dioxin precursors and reducing the cost of exhaust gas treatment. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation process of Example 1 of the present invention; Figure 2 This is a diagram of the pyrolysis apparatus of Embodiment 4 of the present invention; Figure 3 This is a flowchart of the BCR experiment during the detection process of this invention; Figure 4 These are diagrams showing the occurrence morphologies of Zn in pyrolytic carbon of Examples 4-6 and Comparative Examples 1-6 according to the present invention; Figure 5 These are diagrams showing the occurrence morphologies of Pb in pyrolytic carbon of Examples 4-6 and Comparative Examples 1-6. Figure 6 These are diagrams showing the occurrence morphology of Cr in the pyrolytic carbon of Examples 4-6 and Comparative Examples 1-6 according to the present invention; Figure 7 The diagram shows the occurrence morphology of Cd in the pyrolytic carbon of Examples 4-6 and Comparative Examples 1-6. Detailed Implementation

[0027] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0028] The municipal sludge samples used in the experiment came from a wastewater treatment plant in Shenzhen, Guangdong Province. To eliminate differences in heat and mass transfer caused by uneven particle size of the raw materials during pyrolysis, the sludge samples were dried, crushed, and sieved through a 100-mesh sieve. Sludge particles smaller than 100 mesh were placed in wide-mouth bottles, sealed, and stored for later use. The raw sepiolite (SEP) used in the experiment was purchased from Sinopharm Group and was of chemical purity.

[0029] Example 1: Preparation of a heavy metal stabilizer like Figure 1 As shown, 10 g of raw sepiolite (SEP) (purchased from Sinopharm Group, chemically pure grade) was weighed into a beaker, and 4 mol / L hydrochloric acid was added at a mass ratio of 1:1. The mixture was stirred in a constant temperature water bath at 20℃ for 24 h. After the reaction was completed, the mixture was centrifuged at 3000 rpm, the precipitate was collected, and dried in an oven at 105℃ for 24 h. The dried sample was ground to particles smaller than 100 mesh, sealed, and stored to obtain hydrochloric acid-activated and modified sepiolite as a heavy metal stabilizer, named 4H-SEP.

[0030] Example 2: Preparation of a heavy metal stabilizer 10 g of raw sepiolite (SEP) (purchased from Sinopharm Group, chemically pure grade) was weighed into a beaker, and 4 mol / L hydrochloric acid was added at a mass ratio of 1:2. The mixture was stirred in a 10℃ constant temperature water bath for 28 h. After the reaction was completed, the precipitate was separated by centrifugation at 4000 rpm, and then dried in an oven at 110℃ for 20 h. The dried sample was ground to particles smaller than 180 mesh, sealed, and stored to obtain hydrochloric acid-activated and modified sepiolite as a heavy metal stabilizer, named 4H-SEP.

[0031] Example 3: Preparation of a heavy metal stabilizer 10 g of raw sepiolite (SEP) (purchased from Sinopharm Group, chemically pure grade) was weighed into a beaker, and 4 mol / L hydrochloric acid was added at a mass ratio of 2:1. The mixture was stirred in a 30℃ constant temperature water bath for 20 h. After the reaction was completed, the precipitate was separated by centrifugation at 2000 rpm, and then dried in a 90℃ oven for 28 h. The dried sample was ground to particles smaller than 140 mesh, sealed, and stored to obtain hydrochloric acid-activated and modified sepiolite as a heavy metal stabilizer, named 4H-SEP.

[0032] Example 4: Application of heavy metal stabilizers in sludge pyrolysis (1) such as Figure 2As shown, 10.0 g of municipal sludge from a wastewater treatment plant in Shenzhen, Guangdong Province, with a particle size less than 100 mesh, was weighed and mixed evenly with 1.0 g of modified sepiolite (4H-SEP) prepared in Example 1. The uniformly mixed material was fed into a tube furnace (MF-1600C-S; Anhui Beiyike Equipment Technology Co., Ltd.) using a corundum ceramic boat. Under the control of a rotor flow meter (LZB-3W; Wochuangte), nitrogen was purged at a constant flow rate of 600 mL / min for 10 min. The temperature was increased at a rate of 10 °C / min while ensuring the airtightness of the system and an inert atmosphere. The pyrolysis temperature of the tube furnace was controlled to the set point of 400 °C by a temperature controller. Subsequently, pulse width modulation was used to turn the heater on and off every 10 seconds to maintain a constant pyrolysis temperature in the reactor. After the reaction temperature reached the set temperature, pyrolysis was carried out at a constant temperature for 1 hour.

[0033] After pyrolysis is complete, turn off the heater, continue to purge with nitrogen, and remove and seal the pyrolyzed carbon after it has cooled.

[0034] Examples 5-6: Examples 5 and 6 differ from Example 4 only in the pyrolysis temperature; the remaining steps and conditions are the same as in Example 4, and all use the 4H-SEP prepared in Example 1 as the heavy metal stabilizer. The raw materials and pyrolysis temperatures used in Examples 5 and 6 are specifically shown in Table 1. Table 1 Comparative Examples 1-6: The only difference between Comparative Examples 1-6 and Example 4 is the pyrolysis raw materials and / or pyrolysis temperature used; the remaining steps and conditions are the same as in Example 4. The specific raw materials and pyrolysis temperatures used in Comparative Examples 1-6 are shown in Table 2. Table 2 Performance testing: The pyrolysis carbon obtained from the pyrolysis products of Examples 4-6 and Comparative Examples 1-6 was used to extract heavy metals in different forms using the EU's BCR three-step extraction method, such as... Figure 3 As shown, the different forms of heavy metals extracted were identified as F1 (exchangeable extract), F2 (reduced extract), F3 (oxidized extract), and F4 (residual extract). The concentrations of Cd, Pb, Cr, and Zn in the F1, F2, F3, and F4 extracts were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) (OPTIMA 8000DV; PerkinElmer, USA). The proportions of different forms of Cd, Pb, Cr, and Zn were calculated. The results are shown below. Figures 4 to 7 As shown.

[0035] Depend onFigures 4 to 7 We can obtain: (1) With the increase of sludge pyrolysis temperature, the proportion of residual Cd, Pb, Cr, and Zn (F4) increases to varying degrees. According to Comparative Examples 1, 3, and 5, the proportion of stable heavy metals (F3, F4) in pyrolysis char increases after the addition of raw sepiolite (SEP). According to Examples 4, 5, and 6, acid-modified sepiolite (4H-SEP) further promotes the transformation of unstable heavy metal components (F1, F2) to relatively stable components (F3, F4) in pyrolysis char compared to raw sepiolite (SEP). This trend gradually increases with increasing temperature. Within the studied temperature range, Zn and Pb in pyrolysis char mainly exist in the form of F4 after the addition of 4H-SEP.

[0036] (2) The excellent properties of 4H-SEP, with its water channels and pores, create a large specific surface area, providing sufficient sites for the adsorption of a large amount of substances. When Mg 2+ After being eluted by acid, it is replaced by H. + The breaking of the Si-O-Mg-O-Si bond opens up internal channels, significantly increasing the specific surface area. At the same time, the breaking of the Si-O-Mg-O-Si bond produces two Si-OH groups. These ion groups can not only interact with the molecules of the adsorbed substance, but also undergo surface complexation adsorption with heavy metal ions, thereby further stabilizing the heavy metals.

[0037] In summary, the heavy metal stabilizer prepared by this invention is used in sludge pyrolysis. During the pyrolysis process, the heavy metal stabilizer of this invention fixes heavy metals in a stable form in the pyrolysis product char through surface adsorption, ion complexation and high-temperature encapsulation, thereby reducing the emission of heavy metals during pyrolysis and reducing the ecological and usage risks of the pyrolysis product char.

[0038] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a heavy metal stabilizer, characterized in that, The process includes the following steps: weigh sepiolite, add hydrochloric acid and place in a constant temperature water bath, then centrifuge to obtain a precipitate, and dry and grind the precipitate to obtain a heavy metal stabilizer.

2. The method for preparing a heavy metal stabilizer according to claim 1, characterized in that, The mass ratio of sepiolite to hydrochloric acid is 1~2:1~2, and the concentration of hydrochloric acid is 3mol / L~4mol / L.

3. The method for preparing a heavy metal stabilizer according to claim 1, characterized in that, The particle size of the heavy metal stabilizer is 100 mesh to 180 mesh.

4. The method for preparing a heavy metal stabilizer according to claim 1, characterized in that, The constant temperature water bath lasts for 20 to 28 hours, and the temperature is 10°C to 30°C.

5. The method for preparing a heavy metal stabilizer according to claim 1, characterized in that, The drying temperature is 90℃~110℃, and the time is 20 h~28 h.

6. A heavy metal stabilizer, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 5.

7. The application of a heavy metal stabilizer, characterized in that, The heavy metal stabilizer described in claim 6 is used in sludge pyrolysis.

8. A method for pyrolysis of sludge, characterized in that, The specific steps of the sludge pyrolysis are as follows: the sludge and the heavy metal stabilizer described in claim 6 are mixed and pyrolyzed under an inert atmosphere.

9. A method for sludge pyrolysis according to claim 8, characterized in that, The mass ratio of the sludge to the heavy metal stabilizer is 8~15:

1.

10. A method for sludge pyrolysis according to claim 8, characterized in that, The pyrolysis temperature is 400℃~600℃, and the time is 0.5 h~1.5 h; the heating rate is 8℃ / min~12℃ / min.

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