Preparation method of adsorbent for removing heavy metals in municipal sludge

Abstract

The invention discloses a preparation method of an adsorbent for removing heavy metals in municipal sludge. The method comprises the synthesis and modification processes of the adsorbent. The preparation method comprises the following steps: firstly, preparing an adsorbent precursor, preparing a mixed solution according to the ratio of a calcium source to a silicon source to sodium hydroxide to water being 4: (5-6): (11-40): (72-175), then transferring the obtained mixed solution into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, and reacting for 10-12 hours under the conditions of 180-190 DEG C and 0.8-1.0 MPa; after the reaction is finished, washing, drying and grinding to obtain an adsorbent precursor; and then preparing the heavy metal adsorbent: mixing cerium chloride and water according to a mass ratio of 1: (30-50), and stirring for 30-60 minutes in a room temperature environment. The mass ratio of the adsorbent precursor to the cerium chloride solution is 1: (20-25), stirring at room temperature for 2-4 hours, standing for 1-2 hours, alternately washing with ethanol and deionized water for 3-5 times, and finally drying to obtain the adsorbent. The prepared adsorbent can be used for removing the heavy metals in the municipal sludge, the amount ratio of the adsorbent to the municipal sludge is 1: (200-250) when the adsorbent is used, and the highest value of the removal efficiency of each group after the reaction is carried out for 50-70 minutes at the temperature of 25-50 DEG C reaches 90% or above. The method effectively improves the removal effect of the heavy metals in the municipal sludge, and provides a solution for reducing the content of the heavy metals in the municipal sludge.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and environmental engineering water treatment technology, specifically relating to a method for preparing an adsorbent for removing heavy metals from urban sewage sludge. Background Technology

[0002] Heavy metals in urban sludge accumulate through industrial wastewater mixing and domestic sewage enrichment, posing multi-layered hazards to the environment and human health. These heavy metals are non-biodegradable and easily accumulate through the food chain, seriously threatening ecosystem stability and human health. Therefore, efficient treatment of wastewater containing heavy metals has become a core requirement in environmental governance. Current mainstream treatment technologies, such as chemical precipitation and ion exchange, have significant limitations: chemical precipitation requires the addition of large amounts of reagents and easily generates secondary sludge; ion exchange is costly and poorly adaptable to complex wastewater. Adsorption, due to its simple operation, controllable cost, and lack of secondary pollution, has become the preferred approach. The key lies in developing highly efficient adsorption materials.

[0003] The crystal structure of tobermorite consists of a central calcium-oxygen layer and two flanking silicon-oxygen tetrahedral chain layers, forming a typical "sandwich" layered structure. Exchangeable calcium ions (Ca) exist between the layers. 2+ ) and a vast interlayer domain. Ca between structural layers 2+ It can undergo efficient ion exchange reactions with heavy metal ions in solution, which is one of its main mechanisms for removing heavy metals. Its surface structure has a large number of negatively charged silanol groups (Si-OH) and unsaturated sites, which exhibit extremely strong electrostatic attraction and surface complexation ability for positively charged heavy metal cations.

[0004] Compared to the heavy metal removal technologies used in patents CN120842579A ("Refining Method of Polydimethylsiloxane") and CN106279548A ("A Polyvinyl Alcohol Hydrogel for Treating Wastewater Containing Heavy Metal Ions and Its Preparation Method"), this invention uses industrial solid waste as raw material to synthesize tobermorite as an adsorption substrate, significantly reducing raw material costs. Furthermore, compared to the process in patent CN112266070A ("A Method and Apparatus for Passivating Heavy Metals in Desulfurization Wastewater"), which involves thoroughly mixing coal fly ash with desulfurization wastewater containing an alkali activator, then adding polysulfonate (SNF) and triethanolamine (TEA), followed by stirring, drying, and curing to achieve heavy metal passivation, this invention eliminates the need for complex multi-step curing processes, avoids long reaction and curing cycles, and offers higher treatment efficiency and practical application feasibility. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing an adsorbent for removing heavy metals from urban sludge. The adsorbent can solidify heavy metals and has a high removal rate and fast removal speed, with broad application prospects.

[0006] To address the aforementioned technical problems, embodiments of the present invention provide a method for preparing an adsorbent for removing heavy metals from urban sewage sludge, characterized by comprising the following steps: (1) Prepare a mixed solution with a ratio of calcium source: silicon source: sodium hydroxide: water = 4:5~6:11~40:72~175. Then transfer the mixed solution into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner for hydrothermal reaction. After the reaction, take it out, wash, dry and grind it to obtain the adsorbent precursor. (2) Mix the adsorbent precursor obtained in step (1) with cerium chloride solution, stir, let stand and filter. After filtration, wash with ethanol and pure water alternately 3~5 times, and then dry to obtain the adsorbent.

[0007] In step (1), the silicon source is selected from one or two siliceous materials in industrial solid waste such as silica fume and fly ash, with SiO2 in silica fume ≥ 85% and SiO2 in fly ash ≥ 40%.

[0008] In step (1), the calcium source is selected from one or two calcium-based materials in industrial solid waste such as industrial lime and carbide slag, with industrial lime containing ≥85% CaO and carbide slag containing ≥60% CaO.

[0009] In step (1), the hydrothermal reaction temperature is 180-190℃, the time is 8-12h, and the pressure is 0.8-1.0MPa.

[0010] In step (2), the ratio of cerium chloride to water is 1:30-50, and the ratio of adsorbent precursor to cerium chloride solution is 1:20-25.

[0011] In step (2), the stirring time of cerium chloride and water is 30-60 min; the stirring time of adsorbent precursor and cerium chloride solution is 2-4 h, and the standing time is 1-2 h.

[0012] Beneficial effects: Compared with the adsorbent precursor, the adsorbent exhibits a higher adsorption capacity under the same adsorption rate conditions; the introduction of rare earth elements provides more active sites, enhancing the adsorption and ion exchange capacity of heavy metal ions, thus making it more suitable for the treatment of high-concentration wastewater. Detailed Implementation

[0013] The present invention is further described in detail through the following embodiments, but the technical content described in these embodiments is illustrative rather than limiting, and should not be construed as limiting the scope of protection of the present invention.

[0014] The technical solution of the present invention will be further described below with reference to four specific embodiments.

[0015] The adsorption performance of heavy metal adsorbents in urban sewage sludge was studied using a static adsorption method. First, the initial content of heavy metal ions in the urban sewage sludge was determined. According to the national standard "Solid Waste—Leaching Toxicity Leaching Method: Sulfuric Acid-Nitric Acid Method" (HJ / T 299-2007), a leaching toxicity test was conducted. Sulfuric acid and nitric acid were mixed at a mass ratio of 2:1, and water was added to adjust the pH to 3.2 (±0.05). The liquid-to-solid ratio was controlled at 10:1 for the leaching reaction. The leachate was filtered using a circulating vacuum pump, and the filtrate was collected. The concentration of heavy metal ions in the filtrate was determined by flame atomic absorption spectrometry. The results are shown in Table 1.

[0016] Table 1. Heavy metal ion content in sludge (mg / L) Example 1: Using fly ash as the silicon source and industrial lime as the calcium source, a mixed solution was prepared in a ratio of calcium source: silicon source: sodium hydroxide: water = 4:5:13:77. The mixed solution was transferred into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 180°C and 0.8 MPa for 8 hours. The reaction product was washed, dried, and ground to obtain the adsorbent precursor. A cerium chloride solution was prepared at a ratio of 1:30. The adsorbent precursor and cerium chloride solution were mixed at a ratio of 1:20. After stirring for 2 hours, settling for 1 hour, filtering, washing, and drying, the adsorbent was obtained. Subsequently, the adsorbent and urban sludge were added to a heavy metal leaching solution at a ratio of 1:200 and subjected to an adsorption reaction at 25°C for 50 minutes. After adsorption, the solution was filtered, the filtrate was collected, and the concentration of the target ions was measured. The removal efficiency of the adsorbent was calculated based on this. The results are shown in Tables 2 and 3.

[0017] Example 2: Using silica fume as the silicon source and industrial lime as the calcium source, a mixed solution was prepared in the ratio of calcium source:silicon source:sodium hydroxide:water = 4:5.2:19:92. The mixture was transferred into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 185℃ and 0.85MPa for 9 hours. The reaction product was washed, dried, and ground to obtain the adsorbent precursor. A cerium chloride solution was prepared at a ratio of 1:38. The adsorbent precursor and cerium chloride solution were mixed at a ratio of 1:22. After stirring for 2.5 hours, settling for 1 hour, filtering, washing, and drying, the adsorbent was obtained. Subsequently, the adsorbent and urban sludge were added to a heavy metal leaching solution at a ratio of 1:215. The adsorption reaction was carried out at 30℃ for 55 minutes. After adsorption, the solution was filtered, the filtrate was collected, and the concentration of the target ions was measured. The removal efficiency of the adsorbent was calculated based on this. The results are shown in Tables 2 and 3.

[0018] Example 3: Using fly ash as the silicon source and carbide slag as the calcium source, a mixed solution was prepared according to the ratio of calcium source: silicon source: sodium hydroxide: water = 4:5.5:26:116. The mixed solution was transferred into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 190℃ and 0.9MPa for 10 hours. The reaction product was washed, dried, and ground to obtain the adsorbent precursor. A cerium chloride solution was prepared at a ratio of 1:45. The adsorbent precursor and cerium chloride solution were mixed at a ratio of 1:23. After stirring for 3 hours, settling for 1.5 hours, filtering, washing, and drying, the adsorbent was obtained. Subsequently, the adsorbent and urban sludge were added to a heavy metal leaching solution at a ratio of 1:230 and subjected to an adsorption reaction at 35℃ for 60 minutes. After adsorption, the solution was filtered, the filtrate was collected, and the concentration of the target ions was measured. The removal efficiency of the adsorbent was calculated based on this. The results are shown in Tables 2 and 3.

[0019] Example 4: Using silica fume as the silicon source and carbide slag as the calcium source, a mixed solution was prepared according to the ratio of calcium source:silicon source:sodium hydroxide:water = 4:6:39:161. The mixed solution was transferred into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner and subjected to a hydrothermal reaction at 185℃ and 0.95MPa for 11 hours. The reaction product was washed, dried, and ground to obtain the adsorbent precursor. A cerium chloride solution was prepared at a ratio of 1:50. The adsorbent precursor and cerium chloride solution were mixed at a ratio of 1:25. After stirring for 4 hours, settling for 2 hours, filtering, washing, and drying, the adsorbent was obtained. Subsequently, the adsorbent and urban sludge were added to a heavy metal leaching solution at a ratio of 1:250 and subjected to an adsorption reaction at 40℃ for 70 minutes. After adsorption, the solution was filtered, the filtrate was collected, and the concentration of the target ions was measured. The removal efficiency of the adsorbent was calculated based on this. The results are shown in Tables 2 and 3.

[0020] Table 2 Heavy metal removal efficiency (%) in urban sewage sludge

[0021] Table 3. Heavy metal adsorption capacity in urban sewage sludge (mg / g)

Claims

1. A method for preparing an adsorbent for removing heavy metals from urban sewage sludge, characterized in that, The following steps are included: (1) Prepare a mixed solution according to the ratio range of calcium source: silicon source: sodium hydroxide: water = 4:5~6:11~40:72~175. Then, transfer the mixed solution into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner for hydrothermal reaction. After the reaction, take it out, wash, dry and grind it to obtain the adsorbent precursor. (2) The adsorbent precursor obtained in step (1) is mixed with cerium chloride solution, stirred, allowed to stand, and filtered. After filtration, it is washed with ethanol and pure water alternately 3 to 5 times, and then dried to obtain the adsorbent.

2. The method according to claim 1, characterized in that, The silicon source is selected from one or two siliceous materials in industrial solid waste such as silica fume and fly ash, with SiO2 ≥ 85% in silica fume and SiO2 ≥ 40% in fly ash.

3. The method according to claim 1, characterized in that, The calcium source is selected from one or two calcium-based materials in industrial solid waste such as industrial lime and carbide slag, with industrial lime containing ≥85% CaO and carbide slag containing ≥60% CaO.

4. The method for preparing an adsorbent for removing heavy metals from urban sewage sludge according to claim 1, characterized in that, In step (1), the hydrothermal reaction temperature is 180-190℃, the time is 8-12h, and the pressure is 0.8-1.0MPa.

5. A method for preparing an adsorbent for removing heavy metals from urban sludge according to claim 1, characterized in that, In step (2), the ratio of cerium chloride to water is 1:30 to 50, and the ratio of adsorbent precursor to cerium chloride solution is 1:20 to 25.

6. The method for preparing an adsorbent for removing heavy metals from urban sewage sludge according to claim 1, characterized in that, In step (2), the stirring time of cerium chloride and water is 30-60 min; the stirring time of adsorbent precursor and cerium chloride solution is 2-4 h, and the standing time is 1-2 h.

7. Add the adsorbent to the heavy metal leachate of urban sludge. When using it, the ratio of adsorbent to urban sludge is 1:200-250. React at 25-50℃ for 50-70 min to remove heavy metal ions.

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