Closed-loop dechlorination and desalination method for incineration fly ash

Abstract

The invention relates to the technical field of solid waste treatment, and provides a closed-loop dechlorination and desalination method for incineration fly ash. Soluble and insoluble chlorine salts in the incineration fly ash are removed through alkali washing, and then heavy metals and chlorine salts in alkali washing waste liquid are removed through heavy metal removal, primary dechlorination and secondary dechlorination. The Ca-Al layered double hydroxides obtained in the process can be circularly used for removing heavy metals, and the recovered alkali solution can be circularly used for alkali washing. According to the method, the removal efficiency of chlorine salts, especially insoluble chlorine salts, in the incineration fly ash is remarkably improved, meanwhile, removal of sulfate is promoted, calcium in the fly ash is reserved, and resource utilization is facilitated. And meanwhile, secondary environmental pollution caused by wastewater is effectively prevented. The byproduct Ca-Al layered bimetal hydroxide has a wide application prospect in the fields of gas adsorption, wastewater purification, catalysis and the like due to unique interlayer ion exchange property and excellent adsorption capacity, and has a good economic value.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste treatment, and in particular to a closed-loop dechlorination and desalination method for incineration fly ash. Background Art

[0002] In recent years, with the accelerated advancement of urbanization, the treatment of urban domestic waste has become one of the major challenges facing the world. Among the methods of domestic waste treatment, the proportion of incineration treatment has increased year by year. The incineration of domestic waste will produce 3-5wt% of waste incineration fly ash. With the increase in the amount of waste and the incineration ratio, the output of waste incineration fly ash is also increasing year by year. At present, the main resource utilization method of incineration fly ash is cement clinker production and concrete manufacturing. However, the composition of incineration fly ash is relatively complex and contains a large amount of chloride salts, which will cause problems such as equipment corrosion and product quality degradation.

[0003] In the prior art, water washing pretreatment is a common method for removing chloride salts in fly ash resource utilization, but this method can only remove soluble chloride salts in incineration fly ash, and there are challenges in removing insoluble chloride salts and sulfates. Insoluble chloride salts in incineration fly ash will be released in certain environments (such as alkali stimulation), resulting in a decrease in product quality. In addition, water washing pretreatment will produce a large amount of waste liquid, which is rich in high concentrations of heavy metals and chloride salts, which will cause harm to the environment and human health. Moreover, the disposal methods of waste liquid containing high concentrations of heavy metals and chloride salts in the prior art have technical problems such as low efficiency, secondary pollution of waste liquid and high cost. Summary of the invention

[0004] The invention provides a closed-loop dechlorination and desalination method for incineration fly ash, which is used to solve the technical problems in the prior art of low chlorine and salt removal efficiency and secondary pollution of the environment caused by waste liquid.

[0005] The present invention provides a closed-loop dechlorination and desalination method for incineration fly ash, comprising the following steps:

[0006] The incineration fly ash is mixed with an alkaline solution for alkaline washing, and the alkaline washing fly ash and the alkaline washing waste liquid are obtained after solid-liquid separation;

[0007] After adjusting the pH of the alkali washing waste liquid, Ca-Al layered double hydroxide is added to remove heavy metals, and a secondary waste liquid is obtained after solid-liquid separation;

[0008] The secondary waste liquid is mixed with a calcium-aluminum-containing reagent for primary dechlorination, and a Ca-Al layered double metal hydroxide and a tertiary waste liquid are obtained after solid-liquid separation;

[0009] The tertiary waste liquid is mixed with a calcium-aluminum-containing reagent for secondary dechlorination, and after solid-liquid separation, a Ca-Al layered double metal hydroxide and a recovered alkaline solution are obtained;

[0010] The Ca-Al layered double metal hydroxide obtained from the primary dechlorination and the secondary dechlorination is used for heavy metal removal, and the recovered alkaline solution is used for alkaline washing.

[0011] According to a closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention, the alkaline solution is a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 1 mol / L.

[0012] According to a closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention, the liquid-to-solid ratio of the alkaline solution to the incineration fly ash is 5 to 8 mL:1 g.

[0013] According to a closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention, the alkali washing is carried out under stirring conditions, the stirring time is 20 to 40 minutes, and the stirring rate is 400 to 600 r / min.

[0014] According to a closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention, the alkaline washing waste liquid is adjusted to a pH of 7-9.

[0015] According to a closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention, the liquid-to-solid ratio of the alkali washing waste liquid to the Ca-Al layered double metal hydroxide is 1L:4-8g.

[0016] According to a closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention, the heavy metal removal is carried out under stirring conditions, the stirring time is 20 to 40 minutes, and the stirring rate is 400 to 600 r / min.

[0017] According to a closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention, the calcium-aluminum-containing reagent is sodium metaaluminate and calcium oxide.

[0018] According to a closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention, the primary dechlorination and secondary dechlorination are carried out under ultrasonic and stirring conditions, the ultrasonic power is 200-600W, the stirring time is 40-60min, and the stirring rate is 400-600r / min.

[0019] According to a closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention, in the primary dechlorination, n(Ca):n(Al):n(Cl)=2-2.5:1-1.2:1, and in the secondary dechlorination, n(Ca):n(Al):n(Cl)=7:2.5-3:1.

[0020] The closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention removes soluble and insoluble chloride salts in the incineration fly ash by alkali washing, removes heavy metals from the alkali washing solution by adjusting pH and adding Ca-Al layered double metal hydroxides, and recovers the Ca-Al layered double metal hydroxide and the alkali solution by primary dechlorination and secondary dechlorination, thereby solving the technical problems of low efficiency of the prior art for treating waste liquid containing high-concentration heavy metals and chloride salts, secondary pollution to the environment caused by the waste liquid, and high cost, and significantly reduces the soluble chloride salt content and the total chlorine content in the incineration fly ash, promotes the removal of sulfate in the incineration fly ash, and also realizes the retention of calcium in the incineration fly ash, which is beneficial to the resource utilization of the incineration fly ash in the later stage; significantly reduces the heavy metal content in the waste liquid, can generate an alkali solution and a Ca-Al layered double metal hydroxide for alkali washing and heavy metal removal, realizes closed-loop dechlorination and desalination, avoids secondary pollution to the environment by the waste liquid, and effectively reduces the beneficial effect of process cost. In addition, the Ca-Al layered double hydroxide produced by the present invention has special interlayer ion exchangeability and excellent adsorption capacity, and can also be used as an adsorbent in gas adsorption, wastewater purification, catalysis and other scenarios, and has good economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 The present invention is a schematic flow chart of the closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention.

[0023] Figure 2 1 is the XRD diagram of the Ca-Al layered double hydroxide produced in Example 1 of the present invention and Comparative Example 6. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Combine the following Figure 1-2 The closed-loop dechlorination and desalination method of incineration fly ash of the present invention is described.

[0026] Figure 1The present invention is a schematic flow chart of the closed-loop dechlorination and desalination method for incineration fly ash provided by the present invention.

[0027] like Figure 1 As shown, the present invention provides a closed-loop dechlorination and desalination method for incineration fly ash, comprising the following steps:

[0028] The incineration fly ash is mixed with an alkaline solution for alkaline washing, and the alkaline washing fly ash and the alkaline washing waste liquid are obtained after solid-liquid separation;

[0029] After adjusting the pH of the alkali washing waste liquid, Ca-Al layered double hydroxide is added to remove heavy metals, and a secondary waste liquid is obtained after solid-liquid separation;

[0030] The secondary waste liquid is mixed with a calcium-aluminum-containing reagent for primary dechlorination, and a Ca-Al layered double metal hydroxide and a tertiary waste liquid are obtained after solid-liquid separation;

[0031] The tertiary waste liquid is mixed with a calcium-aluminum-containing reagent for secondary dechlorination, and after solid-liquid separation, a Ca-Al layered double metal hydroxide and a recovered alkaline solution are obtained;

[0032] The Ca-Al layered double metal hydroxide obtained from the primary dechlorination and the secondary dechlorination is used for heavy metal removal, and the recovered alkaline solution is used for alkaline washing.

[0033] In the present invention, the alkaline solution is a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 1 mol / L.

[0034] In the present invention, the liquid-to-solid ratio of the alkaline solution to the incineration fly ash is 5 to 8 mL: 1 g, preferably 6 to 7 mL: 1 g.

[0035] In the present invention, the alkali washing is carried out under stirring conditions, the stirring time is 20 to 40 minutes, preferably 25 to 35 minutes, and more preferably 28 to 32 minutes; the stirring rate is 400 to 600 r / min, preferably 450 to 550 r / min, and more preferably 480 to 520 r / min.

[0036] In the present invention, the pH of the alkali washing waste liquid is adjusted to 7-9.

[0037] In the present invention, the liquid-to-solid ratio of the alkali washing waste liquid to the Ca-Al layered double metal hydroxide is 1L:4-8g, preferably 1L:5-7g.

[0038] In the present invention, the heavy metal removal is carried out under stirring conditions, the stirring time is 20 to 40 minutes, preferably 25 to 35 minutes, and more preferably 28 to 32 minutes; the stirring rate is 400 to 600 r / min, preferably 450 to 550 r / min, and more preferably 480 to 520 r / min.

[0039] In the present invention, the calcium-aluminum-containing reagent is sodium metaaluminate and calcium oxide.

[0040] In the present invention, the primary dechlorination and the secondary dechlorination are carried out under ultrasonic and stirring conditions, the ultrasonic power is 200-600W, preferably 300-500W, and more preferably 350-450W; the stirring time is 40-60min, preferably 45-55min, and more preferably 48-52min; the stirring rate is 400-600r / min, preferably 450-550r / min, and more preferably 480-520r / min.

[0041] In the present invention, in the primary dechlorination, n(Ca):n(Al):n(Cl)=2-2.5:1-1.2:1, preferably 2.2-2.4:1-1.2:1; in the secondary dechlorination, n(Ca):n(Al):n(Cl)=7:2.5-3:1, preferably 7:2.6-2.8:1.

[0042] Figure 2 1 is the XRD diagram of the Ca-Al layered double hydroxide produced in Example 1 of the present invention and Comparative Example 6.

[0043] like Figure 2 As shown in Figure 1, the diffraction peak intensity of the Ca-Al layered double hydroxide in Example 1 after ultrasonic treatment is significantly enhanced, while the diffraction peak intensity of Ca(OH)2 is significantly reduced, and no Ca3Al2(OH) 12 The diffraction peaks indicate that ultrasonic treatment promotes the dissolution and dispersion of calcium oxide, always ensuring that the AlO2 content in the solution is at an appropriate level and avoiding the by-product Ca3Al2(OH) 12 The formation of Ca-Al layered double hydroxide was promoted, which promoted the removal of chloride salts and significantly improved the purity of Ca-Al layered double hydroxide.

[0044] Example 1

[0045] The incineration fly ash is mixed with 1mol / L sodium hydroxide solution at a liquid-solid ratio of 7mL:1g, and stirred at a speed of 500r / min for 30min for alkali washing, and alkali washing fly ash and alkali washing waste liquid are obtained after solid-liquid separation. After the pH of the alkali washing waste liquid is adjusted to 7, Ca-Al layered double metal hydroxide is added at a liquid-solid ratio of 1L:4g to the alkali washing waste liquid and Ca-Al layered double metal hydroxide, and stirred at a speed of 500r / min for 30min to remove heavy metals, and a secondary waste liquid is obtained after solid-liquid separation. Sodium aluminate and calcium oxide are added to the secondary waste liquid at a ratio of n(Ca):n(Al):n(Cl)=2.5:1.2:1, and under the condition of ultrasonic treatment with an ultrasonic power of 600W, a primary dechlorination is carried out at a speed of 500r / min for 60min, and a Ca-Al layered double metal hydroxide and a tertiary waste liquid are obtained after solid-liquid separation. Sodium metaaluminate and calcium oxide are added to the tertiary waste liquid in a ratio of n(Ca):n(Al):n(Cl)=7:3:1, and the secondary dechlorination is carried out under the condition of ultrasonic treatment with an ultrasonic power of 600W and stirring at a speed of 500r / min for 60min, and Ca-Al layered double metal hydroxide and recovered alkaline solution are obtained after solid-liquid separation. The Ca-Al layered double metal hydroxide obtained in the primary dechlorination and the secondary dechlorination is used for heavy metal removal, and the recovered alkaline solution is used for alkaline washing.

[0046] Comparative Example 1

[0047] The incineration fly ash was mixed with deionized water at a liquid-to-solid ratio of 7 mL:1 g, and washed with water at a rotation speed of 500 r / min for 30 min. After solid-liquid separation, washed fly ash and washed waste liquid were obtained.

[0048] After testing, the soluble chloride content, total chlorine content, sulfate content and calcium content in the alkali-washed fly ash obtained in Example 1 and the water-washed fly ash obtained in Comparative Example 1 are shown in Table 1. Table 1 Soluble chloride content, total chlorine content, sulfate content and calcium content in the alkali-washed fly ash obtained in Example 1 and the water-washed fly ash obtained in Comparative Example 1 (%)

[0049]

[0050] It can be seen from the test results in Table 1 that: compared with water washing, the alkali washing proposed in the present invention can significantly reduce the soluble chloride content and total chlorine content in the incineration fly ash, and the soluble chloride content is less than 1%, which meets the requirements of standard HJ1134-2020; at the same time, the present invention can promote the removal of sulfate in the incineration fly ash, while achieving calcium retention, which is beneficial to the later resource utilization of the incineration fly ash.

[0051] Comparative Example 2

[0052] The alkali-washing waste liquid obtained in Example 1 was added with Ca-Al layered double metal hydroxide at a liquid-solid ratio of 1 L:4 g, and stirred at a speed of 500 r / min for 30 min to remove heavy metals, and a secondary waste liquid was obtained after solid-liquid separation. The secondary waste liquid was centrifuged and filtered with a 0.45 μm filter membrane.

[0053] Comparative Example 3

[0054] After adjusting the pH of the alkali-washing waste liquid obtained in Example 1 to 7, the waste liquid was stirred at a speed of 500 r / min for 30 minutes to remove heavy metals, and the secondary waste liquid was obtained after solid-liquid separation. The secondary waste liquid was centrifuged and filtered with a 0.45 μm filter membrane.

[0055] After testing, the heavy metal concentrations in the secondary wastewater under different heavy metal removal processes are shown in Table 2.

[0056] Table 2 Heavy metal concentrations in secondary wastewater under different heavy metal removal processes (mg / L)

[0057]

[0058] Note: nd means not detected.

[0059] It can be seen from the test results in Table 2 that under the combined action of pH adjustment and a small amount of Ca-Al layered double hydroxide, the heavy metal concentration in the waste liquid is significantly reduced, and meets the quality limit of the third category of groundwater in GB / T14848-2017, and can be reused after further treatment.

[0060] Comparative Example 4

[0061] The secondary waste liquid obtained in Example 1 was added with sodium aluminate and calcium oxide in a ratio of n(Ca):n(Al):n(Cl)=1.5:1.4:1, and stirred at a speed of 500r / min for 60min for primary dechlorination, and Ca-Al layered double metal hydroxide and tertiary waste liquid were obtained after solid-liquid separation. Sodium aluminate and calcium oxide were added to the tertiary waste liquid in a ratio of n(Ca):n(Al):n(Cl)=7:3:1, and stirred at a speed of 500r / min for 60min for secondary dechlorination, and Ca-Al layered double metal hydroxide and recovered alkaline solution were obtained after solid-liquid separation. The recovered alkaline solution was centrifuged and filtered with a 0.45μm filter membrane.

[0062] Comparative Example 5

[0063] The secondary waste liquid obtained in Example 1 was added with sodium aluminate and calcium oxide in a ratio of n(Ca):n(Al):n(Cl)=2.5:1.2:1, and stirred at a speed of 500r / min for 60min for primary dechlorination, and Ca-Al layered double metal hydroxide and tertiary waste liquid were obtained after solid-liquid separation. Sodium aluminate and calcium oxide were added to the tertiary waste liquid in a ratio of n(Ca):n(Al):n(Cl)=5:3.5:1, and stirred at a speed of 500r / min for 60min for secondary dechlorination, and Ca-Al layered double metal hydroxide and recovered alkaline solution were obtained after solid-liquid separation. The recovered alkaline solution was centrifuged and filtered with a 0.45μm filter membrane.

[0064] Comparative Example 6

[0065] The secondary waste liquid obtained in Example 1 was added with sodium aluminate and calcium oxide in a ratio of n(Ca):n(Al):n(Cl)=2.5:1.2:1, and stirred at a speed of 500r / min for 60min for primary dechlorination, and Ca-Al layered double metal hydroxide and tertiary waste liquid were obtained after solid-liquid separation. Sodium aluminate and calcium oxide were added to the tertiary waste liquid in a ratio of n(Ca):n(Al):n(Cl)=7:3:1, and stirred at a speed of 500r / min for 60min for secondary dechlorination, and Ca-Al layered double metal hydroxide and recovered alkaline solution were obtained after solid-liquid separation. The recovered alkaline solution was centrifuged and filtered with a 0.45μm filter membrane.

[0066] After testing, the dechlorination efficiency under different processes is shown in Table 3.

[0067] Table 3 Dechlorination efficiency under different processes

[0068]

[0069] It can be seen from the test results in Table 3 that the molar ratio of Ca, Al and Cl has a significant effect on the removal efficiency of chloride salts in wastewater. At the same time, ultrasonic assistance can significantly enhance the removal effect of chloride salts.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A closed-loop dechlorination and desalination method for incineration fly ash, characterized in that: The following steps are involved: The incineration fly ash is mixed with an alkaline solution for alkaline washing, and the alkaline washing fly ash and the alkaline washing waste liquid are obtained after solid-liquid separation; After adjusting the pH of the alkali washing waste liquid, Ca-Al layered double hydroxide is added to remove heavy metals, and a secondary waste liquid is obtained after solid-liquid separation; The secondary waste liquid is mixed with a calcium-aluminum-containing reagent for primary dechlorination, and a Ca-Al layered double metal hydroxide and a tertiary waste liquid are obtained after solid-liquid separation; The tertiary waste liquid is mixed with a calcium-aluminum-containing reagent for secondary dechlorination, and after solid-liquid separation, a Ca-Al layered double metal hydroxide and a recovered alkaline solution are obtained; The Ca-Al layered double metal hydroxide obtained from the primary dechlorination and the secondary dechlorination is used for heavy metal removal, and the recovered alkaline solution is used for alkaline washing.

2. The method for closed-loop dechlorination and desalination of incineration fly ash according to claim 1, characterized in that: The alkaline solution is a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 1 mol / L.

3. The method for closed-loop dechlorination and desalination of incineration fly ash according to claim 1, characterized in that: The liquid-to-solid ratio of the alkaline solution to the incineration fly ash is 5-8 mL:1 g.

4. The method for closed-loop dechlorination and desalination of incineration fly ash according to claim 1, characterized in that: The alkali washing is carried out under stirring conditions, the stirring time is 20 to 40 minutes, and the stirring rate is 400 to 600 r / min.

5. The method for closed-loop dechlorination and desalination of incineration fly ash according to claim 1, characterized in that: The pH of the alkaline washing waste liquid is adjusted to 7-9.

6. The method for closed-loop dechlorination and desalination of incineration fly ash according to claim 1, characterized in that: The liquid-to-solid ratio of the alkali washing waste liquid to the Ca-Al layered double metal hydroxide is 1L:4-8g.

7. The method for closed-loop dechlorination and desalination of incineration fly ash according to claim 1, characterized in that: The heavy metal removal is carried out under stirring conditions, the stirring time is 20 to 40 minutes, and the stirring rate is 400 to 600 r / min.

8. The method for closed-loop dechlorination and desalination of incineration fly ash according to claim 1, characterized in that: The calcium-aluminum-containing reagent is sodium metaaluminate and calcium oxide.

9. The method for closed-loop dechlorination and desalination of incineration fly ash according to claim 1, characterized in that: The primary dechlorination and the secondary dechlorination are carried out under ultrasonic and stirring conditions, the ultrasonic power is 200-600W, the stirring time is 40-60min, and the stirring rate is 400-600r / min.

10. The method for closed-loop dechlorination and desalination of incineration fly ash according to claim 1, characterized in that: In the primary dechlorination, n(Ca):n(Al):n(Cl)=2-2.5:1-1.2:1, and in the secondary dechlorination, n(Ca):n(Al):n(Cl)=7:2.5-3:1.

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