Method for recovering zinc from medical waste incineration fly ash

Abstract

The present application relates to the field of heavy metal resource recycling, and relates to a method for recycling zinc element in medical waste incineration fly ash, comprising the following steps: washing the fly ash with contaminated liquid, filtering, obtaining a first filtrate and a first filter residue, and drying the first filtrate to obtain a powder; mixing the new fly ash with the obtained powder and heating, mixing the residue at the end of heating with the first filter residue and continuing to heat, repeating the operation, continuously feeding gas and setting a filter plate at the gas outlet during the operation; washing the filter plate with water, filtering the washing liquid, and collecting zinc oxide. Compared with the prior art, the present application has the advantages of saving raw material cost, treating permeate liquid, domestic sewage and the like together with fly ash, and the like.

Description

Technical Field

[0001] This invention relates to the field of heavy metal resource recycling, and in particular to a method for recycling zinc from fly ash from medical waste incineration. Background Technology

[0002] Medical waste refers to waste generated by medical and health institutions during medical treatment, prevention, healthcare, and other related activities that possess direct or degradable infectiousness, toxicity, or other hazards. Currently, the main methods for treating and disposing of medical waste in my country are incineration and non-incineration methods.

[0003] Fly ash is a solid byproduct produced during waste incineration. After municipal solid waste is incinerated, the waste is converted into fly ash, bottom ash, flue gas, slag, and heat energy. Fly ash consists of tiny particles emitted during the combustion of municipal solid waste and is classified as hazardous waste. Furthermore, fly ash contains a large amount of soluble salts and volatile heavy metals that can be utilized as resources. Boiler ash has a high content of calcium and zinc. Zinc has good calendering properties, wear resistance, corrosion resistance, and castability, and also has good mechanical properties at room temperature, making it suitable for alloying with various metals to form high-performance alloys.

[0004] Currently, the technology for separating and extracting heavy metals from fly ash in my country is still in its initial stage. The main limiting factors are that the value of the recovered metals is difficult to cover the extraction cost, and there are also problems such as incomplete treatment of heavy metals. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for recovering zinc from fly ash in medical waste incineration. This experiment studies the boiler ash produced after the incineration of medical waste, i.e., fly ash. Separating and extracting valuable pollutants from fly ash can not only reduce the harmfulness of fly ash, but also reduce the mining of primary minerals. This method can obtain high-purity ZnCl2, and after pH adjustment with liquid, a precipitate is obtained. The precipitate is a mixture of heavy metal hydroxides, and the two account for more than 95% of the original fly ash, thus achieving the enrichment of heavy metal elements in the ash.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for recovering zinc from fly ash from medical waste incineration includes the following steps:

[0008] S1: The fly ash is washed with polluting liquid and filtered to obtain the first filtrate and the first filter residue. The first filtrate is dried to obtain powder.

[0009] S2: Mix the new fly ash with the powder obtained in S1 and heat it. Mix the residue after heating with the first filter residue, continue heating, and repeat the operation. During this period, gas is continuously introduced and a filter plate is set at the gas outlet.

[0010] S3: Wash the filter plate with water, filter the washing liquid to obtain a second filtrate and a second filter residue, adjust the pH of the second filtrate to obtain a precipitate, calcine the precipitate and collect the zinc oxide.

[0011] Furthermore, in step S1, the polluted liquid is one or a mixture of leachate, domestic sewage, and high-salt wastewater.

[0012] Furthermore, in step S1, the solid-liquid ratio of the fly ash to the polluted liquid is 1:1 to 1:3.

[0013] Furthermore, in step S2, the mass ratio of the new fly ash to the powder obtained in S1 is 1:8 to 1:15.

[0014] Furthermore, in step S2, the heating temperature for mixing and heating the new fly ash with the powder obtained in S1 is 650-900℃.

[0015] Furthermore, in step S2, the gas space velocity of the introduced gas is 100-500 h⁻¹. -1 .

[0016] Furthermore, in step S2, the temperature at the gas outlet is 150-200°C.

[0017] Furthermore, in step S2, the size of the filter plate is the size of the gas outlet, the thickness is 10-20mm, and the ppi is 150-200.

[0018] Furthermore, in step S2, the repeated operation is performed 8-15 times.

[0019] Furthermore, in step S3, the pH is adjusted to 9-12, and the precipitate is calcined at a temperature of 900-1200℃ for 3-10 hours.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] This invention discloses a method for recovering zinc from fly ash incinerated from medical waste. The fly ash is washed with water at a solid-liquid ratio of 1:1 to 1:3. The solid and liquid are filtered, and the dried liquid is mixed with the fly ash again. The mixture is heated and filtered. The resulting solid is added back into the fly ash at a ratio of 1:8 to 1:15, and this process is repeated. The resulting mixed solid is washed with water at a solid-liquid ratio of 1:3 to 1:5. Insoluble matter is filtered, and the pH of the liquid is adjusted to obtain a precipitate of zinc oxide with a purity of over 99%. The filtered liquid is dried to obtain a regenerated zinc precipitate. In this experiment, the dried liquid becomes a regenerated zinc precipitate that can be recycled, saving raw material costs. The ceramic filtration device can obtain high-purity ZnCl2 with a zinc recovery rate greater than 95%. The liquid pH is adjusted to 9-12, and the precipitate is a mixed heavy metal hydroxide, accounting for up to 95% of the original fly ash, thus achieving the enrichment of heavy metal elements in the fly ash. Detailed Implementation

[0022] The present invention will now be described in detail with reference to specific embodiments.

[0023] The following embodiments are implemented based on the above-described technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0024] The following are more detailed implementation examples, which further illustrate the technical solution of the present invention and the technical effects that can be obtained.

[0025] In the following embodiments, unless otherwise specified, the raw materials, reagents or processing techniques are all conventional commercial products or conventional processing techniques in the art.

[0026] In the following examples: fly ash comes from a medical waste incineration plant in the Yangtze River Delta, domestic sewage comes from a waterworks in Shanghai, and high-salinity wastewater comes from the Shanghai Chemical Industry Park.

[0027] Example 1

[0028] This embodiment provides a method for recovering zinc from fly ash from medical waste incineration, including the following steps:

[0029] 1) Wash fly ash with water at a solid-liquid ratio of 1:3 for 15 minutes. The liquid is domestic sewage. Filter the solid and liquid to obtain the first filtrate and the first filter residue. Dry the first filtrate at 120°C to obtain a powdered "zinc fluxing agent" with a highly complex structure of salt and organic matter.

[0030] 2) Take another fly ash and mix it with the powder obtained in step 1) at a ratio of 1:15. Heat it at 650℃ for 2 hours. During the entire process, air is introduced and the gas space velocity is 100 h⁻¹. -1A ceramic filter plate with a ppi of 150 is installed at the gas outlet (gas temperature is 150℃) and a pressure drop of 0.05MPa is placed before and after the ceramic filter plate.

[0031] 3) Remix the residue from step 2) with the first filter residue at a mass ratio of 1:8, heat at 650℃ for 2 hours, and continue to introduce air at a flow rate of 100 h / min. -1 Repeat the operation 10 times until the pressure drop across the ceramic filter plate reaches 1.0 MPa.

[0032] 4) Wash the ceramic filter plate with water, using 3 times the volume of the ceramic filter plate, for 30 minutes to obtain the second filtrate and the second filter residue. Adjust the pH of the second filtrate to 9 to obtain a precipitate. Calcine the precipitate at 1000℃ for 6 hours to obtain zinc oxide. The liquid other than the precipitate is a regenerated "zinc fluxing agent" that can be recycled.

[0033] Example 2

[0034] This embodiment provides a method for recovering zinc from fly ash from medical waste incineration, including the following steps:

[0035] 1) Wash fly ash with water for 20 minutes at a solid-liquid ratio of 1:1. The liquid is high-salt wastewater. Filter the solid and liquid to obtain the first filtrate and the first filter residue. Dry the first filtrate at 120°C to obtain a powdered "zinc fluxing agent" with a highly complex structure of salt and organic matter.

[0036] 2) Take another fly ash and mix it with the powder obtained in step 1) at a ratio of 1:10. Heat at 750℃ for 2 hours. During the entire process, hydrogen chloride gas is introduced at a flow rate of 300 h⁻¹. -1 A ceramic filter device with a ppi of 200 and a pressure drop of 0.1 MPa is installed at the gas outlet (gas temperature is 150℃).

[0037] 3) Mix the residue from step 2) with the first filter residue at a mass ratio of 1:10, heat at 750℃ for 2 hours, and continue to purge with air at a gas hourly space velocity of 300 h⁻¹. -1 Repeat the operation 10 times until the pressure drop across the ceramic filter plate reaches 1.2 MPa.

[0038] 4) Wash the ceramic filter plate with water, using three times the volume of the ceramic filter plate, for 45 minutes to obtain a second filtrate and a second filter residue. Adjust the pH of the second filtrate to 10 to obtain a precipitate. Calcine the precipitate at 1100℃ for 6 hours to obtain zinc oxide. The liquid other than the precipitate is a regenerated "zinc fluxing agent" that can be recycled.

[0039] Example 3

[0040] This embodiment provides a method for recovering zinc from fly ash from medical waste incineration, including the following steps:

[0041] 1) Wash fly ash with water at a solid-liquid ratio of 1:3 for 30 minutes. The liquid is high-salt wastewater. Filter the solid and liquid to obtain the first filtrate and the first filter residue. Dry the first filtrate at 120°C to obtain a powdered "zinc fluxing agent" with a highly complex structure of salt and organic matter.

[0042] 2) Take another fly ash and mix it with the powder obtained in step 1) in a ratio of 1:8. Heat the mixture at 750°C for 2 hours, and pass hydrogen chloride gas through it at a space velocity of 300 h⁻¹ throughout the process. -1 A ceramic filter plate with a ppi of 150 is installed at the gas outlet (gas temperature is 150℃) and a pressure drop of 0.05MPa is applied across the ceramic plate.

[0043] 3) Mix the residue from step 2) with the first filter residue at a mass ratio of 1:8, heat at 750℃ for 2 hours, and continue to purge with air at a gas hourly space velocity of 300 h⁻¹. -1 Repeat the operation 10 times until the pressure drop across the ceramic filter plate reaches 1.0 MPa.

[0044] 4) Wash the ceramic filter plate with water, using 5 times the volume of the ceramic filter plate, for 30 minutes to obtain the second filtrate and the second filter residue. Adjust the pH of the second filtrate to 10 to obtain a precipitate. Calcine the precipitate at 1200℃ for 6 hours to obtain zinc oxide. The liquid other than the precipitate is a regenerated "zinc fluxing agent" that can be recycled.

[0045] Example 4

[0046] This embodiment provides a method for recovering zinc from fly ash from medical waste incineration, including the following steps:

[0047] 1) Wash fly ash with water at a solid-liquid ratio of 1:3 for 15 minutes. The liquid is high-salt wastewater. Filter the solid and liquid to obtain the first filtrate and the first filter residue. Dry the first filtrate at 120°C to obtain a powdered "zinc fluxing agent" with a highly complex structure of salt and organic matter.

[0048] 2) Take another fly ash and mix it with the powder obtained in step 1) at a ratio of 1:15. Heat the mixture at 850°C for 2 hours, and pass hydrogen chloride gas through it at a space velocity of 500 h⁻¹ throughout the process. -1 A ceramic filter plate with a ppi of 150 is installed at the gas outlet (gas temperature is 150℃) and a pressure drop of 0.05MPa is applied across the ceramic plate.

[0049] 3) Mix the residue from step 2) with the first filter residue at a mass ratio of 1:10, heat at 750℃ for 2 hours, and continue to purge with air at a gas hourly space velocity of 500 h⁻¹.-1 Repeat the operation 10 times until the pressure drop across the ceramic filter plate reaches 1.0 MPa.

[0050] 4) Wash the ceramic filter plate with water, using 3 times the volume of the ceramic filter plate, for 30 minutes to obtain the second filtrate and the second filter residue. Adjust the pH of the second filtrate to 9 to obtain a precipitate. Calcine the precipitate at 1100℃ for 5 hours to obtain zinc oxide. The liquid other than the precipitate is a regenerated "zinc fluxing agent" that can be recycled.

[0051] Example 5

[0052] The only difference between Example 5 and Example 1 is that the gas space velocity in steps 2) and 3) is 300 h⁻¹. -1 Other preparation methods and conditions are the same as in Example 1.

[0053] Example 6

[0054] The only difference between Example 6 and Example 1 is that the gas space velocity in steps 2) and 3) is 500 h⁻¹. -1 Other preparation methods and conditions are the same as in Example 1.

[0055] Example 7

[0056] The only difference between Example 7 and Example 1 is that the gas space velocity in steps 2) and 3) is 600 h⁻¹. -1 Other preparation methods and conditions are the same as in Example 1.

[0057] Example 8

[0058] The only difference between Example 8 and Example 2 is that the heating temperature in steps 2) and 3) is 850°C. The other preparation methods and conditions are the same as in Example 2.

[0059] Example 9

[0060] The only difference between Example 9 and Example 2 is that the heating temperature in steps 2) and 3) is 900℃. The other preparation methods and conditions are the same as in Example 2.

[0061] Example 10

[0062] The only difference between Example 10 and Example 2 is that a ceramic filter plate is placed at a gas temperature of 200°C in steps 2) and 3). The other preparation methods and conditions are the same as in Example 2.

[0063] Example 11

[0064] The only difference between Example 11 and Example 2 is that a ceramic filter plate is placed at a gas temperature of 250°C in steps 2) and 3). The other preparation methods and conditions are the same as in Example 2.

[0065] Example 12

[0066] The only difference between Example 12 and Example 2 is that in step 1), the fly ash is washed with water at a solid-liquid ratio of 1:3 for 15 minutes. The other preparation methods and conditions are the same as in Example 2.

[0067] Example 13

[0068] The only difference between Example 13 and Example 2 is that in step 4), the fly ash is washed with water at a solid-liquid ratio of 1:5 for 30 minutes. The other preparation methods and conditions are the same as in Example 2.

[0069] For Examples 1-13, the zinc content (Zn%) in the ceramic filter device was determined by ICP detection, and the results are shown in Appendix Table 1.

[0070] Example 1 61 Example 2 62 Example 3 62 Example 4 61 Example 5 62 Example 6 61 Example 7 58 Example 8 62 Example 9 61 Example 10 62 Example 11 56 Example 12 62 Example 13 61

[0071] As shown in Examples 1-4, the method for recovering zinc from fly ash incinerated from medical waste using this invention has low raw material costs and can efficiently recover zinc. However, comparing Examples 5-7 with Example 1, it is evident that increasing the gas flow rate and space velocity reduces the gas residence time, leading to excessive oxidation and affecting the content of heavy metal hydroxides formed. Furthermore, comparing Examples 8-11 with Example 2, it is clear that during high-temperature incineration in the grate furnace, since most heavy metals volatilize and form metal chlorides with chlorine in the fly ash, the mixture of fresh fly ash and the "zinc fusion accelerator" solid should be heated at 650-900℃, and the pH of the liquid should be controlled between 9-12 to obtain a solid mixture with a high zinc content. Comparing Examples 12-13 with Example 2, it is evident that an unreasonable solid-liquid ratio will affect the recovery and reuse efficiency of heavy metals in fly ash. When the solid-liquid ratio is too low, the excessive liquid phase makes it difficult to recover heavy metal elements; while when the solid-liquid ratio is too high, it will increase the processing cost and reduce the element recovery rate. Therefore, it is very important to reasonably control the solid-liquid ratio, which can improve the catalyst recovery rate and reuse value. At the same time, the washing time of fly ash also affects the recovery efficiency of heavy metal elements. Too short a washing time will result in the chloride salts in the fly ash not being fully dissolved, while too long a washing time will reduce the economic efficiency of the washing process. Therefore, the solid-liquid ratio of fly ash in step 1) should be controlled at 1:1-1:3, and the time should be 15-30 min. In step 4), the solid-liquid ratio of fly ash in step 4) should be controlled at 1:3-1:5, and the time should be controlled at 30-45 min.

[0072] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for recovering zinc from fly ash from medical waste incineration, characterized in that, Includes the following steps: S1: The fly ash is washed with pollutant liquid, filtered, and a first filtrate and a first filter residue are obtained. The first filtrate is dried to obtain powder. The pollutant liquid is one or a mixture of permeate, domestic sewage, and high-salt wastewater. S2: Mix the new fly ash with the powder obtained in S1 and heat it to a temperature of 650-900℃. Mix the residue after heating with the first filter residue and continue heating. Repeat the operation while continuously introducing gas. Set a ceramic filter plate at the gas outlet. The temperature at the gas outlet is 150-200℃ and the ppi of the ceramic filter plate is 150-200. Repeat the operation until the pressure drop across the ceramic filter plate reaches 1.0MPa. S3: Wash the ceramic filter plate with water, filter the washing liquid to obtain the second filtrate and the second filter residue, adjust the pH of the second filtrate to 9-12 to obtain the precipitate, calcine the precipitate at 900-1200℃ for 3-10 hours, and collect the zinc oxide.

2. The method for recovering zinc from fly ash of medical waste incineration according to claim 1, characterized in that, In step S1, the solid-liquid ratio of the fly ash to the polluted liquid is 1:1 to 1:

3.

3. The method for recovering zinc from fly ash of medical waste incineration according to claim 1, characterized in that, In step S2, the mass ratio of the new fly ash to the powder obtained in S1 is 1:8-1:

15.

4. The method for recovering zinc from fly ash of medical waste incineration according to claim 1, characterized in that, In step S2, the gas space velocity of the introduced gas is 100-500 h⁻¹. -1 .

5. The method for recovering zinc from fly ash of medical waste incineration according to claim 1, characterized in that, In step S2, the repeated operation is performed 8-15 times.

6. The method for recovering zinc from fly ash of medical waste incineration according to claim 1, characterized in that, In step S2, the thickness of the ceramic filter plate is 10-20mm, and its size is the same as the gas outlet size.