System and method for enhancing fly ash water washing dechlorination effect and reducing heavy metal leaching toxicity

Abstract

The present invention belongs to the field of environmental protection technology, and relates to a system and method for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching. The method and system are as follows: firstly, the fly ash material composition is detected by X-ray fluorescence spectroscopy analysis and the fly ash acid neutralization capacity is calculated; the phosphoric acid addition amount of the washing liquid is calculated according to the fly ash acid neutralization capacity and the phosphoric acid washing liquid is prepared; the fly ash is washed with phosphoric acid washing liquid, and the pH value of the washing system endpoint is adjusted by pH value monitoring and control equipment during the washing process. The present invention can reduce the leaching of heavy metals in the fly ash during the washing process while enhancing the dechlorination effect of fly ash washing, thereby reducing the heavy metal content in the washing waste liquid and saving the washing liquid treatment cost.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection, and relates to a system and method for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] According to the inventor's research, during the process of water washing and dechlorination of fly ash from the incineration of municipal solid waste, heavy metals in the fly ash will leach into the washing liquid, resulting in a high content of heavy metals in the washing liquid, thereby increasing the subsequent treatment cost of the washing liquid. Summary of the invention

[0004] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a system and method for enhancing the dechlorination effect of fly ash washing and effectively reducing the toxicity of heavy metal leaching, which can reduce the leaching of heavy metals in fly ash while enhancing the dechlorination effect of fly ash washing, thereby reducing the heavy metal concentration in the washing waste liquid and saving the cost of washing waste liquid treatment.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] The first aspect of the present invention provides a method for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching, comprising:

[0007] To test the material composition of fly ash and calculate the acid neutralization capacity of fly ash;

[0008] Calculate the amount of phosphoric acid added to the water wash solution based on the fly ash acid neutralization capacity and prepare the phosphoric acid water wash solution;

[0009] Use phosphoric acid water washing liquid to wash the fly ash, monitor the pH value during the washing process, and adjust the pH value range of the washing system end point to 7±1;

[0010] After the washing is completed, the slurry mixture obtained by washing is subjected to solid-liquid separation, and the fly ash and the washing waste liquid are collected separately;

[0011] Adding an organic precipitant or an inorganic agent to the water-washing waste liquid, removing heavy metals in the water-washing waste liquid by precipitation separation, and collecting the detoxified water-washing waste liquid;

[0012] The detoxified water washing waste liquid is efficiently evaporated to recover chloride salt and water to obtain the product.

[0013] The second aspect of the present invention provides a system for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching, comprising: a fly ash component detection device, a data processing device, an acid washing liquid preparation device, a water washing device, a dynamic detection and adjustment pH device, a solid-liquid separation device, a detoxification device, and a high-efficiency evaporator;

[0014] The pickling liquid preparation device is connected with the water washing device, the solid-liquid separation device, the detoxification device, and the high-efficiency evaporator in sequence;

[0015] The water washing device is also connected to a dynamic detection and pH adjustment device;

[0016] The data processing device comprises: a module for calculating the acid neutralization capacity of fly ash and a module for calculating the amount of acid added; the data processing device is connected to the fly ash component detection device and the pickling liquid preparation device respectively.

[0017] The module for calculating the acid neutralization capacity of fly ash, the module for calculating the amount of acid added, and the pickling liquid configuration device are automatically controlled by PLC.

[0018] The third aspect of the present invention provides the use of a phosphoric acid solution in washing out some of the poorly soluble and insoluble chloride salts in fly ash.

[0019] Beneficial Effects of the Invention

[0020] (1) The present invention adds phosphoric acid into the water washing unit to control the endpoint pH value of the water washing system, thereby reducing the leaching of heavy metals in the fly ash. At the same time, phosphate radicals can react with heavy metal ions to form phosphate precipitates, further reducing the heavy metal concentration in the water washing wastewater.

[0021] (2) The present invention uses phosphoric acid solution as the washing liquid. While reducing the heavy metal concentration in the washing waste liquid, the addition of phosphoric acid can wash out some of the insoluble and insoluble chloride salts (Friedel's salts) in the fly ash, thereby increasing the washing rate of chloride salts.

[0022] (3) The heavy metal concentration in the washing wastewater produced by the present invention is low, thereby reducing the subsequent heavy metal treatment cost and improving the purity of the recovered chloride salt.

[0023] (4) Compared with the conventional method for optimizing the endpoint pH value of the fly ash heavy metal leaching solution, the present invention dynamically adjusts the pH value of the water washing system in a specific water washing section so that the pH value is always within a predetermined pH range, thereby effectively reducing the heavy metal content in the fly ash water washing solution and improving the leaching rate of chloride salts. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0025] Figure 1 Conceptual curves of heavy metal dissolution behavior in fly ash under different endpoint pH conditions;

[0026] Figure 2 A systematic process to enhance the dechlorination effect of fly ash washing and reduce the toxicity of heavy metal leaching. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0028] After the incineration of domestic waste, the flue gas passes through the dust removal equipment to produce tiny particles called fly ash, which contains a large amount of chloride salts and heavy metals. During the process of washing and dechlorinating the fly ash, heavy metals will leach into the washing liquid.

[0029] In view of the high heavy metal content and high treatment cost in fly ash washing wastewater, the present invention proposes a method for reducing the heavy metal content in fly ash washing liquid by controlling the endpoint pH value of the washing system.

[0030] On the one hand, a method for reducing the leaching of heavy metals in fly ash is provided by controlling the endpoint pH value of the water washing system by preparing a phosphoric acid water washing solution.

[0031] During the water washing process, the leaching behavior of heavy metals in fly ash is related to the endpoint pH value of the water washing system. Different heavy metals have different leaching behaviors, which conform to one of the three leaching behavior modes (cationic, oxyanionic, and amphoteric), such as Figure 1 As shown. Among them, the amphoteric leaching mode metals (Pb, Zn) have high content in fly ash and large leaching amount, and their concentration in the water washing wastewater is easy to exceed the discharge concentration limit of the "Comprehensive Wastewater Discharge Standard" (GB 8978-1996). Therefore, when considering the pH value range of the water washing liquid endpoint, Pb and Zn are focused on, and the optimal water washing endpoint pH value range for practical application is finally determined to be 7±1.

[0032] Before washing, the fly ash samples are taken for X-ray fluorescence spectrum analysis to obtain the fly ash material component data. By inputting the fly ash material component data into the program, the acid neutralization capacity and acid addition amount of the fly ash are automatically calculated, and phosphoric acid is automatically added to the washing liquid according to the calculation results to achieve the purpose of controlling the endpoint pH value of the washing system. The automatic calculation of the phosphoric acid addition amount and the addition of phosphoric acid to the washing liquid are realized by a programmable logic controller (PLC).

[0033] On the other hand, a method for real-time monitoring and controlling the pH value of a water washing system during a water washing process is provided. A real-time pH monitoring device is added to the water washing unit, and when the pH value exceeds a preset range, fly ash (when the system pH value is <6) or phosphoric acid (when the system pH value is >8) is automatically added to adjust the pH value of the water washing system.

[0034] After the washing is completed, the mud mixture obtained by washing is separated into solid and liquid, the separated fly ash is output, and the washing waste liquid enters the washing waste liquid treatment unit. The washing waste liquid treatment unit first adds organic precipitants such as TMT-102, MT-103, RS-2568 or inorganic agents such as Na2S, Na2CO3, FeSO4, Ca3(PO4)2 to the washing waste liquid to precipitate and separate and remove heavy metals in the washing liquid. After that, the detoxified washing waste liquid is efficiently evaporated and crystallized to recover chloride salt and water. The recovered water can continue to be used for fly ash washing, or discharged in compliance with standards.

[0035] The mechanism of controlling the endpoint pH value of the water washing system in the present invention is that by calculating the acid neutralization capacity of the fly ash, the H2O that the fly ash needs to consume when the pH value of the system is 7 can be calculated. + The amount of substance can be used to calculate the mass of phosphoric acid required.

[0036] Considering only the main substances in fly ash that can participate in the calculation of acid neutralization capacity, and assuming that all alkaline and acidic substances in fly ash are neutralized, the theoretical calculation formula of fly ash acid neutralization capacity (ANC) is as follows:

[0037]

[0038] Where ANC is the value of the acid neutralization capacity of fly ash; is the mass fraction of Al2O3 in fly ash (%); is the mass fraction of Fe2O3 in fly ash (%); ω CaO is the mass fraction of CaO in fly ash (%); ω MgO is the mass fraction of MgO in fly ash (%); is the mass fraction of K2O in fly ash (%); is the mass fraction of Na2O in fly ash (%); is the mass fraction of SO3 in fly ash (%); is the mass fraction (%) of P2O5 in fly ash.

[0039] When calculating the amount of phosphoric acid to be added, it is assumed that phosphoric acid is completely electrolyzed in water. If the end point pH value of the water washing system is 7, then the H2O2 produced by phosphoric acid electrolysis is + The amount of substance needed to be equal to the ANC of the fly ash. The mass of phosphoric acid required per gram of fly ash is calculated as follows:

[0040]

[0041] Where m is the mass of phosphoric acid required per gram of fly ash (g); ANC is the acid neutralization capacity of fly ash.

[0042] Integrating the above two formulas and converting the units, we can get the mass of phosphoric acid that needs to be added per kilogram of fly ash:

[0043]

[0044] Where m is the mass of phosphoric acid required to be consumed per kilogram of fly ash (kg); is the mass fraction of Al2O3 in fly ash (%); is the mass fraction of Fe2O3 in fly ash (%); ω CaO is the mass fraction of CaO in fly ash (%); ω MgO is the mass fraction of MgO in fly ash (%); is the mass fraction of K2O in fly ash (%); is the mass fraction of Na2O in fly ash (%); is the mass fraction of SO3 in fly ash (%); is the mass fraction (%) of P2O5 in fly ash.

[0045] In addition, the pH value of the water washing system is monitored in real time during the fly ash water washing process, and fly ash (when the system pH value is <6) or phosphoric acid (when the system pH value is >8) is automatically added to adjust the pH value of the water washing system to within the range of 7±1. The real-time monitoring and adjustment system for pH value is activated when 70% of the water washing time has passed.

[0046] A typical embodiment of the present invention provides a method for reducing the heavy metal content in water washing wastewater and improving the leaching rate of chloride salts from fly ash, by preparing a phosphoric acid water washing solution and dynamically monitoring and regulating the pH value of the water washing unit to control the endpoint pH value of the water washing system, reduce the leaching of heavy metals in the fly ash and improve the leaching rate of chloride salts;

[0047] The mass of phosphoric acid required to prepare phosphoric acid water wash solution is obtained from the acid neutralization capacity data and calculation formula of fly ash;

[0048] The acid neutralization capacity of fly ash is obtained from the fly ash material composition data and calculation formula;

[0049] The pH value control of the water washing system endpoint is achieved by preparing phosphoric acid water washing solution and water washing unit pH value monitoring and control equipment;

[0050] In some embodiments, the liquid-to-solid ratio of fly ash to water wash liquid is 3:1 to 4:1 L / kg.

[0051] In some embodiments, the water washing time is 15 to 30 minutes.

[0052] In some embodiments, the water washing stirring frequency is 300-500 r / min.

[0053] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0054] Example 1

[0055] Take 10g of fly ash sample from a batch of fly ash and dry it. Take 5g of fly ash sample after drying and use X-ray fluorescence spectrometer to analyze the compound composition, and obtain the mass fraction data of CaO, Fe2O3, Al2O3, Na2O, K2O, MgO, P2O5, and SO3 (16.8%, 3.65%, 6.75%, 15.2%, 8.13%, 3.45%, 1.55%, and 6.88%, respectively). The data is imported into the program, and the system automatically executes the entire water washing process. Among them, the liquid-solid ratio of water washing liquid to fly ash is 4:1L / kg, the water washing time is 25 minutes, and the water washing stirring frequency is 400r / min. After the water washing time exceeds 17.5 minutes, start the real-time monitoring and pH adjustment system to control the pH within the range of 7±1.

[0056] After the washing, 10 mL of untreated washing waste liquid was taken, and the total chlorine content was determined using a Dion ICS-1000 ion chromatograph, and the heavy metal content was determined using an inductively coupled plasma mass spectrometer (ICP-MS). The results showed that the total chlorine removal rate of fly ash reached 91.87%. Compared with traditional washing (i.e., no pH control was performed during the entire washing process), the content of Zn in the washing waste liquid of this method was reduced by 82.43%, the content of Pb was reduced by 89.3%, the content of Cu was reduced by 16.93%, and the content of Cd was reduced by 38.39%. The above heavy metal concentrations in the washing waste liquid did not exceed the "Comprehensive Wastewater Discharge Standard" (GB 8978-1996).

[0057] Example 2

[0058] 10g of fly ash samples from a batch of fly ash were dried, and 5g of fly ash samples were used to analyze the compound composition using an X-ray fluorescence spectrometer to obtain the mass fraction data of CaO, Fe2O3, Al2O3, Na2O, K2O, MgO, P2O5, and SO3 (22.54%, 2.92%, 8.01%, 15.74%, 17.56%, 2.68%, 1.26%, and 5.27%, respectively). The data was imported into the program, and the system automatically executed the entire water washing process. Among them, the liquid-solid ratio of water washing liquid and fly ash was 4:1L / kg, the water washing time was 20 minutes, and the water washing stirring frequency was 300r / min. After the water washing time exceeded 14 minutes, the real-time monitoring and pH adjustment system was started to control the pH within the range of 7±1.

[0059] After the washing, 10 mL of untreated washing waste liquid was taken, and the total chlorine content was determined using a Dion ICS-1000 ion chromatograph, and the heavy metal content was determined using an inductively coupled plasma mass spectrometer (ICP-MS). The results showed that the total chlorine removal rate of fly ash reached 90.41%. Compared with traditional washing, this method reduced the Zn content in the washing waste liquid by 81.89%, the Pb content by 87.6%, the Cu content by 14.45%, and the Cd content by 36.97%. The above heavy metal concentrations in the washing waste liquid did not exceed the "Comprehensive Wastewater Discharge Standard" (GB 8978-1996).

[0060] Example 3

[0061] 10g of fly ash samples from a batch of fly ash were dried, and 5g of fly ash samples were used to analyze the compound composition using an X-ray fluorescence spectrometer to obtain the mass fraction data of CaO, Fe2O3, Al2O3, Na2O, K2O, MgO, P2O5, and SO3 (23.16%, 2.07%, 11.24%, 12.41%, 7.17%, 3.54%, 1.74%, and 7.22%, respectively). The data was imported into the program, and the system automatically executed the entire water washing process. Among them, the liquid-solid ratio of water washing liquid and fly ash was 4:1L / kg, the water washing time was 30 minutes, and the water washing stirring frequency was 500r / min. After the water washing time exceeded 21 minutes, the real-time monitoring and pH adjustment system was started to control the pH within the range of 7±1.

[0062] After the washing, 10 mL of untreated washing waste liquid was taken, and the total chlorine content was determined using a Dion ICS-1000 ion chromatograph, and the heavy metal content was determined using an inductively coupled plasma mass spectrometer (ICP-MS). The results showed that the total chlorine removal rate of fly ash reached 92.63%. Compared with traditional washing, this method reduced the Zn content in the washing waste liquid by 82.47%, the Pb content by 89.85%, the Cu content by 16.67%, and the Cd content by 37.49%. The above heavy metal concentrations in the washing waste liquid did not exceed the "Comprehensive Wastewater Discharge Standard" (GB 8978-1996).

[0063] Example 4

[0064] 10g of fly ash samples from a batch of fly ash were dried, and 5g of fly ash samples were used to analyze the compound composition using an X-ray fluorescence spectrometer to obtain the mass fraction data of CaO, Fe2O3, Al2O3, Na2O, K2O, MgO, P2O5, and SO3 (27.25%, 3.1%, 13.04%, 5.84%, 5.37%, 3.16%, 1.33%, and 6.49%, respectively). The data was imported into the program, and the system automatically executed the entire water washing process. Among them, the liquid-solid ratio of water washing liquid and fly ash was 3:1L / kg, the water washing time was 30 minutes, and the water washing stirring frequency was 500r / min. After the water washing time exceeded 21 minutes, the real-time monitoring and pH adjustment system was started to control the pH within the range of 7±1.

[0065] After the washing, 10 mL of untreated washing waste liquid was taken, and the total chlorine content was determined using a Dion ICS-1000 ion chromatograph, and the heavy metal content was determined using an inductively coupled plasma mass spectrometer (ICP-MS). The results showed that the total chlorine removal rate of fly ash reached 91.78%. Compared with traditional washing, this method reduced the Zn content in the washing waste liquid by 83.05%, the Pb content by 88.57%, the Cu content by 17.35%, and the Cd content by 37.94%. The above heavy metal concentrations in the washing waste liquid did not exceed the "Comprehensive Wastewater Discharge Standard" (GB 8978-1996).

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching, characterized in that: include: To test the material composition of fly ash and calculate the acid neutralization capacity of fly ash; Calculate the amount of phosphoric acid added to the water wash solution based on the fly ash acid neutralization capacity and prepare the phosphoric acid water wash solution; Use phosphoric acid water washing liquid to wash the fly ash, monitor the pH value during the washing process, and adjust the pH value range of the washing system endpoint to 7±1, specifically: Add a real-time pH monitoring device to the water washing unit. When the pH value of the water washing system is less than 6, fly ash is automatically added to adjust the pH value of the water washing system to 7±1. When the pH value of the water washing system is greater than 8, phosphoric acid is automatically added to adjust the pH value of the water washing system to 7±1. The real-time monitoring and pH adjustment system starts when 70% of the water washing time has passed. After the washing is completed, the slurry mixture obtained by washing is subjected to solid-liquid separation, and the fly ash and the washing waste liquid are collected separately; Adding an organic precipitant or an inorganic agent to the water-washing waste liquid, removing heavy metals in the water-washing waste liquid by precipitation separation, and collecting the detoxified water-washing waste liquid; The detoxified water-washing waste liquid is evaporated efficiently to recover chloride salt and water to obtain; The liquid-to-solid ratio of fly ash and water washing liquid is 3:1~4:1 L / kg.

2. The method for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching according to claim 1, characterized in that: The detection adopts X-ray fluorescence spectroscopy analysis.

3. The method for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching according to claim 1, characterized in that: The mass of phosphoric acid required to be added per kilogram of fly ash is calculated using the following formula: In the formula, m is the mass of phosphoric acid required per kilogram of fly ash (kg); ω Al 2 O 3 is the mass fraction of Al2O3 in fly ash; ω Fe 2 O 3 is the mass fraction of Fe2O3 in fly ash; ω CaO is the mass fraction of CaO in fly ash; ω MgO is the mass fraction of MgO in fly ash; ω K 2 O is the mass fraction of K2O in fly ash; ω Na 2 O is the mass fraction of Na2O in fly ash; ω SO 3 is the mass fraction of SO3 in fly ash; ω P 2 O 5 is the mass fraction of P2O5 in fly ash.

4. The method for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching according to claim 1, characterized in that: Automatic calculation of the amount of phosphoric acid to be added and addition of phosphoric acid to the water wash solution are achieved through a programmable logic controller PLC.

5. The method for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching according to claim 1, characterized in that: The organic precipitant is at least one of TMT-102, MT-103 and RS-2568.

6. The method for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching according to claim 1, characterized in that: The inorganic agent is at least one of Na2S, Na2CO3, FeSO4, and Ca3(PO4)2.

7. A system for enhancing the dechlorination effect of fly ash washing and reducing the toxicity of heavy metal leaching, characterized in that: A method for achieving the enhanced fly ash water washing and dechlorination effect and reducing the toxicity of heavy metal leaching as described in any one of claims 1 to 6, comprising: a fly ash component detection device, a data processing device, a pickling liquid preparation device, a water washing device, a dynamic detection and adjustment pH device, a solid-liquid separation device, a detoxification device, and a high-efficiency evaporator; The pickling liquid preparation device is connected with the water washing device, the solid-liquid separation device, the detoxification device, and the high-efficiency evaporator in sequence; The water washing device is also connected to a dynamic detection and pH adjustment device; The data processing device comprises: a module for calculating the acid neutralization capacity of fly ash and a module for calculating the amount of acid added; the data processing device is connected to the fly ash component detection device and the pickling liquid preparation device respectively. The module for calculating the acid neutralization capacity of fly ash, the module for calculating the amount of acid added, and the pickling liquid configuration device are automatically controlled by PLC.

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