Ion exchange driven incineration fly ash short process wet treatment method

Abstract

The application discloses a kind of ion exchange driven incineration fly ash short process wet treatment method, belong to solid waste treatment technical field.The method of the application includes the following steps: original incineration fly ash is mixed with leaching liquid NaCl or KCl solution according to 2~5 L / kg liquid-solid ratio, through high concentration Na + ,K + Competitive ion exchange with heavy metal ions, efficient leaching of heavy metals and soluble salt in fly ash;After solid-liquid separation, gradient dilution leaching is used to further remove residual soluble salt and heavy metal;Leaching waste liquid and leaching liquid are treated according to the concentration of heavy metals and salt, realizing salt recycling and recycling of heavy metal resources.The application can effectively remove more than 80% of soluble salt and heavy metal in fly ash, and the salt recycling rate is more than 85%, the process is short, the cost is low, and the environment is friendly, which provides an innovative solution for efficient and harmless treatment and resource utilization of fly ash.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste treatment, in particular to a short-process wet treatment method of ion exchange driven incineration fly ash. BACKGROUND

[0002] With the acceleration of urbanization and the improvement of township garbage collection and transportation system, the amount of household garbage is increasing. Garbage incineration technology has become the main garbage disposal method in China due to its large processing capacity, significant volume and mass reduction effect, and the ability to recover heat and electrical energy. However, hazardous waste fly ash is generated during the garbage incineration process, mainly from the fine ash settled at the bottom of the flue and the capture material of the flue gas purification system, which contains inorganic salts and heavy metals such as Pb, Cd, Zn, Cu, and excess reagents such as lime added during flue gas purification. At the same time, fly ash also contains dioxin persistent organic pollutants. If fly ash is not properly treated, it can easily pollute soil, water and air, threatening ecological environment safety and human health.

[0003] In recent years, with the improvement of environmental protection requirements and the promotion of the concept of circular economy, fly ash treatment technology is developing towards resource utilization. The water washing desalination technology takes advantage of the fact that chloride salts in fly ash are easily soluble in water, and separates chloride salts from fly ash through water washing, which not only reduces the risk of fly ash, but also recovers and produces industrial salt, and has good application prospects.

[0004] The soluble salt content in fly ash is relatively high, and if it is directly subjected to subsequent stabilization, solidification or resource utilization, it will affect the treatment effect and product performance. Through the water washing process, the soluble salt is dissolved in water, which can significantly reduce the salt content in fly ash, creating favorable conditions for subsequent treatment processes. At the same time, part of the soluble heavy metals will be taken out with the soluble salt, thereby reducing the leaching risk of heavy metals and reducing their potential harm to the environment. From the perspective of resource recovery and compliance disposal, fly ash treated by water washing is more likely to meet the requirements of subsequent resource utilization such as the preparation of building materials, realizing the transformation of waste into treasure.

[0005] Currently, fly ash water washing process mostly uses three-stage countercurrent washing, fresh water enters from the third stage, contacts with fly ash countercurrently, and then is used as the second washing water, and finally is discharged from the first stage. This process can reduce water consumption to a certain extent, and through multi-stage washing and full contact with fly ash, it can improve washing efficiency; but it has complex equipment, requires three-stage washing devices, supporting conveying devices, solid-liquid separation devices, etc., which requires high initial equipment investment; the pipeline is easy to be blocked during operation, and the maintenance cost is high.

[0006] Therefore, there is an urgent need to develop a short-process wet treatment method of fly ash that can effectively separate soluble salts and heavy metals in fly ash while reducing equipment investment and operation and maintenance requirements, to realize efficient and harmless treatment and resource utilization of incineration fly ash. SUMMARY

[0007] To solve the technical problems of low heavy metal removal efficiency, complex process flow and low resource utilization degree in the existing fly ash treatment technology, the application provides a short process wet treatment method of ion exchange driven incineration fly ash.

[0008] The application aims to provide a short process wet treatment method of ion exchange driven incineration fly ash, comprising the following steps:

[0009] S1, stirring and mixing the original incineration fly ash with high-concentration leaching solution, and separating the solid and liquid to obtain leaching solution and fly ash residue;

[0010] S2, providing leaching solution and water with different concentration gradients;

[0011] S3, using the leaching solution and water provided in step S2 to leach the fly ash residue obtained in step S1 multiple times: the concentration of the leaching solution used in the multiple leaching is from high to low, and finally the solid and liquid are separated to obtain leached fly ash residue and leaching separation solution;

[0012] S4, recycling the leaching separation solution obtained in each leaching in step S3.

[0013] In some embodiments of the application, in step S1, the concentration of the leaching solution is more than 80wt% of the saturation concentration; and the leaching solution comprises NaCl and / or KCl solution.

[0014] In some embodiments of the application, in step S1, the liquid-solid ratio of the leaching solution to the original incineration fly ash is 2-5 L / kg; the stirring speed is 200-600 r / min, the temperature is 20-30℃, and the stirring time is 15-60 min.

[0015] In some embodiments of the application, in step S1, the recycling of the leaching solution comprises the following steps:

[0016] (1) when the total concentration of heavy metals in the salt solution in the leaching solution is ≤100 mg / L, the leaching solution is directly recycled for leaching experiment;

[0017] (2) when the total concentration of heavy metals in the salt solution in the leaching solution is 100-500 mg / L, the leaching solution is recycled after pH adjustment and precipitation treatment;

[0018] (3) when the total concentration of heavy metals in the salt solution in the leaching solution is > 500 mg / L or < 70% of the saturation concentration, a membrane treatment method is used to separate the heavy metals and inorganic salts. Further, in the membrane treatment, a nanofiltration membrane or a reverse osmosis membrane is used to separate the leaching waste liquid containing high-concentration heavy metals to obtain a concentrated liquid and a clear liquid, the membrane separation has a molecular weight cut-off of 200-1000 Da, and the concentrated liquid is subjected to heavy metal recovery treatment.

[0019] In some embodiments of the present application, in step S1, a centrifugation or plate-and-frame pressure filtration method is used to separate the leaching liquid containing high-concentration heavy metals and fly ash residues;

[0020] In some embodiments of the present application, in step S2, the leaching solution is a sodium chloride solution.

[0021] In some embodiments of the present application, in step S2, the different concentration gradients are 40-50%, 10-20%, 4-7% and 0% of the saturation salt concentration in the leaching solution. The gradient cleaning is provided to remove the saturated salt solution carried by the residues in the first separation, and the different gradients are beneficial to the subsequent recycling of the leaching waste liquid.

[0022] In some embodiments of the present application, the solid-liquid separation equipment used in the present application is used for multiple gradient leaching, without the need for additional multiple equipment, and the multiple leaching only needs to replace the leaching liquid, without the need for transporting slurry and the like.

[0023] In some embodiments of the present application, in step S2, the liquid-solid ratio of the leaching liquid to fly ash is 0.5-1 L / kg. Uniform water distribution is required during the leaching process to leach as much fly ash as possible.

[0024] In some embodiments of the present application, in step S3, the number of times of multiple leaching is 2-4 times, and is further preferably 3 or 4 times.

[0025] In some embodiments of the present application, in step S3, the water content of the fly ash after leaching is 35-50%, the removal rate of soluble salts is 85-95%, the removal rate of soluble Pb is 66-80%, and the removal rate of soluble Zn is 70-85%.

[0026] In some embodiments of the present application, in step S4, the leaching separation liquid is used according to the water quality characteristics:

[0027] (1) the leaching liquid in which the total concentration of heavy metals is < 100 mg / L and the salt concentration is > 50% of the saturation concentration is used for the next batch of leaching experiments after supplementing the salt content;

[0028] (2) the leaching liquid in which the total concentration of heavy metals is < 100 mg / L and the salt concentration is ≤ 50% of the saturation concentration is used for the subsequent leaching process;

[0029] (3) The total concentration of heavy metals in the elution separation solution is ≥100 mg / L, and the elution separation solution is combined with the leaching waste liquid in step S1 for treatment.

[0030] In some embodiments of the present application, the solid-liquid separation is performed by filtration or centrifugation.

[0031] The above technical solutions of the present application have the following advantages compared with the prior art:

[0032] The core innovation of the present application is to utilize the competitive ion exchange effect of high-concentration Na + , K + ions and heavy metal ions in fly ash. In a saturated salt solution, the concentration of Na + , K + ions is much higher than that of heavy metal ions. According to the mass action law and ion selectivity theory, the excess Na + , K + ions can effectively replace Pb 2+ , Zn 2+ and other heavy metal ions on the surface and pores of fly ash particles, breaking the limitation of the traditional water washing concentration gradient. High-concentration chloride ions can also form high-chlorine complexes with heavy metals, enhancing the dissolution effect of heavy metals. At the same time, the saturated salt solution has extremely high ionic strength, which can produce a significant ionic strength effect, compressing the thickness of the double electric layer on the particle surface and weakening the electrostatic binding force between heavy metal ions and the solid surface, thereby promoting the desorption of heavy metals.

[0033] The present application innovatively adopts a salt concentration gradient decreasing elution strategy to achieve complete removal of heavy metals. The high-concentration stage mainly removes residual strongly bound heavy metals, the medium and low-concentration stages remove weakly bound heavy metals and excess salt, and finally, clean water is used to remove the surface-attached salt to ensure that the salt content of the treated fly ash meets the standard; and the NaCl and KCl used in the present application can be derived from the salt products of fly ash leaching liquid (water washing waste liquid) evaporation, without the need for purchase, which can greatly reduce the cost. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to make the content of the present application more easily understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the drawings, wherein,

[0035] Figure 1 FIG. 1 is a schematic diagram of a short-process wet treatment method of incineration fly ash driven by ion exchange according to the present application. DETAILED DESCRIPTION

[0036] The present application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not limiting to the present application.

[0037] The ion exchange driven short process wet treatment method of incineration fly ash is suitable for fly ash generated by incineration of raw materials such as household garbage and biomass, and is used for separating soluble salts and dissolving heavy metals.

[0038] Example 1

[0039] The ion exchange driven short process wet treatment method of incineration fly ash is suitable for fly ash generated by incineration of raw materials such as household garbage and biomass, and is used for separating soluble salts and dissolving heavy metals.

[0040] (1) Fly ash: A waste incineration power plant daily handles 1500 tons of garbage, adopts grate furnace incineration process, and the daily production of fly ash is about 30 tons. Among them, the pH of fly ash is 12.2, and the main components are chlorine content 12.5%, calcium content 28.3%, potassium content 3.1%, sodium content 5.8%, and sulfur content 1.3%; heavy metal content: Pb 2500 mg / kg, Zn 7500 mg / kg.

[0041] (2) Prepare a saturated NaCl solution with a concentration of 340 g / L, take 10 kg of fly ash in step (1) and place it in a stirring reactor, add the prepared saturated sodium chloride solution according to the liquid-solid ratio of 3 L / kg, stir at room temperature at a speed of 350 r / min for 20 min, and centrifugal separation to obtain leaching solution and fly ash residue; Among them, the concentration of Pb in the leaching solution is 550 mg / L, and the concentration of Zn is 2000 mg / L, and a nanofiltration membrane with a molecular weight cut-off of 500 Da is used for separation to obtain clear liquid and concentrated liquid; Among them, the salt concentration of the clear liquid is 280 g / L, which is recycled for the next leaching; The concentrated liquid can be used for the recovery of heavy metals (mainly including lead and zinc).

[0042] (3) Respectively configure NaCl solutions with concentrations of 180 g / L, 72 g / L and 18 g / L, and use a liquid-solid ratio of 0.5 L / kg to sequentially leach the fly ash residue obtained in step (2), and then wash with clean water. Among them, the first stage leaching separation liquid contains a total heavy metal concentration of 800 mg / L and a NaCl concentration of 200 g / L, which is mixed with the leaching solution and recycled after membrane treatment; The second stage leaching separation liquid contains a total heavy metal concentration of 200 mg / L and a NaCl concentration of 100 g / L, which is treated together with the leaching solution; The third stage leaching liquid contains heavy metals 30 mg / L, and the NaCl concentration is 20 g / L, which can be used for the second stage leaching of the next time after supplementing salt; The fourth stage leaching liquid contains heavy metals 5 mg / L, and the NaCl concentration is 5 g / L, which can be used for the third stage leaching of the next time after supplementing salt.

[0043] The water content of the fly ash after leaching and gradient elution was 40%, the removal rate of soluble salt was 90%, the removal rate of soluble Pb was 76%, and the removal rate of soluble Zn was 80%. The fly ash residue after elution was dewatered to obtain fly ash residue, and the leaching liquid obtained by leaching the fly ash residue according to the method of HJ 557-2010 was free of Pb and Zn.

[0044] Comparative Example 1

[0045] The present comparative example provides a short-process wet treatment method of ion exchange driven incineration fly ash, which is similar to the treatment method of Example 1, and the difference lies in that the saturated NaCl solution in step (2) is replaced by water, which is shown as follows:

[0046] (2) Provide water as leaching liquid, take 10 kg of fly ash in step (1) and place it in a stirring reactor, add distilled water according to the liquid-solid ratio of 3 L / kg, stir at room temperature at a speed of 350 r / min for 20 min, and the Pb concentration in the separated solution is 250 mg / L and the Zn concentration is 1250 mg / L.

[0047] Comparative Example 2

[0048] The present comparative example provides a short-process wet treatment method of ion exchange driven incineration fly ash, which is similar to the treatment method of Example 1, and the difference lies in that the concentration of saturated NaCl solution in step (2) is replaced by 5 g / L, which is shown as follows:

[0049] (2) Prepare a saturated NaCl solution with a concentration of 5 g / L, take 10 kg of fly ash in step (1) and place it in a stirring reactor, add the prepared NaCl solution according to the liquid-solid ratio of 3 L / kg, stir at room temperature at a speed of 350 r / min for 20 min, and the Pb concentration in the separated solution is 260 mg / L and the Zn concentration is 1350 mg / L.

[0050] Comparative Example 3

[0051] The present comparative example provides a short-process wet treatment method of ion exchange driven incineration fly ash, which is similar to the treatment method of Example 1, and the difference lies in that the NaCl solution in step (3) is replaced by distilled water, which is shown as follows:

[0052] (3) The fly ash residue produced in step (2) is eluted with distilled water at the same liquid-solid ratio. The water content of the fly ash after elution is 42%, the removal rate of soluble salt is 70%, the removal rate of Pb is 50%, and the removal rate of Zn is 70%. The dewatered fly ash residue after elution is leached according to the method of HJ 557-2010, and the leaching liquid is free of Pb and Zn. The elution waste liquid needs to be treated.

[0053] Obviously, the above-mentioned embodiments are only examples for clearly illustrating the present application, and are not intended to limit the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and also impossible to enumerate all the embodiments. The obvious changes or variations derived from the above description are still within the protection scope of the present application.

Claims

1. An ion exchange driven short process wet treatment method of incinerated fly ash, characterized by, The method comprises the following steps: S1, stirring and mixing the original incineration fly ash with high-concentration leaching solution, and separating the fly ash residue and the leaching solution through solid-liquid separation; S2, providing elution solution and water with different concentration gradients; S3, using the elution solution and water provided in step S2 to elute the fly ash residue obtained in step S1 multiple times, wherein the concentration of the elution solution used in the multiple elution processes is from high to low, and the eluted fly ash residue and elution separation solution are obtained through solid-liquid separation; S4, recycling the elution separation solution obtained in each elution process in step S3; In step S1, the concentration of the leaching solution is more than 80 wt% of the saturated concentration, and the leaching solution comprises NaCl and / or KCl solution; In step S2, the different concentration gradients are 40-50%, 10-20%, 4-7% and 0% of the saturated salt concentration in the elution solution.

2. An ion exchange driven incineration fly ash short process wet treatment method according to claim 1, characterized in that, In step S1, the liquid-solid ratio of the leaching solution to the original incineration fly ash is 2-5 L / kg, the stirring speed is 200-600 r / min, the temperature is 20-30℃, and the stirring time is 15-60 min.

3. An ion exchange driven incineration fly ash short process wet treatment method according to claim 1, characterized in that, In step S4, the recycling of the leaching solution comprises the following steps: (1) when the total concentration of heavy metals in the salt solution in the leaching solution is less than or equal to 100 mg / L, the leaching solution is directly recycled for leaching experiments; (2) when the total concentration of heavy metals in the salt solution in the leaching solution is 100-500 mg / L, the leaching solution is recycled after pH adjustment and precipitation treatment; (3) when the total concentration of heavy metals in the salt solution in the leaching solution is greater than 500 mg / L or less than 70% of the saturated concentration, a membrane treatment method is used to separate the heavy metals and inorganic salts.

4. An ion exchange driven incinerator fly ash short process wet treatment method according to claim 1, characterized by, In step S1, the fly ash residue and the leaching solution are separated through centrifugation or plate and frame filter pressing.

5. An ion exchange driven incinerator fly ash short process wet treatment method according to claim 1, characterized by, In step S2, the elution solution is NaCl and / or KCl solution, and the same salt solution is used as the leaching solution.

6. An ion exchange driven incinerator fly ash short process wet treatment method according to claim 1, characterized by, In step S2, the liquid-solid ratio of the elution solution to the fly ash is 0.5-1 L / kg.

7. An ion exchange driven incinerator fly ash short process wet treatment method according to claim 1, characterized by, In step S3, the water content of the eluted fly ash is 35-50%, the removal rate of soluble salt is 85-95%, the removal rate of soluble Pb is 66-80%, and the removal rate of soluble Zn is 70-85%.

8. An ion exchange driven incinerator fly ash short process wet treatment method according to claim 1, characterized by, In step S4, the elution separation solution is used according to the water quality characteristics: (1) when the total concentration of heavy metals in the elution separation solution is less than 100 mg / L and the salt concentration is greater than 50% of the saturated concentration, the elution separation solution is used for the next batch of leaching experiments after supplementing salt; (2) when the total concentration of heavy metals in the elution separation solution is less than 100 mg / L and the salt concentration is less than or equal to 50% of the saturated concentration, the elution separation solution is used for subsequent elution processes; (3) when the total concentration of heavy metals in the elution separation solution is greater than or equal to 100 mg / L, the elution separation solution is combined with the leaching solution in step S1 for treatment.

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