Method and device for preparing ceramsite by coupling heavy metal polluted soil with fly ash

Abstract

The invention discloses a method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash. The method comprises the steps of S1, fly ash dechlorination, S2, mixing and ball milling, S3, dry granulation and S4, ceramsite sintering. The invention also discloses a device for preparing ceramsite by coupling heavy metal polluted soil with fly ash, the device is a washing tank, and the washing tank comprises a tank body, a central stirring shaft, a spiral stirring blade, an air distribution ring, an air inlet pipe, an air return pipe and a driving motor. According to the method for preparing the ceramsite by coupling the heavy metal contaminated soil with the fly ash, secondary utilization of the heavy metal contaminated soil and the fly ash can be achieved, and heavy metal in the soil and the fly ash is solidified and converted into valuable resources. And on the whole preparation process method, the preparation links are few, raw materials which are high in risk degree or easily cause secondary pollution are not adopted, and the method is convenient to popularize and apply. The invention further provides a water washing tank, circulation of an internal mixture is improved through air-entrapping water washing, and the water washing effect of the water washing tank is improved.

Description

Technical Field

[0001] The invention relates to the technical field of pollution control, and in particular to a method and a device for preparing ceramsite by coupling heavy metal contaminated soil with fly ash. Background Art

[0002] Heavy metal pollution in soil refers to the phenomenon that the heavy metal content in the soil exceeds the natural background value and ecological risk threshold due to industrial emissions and other behaviors. This pollution not only affects the ecological function of the soil and agricultural production, but may also accumulate in the human body through the food chain, posing a threat to human health. The remediation technologies for heavy metal contaminated soil include physical remediation, chemical remediation and biological remediation.

[0003] Incineration fly ash is a byproduct of the waste incineration process, containing high concentrations of heavy metals such as lead, copper, cadmium, chromium and zinc, as well as harmful organic pollutants such as dioxins and furans. Due to its high environmental risk, fly ash is classified as hazardous waste. There are various methods for treating fly ash, including chemical extraction, stabilization, cement solidification and high-temperature melting solidification, in order to reduce its toxicity and environmental release risks and achieve safe disposal.

[0004] Ceramic aggregate is a man-made lightweight aggregate widely used in the construction industry. Its production raw materials can be derived from various solid wastes, which not only reduces the exploitation of natural resources, but also realizes the resource utilization of waste. It helps to reduce the environmental burden. The use of heavy metal contaminated soil and fly ash to prepare ceramsite is an innovative waste treatment and resource utilization technology. This method uses contaminated soil and fly ash as raw materials, and after a specific process treatment, it is converted into ceramsite products that can be used in the construction industry. This not only solves the environmental problems of soil and fly ash, but also converts them into valuable resources, achieving a win-win situation of environmental protection and economic benefits. In the development and practice of related technologies, the following problems were found: there will be more chloride ions in the fly ash of garbage incineration. If it cannot be pretreated, it will volatilize in the subsequent sintering process, which is easy to cause secondary pollution. In addition, if the chlorine content in ceramsite is too high, it will also make the heavy metals solidified in it easier to leach; currently, water washing is mainly used for dechlorination, but the effect of a single water washing is often not good, and multiple water washing tanks need to be set up for multiple water washings, and the equipment occupies a large area. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing ceramsite by coupling fly ash with heavy metal contaminated soil, so as to solve the problems existing in the prior art.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the present invention provides a method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash, comprising the following steps: S1, fly ash dechlorination: dechlorination treatment of fly ash is carried out by aeration and water washing, and solid-liquid separation of the washed mixture is carried out to obtain a solid fly ash pretreatment product; S2, mixed ball milling: fly ash pretreatment product, heavy metal contaminated soil, and crushed waste glass powder are mixed and ball milled to obtain ash-soil mixed powder; S3, dry granulation: adding an appropriate amount of water to the ash-soil mixed powder for dry granulation to obtain ceramsite to be sintered; S4, ceramsite sintering: sintering the ceramsite to be sintered to obtain ceramsite.

[0007] Furthermore, the step S1 includes the following specific steps: crushing and sieving the fly ash and then conveying it to a water washing tank, adding sufficient water into the water washing tank, the mass ratio of fly ash to water is 1: (5-10), then introducing carbon dioxide gas into the water washing tank and stirring, after washing for a certain period of time, conveying the mixture in the water washing tank to a solid-liquid separator, the solid-liquid separator performs solid-liquid separation to obtain a solid component as a fly ash pretreatment product, and the liquid is treated as chlorine-containing wastewater and incorporated into the wastewater treatment system.

[0008] Furthermore, the solid-liquid separator can be any one of a centrifugal dehydrator and a horizontal screw dehydrator.

[0009] Furthermore, the moisture content of the fly ash pretreatment product in step S1 is controlled at 70% to 80%.

[0010] Furthermore, in step S2, the fly ash pretreatment product accounts for 30% to 50% of the total mass of the mixture, the heavy metal contaminated soil accounts for 40% to 65% of the total mass of the mixture, and the glass powder accounts for 5% to 10% of the total mass of the mixture.

[0011] Furthermore, the specific process parameters of the ceramsite sintering in step S4 are controlled as follows: S41, preheating stage, preheating temperature 300-500 degrees, insulation time 0.5-1 hour; S42, heating stage, heating temperature 1200-1500 degrees, insulation time 0.5-1 hour; S42, cooling stage, cooling to 400-500 degrees with the furnace, and then rapidly cooling at a cooling rate of not less than 200 degrees per minute.

[0012] The present invention also discloses a device for preparing expanded clay using heavy metal contaminated soil coupled with fly ash, the device being a water washing tank, comprising a tank body, a central stirring shaft, spiral stirring blades, an air distribution ring, an air inlet pipe, an air return pipe, and a driving motor; the tank body is an internally hollow cavity structure, a fly ash feed port is provided at the upper portion, and an outflow pipe is provided at the lower portion; the central stirring shaft is arranged at the center of the tank body, and the top passes through the tank body and is connected to the driving motor; a spiral stirring blade is provided on the outer side of the central stirring shaft; the air distribution ring is a tubular structure bent into a circle, and an array of air outlet holes is provided on the top of the outer wall, which are arranged on the outer side of the spiral stirring blade and at the lower portion of the tank body; the air inlet pipe extends into the tank body and is connected to the air distribution ring, and a return air pipe is also provided on the top of the tank body, one end of which is connected to the inner cavity of the tank body, and the other end is connected to the air inlet pipe.

[0013] Furthermore, the water washing tank also includes an inner tube, which is arranged on the outside of the spiral stirring blade and is coaxial with the tank body. The air distribution pipe is arranged at the lower part of the inner tube, and its outer diameter is smaller than the inner diameter of the inner tube.

[0014] Furthermore, the washing tank also includes a plurality of inner tubes, which are arranged on the outside of the spiral stirring blades, and adjacent inner tubes are provided with gaps in the longitudinal direction; the air distribution pipe is arranged at the lower part of the lowest inner tube, and its outer diameter is smaller than the inner diameter of the inner tube.

[0015] The method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash proposed in the present invention can realize the secondary utilization of heavy metal contaminated soil and fly ash, and while solidifying the heavy metals in the soil and fly ash, it also converts them into valuable resources.

[0016] In terms of the overall preparation process, there are fewer preparation links, and no raw materials with high risk or prone to secondary pollution are used, which is convenient for its promotion and application. By adding air and washing, the dechlorination effect of fly ash can be achieved, and the treatment process can be effectively reduced. At the same time, the present invention also provides a washing tank, which improves the washing effect by improving the circulation of the internal mixture. Compared with the multi-stage washing scheme, it has the advantages of small footprint and low equipment investment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of a water washing tank according to an embodiment of the present invention.

[0018] Figure 2 It is a schematic cross-sectional view of a water washing tank according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0020] As attached Figure 1-2 As shown, the present invention relates to a method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash, and the specific steps are as follows: S1. Fly ash dechlorination: The fly ash is dechlorinated by air-entrained water washing, and the mixture after water washing is subjected to solid-liquid separation to obtain a solid fly ash pretreatment product; the water content of the fly ash pretreatment product is controlled at 70% to 80%.

[0021] S2. Mixed ball milling: The fly ash pretreatment product, heavy metal contaminated soil, and crushed waste glass powder are mixed and ball milled to obtain an ash-soil mixed powder, in which the fly ash pretreatment product accounts for 30% to 50% of the total mass of the mixture, the heavy metal contaminated soil accounts for 40% to 65% of the total mass of the mixture, and the glass powder accounts for 5% to 10% of the total mass of the mixture.

[0022] S3. Dry granulation: Add appropriate amount of water to the ash-soil mixed powder for dry granulation to obtain ceramsite to be sintered.

[0023] S4, sintering ceramsite: sintering the ceramsite to be sintered to obtain ceramsite.

[0024] Waste incineration fly ash contains a lot of chloride ions (mass fraction of about 10%), mainly from chlorine-containing organic and inorganic substances in the garbage. Chloride ions in fly ash will volatilize during high-temperature sintering or melting, which can easily lead to equipment corrosion and secondary pollution. In addition, heavy metals in polluted soil and fly ash are more easily leached in an environment containing chloride ions, and chloride ions in fly ash will increase this risk. Therefore, step S1 of this application adopts aeration and water washing to carry out dechlorination treatment, including the following specific steps: crushing and sieving the fly ash and then transporting it to a water washing tank, adding sufficient water to the water washing tank, the mass ratio of fly ash to water is 1: (5-10), then carbon dioxide gas is introduced into the water washing tank and stirred, and after washing for a certain period of time, the mixture in the water washing tank is transported to a solid-liquid separator, and the solid-liquid separator performs solid-liquid separation to obtain a solid component as a fly ash pretreatment product, and the liquid is incorporated into the wastewater treatment system as chlorine-containing wastewater for treatment. The solid-liquid separator can be any one of a centrifugal dehydrator and a horizontal screw dehydrator.

[0025] The mixed ball milling and dry granulation in steps S2 and S4 are carried out using existing equipment.

[0026] The specific process parameters of step S4 ceramsite sintering are controlled as follows: S41, preheating stage, preheating temperature 300-500 degrees, insulation time 0.5-1 hour; S42, heating stage, heating temperature 1200-1500 degrees, insulation time 0.5-1 hour; S42, cooling stage, cooling to 400-500 degrees with the furnace, and then rapidly cooling at a cooling rate of not less than 200 degrees per minute.

[0027] Preheating helps to remove moisture from the green body and prevent the ceramsite from bursting due to rapid evaporation of moisture during high-temperature sintering. Preheating can also reduce the thermal stress caused by rapid temperature changes in the green body and avoid cracks in the ceramsite.

[0028] Sintering at a high temperature of 1200-1500 degrees is used to melt the raw materials to form a glass phase, which can achieve a better solidification effect of heavy metals, reduce the risk of leaching, and improve environmental safety. High temperature also helps to improve the physical properties of ceramsite. In the cooling stage, furnace cooling can reduce the network of fine cracks inside and on the surface of the ceramsite due to excessive temperature difference, reduce the particle strength of the ceramsite, and then after the temperature drops, rapid cooling is beneficial to improve the hardness and strength of the ceramsite.

[0029] The present application provides the following examples to illustrate the above method.

[0030] S1. Fly ash dechlorination: The fly ash is crushed and sieved and then transported to a water washing tank, and sufficient water is added to the water washing tank, with a mass ratio of fly ash to water of 1:10. Then, carbon dioxide gas is introduced into the water washing tank and stirred. After reacting for 2 hours, the mixture in the water washing tank is transported to a solid-liquid separator, and the solid-liquid separator performs solid-liquid separation to obtain a solid component as a fly ash pretreatment product, and the liquid is incorporated into the wastewater treatment system as chlorine-containing wastewater for treatment. The solid-liquid separator is a horizontal screw dehydrator, and the water content of the fly ash pretreatment product is controlled at 75%.

[0031] S2. Mixed ball milling: The fly ash pretreatment product, heavy metal contaminated soil and crushed waste glass powder are mixed and ball milled to obtain an ash-soil mixed powder, in which the fly ash pretreatment product accounts for 40% of the total mass of the mixture, the heavy metal contaminated soil accounts for 50% of the total mass of the mixture, and the glass powder accounts for 10% of the total mass of the mixture.

[0032] S3. Dry granulation: Add appropriate amount of water to the ash-soil mixed powder for dry granulation to obtain ceramsite to be sintered.

[0033] S4, sintering of ceramsite: sintering the ceramsite to be sintered to obtain ceramsite, and the specific process parameters are controlled as follows: in the preheating stage, the preheating temperature is 350 degrees and the insulation time is 0.5 hours; then gradually heating to 1350 degrees and the insulation time is 0.5 hours; cooling to 400 degrees with the furnace, and then quickly cooling to room temperature by air cooling.

[0034] In this embodiment, the main heavy metals in the fly ash are Zn (zinc), Cr (chromium), and Pb (lead), and the contents are relatively small, with the Zn (zinc) content being 405 mg / kg, the Cr (chromium) content being 0.27 mg / kg, and the Pb (lead) content being 0.73 mg / kg; the main heavy metals in the heavy metal contaminated soil are Cr (chromium) and Pb (lead), with the Cr (chromium) content being 448 mg / kg and the Pb (lead) content being 575 mg / kg.

[0035] The ceramsite obtained in the above example was tested for heavy metal leaching using the standard GB5085.2-1997 "Toxicity leaching method for solid waste leaching", and the leaching amounts of Zn (zinc), Cr (chromium), and Pb (lead) were 0.32 mg / L, 0.042 mg / L, and 0.074 mg / L, respectively. The physical properties of the ceramsite were tested and the bulk density of the ceramsite was 814 kg / m 3 , cylinder pressure strength is 12.12Mp, and water absorption is 5.34%.

[0036] In the above embodiment, the improved water washing tank of the applicant is used, and its specific structure is as shown in the attached Figure 1 , 2 As shown, the water washing tank includes a tank body 1, a central stirring shaft 2, a spiral stirring blade 3, an inner tube 4, an air distribution ring 5, an air inlet pipe 6, an air return pipe 7, and a driving motor 8.

[0037] The tank body 1 is a hollow cavity structure, with a fly ash feed inlet 11 disposed at the top and a mixture outflow pipe 12 disposed at the bottom.

[0038] The central stirring shaft 2 is arranged in the center of the tank body 1, the top passes through the tank body 1 and is connected to the drive motor 8 and the top is rotatably connected to the tank body 1 through a bearing, and the lower part is rotatably connected to the lower part of the tank body 1 (the inner wall of the outflow pipe 12 in the figure) through a bearing and a connecting plate.

[0039] A spiral stirring blade 3 is arranged outside the central stirring shaft.

[0040] A plurality of inner tubes 4 are arranged outside the spiral stirring blade 3, two of which are shown in the figure, arranged between the spiral stirring blade 3 and the inner wall of the tank body 1, and fixedly connected to the inner wall of the tank body 1 through an inner connecting plate. The tank body 1, the central stirring shaft 2, the spiral stirring blade 3, and the inner tubes 4 are coaxial. A gap is arranged between adjacent inner tubes 4 in the longitudinal direction.

[0041] An air distribution ring 5 is arranged at the lower part of the lowest inner tube 4. The air distribution ring 5 is a tubular structure bent into a circle. An array of air outlet holes is arranged on the top of the outer wall. It is arranged on the outside of the spiral stirring blade 3 and below the inner tube 4. Its outer diameter is smaller than the inner diameter of the inner tube 4.

[0042] The air inlet pipe 6 extends into the tank body 1 and communicates with the air distribution ring 5 , and the air inlet pipe 6 is connected to the carbon dioxide gas supply device.

[0043] A return air pipe 7 is also provided on the top of the tank body 1, one end of which is connected to the inner cavity of the tank body 1 and the other end is connected to the air inlet pipe 6. A one-way valve, an air pump, etc. may be provided on the return air pipe 7, and its specific structure is conventional knowledge in the field.

[0044] When in use, water and fly ash are added into the tank body 1, and the spiral stirring blade 3 is driven by the driving motor 8 to rotate to achieve stirring of the internal mixture. Then, carbon dioxide gas is filled in through the air inlet pipe 6 and the air distribution ring 5, and stirring is continued. Under the action of the spiral stirring blade and the injected carbon dioxide, the mixture in the tank body will circulate in the area between the inner tube 4 and the tank body 1 and the inner tube 4, thereby improving the water washing effect.

[0045] The purpose of providing a plurality of inner tubes with gaps in the longitudinal direction is mainly to further increase the turbulence in the tank body, which is beneficial to improving the water washing effect. After the water washing is completed, the mixture flows out through the outflow pipe 12 to the solid-liquid separation device.

[0046] It should be noted that, unless otherwise clearly specified and limited, the terms such as "install", "connect", "connect", "fix", "set" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

Claims

1. A method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash, characterized in that: The steps include: S1. Fly ash dechlorination: dechlorination treatment is performed on fly ash by air-entrained water washing, and solid-liquid separation is performed on the mixture after water washing to obtain a solid fly ash pretreatment product; S2, mixed ball milling: the fly ash pretreatment product, heavy metal contaminated soil, and crushed waste glass powder are mixed and ball milled to obtain ash-soil mixed powder; S3, dry granulation: adding an appropriate amount of water to the ash-soil mixed powder for dry granulation to obtain ceramsite to be sintered; S4, sintering ceramsite: sintering the ceramsite to be sintered to obtain ceramsite.

2. According to claim 1, a method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash, characterized in that: The step S1 comprises the following specific steps: crushing and sieving the fly ash and then conveying it to a water washing tank, adding sufficient water into the water washing tank, the mass ratio of fly ash to water being 1:(5-10), then introducing carbon dioxide gas into the water washing tank and stirring it, and after washing for a certain period of time, conveying the mixture in the water washing tank to a solid-liquid separator, the solid-liquid separator performs solid-liquid separation to obtain a solid component as a fly ash pretreatment product, and the liquid is treated as chlorine-containing wastewater and incorporated into a wastewater treatment system.

3. According to claim 2, a method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash, characterized in that: The solid-liquid separator can be any one of a centrifugal dehydrator and a horizontal screw dehydrator.

4. According to claim 1, a method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash, characterized in that: In the step S1, the moisture content of the fly ash pretreatment product is controlled at 70% to 80%.

5. The method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash according to claim 1, characterized in that: In step S2, the fly ash pretreatment product accounts for 30% to 50% of the total mass of the mixture, the heavy metal contaminated soil accounts for 40% to 65% of the total mass of the mixture, and the glass powder accounts for 5% to 10% of the total mass of the mixture.

6. The method for preparing ceramsite by coupling heavy metal contaminated soil with fly ash according to claim 1, characterized in that: The specific process parameters of step S4 ceramsite sintering are controlled as follows: S41, preheating stage, preheating temperature 300-500 degrees, insulation time 0.5-1 hour; S42, heating stage, heating temperature 1200-1500 degrees, insulation time 0.5-1 hour; S42, cooling stage, cooling to 400-500 degrees with the furnace, and then rapidly cooling at a cooling rate of not less than 200 degrees per minute.

7. A device for use in the method for preparing ceramsite by coupling fly ash with heavy metal contaminated soil according to any one of claims 1 to 6, characterized in that: The device is a water washing tank, which includes a tank body, a central stirring shaft, spiral stirring blades, an air distribution ring, an air inlet pipe, an air return pipe, and a driving motor; the tank body is an internal hollow cavity structure, with a fly ash feed port provided at the top and an outflow pipe provided at the bottom; the central stirring shaft is arranged in the center of the tank body, and the top passes through the tank body and is connected to the driving motor; a spiral stirring blade is provided on the outside of the central stirring shaft; the air distribution ring is a tubular structure bent into a circle, and an array of air outlet holes is provided on the top of the outer wall, which is arranged on the outside of the spiral stirring blade and at the bottom of the tank body; the air inlet pipe extends into the tank body and is connected to the air distribution ring, and a return air pipe is also provided on the top of the tank body, one end of which is connected to the inner cavity of the tank body, and the other end is connected to the air inlet pipe.

8. The device for preparing ceramsite by coupling heavy metal contaminated soil with fly ash according to claim 7, characterized in that: The water washing tank also includes an inner tube, which is arranged outside the spiral stirring blade and coaxial with the tank body. The air distribution pipe is arranged at the lower part of the inner tube, and its outer diameter is smaller than the inner diameter of the inner tube.

9. The device for preparing ceramsite by coupling heavy metal contaminated soil with fly ash according to claim 7, characterized in that: The washing tank also includes a plurality of inner tubes, which are arranged outside the spiral stirring blades, and adjacent inner tubes are provided with gaps in the longitudinal direction; the air distribution pipe is arranged at the lower part of the lowest inner tube, and its outer diameter is smaller than the inner diameter of the inner tube.

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