A high temperature sintering method for preparing ceramsite by using heavy metal contaminated soil and fly ash

Abstract

The present invention discloses a high-temperature sintering method for preparing ceramsite from heavy metal contaminated soil and fly ash, the steps of which include using contaminated soil and fly ash as raw materials for preparing ceramsite, pre-treating the contaminated soil, adding a certain amount of fly ash and aging with alkaline water, then granulating with a designed mold, and drying to remove moisture after granulation. Finally, high-temperature sintering treatment is performed, and the finished ceramsite is obtained after cooling. The present invention adopts high-temperature solidification / stabilization technology to improve the solidification efficiency of heavy metals. And the designed mold helps to ensure that the size of the finished ceramsite is basically the same and improve the strength of the product. The addition of fly ash can appropriately reduce the sintering temperature during the calcination process, which is beneficial to reducing energy consumption. Replacing pure water with alkaline water can reduce the activity of heavy metals in the contaminated soil and the volatilization of heavy metals during the calcination process. The coordinated disposal of the two solid wastes into ceramsite products not only reduces the environmental burden, but also realizes resource utilization.

Description

Technical Field

[0001] The invention relates to the technical field of contaminated soil treatment and industrial solid waste treatment and utilization, and in particular to a high-temperature sintering method for preparing ceramsite by using heavy metal contaminated soil and fly ash. Background Art

[0002] Heavy metals accumulated in soil mainly come from human emissions, including mine tailings, heavy metal waste in landfills, biosolids, combustion residues, flue gas, etc., which pose a huge threat to natural ecosystems. At present, the technologies for remediating heavy metal contaminated soil are mainly divided into three categories: physical remediation, chemical remediation, and biological remediation, as well as combined remediation technologies based on the above technologies.

[0003] Fly ash refers to the fine solid particles in the flue gas ash produced by fuel combustion, and is a typical solid waste. If a large amount of fly ash is not controlled or treated, it will cause air pollution, and will silt up the river when it enters the water body. In addition, certain chemical substances in fly ash are harmful to organisms and humans. As a building material, ceramsite has the characteristics of light weight, high strength, thermal insulation, and with the needs of my country's wall material reform policy, its demand has increased year by year, and the market prospects are good. In addition, in order to reduce the exploitation of natural environmental resources and realize the reuse of solid waste, the raw materials for the production of ceramsite are gradually converted into various solid wastes.

[0004] The traditional method of using contaminated soil as raw material requires a calcination temperature of about 1200°C. The green bodies obtained by the granulator used are of different sizes, the strength of the prepared expanded clay is low, and the volatilization of heavy metals during the calcination process can easily pollute the atmospheric environment. Summary of the invention

[0005] The purpose of the present invention is to address the defects of the prior art and provide a high-temperature sintering method for preparing expanded clay by combining heavy metal contaminated soil with fly ash. By designing a mold for forming expanded clay, the heavy metal fixation efficiency can be improved after the high-temperature sintering process, thereby realizing the resource utilization of the two types of waste and preparing high-strength expanded clay.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A high-temperature sintering method for preparing ceramsite by using heavy metal contaminated soil and fly ash, characterized in that it comprises the following steps:

[0008] S1: Pretreatment: After the heavy metal contaminated soil is treated, fly ash accounting for 40-60% of the total weight is added to the heavy metal contaminated soil and stirred evenly to fully mix the heavy metal contaminated soil and the fly ash;

[0009] S2: Aging, adding 15-20% of the total mass of an alkaline aqueous solution to the raw materials mixed and stirred in S1, and stirring evenly, and then drying naturally for 24 hours;

[0010] S3: Granulation, the aged product in S2 is placed in a mold and extruded into a green body, and then dried at 75°C for 6-12h to remove moisture from the green body;

[0011] S4: high temperature sintering, the green body obtained by granulation in S3 is placed in a muffle furnace for high temperature sintering, the sintering conditions are: heating to 400-500°C, pre-burning for 15-25 minutes, then heating to 1050-1100°C, keeping warm for 30 minutes, and naturally cooling after sintering to obtain the finished product.

[0012] Furthermore, in S1, the fly ash added to the heavy metal contaminated soil accounts for 40-60% of the total weight.

[0013] Furthermore, in S1 and S2, the stirring process includes stirring at 135-145 r / min for 2 min, and then stirring at 275-295 r / min for 1 min, which is repeated twice.

[0014] Furthermore, the processing of the heavy metal contaminated soil in S1 includes removing large stones and debris from the heavy metal contaminated soil, drying, crushing and screening.

[0015] Furthermore, the screening is performed using a sieve with a mesh size greater than 80 for screening and retention.

[0016] Furthermore, the alkaline aqueous solution in S2 is a sodium hydroxide aqueous solution with a mass fraction of 0.5-1%.

[0017] Furthermore, the mold in S3 includes a mold body, a pad, a first pressure head, and a second pressure head. The pad is arranged under the mold body. The first pressure head cooperates with the mold body for extrusion molding of raw materials. The second pressure head cooperates with the mold body for extrusion molding of green billets.

[0018] Furthermore, the mixing in S1 and S2 is carried out by using a cement mortar mixer.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention uses a designed mold for granulation, adds a certain amount of fly ash to the heavy metal contaminated soil, and uses alkaline water instead of pure water for aging, which has excellent heavy metal solidification and stabilization effect, lower calcination temperature, energy consumption and heavy metal volatilization, and the mold used for granulation is simple and has the advantages of high yield rate. 2. The stirring process adopts a fast and slow alternating method so that the contaminated soil and fly ash can be fully mixed and uniform under slow and fast alternating stirring. 3. The addition of alkaline water can appropriately reduce the activity of heavy metals in the raw materials after mixing and the volatilization of heavy metals during calcination, reducing the pollution to the atmospheric environment. Aging further disperses the powder after mixing, promotes uniform distribution of moisture, and then improves the molding performance of the raw materials and improves the product quality. 4. The granulation mold can not only ensure the consistency of the size of the raw materials after molding, but also reduce the deformation or cracking of the products during the sintering process, and improve the strength of the ceramsite products. 5. The setting of the sintering program can ensure low energy consumption while effectively fixing / stabilizing heavy metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a process flow chart of an embodiment of the present invention;

[0021] Figure 2 Schematic diagram of the mold structure of an embodiment of the present invention.

[0022] Among them: 1- mold body, 2- pad, 3- first pressure head, 4- second pressure head. DETAILED DESCRIPTION

[0023] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0024] Example 1

[0025] A specific embodiment of a high-temperature sintering method for preparing ceramsite by using heavy metal contaminated soil and fly ash, comprises the following steps:

[0026] S1: Pretreatment, simple treatment of heavy metal contaminated soil, removal of large stones and debris in the soil. After that, the heavy metal contaminated soil is dried, crushed, and sieved with a sieve larger than 80 mesh. Add fly ash of the same mass to the sieved heavy metal contaminated soil and put it into the cement mortar mixer. Set the stirring program through the controller to stir for 2 minutes at 135-145r / min, then stir for 1 minute at 275-295r / min, and repeat twice, so that the contaminated soil and fly ash can be fully mixed under slow and fast alternating stirring.

[0027] S2: Aging, add 15% of the total mass of sodium hydroxide solution to the raw materials mixed and stirred in S1, the mass fraction of the sodium hydroxide solution is 0.5%, and stir evenly, and then dry naturally for 24 hours. The mixed powder is further dispersed, and the moisture distribution is uniform, thereby improving the molding properties of the raw materials and improving the product quality. Alkaline aqueous solution is used instead of pure water. The addition of alkaline aqueous solution can appropriately reduce the activity of heavy metals in the mixed raw materials and the volatilization of heavy metals during calcination, reducing pollution to the atmospheric environment. Excessive alkalinity will cause the activity of certain amphoteric heavy metals to increase again and increase costs, so the concentration of alkaline aqueous solution should not be too high.

[0028] S3: Granulation, the aged product in S2 is placed in a mold and extruded into a cylindrical green body, and then dried at 75°C for 6 hours to remove moisture from the green body. The designed mold can not only ensure the consistency of the size of the raw materials after molding, but also reduce the deformation or cracking of the product during sintering, and improve the strength of the ceramsite product. The size of the green body can be controlled by changing the length and diameter of the mold to prepare the ceramsite green body of ideal size.

[0029] S4: high temperature sintering, the green body obtained by granulation in S3 is placed in a muffle furnace for high temperature sintering, the sintering conditions are: heating to 400℃ at 10℃ / min, pre-burning for 25min, heating to 1100℃ after pre-burning, keeping warm for 30min, where the heating rate is 10℃ / min, and naturally cooling after sintering to obtain the finished product. The setting of the sintering program can ensure low energy consumption while effectively immobilizing / stabilizing heavy metals.

[0030] like Figure 2 As shown, the granulation mold includes a mold body 1, a backing plate 2, a first pressure head 3, and a second pressure head 4. The backing plate 2 is arranged under the mold body 1. The first pressure head 3 cooperates with the mold body 1 for extrusion molding of raw materials. The second pressure head 4 cooperates with the mold body 1 for extrusion molding of green billets. When using the mold, the aged product is first placed in the mold body 1, and then the first pressure head 3 is used for extrusion molding, and then the first pressure head 3 is removed, and finally the second pressure head 4 is used to push the molded cylindrical green billet out of the mold body 1.

[0031] As shown in Table 1, the leaching concentration of heavy metals in the mixed raw materials of heavy metal contaminated soil and fly ash before and after calcination was determined by the "Solid Waste Leaching Toxicity Leaching Method Acetic Acid Buffer Solution Method" (HJ / T 300-2007). The results show that the leaching concentration of heavy metals in ceramsite after calcination meets the Class V limit of the "Surface Water Quality Standard" (GB 3838-2002), which is much lower than the leaching concentration of heavy metals before calcination, and the leaching level is still low within 30 days, indicating that the prepared ceramsite has a good fixation effect on various heavy metals for a long time. In addition, according to the digestion experiment and characterization results, before and after calcination, the volatilization amount of low-boiling point heavy metals including arsenic is very small, that is, the heavy metals in the raw materials are mainly fixed in the ceramsite, and basically will not cause pollution to the atmosphere. The leaching standard refers to the Class V limit of the "Surface Water Quality Standard" GB 3838-2002.

[0032] Target Heavy Metals As(mg / L) Pb(mg / L) Cd(mg / L) Cu(mg / L) Before raw material processing 10.53 4.87 4.24 15.24 After raw material treatment (leaching 24h) 0.014 0 0.001 0.049 After raw material treatment (leaching 30 days) 0.02 0 0.002 0.061 Environmental Limits 0.1 0.1 0.01 1.0

[0033] Table 1 Leaching concentrations of several common heavy metals before and after high-temperature sintering of mixed raw materials

[0034] The main performance indicators of ceramsite, including 1h water absorption, bulk density and cylinder pressure strength, were tested using "Light Aggregate and Its Test Methods Part 2: Light Aggregate Test Method" (GB / T17431.2-2010). The test results show that the prepared ceramsite has a bulk density of 800-900g / m3, a cylinder pressure strength of more than 7MPa, and is a high-strength ceramsite. The 1h water absorption is 2.5%. All the measured indicators meet the requirements of "Light Aggregate and Its Test Methods Part 1: Light Aggregate" (GB / T17431.1-2010).

[0035] Example 2

[0036] The blending amount of fly ash in S1 is set to 20-80%, and the other steps and conditions are the same as those in Example 1. After testing, the heavy metal leaching concentration in the prepared products under different blending ratios meets the Class V limit of the "Surface Water Quality Standard" (GB 3838-2002). However, when the fly ash blending amount is below 40%, the bulk density in the prepared product is very high, approaching or even exceeding 1200kg / m 3 , does not meet the standard of "Light Aggregate and Its Test Methods Part 1: Light Aggregate", indicating that when the amount of fly ash added is low, a higher calcination temperature is required for burning expanded ceramsite. In order to save energy, the amount of fly ash added should not be less than 40%. In addition, with the increase of the amount of fly ash added, the fixation of heavy metals by ceramsite decreases. Considering the environmental risks that heavy metals in ceramsite may cause during long-term use, the amount of fly ash added should not be too much. Table 2 shows the leaching concentration of heavy metals in ceramsite prepared at different fly ash addition amounts.

[0037]

[0038] Table 2 Heavy metal leaching concentrations in ceramsite prepared at different blending ratios

[0039] The product was prepared from pure heavy metal contaminated soil at a gradient of 50°C from 1050 to 1200°C. The results showed that the calcined product did not meet the relevant standards for ceramsite when the calcination temperature was below 1200°C. Compared with the calcination temperature of 1100°C required for the addition of 50% fly ash, the addition of fly ash appropriately reduced the sintering temperature and saved energy consumption.

[0040] Example 3

[0041] A sodium hydroxide solution accounting for 20% of the total mass is added to the raw materials after mixing and stirring in S1, the pre-burning temperature is 500°C, the insulation time is 15 minutes, and the other steps and conditions are the same as those in Example 1. The heavy metal leaching concentration in the prepared product meets the Class V limit of the "Surface Water Quality Standard" (GB 3838-2002), and its physical properties meet the "Light Aggregate and Its Experimental Method Part 1: Light Aggregate" standard.

[0042] The above specific implementation methods are only for illustrating the technical concept and structural features of the present invention, and the purpose is to enable relevant persons familiar with this technology to implement it. However, the above content does not limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should fall within the protection scope of the present invention.

Claims

1. A high-temperature sintering method for preparing ceramsite by using heavy metal contaminated soil and fly ash, characterized in that: The steps include: S1: Pretreatment, treating the heavy metal contaminated soil, including removing large stones and debris from the heavy metal contaminated soil, drying, crushing, and screening, wherein the screening is performed using a sieve larger than 80 meshes, adding fly ash accounting for 50% of the total weight to the heavy metal contaminated soil and stirring evenly, so that the heavy metal contaminated soil and the fly ash are fully mixed; S2: Aging, adding an alkaline aqueous solution with a total mass percentage of 15-20% to the raw materials mixed and stirred in S1, and stirring evenly, and then drying naturally for 24 hours, wherein the alkaline aqueous solution is a sodium hydroxide aqueous solution with a mass fraction of 0.5-1%; S3: granulation, placing the aged product in S2 into a mold for extrusion molding into a green body, and then drying at 75°C for 6-12 hours to remove moisture from the green body, the mold comprising a mold body (1), a backing plate (2), a first pressure head (3), and a second pressure head (4), the backing plate (2) being arranged under the mold body (1), the first pressure head (3) cooperating with the mold body (1) for extrusion molding of the raw material, and the second pressure head (4) cooperating with the mold body (1) for extrusion molding of the green body; S4: high temperature sintering, the green body obtained by granulation in S3 is placed in a muffle furnace for high temperature sintering, the sintering conditions are: heating to 400-500℃, pre-burning for 15-25min, then heating to 1050-1100℃, keeping warm for 30min, and naturally cooling after sintering to obtain the finished product; In S1 and S2, the stirring process includes stirring at 135-145 r / min for 2 minutes, and then stirring at 275-295 r / min for 1 minute, which is repeated twice, and the stirring is carried out using a cement mortar mixer.

Images