Process for solidifying and forming sludge containing hazardous waste

Abstract

The present application relates to hazardous waste treatment technical field, specifically disclose a kind of sludge solidification forming process containing hazardous waste, comprising the following steps: sludge is mixed with sludge dewatering agent uniformly after pressure filtration treatment to obtain filter cake;Filter cake is mixed with aluminum ash, alkali activator, asbestos and stirred uniformly, then bentonite, sulfonated pitch is further mixed and stirred uniformly to obtain mixed material, the mass ratio of filter cake, aluminum ash, alkali activator, asbestos, bentonite, sulfonated pitch is 100:5~10:1~3:3~5:1~3:1~2;The mixed material is placed in dry and ventilated place and is cured and shaped, and the present application can greatly improve the solidification forming effect of sludge, effectively improve the stability of landfill heap and reduce leakage, improve safety, and meet the environmental protection concept of waste control waste, save production cost, effectively increase hazardous waste disposal benefit.

Description

Technical Field

[0001] This invention relates to the field of hazardous waste treatment technology, specifically to a sludge solidification and molding process for hazardous waste. Background Technology

[0002] The waste disposed of in hazardous waste landfills is mostly sludge, including surface treatment sludge, electroplating sludge, and heavy metal sludge. Since most waste-generating units primarily use plate and frame filter presses for solid-liquid separation, the moisture content of this sludge is between 60% and 80%. However, in reality, unstable process control at these waste-generating units can lead to an actual sludge moisture content exceeding 80% upon arrival at the plant. Excessive moisture content causes the sludge to be poorly formed, easily resulting in unstable landfills and making it difficult to meet the pollution control standards for hazardous waste landfills. High sludge moisture content also generates excessive leachate, increasing operating costs. Furthermore, after cement-solidified sludge is washed away or soaked by leachate in the landfill, small voids easily form in the solidified body, leading to structural damage and uneven settlement, ultimately causing landfill instability.

[0003] Currently, cement is the primary agent used in hazardous waste landfills to improve waste solidification. This involves a hydration and gelation reaction between cement and the free water in the sludge, reducing the free water content and increasing the sludge's compressive strength. This method requires a cement content of approximately 30%. However, excessive cement addition can easily increase the leaching corrosivity of the waste to greater than 12, exceeding the requirements of the GB18598-2019 standard for pollution control in hazardous waste landfills. Furthermore, cement only provides a gelling effect, resulting in poor formability and insufficient shear strength after solidification, leading to unstable stacking and a high risk of landslides. Simultaneously, as the final disposal site for hazardous waste, landfills handle diverse and complex hazardous wastes. Leaks can cause incalculable environmental risks; therefore, the stability of hazardous waste landfill stacks is a key concern.

[0004] Existing sludge molding processes are difficult to apply to high-moisture sludge containing hazardous waste. They either fail to consider the reduced stability caused by leachate erosion or soaking after landfilling, or they neglect the sludge's shear strength. For example, Chinese patent CN102503053A mentions an early-strength sludge modifier that uses polycarboxylic acid and carbide slag to adjust the moisture content of high-moisture sludge before plate-and-frame dewatering, reducing the sludge moisture content to around 52% and achieving a compressive strength of around 72 kPa. However, this modifier does not consider the sludge's shear strength or whether it retains sufficient compressive strength after soaking, thus limiting its practical application.

[0005] In summary, the present invention aims to develop a novel sludge solidification and molding process for hazardous waste, in order to further reduce the moisture content and further reduce the generation of leachate in landfills, improve stability and safety, and reduce operating costs. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a sludge solidification and molding process for hazardous waste, so as to further reduce the water content and improve stability and safety.

[0007] The technical problem solved by this invention is achieved by the following technical solution:

[0008] A sludge solidification and molding process for hazardous waste includes the following steps: sludge is mixed evenly with a sludge dewatering agent and then subjected to pressure filtration to obtain a filter cake; the filter cake is mixed with aluminum ash, an alkali activator, and asbestos and stirred evenly; then bentonite and sulfonated asphalt are added and further mixed and stirred evenly to obtain a mixture. The mass ratio of the filter cake, aluminum ash, alkali activator, asbestos, bentonite, and sulfonated asphalt is in the range of 100:5~10:1~3:3~5:1~3:1~2; the mixture is then placed in a dry and ventilated place for curing and molding.

[0009] Furthermore, the mass ratio of sludge to sludge dewatering agent is 100:0.5 to 1.5.

[0010] Furthermore, the sludge dewatering agent is a polycarboxylate superplasticizer, and the particle size of the polycarboxylate superplasticizer is 100-200 mesh.

[0011] Furthermore, the sludge is mixed with a sludge dewatering agent and then pumped to a plate and frame filter press for filtration. The feed pressure of the sludge pump is 0.6 MPa to 0.8 MPa, and the pressing pressure of the plate and frame filter press is 15 to 20 MPa. By using a sludge dewatering agent to adjust the sludge before high-pressure filtration, approximately 30% of the free water in the sludge can be removed, effectively reducing the generation of leachate from the landfill, lowering operating costs, and simultaneously enhancing the sludge formation effect.

[0012] Furthermore, the mass ratio of the filter cake, aluminum ash, alkali activator, asbestos, bentonite, and sulfonated asphalt is in the range of 100:8:2:4:2:1.

[0013] Furthermore, the aluminum ash is secondary aluminum ash. The pretreatment method for secondary aluminum ash is as follows: the secondary aluminum ash is added to water and reacted at a temperature of 75-85℃ for 1-3 hours. After the reaction is completed, it is dried and ball-milled to 100-200 mesh for later use. The fluorides in the secondary aluminum ash can react with the alkaline activator to produce calcium fluoride, thus preventing the fluorides in the aluminum ash from leaching and causing environmental pollution. It also combines with other components to enhance the solidification strength of the sludge. The hydration and gelling effect produced by the activated secondary aluminum ash and the alkaline activator, combined with the aggregate effect of asbestos, can simultaneously enhance the compressive and tensile strength of the sludge, greatly improving the solidification and molding effect of the sludge and effectively improving the stability of the landfill.

[0014] Furthermore, the alkaline activator is one of calcium oxide, calcium hydroxide, and carbide slag, and the particle size of the alkaline activator is 100-200 mesh.

[0015] Furthermore, the asbestos is one or more of waste asbestos, waste rock wool, and waste glass wool. The asbestos pretreatment method is as follows: the asbestos is moistened with water and then broken into strip-shaped structures for later use. Preferably, the dimensions of the broken asbestos are 4-6 cm in length, 1-3 cm in width, and 0.1-0.3 cm in thickness.

[0016] Furthermore, the bentonite pretreatment method involves ball milling the bentonite to 100-200 mesh, and then drying it at 100-200℃ for 0.5-1.5 hours. The treated bentonite can not only adsorb free water in the sludge, but also adsorb a small amount of heavy metals from the sludge, thus effectively reducing the leaching of heavy metals from landfill stockpiles.

[0017] Furthermore, the sulfonated asphalt has a particle size of 100-200 mesh. Using sulfonated asphalt can fill the gaps in sludge, reduce hydration and dispersion, enhance sludge strength, and decrease the possibility of structural damage to the solidified body due to leachate scouring and soaking.

[0018] This invention employs a segmented dewatering method. A sludge dewatering agent releases free water trapped within sludge particles. A plate and frame filter press further removes some of the free water from the sludge. Then, aluminum ash reacts with an alkali activator and water in the sludge to form a compound with hydration and cementing properties. This effectively reduces the sludge's moisture content and solidifies it, enhancing its compressive strength. Asbestos acts as aggregate, increasing the sludge's tensile and shear strength. Bentonite's adsorption properties significantly reduce free water in the sludge, improving its molding effect. Sulfonated asphalt fills the sludge's gaps, reducing hydration and dispersion, enhancing sludge strength, and minimizing the possibility of structural damage due to leachate scouring and soaking.

[0019] Beneficial effects:

[0020] 1. In this invention, the synergistic solidification of various raw material components enables the sludge to be solidified and formed, which not only has compressive strength but also improves shear strength and tensile strength. This greatly improves the solidification and forming effect of the sludge, effectively enhances the stability of the landfill, reduces leachate generation, and improves safety.

[0021] 2. This invention can reduce the moisture content of sludge containing hazardous waste from about 90% to below 40%. By combining multiple methods, it effectively reduces the moisture content of sludge and improves the sludge forming effect.

[0022] 3. The waste asbestos, waste rock wool, waste glass wool, secondary aluminum ash, and carbide slag used in this invention are all waste materials, conforming to the environmental protection concept of treating waste with waste. Furthermore, using waste materials instead of cement as the molding agent saves production costs and landfill capacity, effectively increasing the efficiency of hazardous waste disposal. Traditional cement solidification requires a cement addition of up to 30%, while the comprehensive agent addition of this invention is only about 20%. Compared with current cement solidification methods, this invention can better reduce volume increase and avoid the situation of excessively alkaline sludge due to excessive cement addition, further reducing environmental pollution. Detailed Implementation

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0024] Example 1

[0025] A sludge solidification and molding process for hazardous waste includes the following steps:

[0026] Sludge and sludge dewatering agent are mixed evenly at a ratio of 100:1 and then subjected to filter press treatment to obtain filter cake; wherein the sludge dewatering agent is a polycarboxylate superplasticizer with a particle size of 100-200 mesh. After the sludge and sludge dewatering agent are mixed, they are transported to a plate and frame filter press for filter press treatment by a mud pump. The feeding pressure of the mud pump is 0.6MPa to 0.8MPa, and the pressing pressure of the plate and frame filter press is 15 to 20MPa.

[0027] The filter cake is mixed with aluminum ash, alkali activator, and asbestos and stirred evenly. Then, bentonite and sulfonated asphalt are added and mixed evenly to obtain a mixture. The mass ratio of the filter cake, aluminum ash, alkali activator, asbestos, bentonite, and sulfonated asphalt is 100:8:2:4:2:1. The mixture is placed in a dry and ventilated place and cured for 4 days.

[0028] The sludge containing hazardous waste is phosphate sludge with a water content of about 90%.

[0029] The dewatering agent is a polycarboxylate superplasticizer with a particle size of 100-200 mesh. Polycarboxylate superplasticizer is a carboxylic acid grafted multi-component copolymer that can be directionally adsorbed onto the surface of sludge particles, causing the sludge particles to carry the same charge, forming an electrostatic repulsion effect. This promotes the dispersion of sludge particles, disintegrates the flocculated structure, and releases free water trapped due to the sludge's gelling action, while simultaneously dispersing the sludge particles. In this embodiment, the polycarboxylate superplasticizer is a solid powder with a particle size of 100-200 mesh. The lower particle size allows the polycarboxylate superplasticizer to be more easily dispersed in the sludge system without introducing new water.

[0030] The aluminum ash is secondary aluminum ash, which is the residue after primary aluminum ash has been recycled through roasting. Its main components are alumina, aluminum nitride, aluminum carbide, a small amount of metallic aluminum, and a certain amount of fluoride salts. Alumina accounts for approximately 50% of the secondary aluminum ash. During pretreatment, the secondary aluminum ash undergoes an 80℃ water immersion reaction to eliminate the reactivity of metallic aluminum, aluminum nitride, and aluminum carbide. It is then dried and ball-milled to a 100-200 mesh powder. The treated aluminum ash exhibits high alumina activity and no longer exhibits abnormal reactions such as gas production.

[0031] In this embodiment, the alkaline activator is calcium carbide slag, which is mainly the residue after the hydrolysis of calcium carbide, and its main component is calcium hydroxide. Asbestos mainly consists of silicates, alumina, etc. They share characteristics such as fibrous structure, corrosion resistance, high tensile strength, and good stability. The asbestos pretreatment method is as follows: after wetting the asbestos with water, it is crushed into strips for later use. The crushed asbestos should be approximately 5cm long, 2cm wide, and 0.2cm thick. Crushing it too finely or making it too large will not yield ideal results.

[0032] The main chemical components of bentonite are silicon dioxide, aluminum oxide, and water. Bentonite has strong hygroscopic properties, capable of absorbing 8 to 15 times its own volume of water. It also has a certain adsorption capacity for various gases, liquids, and organic substances, with a maximum adsorption capacity of up to 5 times its own weight. Experiments have shown that the best results are achieved when bentonite is ball-milled to 100-200 mesh and then dried at 150℃ for 1 hour.

[0033] Sulfonated asphalt is petroleum asphalt that has undergone sulfonation treatment. Because sulfonated asphalt contains sulfonic acid groups, it has a strong hydration effect. When adsorbed onto the surface of sludge, it can prevent the hydration and dispersion of sludge particles, thus preventing collapse. Simultaneously, the water-insoluble portion can fill pores and cracks, acting as a sealant, and can also coat the sludge interface, improving the sludge solidification and shaping effect.

[0034] Example 2

[0035] In this embodiment, the mass ratio of sludge to sludge dewatering agent is 100:0.5; the mass ratio of filter cake, aluminum ash, alkali activator, asbestos, bentonite, and sulfonated asphalt is in the range of 100:6:3:5:3:2, and the rest is the same as in Example 1.

[0036] Example 3

[0037] In this embodiment, the mass ratio of sludge to sludge dewatering agent is 100:1.5; the mass ratio of filter cake, aluminum ash, alkali activator, asbestos, bentonite, and sulfonated asphalt is in the range of 100:5:1:3:1:1, and the rest is the same as in Example 1.

[0038] Comparative Example 1

[0039] In this embodiment, no sludge dewatering agent is added and no plate and frame filter press is used for dewatering; otherwise, it is the same as in Example 1.

[0040] Comparative Example 2

[0041] In this embodiment, no sludge dewatering agent, aluminum ash, or alkali activator is added; otherwise, it is the same as in Example 1.

[0042] Comparative Example 3

[0043] In this embodiment, no asbestos is added, and everything else is the same as in Example 1.

[0044] Comparative Example 4

[0045] In this embodiment, bentonite is not added, and everything else is the same as in Example 1.

[0046] Comparative Example 5

[0047] In this embodiment, sulfonated asphalt is not added, and the rest is the same as in Example 1.

[0048] Comparative Example 6

[0049] In this embodiment, the mass ratio of the filter cake, aluminum ash, alkali activator, asbestos, bentonite, and sulfonated asphalt is 100:20:0.1:8:6:5, and the rest is the same as in Example 1.

[0050] Comparative Example 7

[0051] In this embodiment, the pretreatment method for the secondary aluminum ash is as follows: the secondary aluminum ash is directly dried and ball-milled to 100-200 mesh for later use.

[0052] Compare with Example 8

[0053] In this embodiment, the sludge containing hazardous waste is phosphate sludge with a moisture content of approximately 90%, which is solidified and molded by adding cement. The sludge and cement are mixed evenly at a ratio of 100:30 and then placed in a dry, ventilated area for curing for 4 days.

[0054] According to GB / T 50123-2019 Geotechnical Testing Methods, moisture content tests, unconfined compressive strength tests, and direct shear tests were conducted on Examples 1 and Comparative Examples 1-7. According to GB / T 15555.12-1995 Determination of Corrosivity of Solid Waste by Glass Electrode Method, the leachate corrosivity of Examples 1 and Comparative Examples 1-8 was determined. The volume increase ratio was calculated as the ratio of the volume of the solidified body after solidification to the volume of the original waste.

[0055] Simultaneously, immersion tests were conducted on Examples 1 and Comparative Examples 1-8. The method involved immersing the sludge samples in water for 3 days, followed by unconfined compressive strength tests according to GB / T 50123-2019 Geotechnical Testing Methods. The test results are shown in Table 1.

[0056] Table 1 Test Results

[0057]

[0058]

[0059] As shown in Table 1, the sludge treated by this invention exhibits a significantly reduced moisture content. After entering the landfill, the amount of free water in the landfill converted into leachate due to the volumetric pressure is greatly reduced, resulting in lower leachate levels. Furthermore, the unconfined compressive strength, shear stress, and unconfined compressive strength after immersion are all excellent, demonstrating superior molding performance. The stability and safety of the landfill are effectively guaranteed. As the comparative examples show, all raw material components of this invention are indispensable, and the raw material formula must be controlled within a predetermined range to achieve the desired results, indicating a strong synergistic effect. Compared to traditional cement solidification, this invention more effectively utilizes waste materials, reduces raw material costs, effectively increases the efficiency of hazardous waste disposal, reduces volumetric requirements, and avoids excessively alkaline sludge due to excessive cement addition.

[0060] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A sludge solidification and molding process for hazardous waste, characterized in that, Includes the following steps: After the sludge and sludge dewatering agent are mixed evenly, they are fed into a plate and frame filter press for filtration to obtain filter cake. The pressing pressure of the plate and frame filter press is 15~20MPa. The sludge dewatering agent is a polycarboxylate superplasticizer. The filter cake is mixed with pretreated secondary aluminum ash, alkali activator, and asbestos and stirred evenly. Then, bentonite and sulfonated asphalt are added and mixed evenly to obtain a mixture. The mass ratio of the filter cake, pretreated secondary aluminum ash, alkali activator, asbestos, bentonite, and sulfonated asphalt is in the range of 100:5~10:1~3:3~5:1~3:1~2. Secondary aluminum ash is the residue after primary aluminum ash is recovered by frying. Its main components are aluminum oxide, aluminum nitride, aluminum carbide, a small amount of metallic aluminum and a certain amount of fluoride. The pretreatment method for secondary aluminum ash is as follows: add water to the secondary aluminum ash and react at a temperature of 75~85℃ for 1~3 hours. After the reaction is completed, dry and ball mill to 100~200 mesh for later use. The alkaline activator is one of calcium oxide, calcium hydroxide, and carbide slag. Simply place the mixture in a dry, well-ventilated place to cure and shape it.

2. The sludge solidification and molding process containing hazardous waste according to claim 1, characterized in that, The mass ratio of sludge to sludge dewatering agent is 100:0.5~1.

5.

3. The sludge solidification and molding process containing hazardous waste according to claim 1, characterized in that, The particle size of the polycarboxylate superplasticizer is 100~200 mesh.

4. The sludge solidification and molding process containing hazardous waste according to claim 1, characterized in that, After the sludge is mixed with the sludge dewatering agent, it is transported to the plate and frame filter press by a sludge pump. The feed pressure of the sludge pump is 0.6MPa~0.8MPa.

5. The sludge solidification and molding process containing hazardous waste according to claim 1, characterized in that, The mass ratio of the filter cake, pretreated secondary aluminum ash, alkali activator, asbestos, bentonite, and sulfonated asphalt is 100:8:2:4:2:

1.

6. The sludge solidification and molding process containing hazardous waste according to claim 1, characterized in that, The particle size of the alkali activator is 100~200 mesh.

7. The sludge solidification and molding process containing hazardous waste according to claim 1, characterized in that, The asbestos is one or more of waste asbestos, waste rock wool, and waste glass wool. The asbestos pretreatment method is to wet the asbestos with water and then break it into strip-shaped structures for later use.

8. The sludge solidification and molding process containing hazardous waste according to claim 1, characterized in that, The bentonite pretreatment method is as follows: ball mill the bentonite to 100~200 mesh, and then dry it at 100~200℃ for 0.5~1.5h.

9. The sludge solidification and molding process containing hazardous waste according to claim 1, characterized in that, The particle size of the sulfonated asphalt is 100-200 mesh.

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