A method for preparing ceramsite by using chromium-containing sludge from hazardous waste and secondary aluminum ash and its product

Abstract

The present invention discloses a method for preparing ceramsite by using chromium-containing sludge from hazardous waste and secondary aluminum ash and its product. The method comprises the following steps: uniformly mixing fine chromium-containing sludge, secondary aluminum ash and dolomite ore powder, roasting, cooling, then grinding and uniformly mixing with cyanite ore sludge, adding water and stirring, granulating and drying to obtain green pellets; sintering under an air atmosphere condition and cooling to obtain ceramsite. By means of the combined method of roasting-grinding-hydration-sintering, on the one hand, the collaborative resource utilization of chromium-containing sludge from hazardous waste, secondary aluminum ash, general solid waste cyanite ore sludge and dolomite ore powder is realized, and the low-carbon transformation of chromium-containing sludge and secondary aluminum ash from "hazardous waste landfill" to "building material resource utilization" is achieved; in addition, the leaching concentration of hexavalent chromium in the obtained ceramsite is at least 0.16±0.01 mg / L, which has no hazardous characteristics and has relatively high strength, and has the dual advantages of deep detoxification of pollutants and improvement of material properties.

Description

Technical Field

[0001] The present invention relates to a method for preparing ceramsite by using chromium-containing sludge from hazardous waste and secondary aluminum ash and its product, belonging to the field of harmless treatment and resource utilization of hazardous waste. Background Technique

[0002] Chromium-containing sludge is a kind of hazardous waste with strong toxicity and carcinogenicity generated during the treatment of chromium-containing wastewater in industrial production. At present, the harmless treatment processes of chromium-containing sludge mainly include reagent stabilization, co-disposal in cement kilns, and high-temperature melting. After reagent stabilization, the chromium-containing waste residue still needs to be safely landfilled, but the landfill volume is limited and cannot continuously receive it; for co-disposal in cement kilns, there are strict requirements for the characteristics and quantity of chromium-containing sludge entering the kiln to ensure the quality of cement; the high-temperature melting method has high energy consumption and is also prone to oxidize some trivalent chromium into hexavalent chromium, resulting in an increase in the toxicity of chromium.

[0003] Secondary aluminum ash is an industrial waste recovered from primary aluminum ash after salt bath during the industrial production of aluminum. It has a large annual output and is difficult to be harmlessly treated and resourcefully utilized. The resource utilization methods of secondary aluminum ash are generally divided into pyrometallurgical treatment and hydrometallurgical treatment. However, both of these methods require water washing for denitrification and desalting, which will produce a large amount of irritating ammonia gas and saline wastewater, etc., causing secondary pollution. And there are generally problems of high treatment cost and low product added value in the resource utilization process of secondary aluminum ash, which greatly limits the efficiency of resource utilization of secondary aluminum ash.

[0004] Kyanite ore sludge is an industrial solid waste generated during the purification of medium and low-grade kyanite. At present, due to its fine particle size, high potassium and sodium content, and low alumina content, it is restricted in the process of resource utilization. Therefore, a large amount of kyanite ore sludge is temporarily stored in the tailings pond. This will not only occupy a large amount of land and pollute the environment, but also be a waste of resources.

[0005] Therefore, there is an urgent need for a simple and efficient method for resourcefully treating chromium-containing sludge from hazardous waste and secondary aluminum ash. Summary of the Invention

[0006] Object of the Invention: The technical problem to be solved by the present invention is to provide a simple and efficient method for resourcefully treating chromium-containing sludge from hazardous waste and secondary aluminum ash to prepare ceramsite and its product.

[0007] Technical Solution: To solve the above technical problem, the present invention provides a method for preparing ceramsite by using chromium-containing sludge from hazardous waste and secondary aluminum ash, including the following steps:

[0008] (1) Mix fine chromium-containing sludge, secondary aluminum ash, and dolomite ore powder evenly, and roast the mixed material. After roasting, air cooling is used for cooling to obtain a roasted product;

[0009] (2) Mix the calcined product obtained in step (1) with cyanite ore sludge evenly, then grind to obtain abrasive, add water and stir to prepare a slurry, and then granulate and dry to obtain green balls.

[0010] (3) Sinter the green balls obtained in step (2) under air atmosphere conditions, and obtain ceramsite after cooling.

[0011] Among them, the dry basis mass ratio of the fine chromium-containing sludge, secondary aluminum ash and dolomite ore powder in step (1) is 40-50:28-38:12-22.

[0012] Among them, the calcination temperature in step (1) is 850-1050 °C, and the time is 25-90 minutes; the calcination atmosphere is nitrogen.

[0013] Among them, the dry basis mass ratio of the calcined product and cyanite ore sludge in step (2) is 40-55:45-60.

[0014] Among them, the particle size of the abrasive in step (2) is less than 45 microns.

[0015] Among them, the solid phase mass percentage of the slurry in step (2) is 40%-55%.

[0016] Among them, the particle size of the granulated pellets in step (2) is 10-16 mm.

[0017] Among them, the moisture content of the green balls in step (2) is 3%-5.5%.

[0018] Among them, the sintering temperature in step (3) is 1000-1250 °C, and the sintering time is 45-135 minutes.

[0019] The present invention also provides a ceramsite prepared by the above method, and the leaching concentration of hexavalent chromium in the ceramsite is at least 0.16±0.01 mg / L.

[0020] The principle of the present invention: Through the calcination in an inert atmosphere, the hexavalent chromium in the chromium-containing sludge undergoes an oxidation-reduction reaction with the reducing components (mainly aluminum nitride) of the secondary aluminum ash. The hexavalent chromium is reduced to trivalent chromium, realizing the detoxification of the chromium-containing sludge. At the same time, the nitrogen component of aluminum nitride in the secondary aluminum ash is oxidized to nitrogen gas, realizing harmlessness. At the same time, due to the addition of dolomite ore powder, the temperature of the solidification reaction is reduced, the energy consumption in the reaction process is reduced, and it can also promote the oxidation-reduction reaction between the hexavalent chromium in the chromium-containing sludge and the reducing components (mainly aluminum nitride) of the secondary aluminum ash. After the calcination is completed, air cooling is used for cooling, so that a large amount of amorphous glassy substances are produced in the calcined product, making it have strong reaction activity. Under the grinding action of the rod mill, the particle sizes of the calcined product and cyanite ore sludge are further reduced, and the reaction activity is further enhanced.

[0021] In the process of preparing raw meal balls, calcium and magnesium oxides in the calcined product will react to form hydroxides in an aqueous solution, promoting the hydration reaction of the aluminosilicate active components of the calcined product and cyanite ore sludge, improving the efficiency and effect of chemical reactions, generating a large amount of silica-oxygen, alumina-oxygen and silica-alumina-oxygen network polymer components, and then encapsulating or adsorbing a large amount of chromium components to achieve the stabilization and solidification of chromium.

[0022] During the sintering process, chromium components, aluminum components, magnesium components, calcium components and silicon components in the raw meal balls will form phases such as magnesiochromite and chromaluminate spinel, further realizing the structural fixation of chromium, greatly reducing the oxidation and migration of chromium, and at the same time producing a large amount of aluminosilicate, mullite and other phases, enhancing the structural strength of the ceramsite. In addition, the presence of calcium and magnesium in dolomite powder and potassium and sodium in cyanite ore sludge, which are components with fluxing properties, reduces the calcination and sintering temperature of the material, thereby reducing the energy consumption of the treatment.

[0023] Based on the components and physical and chemical properties of the hazardous waste itself, the present invention realizes the collaborative resource utilization of chromium-containing sludge, secondary aluminum ash, general solid waste cyanite ore sludge and dolomite powder through the combined method of calcination - grinding - hydration - sintering. On the one hand, it realizes the low-carbon transformation of chromium-containing sludge and secondary aluminum ash from "hazardous waste landfill" to "building materials resource utilization"; in addition, the leaching concentration of hexavalent chromium in the obtained ceramsite is as low as 0.16±0.01mg / L, without hazardous characteristics and with high strength, having the dual advantages of deep detoxification of pollutants and improvement of material properties. Through the optimized compounding and ratio of multi-source wastes, the efficient utilization of energy consumption in the whole treatment process is realized, achieving the effect of low-carbon resource utilization of hazardous waste.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0025] 1. The present invention firstly realizes the collaborative resource utilization of chromium-containing sludge and secondary aluminum ash in hazardous waste, makes full use of the chemical characteristics of each component in chromium-containing sludge, secondary aluminum ash, dolomite powder and cyanite ore sludge, and realizes the enhanced solidification of chromium in chromium-containing sludge and the harmlessness of nitrogen components in secondary aluminum ash through the combined method of calcination - grinding - hydration - sintering. At the same time, it realizes the low-carbon transformation of chromium-containing sludge and secondary aluminum ash from "hazardous waste landfill" to "building materials resource utilization";

[0026] 2. Calcination under an inert atmosphere enables the redox reaction of hexavalent chromium in chromium-containing sludge with the reducing components (mainly aluminum nitride) in secondary aluminum ash, reducing hexavalent chromium to trivalent chromium to achieve the detoxification of chromium-containing sludge, and at the same time oxidizing the nitrogen components of aluminum nitride in secondary aluminum ash to nitrogen gas to achieve harmlessness. And the reaction activity of the calcined product and cyanite ore sludge is further enhanced by air cooling;

[0027] 3. During the grinding and hydration process, calcium and magnesium oxides in the calcined product react with water in the aqueous solution to form hydroxides, promoting the hydration reaction of the active components of aluminosilicates in the calcined product and cyanite ore sludge, improving the efficiency and effect of the chemical reaction, generating a large amount of silicon-oxygen, aluminum-oxygen and silicon-aluminum-oxygen network polymer components, and then wrapping or adsorbing a large amount of chromium components to achieve the stabilization and solidification of chromium;

[0028] 4. During the sintering process, chromium components, aluminum components, magnesium components, calcium components and silicon components in the green pellets will form phases such as magnesium chromite and chromalite, further realizing the structural fixation of chromium, greatly reducing the oxidation and migration of chromium, and at the same time, a large amount of aluminosilicate, mullite and other phases will also be produced, enhancing the structural strength of the ceramsite;

[0029] 5. Through the proportioning of raw materials, the efficient utilization of energy consumption in the whole treatment process is realized, and the effect of low-carbon resource utilization of hazardous waste is achieved. The leaching concentration of hexavalent chromium in the obtained ceramsite is as low as 0.16±0.01mg / L, without hazardous characteristics and with relatively high strength. Therefore, the present invention has the dual advantages of deep detoxification of pollutants and improvement of material properties. Description of the Drawings

[0030] Figure 1 It is the process flow chart of the present invention. Detailed Embodiments

[0031] The technical solutions of the present invention will be further described below with reference to the drawings.

[0032] The chemical composition of the chromium-containing sludge is SiO2 3.53%, Al2O3 16.90%, Fe2O3 1.19%, MgO 0.18%, CaO 1.86%, Na2O 2.91%, TiO2 0.61%, ZnO 3.38%, CuO 6.08%, SO3 17.9%, NiO 2.46%, Cr2O3 42.9%, PbO 0.01%, P2O5 0.04, Cl 0.05%.

[0033] The chemical composition of the secondary aluminum ash is SiO2 6.62%, Al2O3 71.60%, Fe2O3 3.24%, CaO 2.44%, Na2O 4.01%, K2O 0.67%, MgO 3.53%, SO3 2.37%, Cl 2.26%, P2O5 0.14%, TiO2 0.19%, CuO 0.39%, BaO 0.10%, Cr2O3 0.19%, MnO 0.67%, ZnO 0.19%, loss on ignition 1.39%.

[0034] The chemical composition of dolomite ore powder is SiO2 11.00%, Al2O3 0.16%, Fe2O3 0.15%, MgO 31.2%, CaO 57.4%, SO3 0.02%, K2O 0.01%, Cr2O3 0.02%, ZnO 0.01%, NiO 0.01%, Cl 0.02%.

[0035] The chemical composition of cyanite ore sludge is SiO2 49.37%, Al2O3 39.13%, Fe2O3 1.30%, TiO2 2.03%, MgO 0.24%, P2O5 0.34%, SO3 0.30%, K2O 2.23%, Na2O 1.16%, CaO 0.17%, BaO 0.04%, loss on ignition 3.69%.

[0036] Example 1

[0037] Mix fine chromium-containing sludge, fine secondary aluminum ash and dolomite ore powder with a total mass of 40 g evenly at a dry basis mass percentage of 40:38:22 to obtain a mixed material; and add the mixed material into a high-temperature furnace for roasting. The roasting temperature is 850 °C, the roasting time is 90 minutes, the roasting atmosphere is nitrogen, and after roasting, air cooling is used for cooling to obtain a roasted product. Among them, the particle sizes of the fine chromium-containing sludge and the fine secondary aluminum ash are both less than 74 μm.

[0038] Mix the roasted product and cyanite ore sludge at a dry basis mass ratio of 55:45, and add the mixed material into a rod mill for grinding. When the particle size of the mixed material is less than 45 microns, the grinding ends. Mix the obtained ground product with water to make a slurry with a solid phase mass percentage of 40%. After mixing evenly, place the material in a granulator for granulation. After granulation is completed, screen the pellets with a particle size of 10 mm and dry them in a vacuum drying oven to obtain green pellets; among them, the moisture content of the green pellets is 3%. Put the green pellets into a high-temperature furnace for sintering. The sintering temperature is 1050 °C, the sintering time is 60 minutes, the roasting atmosphere is air, and after sintering, natural cooling is used to obtain ceramsite A1.

[0039] Adopt the "Solid Waste - Extraction Procedure for Toxicity Characteristic - Sulfuric Acid and Nitric Acid Method" (HJ / T 299 - 2007) to test the heavy metal leaching toxicity of ceramsite A1. The measured leaching concentration of hexavalent chromium in ceramsite A1 is 0.72 ± 0.01 mg / L, and the result is lower than the environmental threshold (5 mg / L); the cylinder compressive strength and bulk density of ceramsite A1 are tested according to the "Lightweight Aggregates and Their Test Methods - Part 2: Test Methods for Lightweight Aggregates" (GB / T 17431.2 - 2010). The result shows that the cylinder compressive strength of ceramsite A1 is 10.23 Mpa, and the bulk density is 870 kg / m3 , meeting the requirements specified in "Lightweight Aggregates and Their Test Methods - Part 1: Lightweight Aggregates" (GB / T 17431.1 - 2010).

[0040] Example 2

[0041] Mix 40 g of fine chromium - containing sludge, fine secondary aluminum ash, and dolomite powder evenly by dry - basis mass percentage of 55:28:17 to obtain a mixed material; then add the mixed material into a high - temperature furnace for roasting. The roasting temperature is 1000 °C, the roasting time is 50 minutes, the roasting atmosphere is nitrogen, and after roasting, it is cooled by air cooling to obtain a roasted product. Among them, the particle sizes of the fine chromium - containing sludge and the fine secondary aluminum ash are both less than 74 μm.

[0042] Mix the roasted product and kyanite ore mud by a dry - basis mass ratio of 50:50, and add the mixed material into a rod mill for grinding. When the particle size of the mixed material is less than 40 microns, the grinding ends. Mix the obtained ground product with water to make a slurry with a solid - phase mass percentage of 55%. After mixing evenly, place the material in a granulator for granulation. After granulation, screen the pellets with a particle size of 12 mm and dry them in a vacuum drying oven to obtain green pellets; among them, the moisture content of the green pellets is 5.5%. Put the green pellets into a high - temperature furnace for sintering. The sintering temperature is 1250 °C, the sintering time is 45 minutes, the roasting atmosphere is air, and after sintering, it is naturally cooled to obtain ceramsite A2.

[0043] Use the "Solid Waste - Extraction Procedure for Toxicity Characteristics - Sulfuric Acid and Nitric Acid Method" (HJ / T 299 - 2007) to test the heavy - metal leaching toxicity of ceramsite A2. The measured leaching concentration of hexavalent chromium in ceramsite A2 is 0.40 ± 0.01 mg / L, and the result is lower than the environmental threshold (5 mg / L); the cylinder compressive strength and bulk density of ceramsite A2 are tested according to "Lightweight Aggregates and Their Test Methods - Part 2: Test Methods for Lightweight Aggregates" (GB / T 17431.2 - 2010). As a result, the cylinder compressive strength of ceramsite A2 is 9.35 Mpa, and the bulk density is 810 kg / m 3 , meeting the requirements specified in "Lightweight Aggregates and Their Test Methods - Part 1: Lightweight Aggregates" (GB / T 17431.1 - 2010).

[0044] Example 3

[0045] Mix 40 g of fine chromium - containing sludge, fine secondary aluminum ash, and dolomite powder evenly by dry - basis mass percentage of 50:38:12 to obtain a mixed material; then add the mixed material into a high - temperature furnace for roasting. The roasting temperature is 1050 °C, the roasting time is 25 minutes, the roasting atmosphere is nitrogen, and after roasting, it is cooled by air cooling to obtain a roasted product. Among them, the particle sizes of the fine chromium - containing sludge and the fine secondary aluminum ash are both less than 74 μm.

[0046] The calcined product and cyanite ore sludge were mixed at a dry basis mass ratio of 40:60, and the mixed material was added to a rod mill for grinding. When the particle size of the mixed material was less than 45 microns, the grinding was completed. The obtained ground product was mixed with water to form a slurry with a solid phase mass percentage of 50%. After mixing evenly, the material was granulated in a granulator. After granulation, pellets with a particle size of 16 mm were screened and dried in a vacuum drying oven to obtain green pellets; among them, the moisture content of the green pellets was 3.5%. The green pellets were put into a high-temperature furnace for sintering. The sintering temperature was 1000 °C, the sintering time was 135 minutes, the roasting atmosphere was air, and after sintering, it was naturally cooled to obtain ceramsite A3.

[0047] The toxicity of heavy metal leaching of ceramsite A3 was tested using the "Solid Waste - Leaching Toxicity Leaching Method - Sulfuric Acid and Nitric Acid Method" (HJ / T 299-2007). The leaching concentration of hexavalent chromium in ceramsite A3 was measured to be 0.16 ± 0.01 mg / L, and the result was lower than the environmental threshold (5 mg / L); the cylinder compressive strength and bulk density of ceramsite A3 were tested according to the "Lightweight Aggregates and Their Test Methods - Part 2: Test Methods for Lightweight Aggregates" (GB / T 17431.2-2010). As a result, the cylinder compressive strength of ceramsite A3 was 9.85 Mpa, and the bulk density was 820 kg / m 3 , meeting the requirements specified in the "Lightweight Aggregates and Their Test Methods - Part 1: Lightweight Aggregates" (GB / T 17431.1-2010).

[0048] Comparative Example 1

[0049] A total of 40 g of fine chromium-containing sludge, fine secondary aluminum ash, and dolomite ore powder were mixed evenly at a dry basis mass percentage of 60:38:2 to obtain a mixed material; and the mixed material was added to a high-temperature furnace for roasting. The roasting temperature was 850 °C, the roasting time was 90 minutes, the roasting atmosphere was nitrogen, and after roasting, it was cooled by air cooling to obtain a calcined product. Among them, the particle sizes of the fine chromium-containing sludge and the fine secondary aluminum ash were both less than 74 μm.

[0050] The calcined product and cyanite ore sludge were mixed at a dry basis mass ratio of 55:45, and the mixed material was added to a rod mill for grinding. When the particle size of the mixed material was less than 45 microns, the grinding was completed. The obtained ground product was mixed with water to form a slurry with a solid phase mass percentage of 40%. After mixing evenly, the material was granulated in a granulator. After granulation, pellets with a particle size of 10 mm were screened and dried in a vacuum drying oven to obtain green pellets; among them, the moisture content of the green pellets was 3%. The green pellets were put into a high-temperature furnace for sintering. The sintering temperature was 1050 °C, the sintering time was 60 minutes, the roasting atmosphere was air, and after sintering, it was naturally cooled to obtain ceramsite B1.

[0051] The toxicity of heavy metal leaching of ceramsite B1 was tested using the method of "Solid Waste - Extraction Procedure for Leaching Toxicity - Sulfuric Acid and Nitric Acid Method" (HJ / T 299 - 2007). The leaching concentration of hexavalent chromium in ceramsite B1 was measured to be 20.46 ± 0.03 mg / L, and the result was higher than the environmental threshold (5 mg / L).

[0052] Comparative Example 2

[0053] Fine chromium - containing sludge, fine secondary aluminum ash, and dolomite ore powder with a total mass of 40 g were mixed evenly at a dry - basis mass percentage of 60:32:8 to obtain a mixed material. The mixed material was added to a high - temperature furnace for roasting. The roasting temperature was 1000 °C, the roasting time was 50 minutes, the roasting atmosphere was nitrogen, and after roasting, it was cooled by air cooling to obtain a roasted product. Among them, the particle sizes of the fine chromium - containing sludge and the fine secondary aluminum ash were both less than 74 μm.

[0054] The roasted product was mixed with kyanite ore mud at a dry - basis mass ratio of 50:50, and the mixed material was added to a rod mill for grinding. The grinding was ended when the particle size of the mixed material was less than 40 microns. The obtained ground product was mixed with water to make a slurry with a solid - phase mass percentage of 55%. After mixing evenly, the material was placed in a granulator for granulation. After granulation, pellets with a particle size of 12 mm were screened and dried in a vacuum drying oven to obtain green pellets; among them, the moisture content of the green pellets was 5.5%. The green pellets were put into a high - temperature furnace for sintering. The sintering temperature was 1250 °C, the sintering time was 45 minutes, the roasting atmosphere was air, and after sintering, it was naturally cooled to obtain ceramsite B2.

[0055] The toxicity of heavy metal leaching of ceramsite 2 was tested using the method of "Solid Waste - Extraction Procedure for Leaching Toxicity - Sulfuric Acid and Nitric Acid Method" (HJ / T 299 - 2007). The leaching concentration of hexavalent chromium in ceramsite B2 was measured to be 20.20 ± 0.04 mg / L, and the result was higher than the environmental threshold (5 mg / L).

[0056] Comparative Example 3

[0057] According to the method of Example 1, under different raw material ratios, roasting conditions, ratios of roasted product to kyanite ore mud, and sintering conditions, ceramsite was prepared, and the toxicity of heavy metal leaching of the ceramsite was tested using the method of "Solid Waste - Extraction Procedure for Leaching Toxicity - Sulfuric Acid and Nitric Acid Method" (HJ / T 299 - 2007). The results are shown in Table 1.

[0058]

[0059] Among them, in the grinding fineness, - 40 microns means the particle size is less than 40 microns; + 40 microns means the particle size is greater than 40 microns.

[0060] It can be seen that the leaching concentration of hexavalent chromium in the ceramsite in Comparative Example 3 is higher than the environmental threshold and is still hazardous.

[0061] Comparative Example 4

[0062] Mix 40 g of fine chromium-containing sludge, fine secondary aluminum ash, and dolomite ore powder in a dry basis mass percentage of 40:38:22 to obtain a mixed material. Among them, the particle sizes of the fine chromium-containing sludge and the fine secondary aluminum ash are both less than 74 μm.

[0063] Mix the mixed material with kyanite ore mud in a dry basis mass ratio of 55:45, and add the mixed material to a rod mill for grinding. When the particle size of the mixed material is less than 45 microns, the grinding ends. Mix the obtained grinding product with water to make a slurry with a solid phase mass percentage of 40%. After mixing evenly, place the material in a granulator for granulation. After granulation is completed, screen the pellets with a particle size of 10 mm and dry them in a vacuum drying oven to obtain green pellets; among them, the moisture content of the green pellets is 3%. Put the green pellets into a high-temperature furnace for sintering, the sintering temperature is 1050 °C, the sintering time is 60 minutes, the roasting atmosphere is air, and after sintering, cool naturally to obtain ceramsite B3.

[0064] Use the "Solid Waste - Extraction Procedure for Toxicity Characteristics - Sulfuric Acid and Nitric Acid Method" (HJ / T 299 - 2007) to test the heavy metal leaching toxicity of ceramsite B3. The measured leaching concentration of hexavalent chromium in ceramsite B3 is 55.68 ± 0.01 mg / L, and the result is higher than the environmental threshold (5 mg / L).

[0065] Comparative Example 5

[0066] Mix 40 g of fine chromium-containing sludge, fine secondary aluminum ash, and dolomite ore powder in a dry basis mass percentage of 40:38:22 to obtain a mixed material; and add the mixed material to a high-temperature furnace for roasting. The roasting temperature is 850 °C, the roasting time is 90 minutes, the roasting atmosphere is nitrogen, and after roasting, use air cooling to obtain a roasted product. Among them, the particle sizes of the fine chromium-containing sludge and the fine secondary aluminum ash are both less than 74 μm.

[0067] Add the roasted product to a rod mill for grinding. When the particle size is less than 45 microns, the grinding ends. Mix the obtained grinding product with water to make a slurry with a solid phase mass percentage of 40%. After mixing evenly, place the material in a granulator for granulation. After granulation is completed, screen the pellets with a particle size of 10 mm and dry them in a vacuum drying oven to obtain green pellets; among them, the moisture content of the green pellets is 3%. Put the green pellets into a high-temperature furnace for sintering, the sintering temperature is 1050 °C, the sintering time is 60 minutes, the roasting atmosphere is air, and after sintering, cool naturally to obtain ceramsite B4.

[0068] The toxicity of heavy metal leaching of ceramsite B4 was tested using the "Solid Waste - Extraction Procedure for Leaching Toxicity - Sulfuric Acid and Nitric Acid Method" (HJ / T 299 - 2007). The leaching concentration of hexavalent chromium in ceramsite B4 was measured to be 68.24 ± 0.04 mg / L, and the result was higher than the environmental threshold (5 mg / L).

Claims

1. A method for preparing ceramsite by using chromium-containing sludge from hazardous waste and secondary aluminum ash, characterized in that, It includes the following steps: (1) Mix fine chromium-containing sludge, secondary aluminum ash and dolomite ore powder evenly, and calcine the mixed materials. After the calcination, air cooling is adopted to obtain a calcined product; the dry basis mass ratio of the fine chromium-containing sludge, secondary aluminum ash and dolomite ore powder is 40-55:28-38:12-22; the temperature of the calcination is 850-1050 °C, and the time is 25-90 minutes; the atmosphere of the calcination is nitrogen; (2) Mix the calcined product obtained in step (1) with kyanite ore sludge evenly, then grind to obtain a grinding material, add water and stir to prepare a slurry, and then granulate and dry to obtain green pellets; the dry basis mass ratio of the calcined product to the kyanite ore sludge is 40-55:45-60; the particle size of the grinding material is less than 45 microns; the solid phase mass percentage of the slurry is 40%-55%; (3) Sinter the green pellets obtained in step (2) under an air atmosphere condition, and obtain ceramsite after cooling; the temperature of the sintering is 1000-1250 °C, and the time is 45-135 minutes.

2. The method according to claim 1, wherein In step (2), the particle size of the granulated pellets is 10-16 mm.

3. The method according to claim 1, wherein In step (2), the moisture content of the green pellets is 3%-5.5%.

4. A ceramsite prepared by the method according to any one of claims 1 to 3.

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