CN110698023A - Method for regulating alkalinity of red mud by pyrolyzing agricultural biomass wastes - Google Patents

Abstract

The invention discloses a method for regulating the alkalinity of red mud by pyrolysis of agricultural biomass waste, belonging to the technical field of environmental protection, comprising the following steps: (1) placing the red mud in a ventilated place to air dry naturally, sieving for treatment, and obtaining a sieved (2) cleaning the straw collected in the farmland, removing the sundries in the straw, drying after cleaning, sieving after crushing, and obtaining the sieved straw; (3) sieving the red mud after the step Place the mixed red mud and straw in an oxidizing atmosphere to conduct a pyrolysis reaction, and obtain the result after the reaction is completed. The present invention neutralizes the alkalinity of red mud by utilizing the product in the biomass pyrolysis process; the present invention adopts straw as an agricultural biomass waste material, and solves the problem of resource utilization of straw and red mud through the synergistic effect of straw and red mud. Mud strong alkaline problem.

Description

A method for regulating the alkalinity of red mud by pyrolysis of agricultural biomass waste

technical field

The invention belongs to the technical field of environmental protection, and in particular relates to a method for regulating the alkalinity of red mud by pyrolysis of agricultural biomass waste.

Background technique

Red mud is a highly alkaline solid waste produced in the alumina production process. For every 1 ton of alumina produced, about 1.0 to 2.0 tons of red mud are produced. A large amount of red mud is mainly deposited. The stock is about 4.6 billion tons, and the red mud stockpile in China exceeds 800 million tons. A large number of red mud deposits cause considerable environmental and safety hazards. The alkaline dust formed by efflorescence on the surface of the yard will cause air pollution. The alkaline substances in red mud will also penetrate into the soil and groundwater through various ways, causing The salinization of the surrounding soil and the pollution of surface water and groundwater, more seriously, the dam break of the red mud yard will bring devastating disasters to the downstream ecological environment. Therefore, how to control the alkalinity of red mud economically and effectively is the priority for the disposal of this type of industrial waste.

At present, the red mud dealkalization methods include seawater neutralization method, gypsum neutralization method, carbon dioxide neutralization method, inorganic acid neutralization method and biological treatment method. Among them, the seawater neutralization method is a method to obtain geographical advantages, and the salinity is higher after the alkali treatment of red mud. The technical economy and alkali control effect of carbon dioxide neutralization are poor, and it is necessary to conduct regulation research in combination with its alkali conversion characteristics. Gypsum neutralization and biological methods are of great significance for the regulation of red mud alkalinity, but due to the dissolution of chemically bound alkalis, the long-term stability regulation of red mud alkalinity cannot be achieved fundamentally. Inorganic acids can be used to achieve neutralization of soluble and chemically bound bases in red mud, but economic and potential secondary pollution effects should be considered. In addition to the above alkaline adjustment methods, microbial fermentation or biomass metabolites can also be used to reduce the alkaline conversion of red mud. However, a long conditioning time is required to obtain the proper pH range.

China has huge reserves of biomass energy. Except a small part of these biomass resources are used as feed, fuel and chemical raw materials, most of these biomass resources are discarded as agricultural waste. In addition to landfilling or direct incineration, biomass can be considered a renewable resource. Therefore, exploring suitable methods for co-processing red mud and agricultural biomass waste to reduce the risk of red mud alkalinity is expected to increase the value of red mud and biomass.

SUMMARY OF THE INVENTION

In view of the high salinity after alkali treatment of red mud in the seawater neutralization method in the prior art, the technical economy and alkali control effect of carbon dioxide neutralization are poor, and it is necessary to carry out control research in combination with its alkaline conversion characteristics. The gypsum neutralization method is chemically combined The dissolution of alkali cannot fundamentally realize the long-term stability regulation of red mud alkalinity, the potential secondary pollution effect of inorganic acid method, and the problem that microbial fermentation method requires a long adjustment time to obtain an appropriate pH range; The purpose is to provide a method for regulating the alkalinity of red mud by pyrolysis of agricultural biomass waste, so as to solve the problem of environmental pollution caused by the alkalinity of red mud.

In order to achieve the above purpose, the present invention provides the following technical solutions: a method for regulating the alkalinity of red mud by pyrolysis of agricultural biomass waste, comprising the following steps:

(1) placing the red mud in a ventilated place to dry naturally, and sieving to obtain the red mud after the sieving;

(2) cleaning the straw collected in the farmland, removing the sundries in the straw, drying after cleaning, sieving after crushing, and obtaining the sieved straw;

(3) the red mud and straw after sieving in steps (1), (2) are placed in a mixing bucket and fully mixed;

(4) The red mud and straw mixed in step (3) are placed in an oxidizing atmosphere to carry out a pyrolysis reaction, and the reaction is obtained after the reaction is completed.

In a preferred solution, in the step (1), the air-drying time is 36-72h, and the sieve is sieved with 80-100 meshes.

In a preferred solution, in the step (2), the straw is one or more of rice straw, barley straw and corn straw.

In a preferred solution, in the step (2), drying is performed for 12-36 hours after cleaning, and then sieved through a 20-40 mesh sieve.

In a preferred solution, in the step (3), the ratio of red mud to straw is 1:(0.5-3).

In a preferred solution, in the step (4), the pyrolysis temperature is 200-400°C.

In a more preferred solution, in the step (4), the pyrolysis temperature is 200-300°C.

In a preferred solution, in the step (4), the heating rate is 10-20°C·min ^-1 .

In a preferred solution, in the step (4), the pyrolysis reaction time is 2h.

Principle of the invention: Currently available biomass utilization methods, as an environmentally friendly and cost-effective technology for biomass recycling, consume less energy with the help of catalysts. These biomasses can be selectively converted into desired bio-oil, gas or biochar under certain temperature conditions. According to previous studies, red mud has the ability to catalyze the reduction, oxidation and acid/alkali conversion of biomass under different atmospheres due to the existence of basic components, alkali metal ions, transition metal oxides and other complex minerals. Ability. Based on this principle, biomass pyrolysis can directly and selectively generate acidic products through the catalysis of red mud, and these acidic products can neutralize the alkaline characteristics of red mud in situ to obtain neutral products.

Compared with the prior art, the beneficial technical effects of the present invention are:

1) The present invention neutralizes the alkalinity of red mud by utilizing the product in the biomass pyrolysis process; the present invention adopts straw as an agricultural biomass waste material, and solves the problem of resource utilization of straw through the synergistic effect of straw and red mud And red mud strong alkaline problem.

2) The raw materials and methods adopted in the present invention are simple and easy to implement, can process red mud on a large scale, and can effectively solve the problems of difficulty in comprehensive utilization caused by alkalinity of red mud and environmental pollution caused by red mud storage.

Description of drawings

Fig. 1 is the change trend of pH value of the product after pyrolysis in Example 1, the product after pyrolysis in Example 2, the product after pyrolysis in Example 3, and the product after pyrolysis in Example 4.

Fig. 2 is the XRD pattern of red mud after pyrolysis of Comparative Example, product after pyrolysis of Example 1, product after pyrolysis of Example 5, product after pyrolysis of Example 6, and product after pyrolysis of Example 7;

In the figure: 1: calcite (Na ₈ Al ₆ Si ₆ O ₂₄ (CO ₃ )(H ₂ O) ₂ ); 2: calcite (CaCO ₃ ); 3: calcite (Ca ₃ (Fe _0.87 Al ) _0.13 ) ₂ (SiO ₄ ) _1.65 (OH) _5.4 ); 4: garnet (Ca ₃ Al ₂ Si ₃ O ₁₂ ).

3 is the FTIR spectrum of the pyrolysis product of Example 1, the pyrolysis product of Example 5, the pyrolysis product of Example 6, the pyrolysis product of Example 7 and the pyrolysis product of Example 8.

FIG. 4 is the simultaneous 3D FTIR spectra of gas components generated during the pyrolysis of the mixture of straw and red mud in Example 1, Example 5, Example 6, Example 7 and Example 8.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments and accompanying drawings:

Red mud is a strong alkaline solid waste with a large stockpile and low comprehensive utilization rate. The present invention utilizes the method of synergistic treatment of agricultural waste straw and red mud to reduce the alkalinity and harm of red mud, and promote the soilization of red mud.

The alkali in red mud mainly occurs in the form of chemical alkali, including cannonite, calcite, garnet, garnet and other mineral states. These chemical bases will continue to slowly dissolve and release OH ^- or CO ₃ ^2- , maintain the high alkalinity of red mud, and make it difficult to effectively control the alkalinity of red mud.

Comparative ratio

The red mud was placed in a ventilated place to air dry for 72 hours and passed through a 100-mesh sieve. Then, it was put into a muffle furnace with a heating rate of 10°C·min ^-1 to 400°C and then pyrolyzed for 2h. After the pyrolyzed red mud was lowered to room temperature, 10 g of it was dispersed in 50 ml of aqueous solution, and the pH value of the supernatant was measured to be 11.35.

Example 1

The straw of agricultural waste was washed with deionized water, dried at 60°C for 24 hours, pulverized with a pulverizer, and passed through a 20-mesh sieve. The red mud was placed in a ventilated place to air dry for 72 hours and passed through a 100-mesh sieve. Then, the treated straw and red mud were mixed and stirred uniformly according to the mass ratio of 1:1, put into a muffle furnace, and then pyrolyzed for 2 h at a heating rate of 10 °C·min ^-1 to 400 °C. After the pyrolyzed product was lowered to room temperature, 10 g of it was dispersed in 50 ml of aqueous solution, and the pH value of the supernatant was measured.

How to measure pH:

Weigh 10 g of the pyrolyzed product, add 100 ml of distilled water, stir and mix evenly, seal with plastic wrap, stir with a magnetic stirrer (150 rpm) for 1 h, and filter the obtained supernatant for pH determination.

In this example, the pH change trend of the product after pyrolysis for 7 days is shown in Figure 1. The pH value of the product after pyrolysis is 8.53, which is far lower than the pH value of 11.35 for red mud only after pyrolysis. And with the increase of time, the change trend of pH value is small, indicating that the pH value of the mixed pyrolysis product of biomass and red mud can be stably maintained within a certain range.

Example 2

The straw of agricultural waste was washed with deionized water, dried at 60°C for 24 hours, pulverized with a pulverizer, and passed through a 20-mesh sieve. The red mud was placed in a ventilated place to air dry for 72 hours and passed through a 100-mesh sieve. Then, the treated straw and red mud were mixed and stirred evenly according to the mass ratio of 1:2, and then put into a muffle furnace at a heating rate of 10°C·min ^-1 to 400°C and then pyrolyzed for 2h. After the pyrolyzed product was lowered to room temperature, 10 g of it was dispersed in 50 ml of aqueous solution, and the pH value of the supernatant was measured.

In this example, the pH change trend of the product after pyrolysis for 7 days is shown in Figure 1. The pH value of the product after pyrolysis is 9.08, which is lower than the pH value of 11.35 for red mud only after pyrolysis. And with the increase of time, the change trend of pH value is small, indicating that the pH of the product after the mixed pyrolysis of biomass and red mud can be stably maintained within a certain range.

Example 3

The straw of agricultural waste was washed with deionized water, dried at 60°C for 24 hours, pulverized with a pulverizer, and passed through a 20-mesh sieve. The red mud was placed in a ventilated place to air dry for 72 hours and passed through a 100-mesh sieve. Then, the treated straw and red mud were mixed and stirred uniformly according to the mass ratio of 1:3, put into a muffle furnace, heated to 400°C at a heating rate of 10°C·min ^-1 , and then pyrolyzed for 2h. After the pyrolyzed product was lowered to room temperature, 10 g of it was dispersed in 50 ml of aqueous solution, and the pH value of the supernatant was measured.

In this example, the pH change trend of the product after pyrolysis for 7 days is shown in Figure 1. The pH value of the product after pyrolysis is 8.86, which is lower than the pH value of 11.35 for red mud only after pyrolysis. And with the increase of time, the change trend of pH value is small, indicating that the pH of the product after the mixed pyrolysis of biomass and red mud can be stably maintained within a certain range.

Example 4

The straw of agricultural waste was washed with deionized water, dried at 60°C for 24 hours, pulverized with a pulverizer, and passed through a 20-mesh sieve. The red mud was placed in a ventilated place to air dry for 72 hours and passed through a 100-mesh sieve. Then, the treated straw and red mud were mixed and stirred evenly according to the mass ratio of 2:1, put into a muffle furnace, and then pyrolyzed for 2 h at a heating rate of 10 °C·min ^-1 to 400 °C. After the pyrolyzed product was lowered to room temperature, 10 g of it was dispersed in 50 ml of aqueous solution, and the pH value of the supernatant was measured.

In this example, the pH change trend of the product after pyrolysis for 7 days is shown in Figure 1. The pH value of the product after pyrolysis is 7.99, which is lower than the pH value of 11.35 after only red mud is pyrolyzed. And with the increase of time, the change trend of pH value is small, indicating that the pH of the product after the mixed pyrolysis of biomass and red mud can be stably maintained within a certain range.

Example 5

The straw of agricultural waste was washed with deionized water, dried at 60°C for 24 hours, pulverized with a pulverizer, and passed through a 20-mesh sieve. The red mud was placed in a ventilated place to air dry for 72 hours and passed through a 100-mesh sieve. Then, the treated straw and red mud were mixed and stirred uniformly according to the mass ratio of 1:1, and then put into a muffle furnace for pyrolysis at a temperature of 350 °C and a heating rate of 10 °C·min ^-1 for 2 h. After the pyrolyzed product was lowered to room temperature, 10 g of it was dispersed in 50 ml of aqueous solution, and the pH value of the supernatant was measured.

In this example, the pH of the product after pyrolysis is shown in Table 1. From Table 1, it can be seen that the pH value of the product after pyrolysis at 350°C is 8.14, which is lower than the pH value of 11.35 for red mud only after pyrolysis of red mud.

Example 6

The straw of agricultural waste was washed with deionized water, dried at 60°C for 24 hours, pulverized with a pulverizer, and passed through a 20-mesh sieve. The red mud was placed in a ventilated place to air dry for 72 hours and passed through a 100-mesh sieve. Then, the treated straw and red mud were mixed and stirred uniformly according to the mass ratio of 1:1, and then put into a muffle furnace for pyrolysis at a temperature of 300 °C and a heating rate of 10 °C·min ^-1 for 2 h. After the pyrolyzed product was lowered to room temperature, 10 g of it was dispersed in 50 ml of aqueous solution, and the pH value of the supernatant was measured.

In this example, the pH of the product after pyrolysis is shown in Table 1. From Table 1, it can be seen that the pH value of the product after pyrolysis at 300°C is 7.42, which is lower than the pH value of 11.35 for red mud only after pyrolysis.

Example 7

The straw of agricultural waste was washed with deionized water, dried at 60°C for 24 hours, pulverized with a pulverizer, and passed through a 20-mesh sieve. The red mud was placed in a ventilated place to air dry for 72 hours and passed through a 100-mesh sieve. Then, the treated straw and red mud were mixed and stirred uniformly according to the mass ratio of 1:1, and then put into a muffle furnace for pyrolysis at a temperature of 250 °C and a heating rate of 10 °C·min ^-1 for 2 h. After the pyrolyzed product was lowered to room temperature, 10 g of it was dispersed in 50 ml of aqueous solution, and the pH value of the supernatant was measured.

In this example, the pH of the product after pyrolysis is shown in Table 1. From Table 1, it can be seen that the pH value of the product after pyrolysis at 250° C. is 7.33, which is lower than the pH value of 11.35 after only red mud is pyrolyzed.

Example 8

The straw of agricultural waste was washed with deionized water, dried at 60°C for 24 hours, pulverized with a pulverizer, and passed through a 20-mesh sieve. The red mud was placed in a ventilated place to air dry for 72 hours and passed through a 100-mesh sieve. Then, the treated straw and red mud were mixed and stirred uniformly according to the mass ratio of 1:1, and then put into a muffle furnace for pyrolysis at a temperature of 450 °C and a heating rate of 10 °C·min ^-1 for 2 h. After the pyrolyzed product was lowered to room temperature, 10 g of it was dispersed in 50 ml of aqueous solution, and the pH value of the supernatant was measured.

In this example, the pH of the product after pyrolysis is shown in Table 1. From Table 1, it can be seen that the pH value of the product after pyrolysis at 200° C. is 7.89, which is lower than the pH value of 11.35 after only red mud is pyrolyzed.

Table 1

Fig. 2 is the XRD pattern of red mud after pyrolysis of Comparative Example, product after pyrolysis of Example 1, product after pyrolysis of Example 5, product after pyrolysis of Example 6, and product after pyrolysis of Example 7, as can be seen from Fig. 2 , the main alkaline minerals in red mud cannonite, calcite, garnet and garnet still exist in the pyrolysis products at different temperatures. However, compared with the comparative example, that is, the red mud after pyrolysis, the content of these alkaline minerals in the product of the mixed pyrolysis of biomass and red mud is significantly reduced, and the relative content of alkaline minerals in the pyrolysis product at 250 °C is significantly reduced. The lowest levels indicate a reduction in alkaline minerals. This phenomenon is consistent with the low pH results of basic analysis of pyrolysis products at 250°C.

Fig. 3 is the FTIR spectrum of the product after pyrolysis of Example 1, the product after pyrolysis of Example 5, the product after pyrolysis of Example 6, the product after pyrolysis of Example 7 and the product after pyrolysis of Example 8, as can be seen from Fig. 3 , the absorption peak at 3440-3700cm ^-1 represents the OH bond; the absorption peak at 1625-1640cm ^-1 represents the C=O bond of aromatic hydrocarbons; the absorption peak at 1420-1430cm ^-1 represents the aromatic C=C bond. Therefore, the co-pyrolysis of straw and red mud produces organics such as aromatics.

Fig. 4 is the simultaneous 3D FTIR images of the gas components generated during the pyrolysis of the mixture of straw and red mud in Example 1, Example 5, Example 6, Example 7 and Example 8. It can be seen from Fig. 4 that, The absorption peaks at 2350cm ^-1 , 1706cm ^-1 , 1527cm ^-1 and 675cm ^-1 indicated that organic acids, aldehydes, ketones and aromatic hydrocarbons were produced during the co-pyrolysis of straw and red mud. Therefore, the acidic organics produced by the co-pyrolysis of straw and red mud neutralize some of the alkaline substances in the red mud, which reduces the pH value.

Claims (9)

1. a method for regulating and controlling red mud alkalinity by pyrolysis of agricultural biomass waste, is characterized in that, comprises the following steps: (1) placing the red mud in a ventilated place to dry naturally, and sieving to obtain the red mud after the sieving; (2) cleaning the straw collected in the farmland, removing the sundries in the straw, drying after cleaning, sieving after crushing, and obtaining the sieved straw; (3) the red mud and straw after sieving in steps (1), (2) are placed in a mixing bucket and fully mixed; (4) The red mud and straw mixed in step (3) are placed in an oxidizing atmosphere to carry out a pyrolysis reaction, and the reaction is obtained after the reaction is completed. 2 . The method for adjusting the alkalinity of red mud by pyrolysis of agricultural biomass waste according to claim 1 , wherein, in the step (1), the air-drying time is 36-72 h, and the sieve is 70-100 mesh. 3 . 3. The method for adjusting the alkalinity of red mud by pyrolysis of agricultural biomass waste according to claim 1, wherein in the step (2), the straw is one of rice straw, barley straw and corn straw or more. 4. The method for adjusting the alkalinity of red mud by pyrolysis of agricultural biomass waste according to claim 1 or 3, wherein in the step (2), drying is performed for 12-36 hours after cleaning, and the drying is performed for 20-40 hours. mesh screen. 5. The method for adjusting the alkalinity of red mud by pyrolysis of agricultural biomass waste according to claim 1, wherein in the step (3), the ratio of red mud to straw is 1:(0.5～3) . 6 . The method for adjusting the alkalinity of red mud by pyrolysis of agricultural biomass waste according to claim 1 , wherein, in the step (4), the pyrolysis temperature is 200-400° C. 7 . 7 . The method for adjusting the alkalinity of red mud by pyrolysis of agricultural biomass waste according to claim 1 or 6 , wherein in the step (4), the pyrolysis temperature is 200-300° C. 8 . 8 . The method for adjusting the alkalinity of red mud by pyrolysis of agricultural biomass waste according to claim 1 or 6 , wherein in the step (4), the heating rate is 10-20° C.·min ⁻¹ . 9 . 9. The method for adjusting the alkalinity of red mud by pyrolysis of agricultural biomass waste according to claim 1 or 6, wherein in the step (4), the pyrolysis reaction time is 2h.

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